Volume 47,Issue 7,2018 Table of Contents
2018, 47(7):1951-1957.
Abstract:
Iron-gallium (FeGa) thin film has the unique advantages in designing integrated magnetic sensors or chips due to its relatively large magnetostrictive constant compared with other soft magnetic materials. In this work, non-magnetic doping and laminating methods have been employed to control the magnetic and electric properties of this alloy film. By doping certain amount of boron (B), the coercivities are largely decreased for samples of thickness less than ~30 nm. For thicker films, we find that inserting an ultrathin Al2O3 middle layer is very helpful to control the coercivities with negligible influence on saturation magnetization (Ms). The smallest easy-axis coercivity of 0.98 Oe is obtained in the multilayer film FeGaB(25nm)/ Al2O3(0.5nm)/ FeGaB(25nm). In this case, the resistivity is enhanced by 1.5 times compared with the 50 nm single layer film. Structural characterizations were carried out, which indicate the reductions of crystalline quality and physical dimension of the magnetic grains playing important roles in softening the magnetic properties. Besides, the influences of magnetostatic interaction and morphology characteristics are also considered in facilitating domain reversal. High permeability spectra with gigahertz response are obtained for our multilayer films. The methodology applied here, i.e., enhancing magnetic and electric performance by introducing ultrathin non-magnetic layers, could be translated to other species of soft magnetic materials as well.
Iron-gallium (FeGa) thin film has the unique advantages in designing integrated magnetic sensors or chips due to its relatively large magnetostrictive constant compared with other soft magnetic materials. In this work, non-magnetic doping and laminating methods have been employed to control the magnetic and electric properties of this alloy film. By doping certain amount of boron (B), the coercivities are largely decreased for samples of thickness less than ~30 nm. For thicker films, we find that inserting an ultrathin Al2O3 middle layer is very helpful to control the coercivities with negligible influence on saturation magnetization (Ms). The smallest easy-axis coercivity of 0.98 Oe is obtained in the multilayer film FeGaB(25nm)/ Al2O3(0.5nm)/ FeGaB(25nm). In this case, the resistivity is enhanced by 1.5 times compared with the 50 nm single layer film. Structural characterizations were carried out, which indicate the reductions of crystalline quality and physical dimension of the magnetic grains playing important roles in softening the magnetic properties. Besides, the influences of magnetostatic interaction and morphology characteristics are also considered in facilitating domain reversal. High permeability spectra with gigahertz response are obtained for our multilayer films. The methodology applied here, i.e., enhancing magnetic and electric performance by introducing ultrathin non-magnetic layers, could be translated to other species of soft magnetic materials as well.
2018, 47(7):1958-1964.
Abstract:
The effects of cold rolling reduction and annealing temperatures on the formation of cube texture and microstructural evolution have been investigated in Cu-44%Ni alloy. The results showed that the recrystallized cube texture is strengthened by either increasing the rolling reduction or increasing the annealing temperature. And the strong cube texture can be observed for the severely cold-rolled (> 90%) alloy after annealing at high temperature (> 900 °C). On the other hand, high-angle grain boundaries (HAGBs) and Annealing twin boundaries (Σ3 boundaries) decreases with the increase of rolling reduction. However, during isochronal annealing, the trend of Σ3 boundaries is consistent with that of HAGBs, which firstly increase during recrystallization process and then decrease with further increasing temperature. After annealing at 1100 °C for 1 h, the 99% cold-rolled Cu-44%Ni revealed that the fraction of the cube texture is 99.8% and the fractions of HAGBs and Σ3 boundaries are 2.5% and 1.3%, respectively.
The effects of cold rolling reduction and annealing temperatures on the formation of cube texture and microstructural evolution have been investigated in Cu-44%Ni alloy. The results showed that the recrystallized cube texture is strengthened by either increasing the rolling reduction or increasing the annealing temperature. And the strong cube texture can be observed for the severely cold-rolled (> 90%) alloy after annealing at high temperature (> 900 °C). On the other hand, high-angle grain boundaries (HAGBs) and Annealing twin boundaries (Σ3 boundaries) decreases with the increase of rolling reduction. However, during isochronal annealing, the trend of Σ3 boundaries is consistent with that of HAGBs, which firstly increase during recrystallization process and then decrease with further increasing temperature. After annealing at 1100 °C for 1 h, the 99% cold-rolled Cu-44%Ni revealed that the fraction of the cube texture is 99.8% and the fractions of HAGBs and Σ3 boundaries are 2.5% and 1.3%, respectively.
2018, 47(7):1965-1972.
Abstract:
With continuously growing oil and gas demand, exploitation of highly sour reservoirs brings large corrosion risks due to the coupling effects of corrosive factors including elemental sulfur, CO2, and formation water. In the present work, corrosion behavior of P110 tubing steel in simulated oilfield formation water containing elemental sulfur and CO2 was investigated by immersion tests and electrochemical measurements. The results indicated that increasing temperature accelerated the corrosion rate of P110 tubing steel, promoted the formation of iron sulfide, and caused serious pitting corrosion. However, influence of temperature varied at different temperature range mainly due to the different corrosion-controlling species like CO2 at low temperatures and elemental sulfur at high temperatures. Based on the results, the coupling effects of elemental sulfur and carbon dioxide were discussed.
With continuously growing oil and gas demand, exploitation of highly sour reservoirs brings large corrosion risks due to the coupling effects of corrosive factors including elemental sulfur, CO2, and formation water. In the present work, corrosion behavior of P110 tubing steel in simulated oilfield formation water containing elemental sulfur and CO2 was investigated by immersion tests and electrochemical measurements. The results indicated that increasing temperature accelerated the corrosion rate of P110 tubing steel, promoted the formation of iron sulfide, and caused serious pitting corrosion. However, influence of temperature varied at different temperature range mainly due to the different corrosion-controlling species like CO2 at low temperatures and elemental sulfur at high temperatures. Based on the results, the coupling effects of elemental sulfur and carbon dioxide were discussed.
2018, 47(7):1973-1979.
Abstract:
The post-weld heat treatment(PWHT) is carried out to Al-Li alloy joints welded by electron beam welding(EBW), and the behaviour of intergranular corrosion(IGC), exfoliation corrosion(EXCO) and electrochemical corrosion of different zones of welded joint before and after PWHT are investigated. Results show that the quantity of phase T1(Al2CuLi) in grain boundry of weldment increased after solution and aging treatment, and the obvious precipitate free zone(PFZ) generated to grain boundry. The IGC does not occur to joint in as-welded(AW) condition, while the pitting corrosion occurs to both heat-affected zone(HAZ) and base metal of welded joint. The susceptibility to IGC of joint increased after aging treatment, both the pitting corrosion and IGC occurred to HAZ, and the severe IGC produced to base metal. It has excellent EXCO resistance for both weld metal and HAZ in AW condition, while the susceptibility to EXCO is higher for base metal. The EXCO resistance can be improved to base metal after aging treatment, however the susceptibility to EXCO will increase to HAZ. Results of electrochemical corrosion measurement show that, compared to the weldment after aging treatment, the self-corrosion potential of weldment is a little higher in AW condition, and its density of self-corrosion current is lower, consequently, it has the relatively better corrosion resistance.
The post-weld heat treatment(PWHT) is carried out to Al-Li alloy joints welded by electron beam welding(EBW), and the behaviour of intergranular corrosion(IGC), exfoliation corrosion(EXCO) and electrochemical corrosion of different zones of welded joint before and after PWHT are investigated. Results show that the quantity of phase T1(Al2CuLi) in grain boundry of weldment increased after solution and aging treatment, and the obvious precipitate free zone(PFZ) generated to grain boundry. The IGC does not occur to joint in as-welded(AW) condition, while the pitting corrosion occurs to both heat-affected zone(HAZ) and base metal of welded joint. The susceptibility to IGC of joint increased after aging treatment, both the pitting corrosion and IGC occurred to HAZ, and the severe IGC produced to base metal. It has excellent EXCO resistance for both weld metal and HAZ in AW condition, while the susceptibility to EXCO is higher for base metal. The EXCO resistance can be improved to base metal after aging treatment, however the susceptibility to EXCO will increase to HAZ. Results of electrochemical corrosion measurement show that, compared to the weldment after aging treatment, the self-corrosion potential of weldment is a little higher in AW condition, and its density of self-corrosion current is lower, consequently, it has the relatively better corrosion resistance.
2018, 47(7):1980-1985.
Abstract:
The effect of cold deformation and aging on the microstructure and properties of Cu-3Ti-2Mg alloy was investigated. The microstructure and phase constituents were characterized by optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD), transmission electron microscope (TEM) and electron backscattering diffraction (EBSD), and the hardness and electrical conductivity were measured as well. The results show that the microstructure of as-cast Cu-3Ti-2Mg alloy is consisted of Cu2Mg phase, plate-like Cu4Ti phase and Cu matrix. The microstructural characterizations revealed that the β′-Cu4Ti phase precipitate from the supersaturated Cu matrix during aging. However, excessive aging causes the phase transformation from metastable, coherent β"-Cu4Ti to equilibrium, incoherent Cu3Ti phases. In the range of experiments, the optimum process for Cu-3Ti-2Mg alloy is solutized at 700 °C for 4h, cold deformation of 60%, and aging at 450 °C for 2h. The electrical conductivity and hardness of Cu-3Ti-2Mg alloy are 16.7% IACS and 328 HV, respectively.
The effect of cold deformation and aging on the microstructure and properties of Cu-3Ti-2Mg alloy was investigated. The microstructure and phase constituents were characterized by optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD), transmission electron microscope (TEM) and electron backscattering diffraction (EBSD), and the hardness and electrical conductivity were measured as well. The results show that the microstructure of as-cast Cu-3Ti-2Mg alloy is consisted of Cu2Mg phase, plate-like Cu4Ti phase and Cu matrix. The microstructural characterizations revealed that the β′-Cu4Ti phase precipitate from the supersaturated Cu matrix during aging. However, excessive aging causes the phase transformation from metastable, coherent β"-Cu4Ti to equilibrium, incoherent Cu3Ti phases. In the range of experiments, the optimum process for Cu-3Ti-2Mg alloy is solutized at 700 °C for 4h, cold deformation of 60%, and aging at 450 °C for 2h. The electrical conductivity and hardness of Cu-3Ti-2Mg alloy are 16.7% IACS and 328 HV, respectively.
2018, 47(7):1986-1992.
Abstract:
WC-6Co nanocrystalline composite powders without excess C and decarburization phases were synthesized via a facile route including spraying conversion, calcination and in situ reduction-carbonization processes. The phase constituents obtained by XRD showed that the as-prepared powders after each step of the preparation were amorphous, WO3 and Co3O4 phases, WC and Co phases, respectively. The pure WC-Co composite powders could be obtained by a reduction-carbonization process heat treated at 900 °C for 1 h under a hydrogen atmosphere due to the catalytic effect of Co on the carbonation reaction. The effects of heat treated temperature on phase constituents of powders were investigated in a range of 700-900 °C. Morphology and microstructure of powders were observed by SEM and HRTEM. The results indicated that the morphology of powder was spherical. The grain size of WC was about 0.36 μm, and the crystalline size of WC was about 56 nm, which indicated that the WC grain was polycrystalline and comprised of many crystallites. It was also found that the individual particles of WC were bonded together under the action of Co. Furthermore, a few sintering necks could be observed in the composite powders due to the contacts between WC particles. The stoichiometry of WC-Co composite powders could be adjusted easily. Moreover, the formation process and mechanism of the sphere structure are also discussed in this paper.
