Abstract:High-velocity oxygen-fuel (HVOF) sprayed WC-12Co coating can improve system hardness and wear-resistance significantly. However, the coating would suffer decarburization phenomenon due to the high spray temperature and the large cooling rate in the HVOF process. With the application prospect of introducing thick WC-12Co coating into some heavy-load rolling pairs to improve tribological performance and wear-resistance, such as the rolling bearing for thrust vector control in solid rocket engine, this study adopts low-temperature high-velocity liquid fuel spray process to fabricate thick coatings on bearing steel. The modified process with a spray temperature of around 1700 K is realized by the replacement of oxygen by oxygen-nitrogen mixed gas and the introduction of water-cooling system. Phase distribution, elementary composition, microstructure, bonding strength, elastic modulus and microhardness of coatings are investigated to verify the feasibility and advantage of the process. The bonding mechanism between the coating and the substrate is clarified. Based on experimental data and the assumption of WC skeleton structure filled up with cobalt phase, a simple formula of the microhardness of WC-12Co coating is proposed for theoretical predication and coating design.

Abstract:Ni-Al composite coatings were successfully prepared on the surface of P92 ferritic heat-resistant steel by electroplating nickel and low temperature packing cementation aluminum. The anti-oxidation experiment of the composite coating was carried out at 650 °C for 132 h. The micrograph of cross section, chemical element distribution and phase transformation of the coating before and after oxidation were characterized by OM, SEM, EDS and XRD. The experimental results show that all the oxidation kinetics curves of the coatings are in accord with the parabolic law. The average oxidation rate of the composite coating without introducing Ce is 0.4412×10-6 g/(cm2·s). By contrast, the average oxidation rate of the coating with 2% CeCl3 added in the aluminizing agent is 0.2957×10-6 g/(cm2·s), which indicates that the oxidation resistance is obviously improved. However, the addition of excess CeCl3 (4%, 6%) will produce much more holes in the oxidation process and deteriorate the high-temperature oxidation resistance of the coating. In these cases, the oxidation rates of samples are higher than that with 2% CeCl3 addition. Moreover, the addition of Ce element in the coating increases the adhesion of the oxide film and has an inhibitory effect on the inward diffusion of the Al element.

Abstract:Modulated pulsed power magnetron sputtering (MPPMS) has the ability to control ionization rate, energy and quantity of the deposited particle through adjusting the pulsed intensity and duration, thus modifying the nucleation and growth process of the thin film. In this work, nanocrystalline Ti films are deposited by using MPPMS technique in a closed field unbalanced magnetron sputtering (CFUBMS) system under different peak target power densities of the strong-ionized period (Pd). The modulated pulse power (MPP) is employed to modify the Pd by varying pulse lengths and average target powers. The results show that a nanocrystalline Ti film with grain size of 11 nm exhibits a dense microstructure and smooth surface (roughness was 11 nm) when the Pd is 0.86 kW×cm-2. The improved properties of the as-prepared Ti film are discussed.

Abstract:The hard Ni60 (60HRC) self-fluxing alloy powder and soft Ni25-based WC-12Co composite powder are deposited onto the W1813N non-magnetic stainless steel using laser cladding. The microstructure, phase composition and worn track characteristics of Ni60 coating and WC-12Co/Ni25 composite coating produced with laser cladding are analyzed using scanning electron microscopy(SEM), energy dispersive spectrum (EDS), X-ray diffraction (XRD) and a step profiler. The micro-hardness, friction coefficient, profile of worn track and wear mechanism both coatings are investigated. The results show that the microstructure is mainly fine dendrite and equiaxed crystal in the LC Ni60 coating, and the hard Cr23C6, Cr2B phases distributed in the grain boundary of γ-Ni and FeNi solid solution, while WC-12Co particles in the composite coating are uniformly embedded in the Ni25 matrix，and the volume fraction of WC-12Co in the composite coating is 32.5%. The difference value between minimum and maximum hardness in the WC-12Co/Ni25 composite coating reaches up to 648 HV. Therefore the mean friction coefficients both coatings are similar, the volume loss of the LC WC-12Co/Ni25 is only 10% of the LC Ni60. The surface abrasive behaviors of the LC Ni60 coating are ploughed shape and adhesive scraps, but the surface abrasive behaviors of the LC WC-12Co/Ni25 composite coating are adhesive scraps and WC debris. The wear mechanism of the Ni60 coating is abrasive wear and adhesion wear, while the wear mechanism of the WC-12Co/Ni25 coating is adhesion wear. These demonstrate that the WC-12Co/Ni25 coating exhibits better wear resistance than the LC Ni60

Abstract:The oxidation behaviors of Y-Cr-Al coatings by pack cementation process with different Al content were investigated. The results show that the coating with 2% Al content in the pack has a three-layer structure, while the coatings with 2.5% and 3% Al content have two layers. And the main phases in the coating with 2% and 3% Al content are α-Cr and NiAl, respectively. But the main phases in coating with 2.5% Al content is NiAl with several Cr-rich particles and solid solution Cr atoms in the coating. The oxidation test demonstrates that the coated specimen with 2% Al content has the poorest oxidation resistance, but the one with 2.5% Al content has a favorable oxidation resistance.

Abstract:Environmental barrier coatings (EBCs) consisting of a tri-layer structure (Si/Mulltite/ Yb₂SiO₅) were prepared on SiC/SiC ceramic matrix composite (CMC). For decreasing degradation of water-oxygen corrosion for SiC/SiC CMC, a novel EBCs fabrication method of plasma spray-physical vapor deposition (PS-PVD) was proposed in this work. Prior to EBCs preparation, agglomerated Yb₂SiO₅ powders were fabricated by spray dryer. After that dense EBCs were fabricated by PS-PVD technique, where the Yb₂SiO₅ coating with laminar and columnar composited structure was achieved. And the deposition diagram of this special structure was presented. Besides, the thermal cycle performance of PS-PVD EBCs was tested from 1300℃ to room temperature water. No apparent spallation appeared after 30 cycles, which showed the EBCs had a good thermal shock performance.

