Abstract:A novel Ti-6Al-6Mo alloy sample was fabricated by laser solid forming (LSF) using blended elemental powders as raw material. The microstructure of as-deposited sample and the effects of solution and aging treatment on the microstructure and microhardness of LSF Ti-6Al-6Mo alloy were discussed. The results showed that the heat treatment conducted in this study has no significant effect on the morphologies of prior b grains of the alloy. The solution temperature, solution time, and the cooling method after solution treatment have a significant effect on the morphology and size of the α phase in the prior β grains and the microhardness of the LSF Ti-6Al-6Mo alloy. When the aging time exceeds 4 hours, the microstructure and microhardness of the alloy change little with increasing aging time. Based on the analysis of precipitation and strengthening effect of the primary α laths and secondary α laths on the b matrix in LSF Ti-6Al-6Mo alloy under different heat treatment conditions, the influence mechanism of heat treatment on the microstructure and microhardness of LSF Ti-6Al-6Mo was revealed.

Abstract:Micro-arc oxidation (MAO) coatings were prepared on ZL108 aluminum alloy in the Na2SiO3 electrolyte adding graphite micro-particles at different current densities (1, 5, 10, 15 and 20 A/dm2). The characteristics of MAO coatings were studied by SEM, EDS, XRD, eddy-current thickness meter and micro-hardness tester. The result showed that the thickening of MAO coatings led to the increase of the oxidation voltages with the increase of current density. The surface of MAO coatings was porous. The diameter of micro-pore and the size of sintering discs gradually increased. The relative counts of C and Si element on the surface of MAO coatings increased with the increasing of current density. The C element was uniform distribution on the surface of MAO coatings. The C element on cross-sectional of MAO coatings mainly concentrated on outer side. MAO coatings mainly consist of SiC, SiO2, θ-Al2O3, α-Al2O3. The SiC phase derived from the reactions of SiO2 with graphite. With the increase of current density, the MAO coatings hardness increased. MAO coatings prepared at 5A/dm2 exhibited the lowest corrosion rate.

Abstract:During laser deposition manufacturing (LDM) process, melt pool width which is greatly influenced by process parameters is essential for the forming tracks geometry. In this paper, the melt pool geometry evolution was monitored by a CCD camera, and a method of applying Kalman filtering for the melt pool width detection during LDM process was presented to obtain accurate value. Orthogonal experimental design and multiple regression analysis were used to establish an empirical model describing the correlation between the melt pool width and three main process parameters (laser power, scanning speed, and powder feeding rate). And the developed model was verified experimentally. Finally, Particle swarm optimization (PSO) was implemented for prediction of process parameters during the buildup of a thin wall. The results indicate that process parameters analysis and prediction for LDM process could make it possible to acquire an efficient process for the forming tracks geometry control.

Abstract:In this study, an Al-Zn-Mg-Cu alloy with Ni added as alloying element was synthesized via spray deposition. The element was present in the alloy in the form of spherical submicrometer Al₉Fe_0.7Ni_1.3 compound particles. The effects of the particles on the microstructure and mechanical properties of the alloy after a solution treatment were investigated by scanning electron microscopy (SEM) in conjunction with electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and tensile tests. We found that the Al₉Fe_0.7Ni_1.3 compound particles were mainly present near the grain boundaries, revealing a powerful recrystallization inhibition effect during the solution treatment. After the solid solution treatment, the alloy exhibited an ultimate tensile strength of 603 MPa and an elongation at break of 11.79%, and transgranular ductile fracture was identified as the main fracture mechanism. The results show that the presence of the spherical submicrometer Al₉Fe_0.7Ni_1.3 compound particles played a key role on the mechanical properties of the alloy, leading to grain refinement strengthening and Orowan strengthening, and was the main reason for the occurrence of transgranular ductile fracture.

Abstract:Highly spherical powders were successfully produced with a radio frequency plasma system. Six influential parameters, namely position of the inlet nozzle, plasma plate power, chamber pressure, particle size distribution of raw materials, the feeding rate and the flow rate of the carrier gas were changed respectively and the spheroidization ratio was counted with the help of SEM images. The phase structure and morphology of the powders were investigated by XRD and SEM. Morphologies of the surface and cross section indicate that the spherical particles are dense with a relatively smooth surface. Fluidity and bulk density were both improved to be suitable for practical application. Spheroidization ratio as high as 99% has been reached when the position of the inlet nozzle is 12.5cm, the chamber pressure is 14.7psia, the powder feeding rate is 1.742g/min, the plasma plate power is 27.2kW and the average size of raw particles is around 38~63μm.

Abstract:Laser shock peening can enhance fatigue, wear and corrosion resistance of metallic components by generating high-amplitude and large-depth compressive residual stresses on their surface. In our work, a pulse laser with different energies of 20J, 25J and 30J has been employed to peen TC17 titanium alloy. Microstructure evolution of 25J laser shock peened specimen was examined by OM, SEM and TEM. Surface morphology and roughness of 20J, 25J and 30J laser shock peened specimen were studied by confocal laser scanning microscope. Residual stresses of 20J, 25J and 30J laser shock peened specimen were measured based on incremental hole drilling method and ESPI technique. The effects of 20J, 25J and 30J LSP on room temperature tensile properties were further analyzed. Results showed that the average α grain size reduced from 11.17 μm to 6.93 μm after 25J LSP. High density of dislocations and mechanical twins were observed with dislocation density increasing from 8.11×10₁₃ m_-2 to 3.59×10₁₄ m_-2. Surface roughness decreased from 0.922 μm to 0.537 μm and further decreased to 0.305 μm, while surface residual stresses increased from -213 MPa, to 296 MPa and further increased to -774 MPa after 20J, 25J and 30J LSP, respectively. After LSP, the yield strength increased by a value of 30 to 70 MPa and the morphology of the tensile fracture before and after LSP were both ductile fracture, which indicated that LSP induced grain refinement only had a slight effect on the tensile property of TC17 titanium alloy.