WC-6Co nanocrystalline composite powders without excess C and decarburization phases were synthesized via a facile route including spraying conversion, calcination and in situ reduction-carbonization processes. The phase constituents obtained by XRD showed that the as-prepared powders after each step of the preparation were amorphous, WO3 and Co3O4 phases, WC and Co phases, respectively. The pure WC-Co composite powders could be obtained by a reduction-carbonization process heat treated at 900 °C for 1 h under a hydrogen atmosphere due to the catalytic effect of Co on the carbonation reaction. The effects of heat treated temperature on phase constituents of powders were investigated in a range of 700-900 °C. Morphology and microstructure of powders were observed by SEM and HRTEM. The results indicated that the morphology of powder was spherical. The grain size of WC was about 0.36 μm, and the crystalline size of WC was about 56 nm, which indicated that the WC grain was polycrystalline and comprised of many crystallites. It was also found that the individual particles of WC were bonded together under the action of Co. Furthermore, a few sintering necks could be observed in the composite powders due to the contacts between WC particles. The stoichiometry of WC-Co composite powders could be adjusted easily. Moreover, the formation process and mechanism of the sphere structure are also discussed in this paper.
2018, 47(7):1993-1998.
Abstract:
The effect of volume fraction on the coarsening of Pb nanophase in Al-Pb nanocomposite alloys prepared by high energy ball milling has been studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The coarsening of Pb nanophase with different volume fractions in Al-Pb nanocomposite alloys follows the cubic growth law even though the size of the constituent phase was in nanometer range. The coarsening rate of Pb nanophase increases distinctly as the volume fraction increases, the variation of coarsening rate is greater than the theoretical prediction in this composition range. The activation energy for coarsening of Pb nanophase does not vary with volume fraction. The coarsening of Pb nanophase is controlled by grain boundary diffusion for solute atoms in solvent matrix.
The effect of volume fraction on the coarsening of Pb nanophase in Al-Pb nanocomposite alloys prepared by high energy ball milling has been studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The coarsening of Pb nanophase with different volume fractions in Al-Pb nanocomposite alloys follows the cubic growth law even though the size of the constituent phase was in nanometer range. The coarsening rate of Pb nanophase increases distinctly as the volume fraction increases, the variation of coarsening rate is greater than the theoretical prediction in this composition range. The activation energy for coarsening of Pb nanophase does not vary with volume fraction. The coarsening of Pb nanophase is controlled by grain boundary diffusion for solute atoms in solvent matrix.
Zhou Xiangyang
,
Shuai Wang
,
Chi-yuan Ma
,
Bo Long
,
Hui Wang
,
Juan Yang
,
Zhong-cheng Guo
,
Bu-ming Chen
2018, 47(7):1999-2004.
Abstract:
Due to the excellent electrical conductivity and mechanical properties, Al/Pb-Ag alloy has a great potential to be used as an alternative anode for zinc electrowinning. In this work, the effects of Ag content and surface plating with β-PbO2 on the anodic behavior and reaction kinetics have been investigated by cyclic voltammetry (CV), anodic polarization curves, electrochemical impedance spectroscopy (EIS) and corrosion rate test. The phase composition and microscopic morphology of the anode oxide layers after electrolysis were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results indicate that both increasing Ag content and electroplating β-PbO2 layer contribute to the improvement of oxygen evolution activity, electrocatalytic activity and corrosion resistance of the anodes. Al/Pb-0.75%Ag plating β-PbO2 has the lowest oxygen evolution overpotential followed by that of Al/Pb-0.3%Ag plating β-PbO2, Al/Pb-0.75%Ag and Al/Pb-0.3%Ag. Besides, high content of silver is more benefit to improve corrosion resistance compared with electroplating β-PbO2 on anode. In addition, the phase composition of four anodes layer are mainly composed of α-PbO2, β-PbO2, Pb and PbO.
Due to the excellent electrical conductivity and mechanical properties, Al/Pb-Ag alloy has a great potential to be used as an alternative anode for zinc electrowinning. In this work, the effects of Ag content and surface plating with β-PbO2 on the anodic behavior and reaction kinetics have been investigated by cyclic voltammetry (CV), anodic polarization curves, electrochemical impedance spectroscopy (EIS) and corrosion rate test. The phase composition and microscopic morphology of the anode oxide layers after electrolysis were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results indicate that both increasing Ag content and electroplating β-PbO2 layer contribute to the improvement of oxygen evolution activity, electrocatalytic activity and corrosion resistance of the anodes. Al/Pb-0.75%Ag plating β-PbO2 has the lowest oxygen evolution overpotential followed by that of Al/Pb-0.3%Ag plating β-PbO2, Al/Pb-0.75%Ag and Al/Pb-0.3%Ag. Besides, high content of silver is more benefit to improve corrosion resistance compared with electroplating β-PbO2 on anode. In addition, the phase composition of four anodes layer are mainly composed of α-PbO2, β-PbO2, Pb and PbO.
2018, 47(7):2005-2010.
Abstract:
The influence of strain rate of Microstructures, tensile properties and strain hardening behavior of the electron beam welded joint for TC18 titanium alloy under optimized welding parameters were investigated with three slices (top, middle and bottom). The results showed that the welding led to significant microstructural changes across the joint. The microstructure of fusion zone is composed of coarsened β phase and secondary α-phase. Compared with the base metal, the joint slices along the thickness exhibited a lower strength and plasticity but a further higher hardening capacity. The strength and ductility of the bottom slices are higher than those of the middle and top slices. The maximum yield strength and ultimate tensile strength of the welding slices reached the base metal 83% at the strain rate of 1×10-2 s-1. The hardening capacity of welding slices decreased with increasing strain rate. It was significantly enhanced at the middle and bottom slices than the top slice. Tensile fracture occurred in the weld zone.The fracture process of the top slice is cleavage fracture. However, the middle and bottom slices are quasi-cleavage crack.
The influence of strain rate of Microstructures, tensile properties and strain hardening behavior of the electron beam welded joint for TC18 titanium alloy under optimized welding parameters were investigated with three slices (top, middle and bottom). The results showed that the welding led to significant microstructural changes across the joint. The microstructure of fusion zone is composed of coarsened β phase and secondary α-phase. Compared with the base metal, the joint slices along the thickness exhibited a lower strength and plasticity but a further higher hardening capacity. The strength and ductility of the bottom slices are higher than those of the middle and top slices. The maximum yield strength and ultimate tensile strength of the welding slices reached the base metal 83% at the strain rate of 1×10-2 s-1. The hardening capacity of welding slices decreased with increasing strain rate. It was significantly enhanced at the middle and bottom slices than the top slice. Tensile fracture occurred in the weld zone.The fracture process of the top slice is cleavage fracture. However, the middle and bottom slices are quasi-cleavage crack.
2018, 47(7):2011-2016.
Abstract:
Layered Ti-clad diamond/Cu composites used in electronic packaging were prepared by spark plasma sintering (SPS) and hot pressing (HP), respectively. The structure was determined by Scanning Electron Microscopy (SEM) and the thermal properties, including the thermal conductivity (TC) and the coefficient of thermal expansion (CTE) were analyzed. The theoretical TC of the layered composites (446.66 W.m-1K-1) was calculated by the modified Hasselman and Johnson (HJ) model considering the influence of the TiC interface and the CTE was determined by dilatometer. The results show that the sample of SPS has fewer defects than that of HP and the interfacial bonding affects the TC of the composites significantly. A schematic graph of the interface influences is proposed and the TC decreases with the increasing thickness of carbide layer and air pores. In this regard, the composites with a thin carbide layer and no air pores should be processed to achieve a high TC.
Layered Ti-clad diamond/Cu composites used in electronic packaging were prepared by spark plasma sintering (SPS) and hot pressing (HP), respectively. The structure was determined by Scanning Electron Microscopy (SEM) and the thermal properties, including the thermal conductivity (TC) and the coefficient of thermal expansion (CTE) were analyzed. The theoretical TC of the layered composites (446.66 W.m-1K-1) was calculated by the modified Hasselman and Johnson (HJ) model considering the influence of the TiC interface and the CTE was determined by dilatometer. The results show that the sample of SPS has fewer defects than that of HP and the interfacial bonding affects the TC of the composites significantly. A schematic graph of the interface influences is proposed and the TC decreases with the increasing thickness of carbide layer and air pores. In this regard, the composites with a thin carbide layer and no air pores should be processed to achieve a high TC.
2018, 47(7):2017-2022.
Abstract:
The Al-5Nb-RE-B master alloy with a uniform microstructure has been prepared using melt reaction method. The effect of Al-5Nb-RE-B inoculation on aluminum alloy A356 for their grain refinement has been studied. It was found that the grain size of A356 alloy can be reduced from 800 μm to 200 μm by the addition of 1wt.% of the prepared Al-5Nb-RE-B master alloy. The in-depth analysis of the alloys solidified under wide range of cooling rates indicated that Al-5Nb-RE-B inoculation does not only lead to a much finer microstructural features but also makes the final grain size far less sensitive to the cooling rate employed to solidify the material.
The Al-5Nb-RE-B master alloy with a uniform microstructure has been prepared using melt reaction method. The effect of Al-5Nb-RE-B inoculation on aluminum alloy A356 for their grain refinement has been studied. It was found that the grain size of A356 alloy can be reduced from 800 μm to 200 μm by the addition of 1wt.% of the prepared Al-5Nb-RE-B master alloy. The in-depth analysis of the alloys solidified under wide range of cooling rates indicated that Al-5Nb-RE-B inoculation does not only lead to a much finer microstructural features but also makes the final grain size far less sensitive to the cooling rate employed to solidify the material.
2018, 47(7):2023-2027.
Abstract:
The (Ti0.46Cu0.14Zr0.27Ni0.13)1-xSix amorphous filler metal was prepared by arc melting and fast-cooling melt-spinning technologies, and the effect of a certain amount of Si added to the filler metal on its amorphous forming ability was studied. The results show that the filler metal presented the strongest amorphous forming ability when the additive Si reached 0.5%; its wetting area was 3.06 cm2,its supercooled liquid phase region width (?Tx) ?Tx=56 ℃,its reduced glass transition temperature (Trg) Trg=0.5387, and its liquidus temperature was 949 ℃. The vacuum brazing was done for SiC and TC4 using this amorphous alloy as the filler metal, and the shear strength of brazed joint was 80 MPa. The amorphous forming ability of filler metal was improved with addition of Si to the filler metal.
The (Ti0.46Cu0.14Zr0.27Ni0.13)1-xSix amorphous filler metal was prepared by arc melting and fast-cooling melt-spinning technologies, and the effect of a certain amount of Si added to the filler metal on its amorphous forming ability was studied. The results show that the filler metal presented the strongest amorphous forming ability when the additive Si reached 0.5%; its wetting area was 3.06 cm2,its supercooled liquid phase region width (?Tx) ?Tx=56 ℃,its reduced glass transition temperature (Trg) Trg=0.5387, and its liquidus temperature was 949 ℃. The vacuum brazing was done for SiC and TC4 using this amorphous alloy as the filler metal, and the shear strength of brazed joint was 80 MPa. The amorphous forming ability of filler metal was improved with addition of Si to the filler metal.
2018, 47(7):2028-2036.
Abstract:
TiCN films were deposited on AISI 304 stainless steel substrate by combining multi-arc ion plating and magnetron sputtering technique with ionizing titanium and graphite targets in an Ar+N2 mixture gas. The effect of duty ratio on the microstructure and corrosion resistance performance of TiCN films in a NaCl 3.5 wt.% solution was investigated. The results show that the as-deposited films reveal smooth, uniform and dense morphologies, mainly forming a fcc-TiN type structure with Ti-(C,N) bond as well as few a-CNx, and presenting (111) preferred orientation with the increase of duty ratio. TiCN films display a better resistance to corrosion than the bare substrate, as the duty ratio increased, the corrosion resistance property is enhanced gradually. When the duty ratio is 40%, the TiCN film shows the optimal one with a corrosion current density (icorr) of 3.262×10-7 A.cm-2 and a polarization resistance (Rp) of 238.4 kΩ.cm2, respectively. Electrochemical impedance spectroscopy (EIS) of the films also indicate that the penetration behavior of corrosive ions and the local corrosion process are two key factors affecting the electrode corrosion reaction kinetics process, which is in agreement with the polarization curves analysis results.