Abstract:In order to clarify the inhibitory effect of LZO on the oxidation of bond-coat in thermal barrier coatings (TBCs), NiCoCrAlY bond-coat was deposited on 310S substrate by Detonation gun spraying, and single ceramic 8YSZ coating and LZO/8YSZ double ceramic coating were deposited by air plasma spraying technology. The microstructure and phase structure of TBCs before and after high temperature oxidation were analyzed by SEM, EDS and XRD. The results showed that the relative oxidation weight gain of the double ceramic LZO/8YSZ and the single ceramic 8YSZ structure was 2.82 mg/cm2 and 3.13 mg/cm2, respectively. Corresponding the TGO growth rate constant Kp was 5.79 ×10- 2 μm2 / h and 6.26×10- 2 μm2 / h, respectively. And the corresponding thickness distribution range was 3.75-5.25 μm and 5-5.5 μm, respectively after isothermal oxidation (100 hours) at 1100 °C. Compared with the single ceramic 8YSZ TBCs, TGO exhibited obvious characteristics were less oxidation weight gain, low growth rate, and slow β phase transition in bond-coat of the LZO/8YSZ double ceramic TBCs.

Abstract:Laser shock processing (LSP), also known as laser shot peening, is a novel surface strengthening treatment technology. In this paper, the surface roughness, residual stress and microhardness distribution of Ti834 alloy before and after LSP were analyzed by means of surface roughometer, X-ray diffraction and microhardness tester. And the surface morphology and microstructure of the impact area were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The experimental results show that the surface roughness, microhardness and residual compressive stress of Ti834 titanium alloy increase after LSP. Moreover, the depth of the strengthening layer formed after one impact and two impacts was 170 μm and 265 μm, respectively. A large number of dislocation entanglement can be observed in the plastic deformation layer induced by laser shock wave. The increase of dislocation density and the formation of deformation twins are conducive to improvement of mechanical properties of Ti834 alloy subjected to LSP.

Abstract:In this study, cold spray (CS) and low pressure plasma spray (LPPS) were chosen to fabricate the Ni-Ti composite coatings using a mechanically mixed powder of Ni/Ti at the atomic ratio of 1:1 aiming to avoid the oxidation. Upon utilization CS and LPPS techniques, spray processes played a significant role in the microstructures, phase compositions, mechanical property, and wear and corrosion performances of the two coatings. Results show that no oxidation was characterized in these two coatings. Nevertheless, two very different coating structures were found. CS coating showed a much lower porosity and a mechanical bonding of plastically deformed particles, and XRD denoted no NiTi intermetallic was formed during CS deposition. However, high temperature would lead to the significant differences in the LPPS coating, which exhibited a lamellar structure with the formation of Ni-rich and Ti-rich intermetallics around the interface. The LPPS coating presented the excellent performances due to the element diffusion during LPPS process. For example, it yielded a higher hardness value, which was nearly three times higher than that of CS coating. It was also given that a significant reduction of wear rate. In addition, a much higher corrosion potential and a much lower corrosion current also indicated a better corrosion resistance of LPPS coating.

Abstract:In order to obtain low-frequency broadband absorbing materials, carbonyl iron/CoFe₂O₄/PANI ternary composites were prepared by co-precipitation and in-situ polymerization techniques. Using this as a dielectric layer, a metamaterial-based structure was designed based on the idea of metamaterials. The carbonyl iron composite absorbing coating improves the low frequency absorbing properties. The effects of the structural design of metamaterials on the absorbing properties of carbonyl iron/CoFe₂O₄/PANI coatings were analyzed, and the absorbing mechanism of the composite coatings with superstructures was studied and discussed. Through simulation optimization, it is found that when the resistance of the resistive film is 10mΩ/□ and the pattern size of the hollow cross-resistive film is optimal, the composite coating after giving the metamaterial structure at the same thickness has a wider width than the single carbonyl iron coating. The absorption band and the lower absorption frequency are less than -10 dB in the 3.8-6.9 GHz band. Studies have shown that the integration of metamaterial structure into the performance improvement of carbonyl iron coating can effectively improve its low frequency absorbing performance.

Abstract:Al-TiC-CeO2 composite coatings were prepared by laser cladding technique. and the coating structures were investigated by SEM and XRD.The effects of different laser powers on the properties of Al-TiC-CeO2 composite coating have been studied by smicro-hardness tester，X-ray stress measurement instrument, friction and wear test machine and electrochemical workstation. The results show that Al-Fe phase appears in the coatings with different powers and shows a good metallurgical bond with the matrix. With the increase of the laser power, the coating dilution rate gradually increases, the coating is transformed from massive and short rod-like structure into fine granular structure,and fine grain strengthening effect is obvious, the coating composition of the organization more evenly distributed.In addition, with the increase of laser power, the microhardness and wear resistance of the coating surface first decrease and then increase, the residual stress of the coating surface are tensile stress, and the crack size increases with the increase of the stress. When the power is 1.6 KW, the coating showed high corrosion resistance.

Abstract:PreparationSofS0.3C18CrScompositeScoatingsSwithSdifferentSY₂O₃ contentsSonS3Cr14 stainlessSsteelSsubstrateSbySlaserScladdig. The effects of different Y₂O₃ contents on the microstructure, phase composition and hardness of the cladding layer were studied by metallographic microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and microhardness tester. The results show that there are many porous holes in the cladding layer without adding Y₂O₃, and the microstructure of the cladding layer consists of intragranular ferrite, bainite with grain boundary distributed and a small amount of martensite; After adding Y₂O₃, the dendrite length of the cladding layer is reduced and the number decreases, the dendrite tip is passivated and radially coarsening, the length to diameter ratio decreases, meanwhile the pores of the cladding layer decrease, and the cladding layer is purified. The microstructure of the cladding layer is composed of lath martensite and a small amount of bainite in the grain boundary. With the increase of Y₂O₃, the lath martensite is slightly coarsened, the number of bainite decreases obviously, the carbon concentration of bainite carbide increases, and the type of lamellar carbides transforms from low carbon carbide to high carbon carbide. After adding Y2O3, the microhardness of the clad layer is significantly improved,; When added 2% Y₂O₃, the hardening effect of the cladding layer comes up to the best, which was 160 HV0.2 higher than that without adding Y₂O₃.

Abstract:Hot dip plating is used to prepare Pb40Sn60 alloy coatings on copper wires to improve the properties of weldability and corrosion resistance, the microstructure and phase composition of Pb40Sn60 alloy coating under different hot dip plating rates were examined by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). and the mechanical properties of Cu wires with Pb40Sn60 alloy coating under different hot dip plating rates were investigated by the tensile test. The results show that the Pb40Sn60 alloy coatings are all composed of α phase and β phase, and the relative amount of α phase is more than β phase. With the increase of hot dip plating rate, the thickness of Pb40Sn60 alloy coating on copper wire are thickened, and the crystal morphology is change from lamellar or equiaxial to dendritic. The work hardening of copper wires can be eliminated during the hot dip plating process. With the decrease of hot dip plating rate, the strength of copper wires with Pb40Sn60 alloy coating is decrease significantly, and the elongation is not obvious change, the hardness of copper wires substrate shows a slightly decreasing trend, and the hardness of coating shows a slightly decreasing trend. There is beneficial to the crystallization and growth of the coating by increasing the rate of hot dip plating, on the contrary, there is beneficial to remove the work hardening of copper wire substrate by reducing the rate of hot dip plating.

Abstract:In this article, the N5/YSZ/NiCrAlY/( NiCrAlY+YSZ) /NiCrAlY/( NiCrAlY+YSZ) coatings were prepared on Ni-based single crystal alloy (Rene N5) by electron beam physical vapor deposition (EB-PVD). And the sampes were exposed to isothermal oxidation at 1000℃ for 200h and 500h. The microstructural evolution behavior and the mechanism of interface reaction was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The results suggest that the YSZ layer can form an α-Al2O3 active diffusion barrier layer with a “sandwich” structure to refuse the interdiffusion between substrate and mult-NY coating. And the mult-NY coating was transformed to mixed oxide layers gradually during the prcess of cyclic oxidation.

Abstract:The composite ceramic coatings with excellent performance was prepared by micro-arc oxidation with doping CNTs. Influence of CNTs doping method on microstructure, phase composition, wear resistance, corrosion resistance, porosity and pore uniformity were investigated. The results show that the decrease of length to diameter ratio, the change from super hydrophobicity to hydrophobicity and the introduction of oxygen-containing functional groups after modified, increased the dispersion of CNTs in solvents. The addition of CNTs made the coatings smoother and more dense. The coatings were composed of rutile TiO2, anatase TiO2 and CNTs. The addition of CNTs helped to improve the wear resistance and corrosion resistance of coatings. The A-CNTs/MAO coating was not completely damaged after friction test for 20 minutes, showing the best wear resistance. The self-corrosion potential of A-CNTs/MAO coating was -67.61mV, the corrosion current density was 7.43×10-7 A?cm2, and the polarization resistance was 6.84×104 Ω?cm2, showing the best corrosion resistance.

Abstract:Low density carbon bonded carbon fiber composites are thought to be attractive candidates for thermal insulation applications in aerospace due to their unique properties such as low density, high temperature stability and low thermal conductivity. In the present work, an anti-oxidation low density carbon bonded carbon fiber composite was designed and fabricated for high temperature application. Firstly, PyC coating was deposited uniformly on the surface of carbon fibers to improve the mechanical properties of CBCF through CVI process. After deposited for 210h, the tensile strength and pressure strength in thickness was increased by 275% and 341%, respectively. Then, a dual-layer coating was designed and prepared to improve the oxidation resistance of CBCF. High temperature oxidation properties under different temperature were tested using a high temperature muffle furnace in air. Results show that the as-prepared oxidation coating could protect composites effectively under high temperature oxidation conditions. After oxidized at 1700~1750℃ for 300~360s, the mass ablation rates was about 1.1~1.5′10_-5g/(s.cm₂). The formation of a dense glass layer of SiO2 or SiO2 embedded with HfO2 was responsible for the good ablation resistant.

Abstract:Atmospheric plasma spraying (APS) and high velocity oxyen-fuel spraying (HVOF) technology were used to prepare WC-Ni coatings with different spraying parameter. Phase composition and microstructures of coatings were respectively characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The Vickers microhardness, elastic modulus and fracture toughness were also tested using Vicker’s microhardness tester. Wear properties of coatings were tested by pin-on-disk tester. With APS technology, the higher densification and WC decarbonization of coatings were performed by higher power. With HVOF technology, the higher densification and the lower WC decarbonization of coatings were performed at lower spraying distance. Compared to APS technology, the higher densification, mechanical and wear resistance properties, and the lower decarbonization of coatings were performed by HVOF technology. With similar densification of coatings, the preferable wear-resistance was produced with lower decarbonization.

Abstract:As the most representative valve metal, aluminum, magnesium and titanium based materials have many characteristics such as high specific strength, good processing performance and excellent biocompatibility. They are widely used in aerospace, automotive, electronic communication, medical and other major industries. However, the tribological behaviour of aluminum, magnesium and titanium based materials is generally poor. This paper reviews the theoretical basis and application research status of using micro-arc oxidation technology to improve the tribological behaviour of aluminum, magnesium and titanium based materials. The effects of electrolyte systems, electrical parameters and micro-arc oxidation time on the morphology, composition, microstructure and tribological behaviour of micro-arc oxidation coatings are summarized. The direct composite technology and secondary composite technology of micro-arc oxidation are introduced. Finally, the future application and development are prospected.

Abstract:Nanoindentation and Vikers indentation tests were carried out to characterize the hardness and elastic modulus profiles in the vicinity of welding area for TC11/Ti2AlNb alloys with different conditions. Distribution of nano/micro scales mechanical behavior was analyzed combined with the microstructure. It was shown that the decomposed martensite α" phase was the major contributor to the reduction of hardness in the heat affected zone of TC11 alloy. Phases precipitated in welding zone and heat affected zone of Ti2AlNb alloy resulted in the hardness increased. Forging and heat treatment processes can improve the elastic modulus of the welding area. After welding, the elastic modulus was only ~92GPa in the welding zone, but the value was risen up to ~130GPa after heat treatment. Meanwhile, the yield strength of the welding zone increased after deformation treatment, which was consistent with the results that the hardness and elastic modulus variation in the welding area.