TiCN films were deposited on AISI 304 stainless steel substrate by combining multi-arc ion plating and magnetron sputtering technique with ionizing titanium and graphite targets in an Ar+N2 mixture gas. The effect of duty ratio on the microstructure and corrosion resistance performance of TiCN films in a NaCl 3.5 wt.% solution was investigated. The results show that the as-deposited films reveal smooth, uniform and dense morphologies, mainly forming a fcc-TiN type structure with Ti-(C,N) bond as well as few a-CNx, and presenting (111) preferred orientation with the increase of duty ratio. TiCN films display a better resistance to corrosion than the bare substrate, as the duty ratio increased, the corrosion resistance property is enhanced gradually. When the duty ratio is 40%, the TiCN film shows the optimal one with a corrosion current density (icorr) of 3.262×10-7 A.cm-2 and a polarization resistance (Rp) of 238.4 kΩ.cm2, respectively. Electrochemical impedance spectroscopy (EIS) of the films also indicate that the penetration behavior of corrosive ions and the local corrosion process are two key factors affecting the electrode corrosion reaction kinetics process, which is in agreement with the polarization curves analysis results.
2018, 47(7):2037-2041.
Abstract:
A new DC arc plasma concept to produce metal oxides nanoparticles by metal melting, blasting or gasification processes is presented. It is exemplified for the preparation of SnO2, In2O3 single phases nanoparticles and the base of SnO2, In2O3 composite nanoparticles such as In2O3:Sn (ITO), SnO2:Sb (ATO), and SnO2:In:Sb (IATO). X-ray diffraction (XRD) indicated that the doped SnO2 and In2O3 are in single phase with no other secondary phases. Transmission electron microscopy (TEM) showed the particle size ranged from 20 nm to 50 nm for the prepared single phases of nanoparticles with good dispersion. The prepared ITO and ATO nanoparticles were utilized in ITO target and ATO electrode, and their density and electrical properties were tested. The prepared ITO target and ATO electrode show high density and low resistivity and film-forming effect is good for ITO target, implying that the ITO and ATO nanoparticles prepared by DC arc plasma can be applied in the field of flat panel displays and conductive electrodes.
A new DC arc plasma concept to produce metal oxides nanoparticles by metal melting, blasting or gasification processes is presented. It is exemplified for the preparation of SnO2, In2O3 single phases nanoparticles and the base of SnO2, In2O3 composite nanoparticles such as In2O3:Sn (ITO), SnO2:Sb (ATO), and SnO2:In:Sb (IATO). X-ray diffraction (XRD) indicated that the doped SnO2 and In2O3 are in single phase with no other secondary phases. Transmission electron microscopy (TEM) showed the particle size ranged from 20 nm to 50 nm for the prepared single phases of nanoparticles with good dispersion. The prepared ITO and ATO nanoparticles were utilized in ITO target and ATO electrode, and their density and electrical properties were tested. The prepared ITO target and ATO electrode show high density and low resistivity and film-forming effect is good for ITO target, implying that the ITO and ATO nanoparticles prepared by DC arc plasma can be applied in the field of flat panel displays and conductive electrodes.
2018, 47(7):2042-2048.
Abstract:
Interfacial reactions and growth kinetics between molten Mg-40Al and solid Mg-20Ce were investigated. Reaction temperatures were at 475°C, 500°C and 525°C, with reaction time ranging from 5min to 30min. Al11Ce3, Al3Ce and Al2Ce were formed via the reaction of Al and Ce in the diffusion reaction layers. The volume fraction of the intermetallic compounds in the diffusion layer increased with temperature. The growth kinetics of the diffusion reaction layers was well conformed to the parabolic law. The activation energy for the growth of the diffusion reaction layers was 42±3.7kJ/mol. Liquid-solid diffusion experiment can better understand the formation of compounds in the smelting process. Kinetics datum were provided for the formation of the compound during the smelting process.
Interfacial reactions and growth kinetics between molten Mg-40Al and solid Mg-20Ce were investigated. Reaction temperatures were at 475°C, 500°C and 525°C, with reaction time ranging from 5min to 30min. Al11Ce3, Al3Ce and Al2Ce were formed via the reaction of Al and Ce in the diffusion reaction layers. The volume fraction of the intermetallic compounds in the diffusion layer increased with temperature. The growth kinetics of the diffusion reaction layers was well conformed to the parabolic law. The activation energy for the growth of the diffusion reaction layers was 42±3.7kJ/mol. Liquid-solid diffusion experiment can better understand the formation of compounds in the smelting process. Kinetics datum were provided for the formation of the compound during the smelting process.
Luo Liangshun
,
Wang Fuxin
,
Wu Xiaoming
,
Wang Liang
,
Su Yanqing
,
Shi Yaming
,
Guo Jingjie
,
Fu Hengzhi
2018, 47(7):2049-2055.
Abstract:
The paper prepared the cast Ti-6Al-2.5V-1.5Fe-0.15O titanium alloys by the consumable vacuum arc furnace. Thermal simulation experiments are carried out by Gleebee 1500D, and different deformation temperatures (875℃-1100℃),train rates(0.001-1 s-1)and the same deformation degree(60%) were chose. Then phase equations of two phase and single based on Arrhenius model were built, considering the influence of strain. The processing map was built by DMM and Prasad instability criterion. The results show that the alloy is belonging to negative temperature and normal strain sensitivity material. The average thermal activation energy of two phase is 398.824KJ/mol,which is bigger than the pure titanium. The softening is related to the dynamic recrystallization softening mechanism. The average thermal activation energy of single phase is 210.93KJ/mol,slightly more than the pure titanium,The softening is related to the dynamic recovery. The two flow instability zones appear on the processing map,The adiabatic shearing easily happens at medium temperate from 950℃-1070℃ and the high strain rates from 0.31s-1 to 1s-1,The suitable zone for processing is in the strain rates from 0.001s-1to 0.1-1 and temperate from 875℃ to 925 ℃.
The paper prepared the cast Ti-6Al-2.5V-1.5Fe-0.15O titanium alloys by the consumable vacuum arc furnace. Thermal simulation experiments are carried out by Gleebee 1500D, and different deformation temperatures (875℃-1100℃),train rates(0.001-1 s-1)and the same deformation degree(60%) were chose. Then phase equations of two phase and single based on Arrhenius model were built, considering the influence of strain. The processing map was built by DMM and Prasad instability criterion. The results show that the alloy is belonging to negative temperature and normal strain sensitivity material. The average thermal activation energy of two phase is 398.824KJ/mol,which is bigger than the pure titanium. The softening is related to the dynamic recrystallization softening mechanism. The average thermal activation energy of single phase is 210.93KJ/mol,slightly more than the pure titanium,The softening is related to the dynamic recovery. The two flow instability zones appear on the processing map,The adiabatic shearing easily happens at medium temperate from 950℃-1070℃ and the high strain rates from 0.31s-1 to 1s-1,The suitable zone for processing is in the strain rates from 0.001s-1to 0.1-1 and temperate from 875℃ to 925 ℃.
2018, 47(7):2056-2060.
Abstract:
In this paper a split Hopkinson tension bar system is improved by adding wave absorbers into the incident bar and the transmission bar, and the reflected waves in the input and output bar in dynamic tension experiments will be eliminated. The dynamic tension recovery technique is developed by adopting the improved bar system. Dynamic tension and recovery experiments are conducted to obtain the adiabatic and isothermal stress-strain responses of the TC11 alloy at high strain rates. And the adiabatic softening effect is experimentally uncoupled from the strain-rate strengthening and strain hardening effects. The quasi-static tensile tests under different initial temperatures are also carried out to study the thermal softening effect which is described by using Johnson-Cook model. The model is modified by introducing the value of adiabatic temperature rise in dynamic tensile process.When the adiabatic curves of modified model and experiment are in good agreement, the conversion factors of plastic dissipation power to heat at different strain rates will be determined. And the conversion factor of the strain rate 500s-1 is found to be less than that of the strain rate 190s-1.
In this paper a split Hopkinson tension bar system is improved by adding wave absorbers into the incident bar and the transmission bar, and the reflected waves in the input and output bar in dynamic tension experiments will be eliminated. The dynamic tension recovery technique is developed by adopting the improved bar system. Dynamic tension and recovery experiments are conducted to obtain the adiabatic and isothermal stress-strain responses of the TC11 alloy at high strain rates. And the adiabatic softening effect is experimentally uncoupled from the strain-rate strengthening and strain hardening effects. The quasi-static tensile tests under different initial temperatures are also carried out to study the thermal softening effect which is described by using Johnson-Cook model. The model is modified by introducing the value of adiabatic temperature rise in dynamic tensile process.When the adiabatic curves of modified model and experiment are in good agreement, the conversion factors of plastic dissipation power to heat at different strain rates will be determined. And the conversion factor of the strain rate 500s-1 is found to be less than that of the strain rate 190s-1.
2018, 47(7):2061-2066.
Abstract:
Compressive twinning behavior in high-purity titanium was studied by electrical back-scattered diffraction (EBSD) techniques. The results show that {11-24} twins are always accompanied with {11-22} twins in some specific grains, and individual {11-24} twin is not observed in microstructure of the deformed sample. The formation of {11-24} twin is attributed to the changes of local stress states, which induced by the {11-22}-{11-22} twin variants interactions or {11-22} twin interactes with the grain boundaries. The {11-22} and {11-24} twins tend to share a common rotation axis with one of the {11-22} twin variant within an initial grain. In addition, due to the crystal symmetry and the orientation relationships between {11-22} and {11-24} twins, interactions between {11-22} and {11-24} twins inevitably occur, which results in four different types of {11-22}-{11-24} twin junctions.
Compressive twinning behavior in high-purity titanium was studied by electrical back-scattered diffraction (EBSD) techniques. The results show that {11-24} twins are always accompanied with {11-22} twins in some specific grains, and individual {11-24} twin is not observed in microstructure of the deformed sample. The formation of {11-24} twin is attributed to the changes of local stress states, which induced by the {11-22}-{11-22} twin variants interactions or {11-22} twin interactes with the grain boundaries. The {11-22} and {11-24} twins tend to share a common rotation axis with one of the {11-22} twin variant within an initial grain. In addition, due to the crystal symmetry and the orientation relationships between {11-22} and {11-24} twins, interactions between {11-22} and {11-24} twins inevitably occur, which results in four different types of {11-22}-{11-24} twin junctions.
2018, 47(7):2067-2071.
Abstract:
Magneli phase electrode is a potential anode for sewage electrochemical degradation due to its high conductivity and wide electrochemical window. However, few works was done to evaluate the performance of the Magneli phase electrode. In this work, the Magneli phase electrode was prepared by plasma spray methods and examined by accelerating life methods. The result shows that the accelerating life cycle of the Magneli phase electrode is about 320 h. The life cycle of Magneli phase electrode can be extended to 420h by alternating the current direction. The failing reason of the Magneli phase electrode is the exfoliation of the coating, which makes the Ti substrate contact with the solution. Then the passivation the the Ti substrate leads to resistance increasing, consequently increasing of cell voltage.
Magneli phase electrode is a potential anode for sewage electrochemical degradation due to its high conductivity and wide electrochemical window. However, few works was done to evaluate the performance of the Magneli phase electrode. In this work, the Magneli phase electrode was prepared by plasma spray methods and examined by accelerating life methods. The result shows that the accelerating life cycle of the Magneli phase electrode is about 320 h. The life cycle of Magneli phase electrode can be extended to 420h by alternating the current direction. The failing reason of the Magneli phase electrode is the exfoliation of the coating, which makes the Ti substrate contact with the solution. Then the passivation the the Ti substrate leads to resistance increasing, consequently increasing of cell voltage.
2018, 47(7):2072-2079.
Abstract:
The microstructure evolution and phase transformation of Mg-16Zn-5Al alloy were investigated during partial remelting. Results show that when remelting parameter is 440℃+(30~60min) or 460℃+30min, Mg-16Zn-5Al alloy can obtain the idea semi-solid spherical microstructure. The average grain size is 54.9~57.9μm, and the average roundness is 1.18~1.29, and the solid fraction is about 65%. The phases transformation which include MgZn+τ→α-Mg, α-Mg+MgZn+τ→L, α-Mg→L, α-Mg→L and L→α-Mg were occurred during partial remelting. They lead to the initial rapid coarsening of the grain, structure separation, spheroidization of the grain and final merger coarsening. Meanwhile, the subboundary and root remelting within the alloy play an important role in separation of microstructure. The coarsening factor Mn which related with diffusion coefficient at a isothermal period was deduced by LSW theory. The main evolution way of grain is described by Mn at corresponding period.
The microstructure evolution and phase transformation of Mg-16Zn-5Al alloy were investigated during partial remelting. Results show that when remelting parameter is 440℃+(30~60min) or 460℃+30min, Mg-16Zn-5Al alloy can obtain the idea semi-solid spherical microstructure. The average grain size is 54.9~57.9μm, and the average roundness is 1.18~1.29, and the solid fraction is about 65%. The phases transformation which include MgZn+τ→α-Mg, α-Mg+MgZn+τ→L, α-Mg→L, α-Mg→L and L→α-Mg were occurred during partial remelting. They lead to the initial rapid coarsening of the grain, structure separation, spheroidization of the grain and final merger coarsening. Meanwhile, the subboundary and root remelting within the alloy play an important role in separation of microstructure. The coarsening factor Mn which related with diffusion coefficient at a isothermal period was deduced by LSW theory. The main evolution way of grain is described by Mn at corresponding period.
2018, 47(7):2080-2086.
Abstract:
In order to investigate the microstructure evolution of 925 alloy during homogenization and solution treatment, nickel-based superalloy 925 alloy ingots of vacuum-induction-melting and electroslag-remelting were prepared and homogenization and solution tests were carried out. The microstructure and precipitations of 925 samples were studied by optical microscopy,scanning electron microscopy,and energy dispersive spectroscopy．It is found that there exist phases such as TiN, MC, σ phase, γ′ phase and η phase in the ingots， and σ phase, γ′ phase and η phase can be remelted in 1160℃ after 5h. After homogenization at 1160℃ for 20 h,this segregation can almost be eliminated. In solution treatment range of 950℃ to 1070℃, the amount of grain boundary precipitation of M23C6 decreases gradually and the grain size increases quickly.
In order to investigate the microstructure evolution of 925 alloy during homogenization and solution treatment, nickel-based superalloy 925 alloy ingots of vacuum-induction-melting and electroslag-remelting were prepared and homogenization and solution tests were carried out. The microstructure and precipitations of 925 samples were studied by optical microscopy,scanning electron microscopy,and energy dispersive spectroscopy．It is found that there exist phases such as TiN, MC, σ phase, γ′ phase and η phase in the ingots， and σ phase, γ′ phase and η phase can be remelted in 1160℃ after 5h. After homogenization at 1160℃ for 20 h,this segregation can almost be eliminated. In solution treatment range of 950℃ to 1070℃, the amount of grain boundary precipitation of M23C6 decreases gradually and the grain size increases quickly.
2018, 47(7):2087-2092.
Abstract:
In order to research the mechanisms of effect of rare earth microalloying on the impact toughness of HSLA steel, oscillographic impact experiments have been tested by instrumented Charpy impact equipment. The microstructures including: tissues, characteristics of grain boundaries and volume fractions of the retained austenite have been analyzed by scanning electron microscopy (SEM), electron back scattering diffraction (EBSD) and X-ray diffraction (XRD). The solid solution quantity of lanthanum and precipitates of the niobium, titanium and vanadium were quantified by physics-chemical phase analysis. Sizes of the secondary phase precipitates were measured by small angle X–ray scattering (SAXS). The results indicated that, the toughness of the HSLA steel can be enhanced by addition of La into the steel, in particular to prevent cracks propagation. The mechanisms were as follow, the volume fraction of retained austenite, the quantity of high-angle and the low-Σ value coincidence site lattice (CSL) grain boundaries were increased. In addition, precipitates of niobium, titanium and vanadium were decreased and the sizes of the secondary phase precipitates were refined by addition of La into the steel.
In order to research the mechanisms of effect of rare earth microalloying on the impact toughness of HSLA steel, oscillographic impact experiments have been tested by instrumented Charpy impact equipment. The microstructures including: tissues, characteristics of grain boundaries and volume fractions of the retained austenite have been analyzed by scanning electron microscopy (SEM), electron back scattering diffraction (EBSD) and X-ray diffraction (XRD). The solid solution quantity of lanthanum and precipitates of the niobium, titanium and vanadium were quantified by physics-chemical phase analysis. Sizes of the secondary phase precipitates were measured by small angle X–ray scattering (SAXS). The results indicated that, the toughness of the HSLA steel can be enhanced by addition of La into the steel, in particular to prevent cracks propagation. The mechanisms were as follow, the volume fraction of retained austenite, the quantity of high-angle and the low-Σ value coincidence site lattice (CSL) grain boundaries were increased. In addition, precipitates of niobium, titanium and vanadium were decreased and the sizes of the secondary phase precipitates were refined by addition of La into the steel.
2018, 47(7):2093-2099.
Abstract:
In order to investigate the effect of cerium on the carbon segregation in steel, a thermodynamic calculation mold of equilibrium partition coefficient in multi-component alloy is established. The equilibrium partition coefficient of C in Fe-C-Ce system with different cerium content is calculated with Equilib moudle of FactSage. Results show that the effect of cerium on phase transformation is remarkable during solidification. The addition of cerium facilitates austenite transformation and enlarges the L-γ coexist zone. Cerium increases the average equilibrium partition coefficient which means it can mitigate the segregation of C in steel. The optimum addition content of cerium to improve the segregation of C in steel are associated with carbon content. For Fe-0.1%C-x%Ce system, the optimum addition content of cerium ranges from 0.047% to 0.057%. And for Fe-0.25%C-x%Ce system, the optimum addition content of cerium ranges from 0.03% to 0.04%.
In order to investigate the effect of cerium on the carbon segregation in steel, a thermodynamic calculation mold of equilibrium partition coefficient in multi-component alloy is established. The equilibrium partition coefficient of C in Fe-C-Ce system with different cerium content is calculated with Equilib moudle of FactSage. Results show that the effect of cerium on phase transformation is remarkable during solidification. The addition of cerium facilitates austenite transformation and enlarges the L-γ coexist zone. Cerium increases the average equilibrium partition coefficient which means it can mitigate the segregation of C in steel. The optimum addition content of cerium to improve the segregation of C in steel are associated with carbon content. For Fe-0.1%C-x%Ce system, the optimum addition content of cerium ranges from 0.047% to 0.057%. And for Fe-0.25%C-x%Ce system, the optimum addition content of cerium ranges from 0.03% to 0.04%.
2018, 47(7):2100-2106.
Abstract:
Using X-ray microscope, thermal barrier coatings (TBCs) were imaged with a high resolution of 0.5 μm after high temperature cycles. Three-dimensional segmentation and extraction of thermally grown oxide (TGO) was performed. A finite element analysis model of thermal barrier coatings was established based on real three-dimensional (3D) structure of thermally grown oxide, and the effect of creep and thermal cycles on the stress distribution of thermal barrier coatings were researched. The results of finite element analysis show that the stress decreases greatly due to the influence of creep at the keeping stage. The results of three-dimensional thermal stress distribution shows that the thermal stress at the interface between the bond coat and the TGO is the maximum. The stress of thermal barrier coating increases with the increase of thermal cycle number, but the stress tends to be stable after 15 thermal cycles.
Using X-ray microscope, thermal barrier coatings (TBCs) were imaged with a high resolution of 0.5 μm after high temperature cycles. Three-dimensional segmentation and extraction of thermally grown oxide (TGO) was performed. A finite element analysis model of thermal barrier coatings was established based on real three-dimensional (3D) structure of thermally grown oxide, and the effect of creep and thermal cycles on the stress distribution of thermal barrier coatings were researched. The results of finite element analysis show that the stress decreases greatly due to the influence of creep at the keeping stage. The results of three-dimensional thermal stress distribution shows that the thermal stress at the interface between the bond coat and the TGO is the maximum. The stress of thermal barrier coating increases with the increase of thermal cycle number, but the stress tends to be stable after 15 thermal cycles.
2018, 47(7):2107-2112.
Abstract:
A new method for hydrogen storage electrode alloys design was proposed. It combines the calculation of the phase diagram and maximum discharge capacity of an electrode to construct the "phase diagram of electrochemical discharge capacity" for the RE-Mg-Ni-based hydrogen storage electrode alloys. This method can provide guidance for hydrogen storage electrode alloy design with rapid determination of an alloy composition having a high discharge capacity. In RE (Nd, Y, Ce)-Mg-Ni systems, the Nd-Mg-Ni alloys have the highest discharge capacity. The maximum discharge capacity for NdMgNi4 alloy in Nd-Mg-Ni system is 271.06 mAh/g.
A new method for hydrogen storage electrode alloys design was proposed. It combines the calculation of the phase diagram and maximum discharge capacity of an electrode to construct the "phase diagram of electrochemical discharge capacity" for the RE-Mg-Ni-based hydrogen storage electrode alloys. This method can provide guidance for hydrogen storage electrode alloy design with rapid determination of an alloy composition having a high discharge capacity. In RE (Nd, Y, Ce)-Mg-Ni systems, the Nd-Mg-Ni alloys have the highest discharge capacity. The maximum discharge capacity for NdMgNi4 alloy in Nd-Mg-Ni system is 271.06 mAh/g.
2018, 47(7):2113-2119.
Abstract:
Isothermal tensile tests of 2060-T8 Al-Li alloy were conducted on a UTM5000 electronic universal tensile testing machine at deformation temperature ranging from 573 to 648K and strain rate ranging from 0.001 to 0.1s-1. The true stress-strain curves of 2060-T8 Al-Li alloy were obtained and constitutive equation considering the strain compensation as well as correction term was also established. The warm deformation behavior of 2060-T8 Al-Li alloy was investigated by the analysis of tensile fractures using scanning electron microscopy (SEM). The results show that 2060-T8 Al-Li alloy is highly sensitive to deformation temperature and strain rate. The true stress-strain curves show the characteristics of strain hardening followed by flow softening and steady flow characteristic gradually disappears with the increase of deformation temperature and the decrease of strain rate. In addition, 2060-T8 Al-Li alloy is of ductile fracture during warm deformation. The modified constitutive model is in great agreement with the experimental data, which can provide a precondition for the finite element analysis of 2060-T8 Al-Li alloy during warm deformation.
Isothermal tensile tests of 2060-T8 Al-Li alloy were conducted on a UTM5000 electronic universal tensile testing machine at deformation temperature ranging from 573 to 648K and strain rate ranging from 0.001 to 0.1s-1. The true stress-strain curves of 2060-T8 Al-Li alloy were obtained and constitutive equation considering the strain compensation as well as correction term was also established. The warm deformation behavior of 2060-T8 Al-Li alloy was investigated by the analysis of tensile fractures using scanning electron microscopy (SEM). The results show that 2060-T8 Al-Li alloy is highly sensitive to deformation temperature and strain rate. The true stress-strain curves show the characteristics of strain hardening followed by flow softening and steady flow characteristic gradually disappears with the increase of deformation temperature and the decrease of strain rate. In addition, 2060-T8 Al-Li alloy is of ductile fracture during warm deformation. The modified constitutive model is in great agreement with the experimental data, which can provide a precondition for the finite element analysis of 2060-T8 Al-Li alloy during warm deformation.
2018, 47(7):2216-2224.