Abstract:By using Aloe vera leaf extract as both reducing and stabilizing agent, spherical and small size gold nanoparticles were successfully synthesized. The method is a simple, straightforward and eco-friendly approach because of absence of toxic reagent and the neutral pH conditions. The performance and characterization of synthesized gold nanoparticles were examined by UV-visible absorption spectroscopy (UV-vis), dynamic light scattering (DLS), Scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) and powder X-ray diffraction (XRD). The change of color and the absorbance peak in UV-vis spectroscopy indicated the formation of gold nanoparticles. The XRD showed that the particles were highly crystalline in nature. The TEM and SEM illustrated the particles were spherical in shape a narrowly distribution from 20 nm to 60 nm. The FT-IR proved that the gold nanoparticles were capped with extracts, keeping them from agglomeration and oxidation. The effect of reaction temperature, amount of chloroauric acid solution and extracts was also studied. The results display that these parameters play important roles in the generation of gold nanoparticles.

Abstract:Our previous results have shown that comprehensive mechanical properties of titanium alloys can be effectively improved by addition of Fe[1]. We systematically investigate hot deformation behaviors of Ti-6Al-4V-0.35Fe in this study, which is significant to improve plastic deformation ability of titanium alloys. In experiment, we use a Gleeble 3800 thermo-mechanical simulator to obtain the relationship between thermomechanical parameters and flow stress in a range of temperatures (800-950 °C) and strain rates (0.001-10 s-1). The single-peak profiles of the flow curves indicate that dynamic recrystallization (DRX) mechanism dominates the deformation. TEM analysis indicate that the grain size in DRX changes under different deformation temperatures, and finer grains are formed at relatively lower temperature due to the dynamic globularization. The dislocation walls are formed in subgrain boundaries due to dislocation slipping-climbing. The Avrami-type DRX model and the strain compensated multivariable regression model have been applied to fit the experimental stress-strain data during hot deformation. A comparative study between these two types of constitutive models is conducted to represent the flow behavior. It is found that both models have good accuracy in predicting the flow stress of Ti-6Al-4V-0.35Fe alloy. A processing map based on dynamic material model (DMM) at the strain of 0.8 (steady-state flow stage) has been established to identify the flow instability regions and stability regions. The strain rate range of stability region is 0.001-0.6s-1 which has been expanded compared to the range of 0.0003-0.1s-1 of Ti-6Al-4V. Optimal hot working parameters are confirmed to be 920-950 °C and 0.001-0.005 s-1, and nearly complete DRX has taken place. Our results indicate that hot working property of Fe-microalloyed Ti-6Al-4V is better than that of Ti-6Al-4V alloy in 800-950 °C temperature scale, and processing cost has been decreased.

Abstract:Once the metallic materials were subject to stress, a number of independent or alternative mechanisms may initiate and contribute to the deformation. As for the γ-TiAl-based alloys whose deformation kinetics is fairly complex, it is of particular significance to quantify the general constitutive relationship produced by each possible mechanism and identify the predominant mechanism at any specific loading conditions. For this purpose, in the present study Ashby-type deformation mechanism maps concerning six major deformation mechanisms have been constructed for various TiAl alloys with duplex (DP) and near-gamma (NG) microstructures. The general features as well as the effect of grain size on the appearance of the maps have been analyzed in detail. After a detailed discussion, it was believed that the proposed deformation mechanism maps were powerful tools in understanding the deformation mechanisms and predicting the deformation kinetics of DP/NG-TiAl alloys. Especially, they were demonstrated to be useful reference in alloy design and determination of proper processing parameters.

Abstract:In order to clarify the densification behavior of new Ag-Graphene composites prepared by low-pressure compressing and vacuum sintering, Ag-Graphene mixed powders with different graphene content from 0.5wt.% to 2.0wt.% were prepared by 24 h of ball milling and subsequently double action compressed and vacuum sintered. The densities of composites were measured after compressed and sintered, and the compressibility and sinterability of the composites at varying compaction pressures and varying sintering temperatures were also investigated. The experimental results show that the compaction data of all Ag-Graphene powders are fitted to the Balshin equation. The densification parameter (K values) increases with increasing the graphene contents which indicates the increasing of plastic deformation capacity. The Ag-0.5wt.%Graphene composite has the best sinterability. The composite with 1.5wt.% graphene exhibited much enhanced mechanical properties, namely, a tensile strength of 252 MPa can be achieved.

Abstract:The effect of Zn addition on clustering behavior in a pre-aged Al-Mg-Si-Cu alloy and its relation to bake hardening response are investigated. After pre-aging at 100 °C for 3 h, the Zn addition prompts the formation of clusters with a uniform Mg/Si ratio, which can easily transform into β" phases. Consequently, a fine and dense distribution of β" phases is observed in the Al-Mg-Si-Cu alloy with Zn addition during bake hardening treatment at 185 °C for 25 min after pre-aging. This correlates well with the enhanced bake hardening response of the Al-Mg-Si-Cu alloy with Zn addition.

Abstract:In this paper, the effect of calcium (Ca) additions on microstructure, texture and mechanical properties of Mg-4Zn alloy has been investigated. The as-cast alloys consisted of α-Mg dendrites and MgZn phase, and Ca addition also caused the formation of ternary Ca2Mg6Zn3phase. Results showed that Ca elements significantly refined the grain size of extruded sheet and weakened the strong basal textures. Along the transverse direction (TD) of sheet, Mg-4Zn-0.3Ca alloy exhibited an ultimate tensile strength (UTS) of 260 MPa, tensile yield strength (TYS) of 163 MPa. Moreover, the elongation to failure of Ca containing alloy increased up to 24% compared to that of 19% for Mg-4Zn alloy. The recrystallization mechanism and texture evolution of the alloy have been analyzed. What"s more, the strengthening and toughening mechanism, includes the anisotropy of mechanical characteristics, both have been studied.

Abstract:A hyper-eutectic alloy, with nominal composition Ni-42Al-16Mo (at. %), was directionally solidified at growth rates ranging from 12~300μm/s by Liquid Metal Cooling (LMC) technique. Microstructural examination reveals that the NiAl-16Mo alloy was composed of primary Mo dendrite and NiAl/Mo eutectic cell in all the growth conditions employed. With the growth rates increasing from 12μm/s to 300μm/s, the volume fraction of Mo primary dendrite increased from 7.21% to 11.42%, while the size and the arm spacing of Mo primary dendrite reduces simultaneously. The corresponding room temperature fracture toughness (RTFT) and ultimate high temperature compressive strength (UTCS) decrease with increasing of growth rates, the toughening and strengthening mechanism of composite was also discussed.

Abstract:Abstract: In this study, ultrafine grain/nanocrystalline two-phase γ-TiAl based alloy was prepared by high energy ball milling and vacuum hot pressing sintering. Ti, Al and Nb single powder were mixed together to make the nanocrystalline powder with a nominal composition of Ti-45Al-5Nb (at.%). After ball milling, the nanocrystalline powder was sintered at the temperature of 1200 °C with the pressure of 30 MPa. The sintered microstructure consisted of nanocrystalline α2-Ti3Al and the equiaxed γ-TiAl with grains less than 500 nm. The hot compressive flow behavior of Ti-45Al-5Nb alloy was studied using the Gleeble-1500D thermal simulator at deformation temperatures of 1100°C, 1150°C and 1200°C and strain rates of 1×10-4 s?1, 1×10-3 s?1and 1×10-2 s?1. The results reveal that the peak stresses of equiaxed ultrafine microstructure are significantly lower than the alloys with micron-scale structure. The value of peak stress is reached at the early stage of compression (2.5-3% strain), and the flow stress decreases with increasing temperature and decreasing strain rate. A constitutive equation was established based on experimental data which reflects the structural characteristics of the alloy during hot deformation. It shows that the deformation mechanisms are mainly intracrystalline dislocation in γ-TiAl phase and intergranular twins in γ/γ (001).

Abstract:With the long term immersion test of C-ring specimens loaded by two levels of load value, the caustic stress corrosion cracking resistance of three kinds of steam generator tubing alloy 690 in 50% NaOH at 325 ℃was evaluated. The stress value after loading was measured by XRD method and the oxide film after immersion was carefully analyzed. The results show that: (1) The maximum stress value of C-ring specimens is released to a certain extent after loading slowly by screw, and the release amount of load value of the domestic tubes is larger than that of the imported tubes; (2) The domestic tubes and the imported tubes all have good caustic-SCC resistance in 50% NaOH medium at 325℃, and the oxide film characteristic of the domestic tubing A are closer to that of the imported tubing C; (3) The good resistance of caustic stress corrosion of tubing alloy 690 in high concentrated alkaline medium at high temperature is related to the double-layer structured oxide film and the continuous carbide structure along grain boundary.

Abstract:The different degrees of a chemical reaction can be occurred with traditional refractory materials due to the high activity of TiAl alloys, limiting its application in directional solidification castings. In this paper, the BaZrO3 composite mould was prepared by using self-synthesized BaZrO3 powder as the surface layer (yttrium sol as a binder), Al2O3 as a back layer (silica sol as a binder). The influence of BaZrO3 particle size on the compactness of the mould, the morphology of penetration layer after directional solidification of the alloy, and the contaminant content in the alloy were investigated. The evolution of the microstructure of the surface layer and porosity, the interaction between the mould and the alloy, the morphology and composition of the interface, and the contaminant content of the alloy were carried out by using an optical microscope (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), archimedes’ principle, Inductively Coupled Plasma (ICP) and Nitrogen and oxygen analyzer (IGI, LECO TC-436). The results show that the surface of the mould using fine-grained particles as the coating is more dense and smooth after sintering at high temperature, the number of pores between particles is reduced and the size decreases, the porosity of the surface layer decreases from 17.3% to 13.5%. The thickness of the surface layer of the optimized mould is from 1000 μm (2 layers) to 3000 μm (4 layers). The thickness of the adhesive layer between the BaZrO3 surface layer and the Al2O3 back layer is increased from 300μm to 1200μm, and the adhesion is also enhanced. The interface penetration layer between the optimized mould and alloy is reduced from 900μm to 300μm, the penetration of the alloy melt is limited to the surface layer, and no exudate is observed in the back layer. The content of Ba, Zr, O in the alloy are reduced from 89, 16800, 7580ppm to 28, 4760, 3690ppm.

Abstract:The microstructure evolution and dynamic recrystallization mechanism of GH4169 alloy rolled by cross wedge rolling were characterized by means of metallographic microscope and electron backscatter diffraction (EBSD). The effects of equivalent strain, strain rate and temperature on the dynamic recrystallization of GH4169 alloy during cross wedge rolling were investigated by numerical analysis. The results reveal that the shaping characteristics of cross wedge rolling are the main reasons that induce the homogeneous microstructure and different dynamic recrystallization mechanism of GH4169 alloy. Larger reduction of area is beneficial to improve the microstructure homogenization. The non-continuous dynamic recrystallization mechanism is the main form on the surface of the rolled piece, while the core is dominated by continuous dynamic recrystallization mechanism.

Abstract:An experimental investigation was carried out to measure two types of various compression paths on the extruded AZ31 Mg alloy rod at room temperature. The first type is a two-stepped compression with vertical radial directions, which was named as RD1-RD2 compression. The second type is that the compression direction is subsequently extruding and radial directions, which was named as ED-RD1 compression. The variation on grains orientation and mechanical properties during above compressions were analyzed. The obtained results reveal that large amounts of {10-12} extension twins and {10-12}-{10-12} secondary twins activated during deformation. Besides, many crossed twin boundaries formed within grains caused by different twin variants activations. On the whole, twin activation obey the Schmid law. On one hand, for the RD1-RD2 compression, the stress-strain curves of the first and second compressions are almost identical. On the other hand, for the ED-RD1 compression, the stress values of the stress-strain curve of the second compression was significantly higher than that of the first compression.

Abstract:The behavior of commercially pure titanium (TA2) under tension and compression were investigated at different strain rates. Significant tension-compression asymmetry in yielding and strain hardening was observed. With the increment of deformation strain rate, the asymmetry of TA2 increased. The microscopic deformation mechanisms and microstructure evolutions of commercially pure titanium under tension and compression were analyzed using electron backscattered diffraction (EBSD) techniques. The results showed that the compressive deformation of commercially pure titanium was dominated by deformation twinning while the tensile deformation was dominated by the dislocations sliding. The macroscopic tension-compression asymmetry of commercially pure titanium was determined by load sensitivity of microscopic deformation behaviors.