Abstract:
The newly developed Al-Li alloy 2060 has broad application prospects in the field of aeronautics and astronautics with the characteristics of light weight and high strength. In this paper, 2060 Al-Li alloy was tested by means of laser beam welding filled with ER4047 welding wire. The morphology and microstructure of the weld, the micro segregation of the alloy elements, the precipitation of the second phases and the mechanical properties of the weld were studied by means of optical microscope, scanning electron microscope, electron probe micro analyzer(EPMA) and transmission electron microscopy(TEM), X-ray diffractometer (XRD), micro hardness test, tensile test. The results show that the formation of the weld is good in a reasonable welding process. Along the fusion line, there are so fine equiaxed grains, and there exist a large number of equiaxed dendritic crystals and columnar grains in the center of the weld. The micro segregation of the weld is more serious at the grain boundaries, such as Cu, Mg and Si, but the Al elements are less. The main reinforcement phase T1 (Al2CuLi) in the weld are almost all disappeared, and there is a certain amount of TB (Al7Cu4Li) phase precipitation. There are a large number of binary eutectics and ternary eutectics in the grain boundary, more Cu5Si and AlCuxMnx brittle compounds. In the heat affected zone (HAZ), the grain size and the size of the second phase become larger. T1 (Al2CuLi), θ" (Al2Cu) and TB phases are undissolved. Under the optimum process, the hardness of the weld zone is the smallest, with an average of 98.6HV, about 65% of the base metal. The tensile strength of the joint is 354MPa, and the elongation is 4.9%, about 67% and 40.8% of the base metal respectively. The tensile fracture occurs preferentially in the coarse equiaxed grain zone at the upper part of the weld, and gradually extends along the grain boundaries, finally fractured in the columnar grain zone. The fracture morphology belongs to the mixed fracture of toughness and brittleness with a large number of dimples.
The newly developed Al-Li alloy 2060 has broad application prospects in the field of aeronautics and astronautics with the characteristics of light weight and high strength. In this paper, 2060 Al-Li alloy was tested by means of laser beam welding filled with ER4047 welding wire. The morphology and microstructure of the weld, the micro segregation of the alloy elements, the precipitation of the second phases and the mechanical properties of the weld were studied by means of optical microscope, scanning electron microscope, electron probe micro analyzer(EPMA) and transmission electron microscopy(TEM), X-ray diffractometer (XRD), micro hardness test, tensile test. The results show that the formation of the weld is good in a reasonable welding process. Along the fusion line, there are so fine equiaxed grains, and there exist a large number of equiaxed dendritic crystals and columnar grains in the center of the weld. The micro segregation of the weld is more serious at the grain boundaries, such as Cu, Mg and Si, but the Al elements are less. The main reinforcement phase T1 (Al2CuLi) in the weld are almost all disappeared, and there is a certain amount of TB (Al7Cu4Li) phase precipitation. There are a large number of binary eutectics and ternary eutectics in the grain boundary, more Cu5Si and AlCuxMnx brittle compounds. In the heat affected zone (HAZ), the grain size and the size of the second phase become larger. T1 (Al2CuLi), θ" (Al2Cu) and TB phases are undissolved. Under the optimum process, the hardness of the weld zone is the smallest, with an average of 98.6HV, about 65% of the base metal. The tensile strength of the joint is 354MPa, and the elongation is 4.9%, about 67% and 40.8% of the base metal respectively. The tensile fracture occurs preferentially in the coarse equiaxed grain zone at the upper part of the weld, and gradually extends along the grain boundaries, finally fractured in the columnar grain zone. The fracture morphology belongs to the mixed fracture of toughness and brittleness with a large number of dimples.
2018, 47(7):2225-2231.
Abstract:
To investigate the flow stress characteristics and deformation?mechanism of MoLa Alloy,The isothermal compression tests were performed over the ranges of temperature 800-1150oC and the strain rate range of 0.001-10 s -1.The results show that the flow stress increases or remain stable with the increase of strain .But the flow stress decrease with the increase of strain in which the deformation temperature is 1000-1150 ℃ and the strain rate is 0.001s-1.A PSO-BP neural network has been established to describe the changing rule of flow stress with the strain rate and deformation temperature .The correlation coefficient and average?relative?error of the network have been calculated to be 0.995 and 1.48% respectively.So it is clear that the PSO-BP model has?good?accuracy .The intrinsic hot workability maps have been constructed based on the polar reciprocity model at strains of 0.3,0.6 and 0.92.?Combing microstructure observation ,it has been found that the buckling form in instability area mainly was local plastic deformation,and deformation mechanism in stability region mainly was dynamic recovery.The suitable processing parameters ranges of MoLa alloy could be inferred to be the deformation temperature range of 1100-1150 ℃ and the strain rates range of 0.001- 0.05 s-1.
To investigate the flow stress characteristics and deformation?mechanism of MoLa Alloy,The isothermal compression tests were performed over the ranges of temperature 800-1150oC and the strain rate range of 0.001-10 s -1.The results show that the flow stress increases or remain stable with the increase of strain .But the flow stress decrease with the increase of strain in which the deformation temperature is 1000-1150 ℃ and the strain rate is 0.001s-1.A PSO-BP neural network has been established to describe the changing rule of flow stress with the strain rate and deformation temperature .The correlation coefficient and average?relative?error of the network have been calculated to be 0.995 and 1.48% respectively.So it is clear that the PSO-BP model has?good?accuracy .The intrinsic hot workability maps have been constructed based on the polar reciprocity model at strains of 0.3,0.6 and 0.92.?Combing microstructure observation ,it has been found that the buckling form in instability area mainly was local plastic deformation,and deformation mechanism in stability region mainly was dynamic recovery.The suitable processing parameters ranges of MoLa alloy could be inferred to be the deformation temperature range of 1100-1150 ℃ and the strain rates range of 0.001- 0.05 s-1.
2018, 47(7):2120-2125.
Abstract:
The method of molten salt electrolysis was applied for boronizing of Titanium. The experiment was carried out at 930 ℃ for1h, using Borax as the source of boron and Calcium Chloride as supporting electrolyte. The effects of current density on the microstructure and the thickness of the TiB2/TiB layer were investigated and the electrochemical behavior of cathode in molten salt was studied by Cyclic Voltammetry. XRD, SEM and EDS means were applied to analyze phase composition, microstructure and morphology, element content of the borides layer respectively. The results show that the bording layer was composed of TiB2 and TiB, with the thickness of the TiB2 layer being 1.2 to 4.5μm depending on the current density; the thickness of the TiB2 layer changes nonlinearly with the increase of the current density；Analysis of the Cyclic Voltammetry curve shows that the cathodic reaction was mainly the reduction of sodium ions to sodium, then boron was reduced by sodium from B2O3; the borides layer was formed by the diffusion of B atoms into titanium substrate at high temperature.
The method of molten salt electrolysis was applied for boronizing of Titanium. The experiment was carried out at 930 ℃ for1h, using Borax as the source of boron and Calcium Chloride as supporting electrolyte. The effects of current density on the microstructure and the thickness of the TiB2/TiB layer were investigated and the electrochemical behavior of cathode in molten salt was studied by Cyclic Voltammetry. XRD, SEM and EDS means were applied to analyze phase composition, microstructure and morphology, element content of the borides layer respectively. The results show that the bording layer was composed of TiB2 and TiB, with the thickness of the TiB2 layer being 1.2 to 4.5μm depending on the current density; the thickness of the TiB2 layer changes nonlinearly with the increase of the current density；Analysis of the Cyclic Voltammetry curve shows that the cathodic reaction was mainly the reduction of sodium ions to sodium, then boron was reduced by sodium from B2O3; the borides layer was formed by the diffusion of B atoms into titanium substrate at high temperature.
2018, 47(7):2126-2131.
Abstract:
Ultra-fine grained commercially pure (CP) Ti with an average grain size of 120 nm was fabricated by equal channel angular pressing (ECAP) following cold rolling (CR) and swaging at room temperature. Uniaxial tensile creep tests, transmission electron microscope and scanning electron microscope were applied to investigate the creep behavior and mechanism of ultra-fine grained CP Ti. The results showed that a significant creep deformation at room temperature occurred in the ultra-fine grained CP Ti. The steady creep rate increased from 2.8×10-7 s-1 to 1.5×10-4 s-1 as the creep stress increased from 640 MPa to 760 MPa. Ultra-fine grained CP Ti had lower steady creep rate than the coarse-grained CP Ti at the same stress level, which indicated that ultra-fine grained CP Ti had higher creep resistance. The creep mechanism of ultra-fine grained CP Ti is dislocation movement. The creep fracture morphology of ultra-fine grained CP Ti exhibited ductile fracture with dimples.
Ultra-fine grained commercially pure (CP) Ti with an average grain size of 120 nm was fabricated by equal channel angular pressing (ECAP) following cold rolling (CR) and swaging at room temperature. Uniaxial tensile creep tests, transmission electron microscope and scanning electron microscope were applied to investigate the creep behavior and mechanism of ultra-fine grained CP Ti. The results showed that a significant creep deformation at room temperature occurred in the ultra-fine grained CP Ti. The steady creep rate increased from 2.8×10-7 s-1 to 1.5×10-4 s-1 as the creep stress increased from 640 MPa to 760 MPa. Ultra-fine grained CP Ti had lower steady creep rate than the coarse-grained CP Ti at the same stress level, which indicated that ultra-fine grained CP Ti had higher creep resistance. The creep mechanism of ultra-fine grained CP Ti is dislocation movement. The creep fracture morphology of ultra-fine grained CP Ti exhibited ductile fracture with dimples.
2018, 47(7):2132-2136.
Abstract:
Abstract: Direct diffusion bonding of high Nb containing TiAl alloy(TAN) has been conducted at temperatures of 1000℃～1200℃ for 90min under 25MPa in vacuum. The effect of bonding temperature on interfacial microstructure and mechanical properities of joints was studied and the microstructure of joints was detected by using SEM, EDS, XRD and EBSD. The results indicate that the distinct interface can be seen when the temperature is below 1100℃ and the higher temperature promotes interface disappear; recrystallized grains are observed at bonding interface. The number and size of grains increase with the rise of temperature and a lot of α2 phase appears in the area of recrystallization; the highest average shear strength of 105 MPa was achieved when bonded at the temperature of 1150℃ for 90min under 25MPa.
Abstract: Direct diffusion bonding of high Nb containing TiAl alloy(TAN) has been conducted at temperatures of 1000℃～1200℃ for 90min under 25MPa in vacuum. The effect of bonding temperature on interfacial microstructure and mechanical properities of joints was studied and the microstructure of joints was detected by using SEM, EDS, XRD and EBSD. The results indicate that the distinct interface can be seen when the temperature is below 1100℃ and the higher temperature promotes interface disappear; recrystallized grains are observed at bonding interface. The number and size of grains increase with the rise of temperature and a lot of α2 phase appears in the area of recrystallization; the highest average shear strength of 105 MPa was achieved when bonded at the temperature of 1150℃ for 90min under 25MPa.
2018, 47(7):2137-2143.
Abstract:
In order to improve wear and fatigue resistance of titanium alloy, plasma alloying technique was applied to treat TC4 alloy with zirconium followed by nitrogen, and the gradient metallurgical zirconium nitride (ZrN) layer was fabricated. The surface metallurgical layer was then treated by shot peening. The microstructure, chemical composition and microhardness profile of the modified surface layer were then evaluated by using scanning electron microscope, X-ray diffraction, glow-discharge photo-electron spectroscopy and micro- hardness tester. The fatigue behavior and mechanism influencing by the modified surface layer were investigated. The results demonstrate that the uppermost modified layer is composed of ZrN-TiN compound phase (mainly ZrN) and underlying nitrogen-rich Zr-Ti solid solution, and the surface hardness is raised 320%. The modified surface layer dramatically reduces the fatigue resistance of base material, due to the low toughness of ZrN-TiN layer and the increase of surface roughness. After combined with shot peening, the fatigue resistance of TC4 alloy is improved significantly, more than the specimens of both base material and shot peening alone. Since shot peening introduces a deep and high value compressive residual stress into the surface, lowers the roughness and refines the surface microstructure of TC4 titanium, and thus the initiation and early growth of fatigue cracks are restrained.