Abstract:Isothermal thermal compression test is conducted by adopting a Gleeble-3500 thermal simulator, the high temperature rheological behavior of GH2907 superalloy at the forming temperature of 950℃~1100℃, the strain rate of 0.01s_-1~10s_-1 and the strain of 60% is studied. The results show that the flow stress of GH2907 superalloy decreases significantly as the forming temperature increases or the strain rate decreases. The thermal deformation activation energy of the alloy is calculated by Arrhenius hyperbolic sine equation and Zener-Hollomon parameter, and its Q=463.043kJmol_-1. At the same time, the stress-strain curve of the superalloy has obvious dynamic recrystallization (DRX) characteristics, and the strain, forming temperature and strain rate all have a significant effect on the DRX volume fraction. Based on the stress-dislocation relationship and DRX kinetics, the mechanism-type constitutive models of the two stages of work hardening-dynamic recovery and dynamic recrystallization are established to describe the relationship between flow stress, strain rate and forming temperature. According to the error analysis, the correlation coefficient R=0.987, the experimental value is in good agreement with the prediction of the established constitutive equation, and it can be used to accurately characterize the thermal deformation behavior of superalloy.

Abstract:In this work, Grain boundary engineering (GBE) is used to optimize and control the microstructure of this alloy approach to advancing without changing chemical composition of GH3625 alloy, thereby, improving the high temperature microstructure stability and service performance reliability of the alloy. The effect of thermal-mechanical processing on the grain boundary character distribution (GBCD) of GH3625 superalloy was investigated by means of the electron backscattered diffraction (EBSD) technique and orientation image microcopy (OIM). The results show that the optimization of the grain boundary character distribution (GBCD) of GH3625 superalloy is mainly achieved byΣ3_n grain boundaries formed during the recrystallization process, and is mainly affected by the cold deformation and annealing process. The length fraction of low ΣCSL grain boundaries in GH3625 superalloy decreases with the increase of cold deformation and increases with the annealing temperature. Meanwhile, the length fraction of low ΣCSL (coincident site lattice, Σ ≤29 by Palunbo-Aust criterion) grain boundaries increase to more than 63.16 % by thermal-mechanical processing after 35 % cold deformed and subsequent annealing at 1120 ℃ for 15 min. In addition, large sized grain-clusters appear in GH3625 superalloy, and boundaries have Σ3_nmisorientations inside the grains-cluster. The size of the grain-clusters and the amount of Σ3_n grain bounaries inside the grains-cluster decreases with the increase of cold deformation and increases with the annealing temperature.

Abstract:GH4169 alloy samples with V-grooves were experimentally repaired by electromagnetic stirring assisted laser repairing under different magnetic field currents. The morphologies and volume fraction of Laves in the repaired zone were compared, and the contents of Nb element in the matrix g and the hardness of the repaired sample were measured by changing the magnetic field currents to explain the relationship between the magnetic field currents and the element segregation and mechanical properties. The results show that with the assistance of electromagnetic field, the morphology of Laves was obviously changed from reticulate to rod-like and granular shape and its volume fraction were greatly decreased. The content of Nb element in the matrix g was increased with the increasing of the magnetic field currents. When the magnetic stirring current is 60A, the content of Nb element was 3.72 wt.%, and it was increased by 0.33wt.% compared to the sample without electromagnetic stirring.

Abstract:The thermal deformation behavior and heat processability of Ti80 alloy with bimodal microstructure was discussed in temperature of 860 ~ 1020 ℃, strain rate range of 0.001 ~ 10 s_-1 and maximal deformation of 50% by hot simulator, optical microscope and MATLAB software. Results showed that Ti80 alloy is negative temperature and positive strain rate sensitive material. Main softening mechanism changes from dynamic recrystallization to dynamic recovery when temperature increases. In addition, the train compensation constitutive equation and processing map were constructed by MATLAB programming. Correlation coefficient R between the predicted value and the experimental value of constitutive equation is 0.994, and average relative error AARE is 7.443%. The optimum processing parameters interval of Ti80 alloy is [980 ~ 1015 ℃]-[0.013 ~ 0.100 s_-1], which peak of power dissipation h is 64%.

Abstract:To alleviate "titanium Fire" produced during high pressure and friction of titanium alloy, Ti-V-Cr series and Ti-Cu-Al series burn resistant titanium alloys have been developed. In this work, through a modified direct current simulation burning tests, the burning characteristics, e.g., flame height, velocity and burning products are measured to evaluate the burn resistant behavior. It shows the burning behavior and reveals the corresponding burning mechanisms of titanium alloys with different alloying elements. The formation of V2O5 and Cr2O3 oxides during burning of Ti40 alloy enhances the density of oxide layer to block the oxygen diffusion, which leads to excellent burn resistant behavior indicated by the smaller burning velocity and lower flame height. For Ti14 alloys, in comparison, a clear Cu-rich layer is formed at the interface between burning product and heat affected zone, where it consumes oxygen by produces Cu-O compounds and to reduces the burning reaction with Ti-matrix. This work has established a fundamental understanding of how the alloying elements improve the burning resistance of titanium alloys.

Abstract:_:_Titanium_{has excellent corrosion resistance and can be used for long-term operation in boil}_{ing high concentration}_nitric_{acid medium. It is}_{an ideal}_{material for}_re_{processing equipment}_{. In this paper, SEM, EDS, XRD}_and_{XPS characterization methods were used to}_analyze_{the white attachment of the surface of}_CP-_Ti_in_{nitric acid}_with_{fluorine ion and explain its formation mechanism. The results show that when the concentration of fluorine ions is below 50 ppm, the corrosion rate of CP-}_Ti_{appears from large to small and tends to be stable. When the concentration of fluorine ions is 50 ppm and above, the corrosion rate appears from large to small and tends to large presents the "V" pattern. The phase of the white attachment of the surface of}_CP-_Ti_{is TiO}₂_._{The formation mechanism of the attachment is divided into two steps}_:_first_ly_{, the formation of porous}_film_{on the surface of the CP-}_Ti_{; secondly,} _The_TiO₂_{is gro}_{wn on the pore of porous}_film_{as the base point}_and_then_shedding.