In order to improve wear and fatigue resistance of titanium alloy, plasma alloying technique was applied to treat TC4 alloy with zirconium followed by nitrogen, and the gradient metallurgical zirconium nitride (ZrN) layer was fabricated. The surface metallurgical layer was then treated by shot peening. The microstructure, chemical composition and microhardness profile of the modified surface layer were then evaluated by using scanning electron microscope, X-ray diffraction, glow-discharge photo-electron spectroscopy and micro- hardness tester. The fatigue behavior and mechanism influencing by the modified surface layer were investigated. The results demonstrate that the uppermost modified layer is composed of ZrN-TiN compound phase (mainly ZrN) and underlying nitrogen-rich Zr-Ti solid solution, and the surface hardness is raised 320%. The modified surface layer dramatically reduces the fatigue resistance of base material, due to the low toughness of ZrN-TiN layer and the increase of surface roughness. After combined with shot peening, the fatigue resistance of TC4 alloy is improved significantly, more than the specimens of both base material and shot peening alone. Since shot peening introduces a deep and high value compressive residual stress into the surface, lowers the roughness and refines the surface microstructure of TC4 titanium, and thus the initiation and early growth of fatigue cracks are restrained.
2018, 47(7):2144-2150.
Abstract:
The anisotropy caused by columnar β grains are the main challenges in arc additive manufacturing of Ti-6Al-4V. In order to handle these issues, multilayer walls are deposited with different pulse frequencies and heat inputs. Combined with finite element analysis, the influence of pulse frequency and heat input on macrostructure and microstructure of deposited Ti-6Al-4V compounds are investigated. Results indicate that with the increase of pulse frequency, the widths of deposited walls decrease rapidly at first, then increase slightly; columnar β grains transform into equiaxed β grains and the grains get finer, but α phases have no obvious variation. The increasing heat input is beneficial to obtaining equiaxed β grains, but the wall width will enlarge and α phases will be coarser. The width of the specimen is determined by the dimension of the molten pool, which is influenced by the average heat input and the input heat in peak time period. Improving pulse frequency can break the dendrites as well as reduce the temperature gradient, which is conducive to the nucleation. Besides, higher heat input can reduce the temperature gradient as well. Therefore, equiaxed β grains are formed with the increase of pulse frequency and heat input. The morphology of α phases are mainly associated with the cooling rate. Reducing heat input can increase cooling rate and refine α phases.
The anisotropy caused by columnar β grains are the main challenges in arc additive manufacturing of Ti-6Al-4V. In order to handle these issues, multilayer walls are deposited with different pulse frequencies and heat inputs. Combined with finite element analysis, the influence of pulse frequency and heat input on macrostructure and microstructure of deposited Ti-6Al-4V compounds are investigated. Results indicate that with the increase of pulse frequency, the widths of deposited walls decrease rapidly at first, then increase slightly; columnar β grains transform into equiaxed β grains and the grains get finer, but α phases have no obvious variation. The increasing heat input is beneficial to obtaining equiaxed β grains, but the wall width will enlarge and α phases will be coarser. The width of the specimen is determined by the dimension of the molten pool, which is influenced by the average heat input and the input heat in peak time period. Improving pulse frequency can break the dendrites as well as reduce the temperature gradient, which is conducive to the nucleation. Besides, higher heat input can reduce the temperature gradient as well. Therefore, equiaxed β grains are formed with the increase of pulse frequency and heat input. The morphology of α phases are mainly associated with the cooling rate. Reducing heat input can increase cooling rate and refine α phases.
34 Effect of Sr element on the glass forming ability and corrosion properties of bulk Mg-Zn-Ca alloys
2018, 47(7):2151-2158.
Abstract:
In order to improve the glass forming ability of Mg-Zn-Ca alloy, 2mm and 4mm rod samples of Mg-Zn-Ca-Sr alloys with different amount of Sr were prepared by copper mould injection method. Effects of Sr addition on glass forming ability and corrosion properties in simulated body fluids of Mg-Zn-Ca alloys were studied by means of X-ray diffraction, scanning electron microscopy, differential scanning calorimeter and electrochemical test. Results showed that with the increasing content of Sr element, the 2mm rod samples were all in completely amorphous state. While the microstructure of 4 mm rod samples were composed of amorphous phase and crystalline Mg and MgZn phases. However, the volume fraction and particle size were decreased with increasing addition of Sr element, which indicated that the glass forming ability of Mg-Zn-Ca alloy was enhanced with Sr element addition. Mg65Zn30Ca4Sr1 alloy exhibited the highest glass forming ability. The results of electrochemical test demonstrated that Sr-doped samples showed more positive corrosion potential and smaller corrosion current density, which suggested that the corrosion resistance was improved with increasing addition of Sr element. The corrosion resistance of Mg65Zn30Ca4.5Sr0.5 alloy was the highest among the 2mm rod samples, while the corrosion resistance of Mg65Zn30Ca4Sr1 alloy was the best among the 4mm rod samples.
In order to improve the glass forming ability of Mg-Zn-Ca alloy, 2mm and 4mm rod samples of Mg-Zn-Ca-Sr alloys with different amount of Sr were prepared by copper mould injection method. Effects of Sr addition on glass forming ability and corrosion properties in simulated body fluids of Mg-Zn-Ca alloys were studied by means of X-ray diffraction, scanning electron microscopy, differential scanning calorimeter and electrochemical test. Results showed that with the increasing content of Sr element, the 2mm rod samples were all in completely amorphous state. While the microstructure of 4 mm rod samples were composed of amorphous phase and crystalline Mg and MgZn phases. However, the volume fraction and particle size were decreased with increasing addition of Sr element, which indicated that the glass forming ability of Mg-Zn-Ca alloy was enhanced with Sr element addition. Mg65Zn30Ca4Sr1 alloy exhibited the highest glass forming ability. The results of electrochemical test demonstrated that Sr-doped samples showed more positive corrosion potential and smaller corrosion current density, which suggested that the corrosion resistance was improved with increasing addition of Sr element. The corrosion resistance of Mg65Zn30Ca4.5Sr0.5 alloy was the highest among the 2mm rod samples, while the corrosion resistance of Mg65Zn30Ca4Sr1 alloy was the best among the 4mm rod samples.
2018, 47(7):2159-2165.
Abstract:
Based on the better strength, corrosion resistance and plastic processing of Mg-8Sn alloy, Mg-8Sn alloy was prepared successfully in 530～590 ℃ by spark plasma sintering (SPS) in this paper. The microstructures, phases, mechanical properties and corrosion resistance were investigated. The research results showed that the microstructure consisted of α-Mg and Mg2Sn phases, while Mg2Sn was generated at the interface of Mg and Sn. The highest bending strengh of Mg-8Sn-1Zn-1Al was 215 MPa which was obtained at 570 ℃. The best corrosion resistance of Mg-8Sn-1Zn-1Al was obtained at 590 ℃, of which the corrosion potential and the corrosion current were respectively -1.5218 V, 1.9632×10-5 A/cm2. That was because Mg2Sn was existed at particles bonding interface, which had protective effects on α-Mg.
Based on the better strength, corrosion resistance and plastic processing of Mg-8Sn alloy, Mg-8Sn alloy was prepared successfully in 530～590 ℃ by spark plasma sintering (SPS) in this paper. The microstructures, phases, mechanical properties and corrosion resistance were investigated. The research results showed that the microstructure consisted of α-Mg and Mg2Sn phases, while Mg2Sn was generated at the interface of Mg and Sn. The highest bending strengh of Mg-8Sn-1Zn-1Al was 215 MPa which was obtained at 570 ℃. The best corrosion resistance of Mg-8Sn-1Zn-1Al was obtained at 590 ℃, of which the corrosion potential and the corrosion current were respectively -1.5218 V, 1.9632×10-5 A/cm2. That was because Mg2Sn was existed at particles bonding interface, which had protective effects on α-Mg.
2018, 47(7):2166-2171.
Abstract:
The Mg-48Zn-13Y quasicrystal master alloy with high volume fraction of the quasicrystalline phase was prepared by conventional solidification method. The influences of the MZY quasicrystal on microstructures and properties of AM50 alloys were investigated by OM, SEM, EDS, XRD and tensile tests. The results indicated that addition of the MZY quasicrystal to AM50 alloy, the Mg3Zn6Y quasicrystal phase could be left well in AM50 matrix alloy, and the microstructures were obviously refined. The β phase in the microstructures was changed from coarse and continuous to discontinuous strip and granular, and the amount was decreased. When the content of the MZY quasicrystal is up to 6%, the microstructure was greatly refined, and the ultimate tensile strength, yield strength and elongation of the alloy reached to the maximum, 206.63 MPa, 92.50 MPa and 10.04%, respectively. Compared with AM50 alloy, it is improved by 24.59%, 74.9% and 66.15%, respectively. Mechanical properties of AM50 magnesium alloy can be improved significantly by addition of the MZY quasicrystal, which results from the microstructure refinement, the optimization of the morphology and amount of the β phase and the dispersion strengthening effect of the quasicrystal phase has good wettability with the magnesium alloy substrate.
The Mg-48Zn-13Y quasicrystal master alloy with high volume fraction of the quasicrystalline phase was prepared by conventional solidification method. The influences of the MZY quasicrystal on microstructures and properties of AM50 alloys were investigated by OM, SEM, EDS, XRD and tensile tests. The results indicated that addition of the MZY quasicrystal to AM50 alloy, the Mg3Zn6Y quasicrystal phase could be left well in AM50 matrix alloy, and the microstructures were obviously refined. The β phase in the microstructures was changed from coarse and continuous to discontinuous strip and granular, and the amount was decreased. When the content of the MZY quasicrystal is up to 6%, the microstructure was greatly refined, and the ultimate tensile strength, yield strength and elongation of the alloy reached to the maximum, 206.63 MPa, 92.50 MPa and 10.04%, respectively. Compared with AM50 alloy, it is improved by 24.59%, 74.9% and 66.15%, respectively. Mechanical properties of AM50 magnesium alloy can be improved significantly by addition of the MZY quasicrystal, which results from the microstructure refinement, the optimization of the morphology and amount of the β phase and the dispersion strengthening effect of the quasicrystal phase has good wettability with the magnesium alloy substrate.
2018, 47(7):2172-2178.
Abstract:
It is very important to research and master the rule of incremental forming of magnesium alloys carried on ultrasonic vibration under different process parameters for theoretical and practical application.This has significant value of theory and engineering application to solve the deficiencies,such as plate uneven heating and heating slower,along with the changing temperature of the lubricant film caused adhesion in partial higher temperature,along with the rising temperature of the mold strength and service life gradually reduce ect,and to improve the progress of the magnesium alloy plate ultrasonic vibration single point incremental forming.Take square pyramid box for research and the maximum shear stress,reduction ratio,forming accuracy as index to analysis the performance impact of different parameters to the magnesium alloy plate ultrasonic vibration single point incremental forming,such as the tool head size.the thickness and the amplitude. The result show that not only the maximum shear stress and the maximum reduction have been reduced but also the forming accuracy has been improved obviously after applying ultrasonic vibration.Also found that when the tool head diameter is 10mm,thickness from 1.0-1.3mm the amplitude is 0.04mm,it can improve the forming properties obviously.
It is very important to research and master the rule of incremental forming of magnesium alloys carried on ultrasonic vibration under different process parameters for theoretical and practical application.This has significant value of theory and engineering application to solve the deficiencies,such as plate uneven heating and heating slower,along with the changing temperature of the lubricant film caused adhesion in partial higher temperature,along with the rising temperature of the mold strength and service life gradually reduce ect,and to improve the progress of the magnesium alloy plate ultrasonic vibration single point incremental forming.Take square pyramid box for research and the maximum shear stress,reduction ratio,forming accuracy as index to analysis the performance impact of different parameters to the magnesium alloy plate ultrasonic vibration single point incremental forming,such as the tool head size.the thickness and the amplitude. The result show that not only the maximum shear stress and the maximum reduction have been reduced but also the forming accuracy has been improved obviously after applying ultrasonic vibration.Also found that when the tool head diameter is 10mm,thickness from 1.0-1.3mm the amplitude is 0.04mm,it can improve the forming properties obviously.
2018, 47(7):2179-2184.