Abstract:The effects of low melting point elements Cu, Al and Ga on the magnetic properties of Ce₁₇Fe₇₈B₆ alloys prepared by melt spinning technique are studied. The addition of these elements decreases the saturation magnetization, while the coercivity increases to a certain extent. Among the additive elements, the addition of Cu and Ga optimize grain size distribution, Ga addition is the most effective way to improve the coercivity of Ce₁₇Fe₇₈B₆ alloy. The recoil loop of Ce₁₇Fe₇₈B₆ alloy is slightly open. The best overall magnetic properties are obtained for Ce₁₇Fe_77.25B₆Ga_0.75 alloy. Compared with the counterpart Ce-Fe-B alloy, the exchange coupling interaction between the grains of Ce-Fe-B-Ga alloy is enhanced. The recoil loops closes completely and the average recovery permeability decreases, which effectively enhances the resistance of Ce-Fe-B based alloys to external magnetic field interference.

Abstract:The foil-fiber-foil (FFF) method was used to prepare Cf reinforced Ti/Al-based layered composites through vacuum hot pressing (VHP) technology. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction phase analysis (XRD), bending test, and compression test were implemented to explore the microstructure and properties of the materials under different hot pressing parameters. The results show that the optimized parameters of hot-pressing process is 700°C-30MPa-1h. The bending strength and compressive strength of the material can reach 469MPa and 324MPa, respectively. The material structure is a stack of tough and brittle phases. This structure can effectively impede crack propagation and extension of the crack path, absorbing a large a mount of fracture energy, thereby improving the performance of the material. Al3Ti and Ti5Si3 phases are formed at the Ti/Al interface, and Al4C3 and SiC phases are formed at the Al/Cf interface. Si element promotes the bonding of Ti and Al, moreover, promoting the precipitation of the strengthening phase Ti5Si3, improving the wettability between Al and C.324MPa</sub><sub>,</sub> <sub>respectively .</sub><sub>The material structure is a stack of tough and brittle phases. This structure can effectively </sub><sub>impede</sub><sub> crack propagation and </sub><sub>extension of the </sub><sub>crack </sub><sub>path, </sub><sub>absorbing a large amount of fracture energy, thereby improving the performance of the material. Al3Ti and Ti5Si3 phases are formed at the Ti/Al interface, and Al4C3 and SiC phases are formed at the Al/Cf interface. Si element promotes </sub><sub>the bonding of </sub><sub>Ti and Al </sub><sub>, moreover,</sub> <sub>promoting the precipitation of the strengthening phase Ti5Si3</sub><sub>,</sub><sub>improving</sub><sub> the wettability </sub><sub>between</sub><sub> Al and C.</sub>

Abstract:The creep tests were carried out on commercial purity zirconium (CP-Zr) in different states under the stresses of 0.9R_p0.2、0.925R_p0.2、0.95R_p0.2、0.975R_p0.2 at ambient temperature (AT). Steady state creep rate and creep stress were calculated. The microstrutures of CP-Zr before and after annealing and creep tests were analysied. The results indicate that the threshold stress of CP-Zr in different states exists in creep tests at AT. When the creep stress is greater than the threshold stress value, the density of dislocation of CP-Zr obviously increases with the creep stress increasing, the significant dislocation pile-up can be observed at grain boundaries. It is found that the UFG CP-Zr after annealing at 250°C can not only maintain grain size and stable microstructure, but also keep the original high strength and improve the plasticity compared with CG CP-Zr. In addition, the annealing treatment at 250°C can improve the creep properties of UFG CP Zr, weaken the creep stress sensitivity and enhance the creep resistance.

Abstract:LiFePO₄ was prepared by SpraySdrying technique, and then graphene coated LiFePO4 nanocomposites were synthesized through microwave hydrothermal method under low temperature. The morphology, structural properties and particle size distribution of the samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Dynamic Laser Scattering(DLS). Served as cathode materials for Li-ion batteries, the electrochemical performance and dynamic characteristics of electrode process were systematically investigated using constant-current charge-discharge techniques, cyclic voltammetric (CV) and electrochemical impedance spectra (EIS). Compared with LiFePO₄ electrode, graphene coated LiFePO₄ exhibited superior rate capability (125.4 mAh?g-1 at 5C) and endurable cycle life (about 95% capacitance retained after 100 cycles at 5C). The optimum performances of graphene coated LiFePO₄ are attributed to its typical nanocomposite structure, which not only remarkably enhance the electrochemical reversibility but also obviously reduce the charge transfer resistance. The results of this study may pave an effective strategy to improve the electrochemical performance of LiFePO₄ electrode for batteries.

Abstract:Ba0.6Sr0.4TiO3 powder was prepared by sol-gel method, and Ba0.6Sr0.4TiO3 was mixed with FeNi alloy powder by ball milling method. FeNi/Ba0.6Sr0.4TiO3 composite with three different Ba0.6Sr0.4TiO3 powders was successfully prepared. The morphology and composition of FeNi alloy micropowder before and after the addition of Ba0.6Sr0.4TiO3 were analyzed by scanning electron microscopy and X-ray diffractometry. The electromagnetic parameters of FeNi and FeNi/Ba0.6Sr0.4TiO3 composites were measured by vector network analyzer.. The results show that the irregular granular Ba0.6Sr0.4TiO3 powder can be successfully prepared. The Ba0.6Sr0.4TiO3 powder is mostly coated on the surface of the flake FeNi alloy powder, and with more Ba0.6Sr0.4TiO3 powder addition, the thickness of the coating gradually increases, and the shape of the FeNi alloy is gradually blurred. The Ba0.6Sr0.4TiO3 powder coating layer effectively reduces the dielectric loss of the FeNi alloy micropowder, improves the impedance matching performance in the low frequency band, and improves the low frequency absorbing performance. The relationship between the peak frequency of reflection loss and electromagnetic parameters was analyzed by 1/4 wavelength interference cancellation theory. The reflection intensity peak intensity was analyzed by interface reflection model and material impedance matching.