Abstract:
In order to obtain the micro arc oxidation ceramic coatings of high performance and not to reduce the fatigue properties of aluminum alloy, 4 kinds surface conditions of aluminum alloy samples with untreated, high-speed fine particles bombarding treated, micro-arc oxidation treated, high-speed fine particles bombarding + micro-arc oxidation combining treated were prepared by high-speed fine particles bombarding technology and micro-arc oxidation (MAO) technique, and the fatigue lives of these samples were tested by universal fatigue test machine. At the same time, the surface layer microstructure and surface residual stress of these samples were observed and tested by TEM and XRD residual stress tester. Results show that all the surface conditions of the 4 kinds of samples had almost the same shorter fatigue life at high loads, but the fatigue life of these samples with micro-arc oxidation treatment was the shortest among all the samples at low loads, and it was significantly shorter than the untreated samples. The microstructure refinement and residual compressive stress resulted by high-speed fine particles bombarding treatment could effectively suppress the initiation and propagation of fatigue crack, so the fatigue life of the samples of high-speed fine particles bombarding treatment before and after micro-arc oxidation treatment were all improved, and the fatigue life of the two kinds of samples were both longer than the untreated samples, which shows that high-speed fine particles bombardment strengthening treatment could effectively improve the fatigue life of micro-arc oxidation aluminum alloy at lower stress level.
In order to obtain the micro arc oxidation ceramic coatings of high performance and not to reduce the fatigue properties of aluminum alloy, 4 kinds surface conditions of aluminum alloy samples with untreated, high-speed fine particles bombarding treated, micro-arc oxidation treated, high-speed fine particles bombarding + micro-arc oxidation combining treated were prepared by high-speed fine particles bombarding technology and micro-arc oxidation (MAO) technique, and the fatigue lives of these samples were tested by universal fatigue test machine. At the same time, the surface layer microstructure and surface residual stress of these samples were observed and tested by TEM and XRD residual stress tester. Results show that all the surface conditions of the 4 kinds of samples had almost the same shorter fatigue life at high loads, but the fatigue life of these samples with micro-arc oxidation treatment was the shortest among all the samples at low loads, and it was significantly shorter than the untreated samples. The microstructure refinement and residual compressive stress resulted by high-speed fine particles bombarding treatment could effectively suppress the initiation and propagation of fatigue crack, so the fatigue life of the samples of high-speed fine particles bombarding treatment before and after micro-arc oxidation treatment were all improved, and the fatigue life of the two kinds of samples were both longer than the untreated samples, which shows that high-speed fine particles bombardment strengthening treatment could effectively improve the fatigue life of micro-arc oxidation aluminum alloy at lower stress level.
2018, 47(7):2185-2191.
Abstract:
In this paper, the creep-fatigue behavior of a nickel-based superalloy GH720Li widely used for the turbine disk of an aero-engine was experimentally investigated. The cylindrical bars cut from an actual turbine disk were employed. The creep-fatigue tests with different dwell times were performed at 650°C. Experimental results revealed GH720Li is very sensitive to dwell time at 650°C, i.e., at the longer hold time (> 30min), the creep damage is dominant, thus decreases the creep-fatigue life. Then, the mechanism of creep-fatigue failure was discussed by using the SEM analyses of the fracture surface. It was found that with the increase of dwell time, the failure mode of the crack formation zone is transformed from a mixture of transgranular and intergranular to an intergranular failure. In addition, the crack formation zone is transformed from an intergranular fracture to a mixture failure mode. Finally, based on the experimental data, loading patterns transformation method and AMWD method were applied to predict the creep-fatigue life, and the applicability of two models was discussed.
In this paper, the creep-fatigue behavior of a nickel-based superalloy GH720Li widely used for the turbine disk of an aero-engine was experimentally investigated. The cylindrical bars cut from an actual turbine disk were employed. The creep-fatigue tests with different dwell times were performed at 650°C. Experimental results revealed GH720Li is very sensitive to dwell time at 650°C, i.e., at the longer hold time (> 30min), the creep damage is dominant, thus decreases the creep-fatigue life. Then, the mechanism of creep-fatigue failure was discussed by using the SEM analyses of the fracture surface. It was found that with the increase of dwell time, the failure mode of the crack formation zone is transformed from a mixture of transgranular and intergranular to an intergranular failure. In addition, the crack formation zone is transformed from an intergranular fracture to a mixture failure mode. Finally, based on the experimental data, loading patterns transformation method and AMWD method were applied to predict the creep-fatigue life, and the applicability of two models was discussed.
2018, 47(7):2192-2197.
Abstract:
The oxidation reactions of different tool materials under high temperature were derived from the theory of Gibbs free energy function, and the experimental study on the high temperature oxidation of tool materials was carried out. Cemented carbide (YG8), coated cemented carbide and ceramic tool materials were used in this study, and the oxidation products under high temperature were analyzed by SEM and XRD. The results showed that the WC and Co were oxidized into WO3, Co3O4 respectively in the high temperature oxidation tests. With the increase of temperature, oxidation behavior is more severe. For the ceramic tool, onlyTiC is oxidized into TiO2, which showed very good antioxidant properties. The order of oxidation resistance of the three kinds of tool materials is as follows: Ceramic Cutting Tools > Coated Cemented Carbide > YG8.
The oxidation reactions of different tool materials under high temperature were derived from the theory of Gibbs free energy function, and the experimental study on the high temperature oxidation of tool materials was carried out. Cemented carbide (YG8), coated cemented carbide and ceramic tool materials were used in this study, and the oxidation products under high temperature were analyzed by SEM and XRD. The results showed that the WC and Co were oxidized into WO3, Co3O4 respectively in the high temperature oxidation tests. With the increase of temperature, oxidation behavior is more severe. For the ceramic tool, onlyTiC is oxidized into TiO2, which showed very good antioxidant properties. The order of oxidation resistance of the three kinds of tool materials is as follows: Ceramic Cutting Tools > Coated Cemented Carbide > YG8.
2018, 47(7):2198-2204.
Abstract:
Effects of shot peening on high cycle fatigue limitation of the powder metallurgical nickle-based FGH4097 superalloy at room temperature were investigated in this article. Fatigue fracture characteristics and shot peening surface morphology were observed by SEM, the sample surface residual stresses σr and microhardness H were determined by X-ray diffraction stress tester and ultra-small dynamic microhardness tester, and EBSD and TEM were used to observe the microscopic characteristics of the shot peening layer. The results show that compressive residual stresses induced by shot peening are more deeper and more stable than without shot peening, which is beneficial to improve the resistance of fatigue crack initiation and reduce crack propagation rate. And the high dislocation density, a large number of low-angle boundary and a small number of soft orientation grain in the surface layer of shot peening make the fatigue crack difficult to initiate at the surface. So, 20.7% increasing at high cycle fatigue limitation of the FGH4097 superalloy at room temperature.
Effects of shot peening on high cycle fatigue limitation of the powder metallurgical nickle-based FGH4097 superalloy at room temperature were investigated in this article. Fatigue fracture characteristics and shot peening surface morphology were observed by SEM, the sample surface residual stresses σr and microhardness H were determined by X-ray diffraction stress tester and ultra-small dynamic microhardness tester, and EBSD and TEM were used to observe the microscopic characteristics of the shot peening layer. The results show that compressive residual stresses induced by shot peening are more deeper and more stable than without shot peening, which is beneficial to improve the resistance of fatigue crack initiation and reduce crack propagation rate. And the high dislocation density, a large number of low-angle boundary and a small number of soft orientation grain in the surface layer of shot peening make the fatigue crack difficult to initiate at the surface. So, 20.7% increasing at high cycle fatigue limitation of the FGH4097 superalloy at room temperature.
2018, 47(7):2205-2209.
Abstract:
Hot compression tests were carried out to study hot deformation behavior of new Ni-based alloys with different contents of Cr (7 % and 20 %) in the temperature range of 950 ℃ to 1200 ℃ and strain rates ranging from 0.01 s-1 to 10s-1, and processing maps for both alloys were established. The results showed that increasing Cr content significantly enhanced the hot deformation resistance at low temperature and high strain rate, and also increased the apparent activation energy. Comparison of the processing maps of two alloys indicated that safe hot processing range was decreased with the increasing of Cr content.
Hot compression tests were carried out to study hot deformation behavior of new Ni-based alloys with different contents of Cr (7 % and 20 %) in the temperature range of 950 ℃ to 1200 ℃ and strain rates ranging from 0.01 s-1 to 10s-1, and processing maps for both alloys were established. The results showed that increasing Cr content significantly enhanced the hot deformation resistance at low temperature and high strain rate, and also increased the apparent activation energy. Comparison of the processing maps of two alloys indicated that safe hot processing range was decreased with the increasing of Cr content.
43 Effect of SPS Cyclic Heat-Treatment on the Microstructure and Properties of 93W-4.9Ni-2.1Fe Alloy
2018, 47(7):2210-2215.
Abstract:
The effect of vacuum cyclic heat-treatment based on spark plasma sintering (SPS) technique on the microstructure, composition and properties of as-sintered 93W-4.9Ni-2.1Fe tungsten heavy alloy has been studied by optical microscope, SEM, EDS and three-point bending tests. The results show that the matrix penetration into W-W grain boundaries enhances significantly, and the W-W contiguity and dihedral angle decrease gradually with the cycle index increasing. SPS cyclic heat-treatment does not obviously change the micro-hardness and grain size. The matrix is strengthened by the increasing content of tungsten owing to the treatment. The bending strength of the alloy increases significantly after 2 cycles. When the cycles goes up to 20, the average bending strength reaches 2321MPa, which is 160MPa higher than that of the conventional liquid-sintered and solution-treated 93W-4.9Ni-2.1Fe alloy. The microstructure and properties of 93W-4.9Ni-2.1Fe tungsten heavy alloy can be improved apparently by SPS cyclic heat-treatment.
The effect of vacuum cyclic heat-treatment based on spark plasma sintering (SPS) technique on the microstructure, composition and properties of as-sintered 93W-4.9Ni-2.1Fe tungsten heavy alloy has been studied by optical microscope, SEM, EDS and three-point bending tests. The results show that the matrix penetration into W-W grain boundaries enhances significantly, and the W-W contiguity and dihedral angle decrease gradually with the cycle index increasing. SPS cyclic heat-treatment does not obviously change the micro-hardness and grain size. The matrix is strengthened by the increasing content of tungsten owing to the treatment. The bending strength of the alloy increases significantly after 2 cycles. When the cycles goes up to 20, the average bending strength reaches 2321MPa, which is 160MPa higher than that of the conventional liquid-sintered and solution-treated 93W-4.9Ni-2.1Fe alloy. The microstructure and properties of 93W-4.9Ni-2.1Fe tungsten heavy alloy can be improved apparently by SPS cyclic heat-treatment.
2018, 47(7):2232-2239.
Abstract:
Al-Cr-Si-N coatings were deposited by arc ion plating (AIP) technique at various DC bias voltages. The effects of bias voltage on the microstructure, mechanical and wear properties of the Al-Cr-Si-N coatings were investigated. The results show that the Al-Cr-Si-N coatings is mainly composed of the hexagonal structure and the face-centered cubic structure of AlN phase. with the increase of substrate bias, the diffraction peak of the coating is shifted to the small angle. Compressive stress gradually increased, the maximum value of -0.77GPa; coating hardness and friction coefficient change is not obvious. When the negative bias of the substrate is -40V, the characteristic parameters H/E and H3/E* 2 of Al-Cr-Si-N coating are the maximum, which are 0.1475 and 0.3681GPa, respectively. At the same time, the coating had the best wear resistance and the friction coefficient was the lowest.
Al-Cr-Si-N coatings were deposited by arc ion plating (AIP) technique at various DC bias voltages. The effects of bias voltage on the microstructure, mechanical and wear properties of the Al-Cr-Si-N coatings were investigated. The results show that the Al-Cr-Si-N coatings is mainly composed of the hexagonal structure and the face-centered cubic structure of AlN phase. with the increase of substrate bias, the diffraction peak of the coating is shifted to the small angle. Compressive stress gradually increased, the maximum value of -0.77GPa; coating hardness and friction coefficient change is not obvious. When the negative bias of the substrate is -40V, the characteristic parameters H/E and H3/E* 2 of Al-Cr-Si-N coating are the maximum, which are 0.1475 and 0.3681GPa, respectively. At the same time, the coating had the best wear resistance and the friction coefficient was the lowest.