Abstract:The deposited billets of Mg-9Al-3Zn-1Mn-9Ca-1Nd alloy were prepared by spray deposition technique and pre-deformed by extrusion (extrusion temperature 340℃, extrusion ratio 25:1). The formation of Mg-Nd-Zn type LPSO structure on the second phase of magnesium alloy and the relationship between the LPSO phase and the twinning of the second phase were studied by means of SEM , TEM and XRD. The results show that the 6H-LPSO structure phase was formed on the Al₂ (Ca,Nd)-type C15 phase. The formation of dislocation entanglement around the C15 particles and the high concentration of stress around C15 particles is the main cause of the twinning of the C15 particles. The nano-scale C15 particles, pinning dislocations and inhibition of recrystallization grain growth, is the main reason for the formation of (0002) basal and prismatic (100) and pyramidal (101) textures. However, it is easy to form LPSO structure phase when the Nd content is higher in the smaller C15 particles, and that of twinning when the Nd content is lower in the larger C15 particles.

Abstract:The effect of volume energy density on the relative density, microstructure and microhardness of Inconel 738 alloy fabricated by SLM was investigated by methods like SEM、 EBSD and OM. The results show that volume energy density the plays a decisive role in the SLM forming process. With the increase of the volume energy density, the relative density increases first and then decreases. The highest relative density (99.4%) can be achieved at 65.2J/mm3. During solidification, the microstructure of Inconel 738 alloy formed by 2.44×105 K/s SLM has obvious anisotropy in vertical direction and parallel direction. The microstructure parallel to the print direction is "chess board", the vertical to print direction is "fish scale", the overlap zone between layers and different tracks is the refined cellar grains. And the microstructure shows obvious texture, with the increase of the laser body energy density, the texture in the < 001 > direction increases gradually.The hardness of the sample increases with the increase of the laser body energy density. When the hardness value is higher than 65.2J/mm3, the hardness value of Inconel 738 alloy is higher than that of precision casting specimen (410 HV), hardness value is distributed on each surface independently.

Abstract:FeNiHCF was prepared by co-precipitation method, and the influence of synthetic temperature on the sodium storage performance was studied. The microstructure and micromorphology of the as-prepared FeNiHCF were characterized by XRD and SEM. An sodium ion half cell was constructed with FeNiHCF as cathode and sodium as anode, respectively. The sodium storage performance of the prepared FeNiHCF was characterized by cyclic voltammetry and galvanostatic charge/discharge test. The change of synthetic temperature affects the micromorphology and sodium storage performance of the material. The initial sodium content, specific capacity and cycle stability of FeNiHCF prepared at 60℃ are the best. The FeNiHCF prepared at 60℃ is a very promising cathode material for sodium ion batteries.

Abstract:Based on the hot deformation technique, the microstructure and magnetic properties of DyF3-doped hot deformed NdFeB magnets were investigated. The results show that by hot deformation, the magnet obtains flat-shaped grains with obvious C-axis orientation characteristics, and the remanence is increased from 0.77 T of the precursor sintered magnet to 1.34 T, which is increased by nearly 74%. In addition, the hot deformation process can further diffuse DyF3 into the main phase of NdFeB, forming a (Nd, Dy)2Fe14B phase, and lead to reducing the coercivity loss. Electrochemical tests have shown that the hot deformation process increases the corrosion potential of the magnet and reduces the current density. When the deformation condition is 800 ℃/70%, the magnet has the best comprehensive magnetic and electrochemical properties, and its magnetic properties can reach: Br=1.34 T, Hcj=1225 kA/m and (BH)max=286 kJ/m3.

Abstract:In this work, fatigue crack propagation experiment of commercial pure titanium TA2 under different load levels after heat treatment is carried out considering the degree of plastic deformation of crack tip, the adaptability of heat treatment state to different stages of fatigue crack growth. Results show that heat treatment has different effects on the fatigue crack growth rate under different loading conditions. The decrease of fatigue crack growth rate with heat treatment in loading A condition is due to the reduction of the effective load near the threshold region and the increase of the near threshold value. Heat treatment in loading B condition has little effect on the effective load and the plastic deformation of crack tip. The plastic deformation of crack tip is restricted after heat treatment under loading C and D conditions, which leads to the decrease of fatigue crack growth rate.

Abstract:_:_Dynamic _r_{ecrystallization}_{has been considered as an important process for microstructure optimization of metallic materials. In this paper, three different mechanisms of d}_ynamic _r_{ecrystallization}_{(DRX), including}_{discontinuous DRX (DDRX)}_,_{continuous DRX}_{(DDRX) and g}_eometric_DRX(_GDRX_{), are}_summarize_{d by illustrating typical metallic materials. Microstructure characteristics, including}_m_{isorientation}_d_istributions_,_{misorientation}_{accumulation patterns}_{, grain size and its relationship to flow stress, are described}_{in detail}_{. Based on the microstructure evolution of}_{Ti-24Ni-4Zr-8Sn}_{alloy and Ti-25Nb-3Zr-}_3Mo-2Sn_{alloy, the author suggest that, besides the}_essential_{properties having a critical influence on DRX mechanism and}_{microstructure}_{evolution, the}_special_{deformation condition namely a certain matching of temperature, strain rate and strain, also result in}_multiple_dynamic_r_{ecrystallization}_s_.

Abstract:In the field of materials science and engineering, the phase-field method is an indispensable component of computational materials science. The phase-field method has incomparable advantages in simulating and predicting the microstructural and morphological evolutions in materials. The microstructure determines the service performances of materials. In fact, the manipulation of various properties of the solid materials principally depends on the anticipative material microstructures generated through the subtle control on phase transition process. In general, the experimental analysis of the solid-state phase transformation of alloy materials prevailingly focuses on the observation and discussion of the results, but less concerns on the kinetics of phase transitions. The phase-field method based on microscopic diffusion theory is capable of exploring the phase transformation process at the atomic scale, for which other phase-field models are powerless to achieve. This paper systematically reviews the research ideas and results about the application of microscopic phase-field model in solid-state phase transformations. On this basis, the difficulties of current research are expounded, and the development prospect of microscopic phase-field in the field of solid-state phase transition is prospected. Finally, we forecasted the possible developments of microscopic phase-field in the foreseeable future.