2018, 47(7):2240-2244.
Abstract:
The Nb/Nb5Si3 In-Situ composite material strengthened with CNTs were prepared by Spark Plasma Sintering (SPS). The effects of CNTs content on microstructure and properties of Nb/Nb5Si3 in situ composites were investigated. The results show that the composite consists of Nb, α- Nb5Si3, and γ- Nb5Si3 phase. When adding over 2wt% CNTs, the new phase Nb4C3 was formed in the composites. The compressive strength and fracture toughness of composites increase obviously with increasing addition of CNTs. When the addition of CNTs is the 2wt%, the compressive strength and fracture toughness reached the maximum value and increased about 56%, 31% respectively. When the CNTs content added over 2wt%, the compressive strength fracture toughness decreased. The micrographs observed by SEM of fractography show the fracture appearance of the composites belongs to brittle cleavage fracture and partial intercrystalline fracture. The toughening mechanisms of composites are mainly due to the CNTs pullout and bridging.
The Nb/Nb5Si3 In-Situ composite material strengthened with CNTs were prepared by Spark Plasma Sintering (SPS). The effects of CNTs content on microstructure and properties of Nb/Nb5Si3 in situ composites were investigated. The results show that the composite consists of Nb, α- Nb5Si3, and γ- Nb5Si3 phase. When adding over 2wt% CNTs, the new phase Nb4C3 was formed in the composites. The compressive strength and fracture toughness of composites increase obviously with increasing addition of CNTs. When the addition of CNTs is the 2wt%, the compressive strength and fracture toughness reached the maximum value and increased about 56%, 31% respectively. When the CNTs content added over 2wt%, the compressive strength fracture toughness decreased. The micrographs observed by SEM of fractography show the fracture appearance of the composites belongs to brittle cleavage fracture and partial intercrystalline fracture. The toughening mechanisms of composites are mainly due to the CNTs pullout and bridging.
2018, 47(7):2245-2251.
Abstract:
Aluminum lithium alloy is considered to be one of the ideal materials for lightweight structural materials in the aerospace field. The 2198-T851 aluminum lithium alloy 1.8 mm thickness sheet of vacuum electron beam test,analysis the different scanning modes on weld forming and the influence of mechanical properties of joints, and under the optimal welding process welding joint microstructure and mechanical properties. The results show that the working distance is 300mm, the acceleration voltage is U=60kV, the focusing current is If=498mA ,the welding speed V=1200mm/min and the electron beam is Ib=6.8mA, the welding joint without the addition of scanning can obtain good forming and no macro porosity defects.Under the same conditions compared to other add scan mode of welding, derived welding in the process of adding triangle wave scanning, we can not only obtain the forming good macro porosity defects in the welded joints, and the welding joint of the hardness values and tensile strength is improved. The average tensile strength of welded joint is 323.55MPa, and the fracture strength of the joint is 71.5%, The extension rate is up to 86.8% of the elongation of base metal.which is the weakest part of the weld zone.
Aluminum lithium alloy is considered to be one of the ideal materials for lightweight structural materials in the aerospace field. The 2198-T851 aluminum lithium alloy 1.8 mm thickness sheet of vacuum electron beam test,analysis the different scanning modes on weld forming and the influence of mechanical properties of joints, and under the optimal welding process welding joint microstructure and mechanical properties. The results show that the working distance is 300mm, the acceleration voltage is U=60kV, the focusing current is If=498mA ,the welding speed V=1200mm/min and the electron beam is Ib=6.8mA, the welding joint without the addition of scanning can obtain good forming and no macro porosity defects.Under the same conditions compared to other add scan mode of welding, derived welding in the process of adding triangle wave scanning, we can not only obtain the forming good macro porosity defects in the welded joints, and the welding joint of the hardness values and tensile strength is improved. The average tensile strength of welded joint is 323.55MPa, and the fracture strength of the joint is 71.5%, The extension rate is up to 86.8% of the elongation of base metal.which is the weakest part of the weld zone.
2018, 47(7):2252-2256.
Abstract:
Compared to electrochemical supercapacitors, electrostatic supercapacitors have higher power density and reliability, but its energy density are low. In this paper, the MEMS electrostatic supercapacitor with high energy density were prepared based on the high dielectric constant CaCu3Ti4O12(CCTO) film. Firstly, CCTO films were synthesized under the different sintering temperatures (700℃, 800℃, 900℃), through a sol-gel method on silicon substrate. The morphology, phase identification and crystalline of CCTO films were characterized using X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) respectively. The results showed that the CCTO film has the best quality at 800℃. And then, we tested the I-V and C-V characteristics by the metal-insulators-semiconductor capacitor structure, getting the largest hreshold voltage and energy density, which have values of 47 V and 3.2J /cm3. Meanwhile, the paper firstly proposed to research the phenomenon of dielectric charging in the high dielectric constant film and analyzed the influence on electrostatic supercapacitors.
Compared to electrochemical supercapacitors, electrostatic supercapacitors have higher power density and reliability, but its energy density are low. In this paper, the MEMS electrostatic supercapacitor with high energy density were prepared based on the high dielectric constant CaCu3Ti4O12(CCTO) film. Firstly, CCTO films were synthesized under the different sintering temperatures (700℃, 800℃, 900℃), through a sol-gel method on silicon substrate. The morphology, phase identification and crystalline of CCTO films were characterized using X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) respectively. The results showed that the CCTO film has the best quality at 800℃. And then, we tested the I-V and C-V characteristics by the metal-insulators-semiconductor capacitor structure, getting the largest hreshold voltage and energy density, which have values of 47 V and 3.2J /cm3. Meanwhile, the paper firstly proposed to research the phenomenon of dielectric charging in the high dielectric constant film and analyzed the influence on electrostatic supercapacitors.
2018, 47(7):2257-2261.
Abstract:
Metallurgical lead and zinc slag taken as resource of silver, silver modified nanomaterials Ag@SiO2@TiO2 were successfully synthesized by chlorine salt method, St?ber method, sol-gel method and photo-deposited method. X-ray diffraction (XRD)and transmission electron microscopy (TEM) prove that composite Ag@SiO2@TiO2with core-shell structure, which Ag was deposited on anatase TiO2 in the form of cluster with 10 nm diameter. X-ray photoelectron spectroscope (XPS) indicates that in silver modified Ag@SiO2@TiO2, TiO2 was chemisorbed on SiO2 core in Ti-O-Si chemical bond and Ag deposited on TiO2 shell was elementary substance of silver. UV-vis diffuse reflectance spectra (DRS) shows that silver modified Ag@SiO2@TiO2 widened TiO2 response range towards light to expand to visible region. The photocatalytic degradation reaction of rhodamine indicates that silver modified nanocomposite Ag@SiO2@TiO2 possessed the excellt catalytic performance.
Metallurgical lead and zinc slag taken as resource of silver, silver modified nanomaterials Ag@SiO2@TiO2 were successfully synthesized by chlorine salt method, St?ber method, sol-gel method and photo-deposited method. X-ray diffraction (XRD)and transmission electron microscopy (TEM) prove that composite Ag@SiO2@TiO2with core-shell structure, which Ag was deposited on anatase TiO2 in the form of cluster with 10 nm diameter. X-ray photoelectron spectroscope (XPS) indicates that in silver modified Ag@SiO2@TiO2, TiO2 was chemisorbed on SiO2 core in Ti-O-Si chemical bond and Ag deposited on TiO2 shell was elementary substance of silver. UV-vis diffuse reflectance spectra (DRS) shows that silver modified Ag@SiO2@TiO2 widened TiO2 response range towards light to expand to visible region. The photocatalytic degradation reaction of rhodamine indicates that silver modified nanocomposite Ag@SiO2@TiO2 possessed the excellt catalytic performance.
2018, 47(7):2262-2268.
Abstract:
Producing fusion energy by light nuclear fusion reaction is an effective way to solve the energy problem. The materials in the reactor will face harsh working environment. Tungsten, with excellent properties, has become one of the most promising candidate materials in the future nuclear fusion device. But pure tungsten has some problems in the fusion, such as high ductile brittle transition temperature, low recrystallization temperature, irradiation hardening, embrittlement and difficult processing problem. Therefore, researching the tungsten-base material is used to solve the problems. On the basis of analysis of damage behavior of tungsten and tungsten-base materials under plasma irradiation, high heat load and high-energy neutron irradiation. Damage mechanism are discussed. Several key issues which need to be studied hereafter are put forward.
Producing fusion energy by light nuclear fusion reaction is an effective way to solve the energy problem. The materials in the reactor will face harsh working environment. Tungsten, with excellent properties, has become one of the most promising candidate materials in the future nuclear fusion device. But pure tungsten has some problems in the fusion, such as high ductile brittle transition temperature, low recrystallization temperature, irradiation hardening, embrittlement and difficult processing problem. Therefore, researching the tungsten-base material is used to solve the problems. On the basis of analysis of damage behavior of tungsten and tungsten-base materials under plasma irradiation, high heat load and high-energy neutron irradiation. Damage mechanism are discussed. Several key issues which need to be studied hereafter are put forward.
Zhishan Yuan
,
Dezhi Lin
,
Yue Cui
,
Zhaowei Feng
,
Juntao Li
,
Zaiyan Shang
,
Ming Zhu
,
Xiaodong Xiong
,
Xingquan Wang
2018, 47(7):2269-2274.
Abstract:
Research progress on the Ni-Ti-Pd and Ni-Ti-Pt high temperature shape memory alloys at home and abroad in recent years were reviewed, and the effect of chemical composition, thermal mechanical treatment and the training process on martensitic transformation, high temperature performance of one-way and two-way shape memory effect, and functional stability during repeated thermomechanical cycling of high temperature shape memory alloy were analyzed.The results show that the transformation temperature, the width of transformation hysteresis, high temperature martensitic transformation induced plasticity, creep behaviour, and high temperature thermal cycling properties, were significantly affected by the microstructures.The refinement of grain structure were achieved by the addition of Sc, Cu, or B elements, and cold rolling followed by annealling treatments, and the fine dispersed precipitaties of Ti2Ni and Ti2(Ni,Pd) distributed in the matrix were produced by solid solution and aging, and these microstructures were beneficial to the improvement of the high temperature shape memory properties, by the effect of solid solution hardening and precipitation hardening.The preferentially oriented martensite variants, nucleated on the dislocation arrays with the specific stress field obtained during the training under a constant stress, were found to improve the one-way and two-way shape memory properties, and improve the stability of the functional properties and size of the high temperature shape memory alloys.
Research progress on the Ni-Ti-Pd and Ni-Ti-Pt high temperature shape memory alloys at home and abroad in recent years were reviewed, and the effect of chemical composition, thermal mechanical treatment and the training process on martensitic transformation, high temperature performance of one-way and two-way shape memory effect, and functional stability during repeated thermomechanical cycling of high temperature shape memory alloy were analyzed.The results show that the transformation temperature, the width of transformation hysteresis, high temperature martensitic transformation induced plasticity, creep behaviour, and high temperature thermal cycling properties, were significantly affected by the microstructures.The refinement of grain structure were achieved by the addition of Sc, Cu, or B elements, and cold rolling followed by annealling treatments, and the fine dispersed precipitaties of Ti2Ni and Ti2(Ni,Pd) distributed in the matrix were produced by solid solution and aging, and these microstructures were beneficial to the improvement of the high temperature shape memory properties, by the effect of solid solution hardening and precipitation hardening.The preferentially oriented martensite variants, nucleated on the dislocation arrays with the specific stress field obtained during the training under a constant stress, were found to improve the one-way and two-way shape memory properties, and improve the stability of the functional properties and size of the high temperature shape memory alloys.