Abstract:Abstract: To improve the hardness and anti-wear properties of Ti6Al4V alloy, composite coatings were produced on the Ti6Al4V substrate under liquid nitrogen cooling by laser cladding 35wt.% WC/Ni60A. The microstructural evolution and mechanical properties of coatings under liquid nitrogen cooling were investigated. The phase compositions and microstructures were investigated by X-ray diffractometer (XRD), optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), respectively. Sliding wear tests of the composite coatings under different cooling medium and substrate were conducted at 200N with the Si3Ni4 ceramic ball as the counter-body, and the corresponding wear mechanisms are discussed. The results indicated that the coatings both under liquid nitrogen cooling and under air cooling were mainly composed of α(Ti), WC, W2C, TiC, TiNi, Ti2Ni, TiNi3, NiB. Compared with the coating under air cooling , microstructure of the coating under liquid nitrogen cooling is uniform and dense, grain and precipitation phase is more small. The coating under liquid nitrogen cooling shows the sound metallurgical ( the bonding line) free pores and cracks between the coating and the substrate，and the microstructure near the bonding line shows more dense and fine directional solidification microstructure with a highly preferred orientation. The average microhardness of the coating under liquid nitrogen cooling is about 1363 HV0.2, which is 4 times higher than the Ti6Al4V substrate and is 1.61 times than the coating under air cooling. The relative anti-wear resistance of the coating under liquid nitrogen cooling is 5.39 times higher than the Ti6Al4V substrate and is 1.77 times than the coating under air cooling. Liquid nitrogen cooling can effectively improve the microhardness and anti-wear properties of coating.

Abstract:The ability of arcing wire VPPA to reliable control heat and mass transfer let it have unique advantages in arc additive manufacturing. In this paper, single channel multi-layered aluminum alloy specimens were assembled based on the quadratic general rotary unitized design method, and the mathematical model of single side wall forming dimensions and process parameters was established by multiple regression equations. This model can accurately predict the cladding size of single channel multi-layered aluminum alloy specimen. It was found that the plasma current, travelling speed, and wire feeding speed have significant effect on the layer height, and there is an interaction between the plasma current and travelling speed. For the melting width, the plasma current, variable polarity pulse MIG current and travelling speed have main effect. The width stability control strategy of this process was discussed based on the above results. It is found that the control scheme of the plasma current in the arithmetic progression has obvious advantages in the width stability control.

Abstract:The chromium carbide based metal-ceramic monolithic coating and chromium carbide based metal-ceramic/Ni composite coating were prepared by electro-spark deposition. The phase compositions, microstructure, microhardness and tribological properties of monolithic and composite coatings were characterized comparatively by X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness test, friction and wear test. The results indicate that the two kinds of coatings are dense, metallurgically bonded with substrate and have nanocrystalline microstructure. In composite coating, the content of FeCr_0.29Ni_0.16C_0.06plastic phase increases and Ni transition layer exists at the interface, which could release thermal stress via plastic deformation, therefore the number of cracks reduce significantly. Meanwhile, the maximum microhardness of composite coating (1186HV_0.05) is slightly lower than that of monolithic, but it displays the minimum friction coefficient (0.2462), and the wear mass of 1h is only 1/3 of that of monolithic, therefore it displays better tribological properties and the main wear mechanisms are abrasive and fatigue wear.

Abstract:Based on single metal droplet deposition behavior research, and established the three-dimensional numerical calculation model of lap forming entity parts, explores the molten metal drop in little space, large temperature gradient in the sedimentary forming under the environment of melt flow, spreading, coagulation mechanism, reveals the typical cross section on lap forming, the main characteristics of droplet deposition factors and the influence law of forming between morphology, internal quality, obtained the optimum process window, for subsequent complex metal parts of molten drops flow deposits forming provides technical support and reference.

Abstract:Cr2O3 coating was successfully prepared on the surface of 321 steel substrate by electroplating-high temperature oxidation technology. The influence of oxidation treatment and oxidation time were investigated. The microstructures, elemental distribution and morphology of the coatings were characterized by XRD, SEM and EDS, respectively. The hardness, corrosion resistance and hydrogen resistance of the coatings were tested. The results show that the obtained Cr2O3 coating has tightly combined grains with uniform grain size of about 1 μm and low porosity when the oxidation temperature at 700 oC. The existence of a Cr-O transition layer between Cr2O3 coating and the substrate enables interfaces to bond closely. And no holes, cracks and other defects are found in interfaces. The coating exhibits good corrosion resistance, heat resistance of impact performance (300 times), resistance to hydrogen permeability increased by 10.5 times.

Abstract:Maskless localized electrochemical deposition-additive manufacturing technology is a new technology for manufacturing three-dimensional micro metal structure by applying electrochemical depositing principles and additive manufacturing method without reliance on support or mask. The representiative techniques which embody the core content and process features of this new technology are reviewed in this paper: the basic principles and research progress of technology of maskless localized jet electrochemical deposition-additive manufacturing ( Maskless Jet ECD-AM ) and technology of maskless localized direct writing electrochemical deposition-additive manufacturing ( Maskless Direct Writing ECD-AM ). The characteristics, existing problems and future research development trends of the two technologies are analyzed.

Abstract:The cyclic stress responses behaviours and failure modes in the low cyclic fatigue of a nickel-based single crystal superalloys DD11 with [0 0 1] orientation at 980℃ and strain amplitude range of 0.5~1.2% have been investigated. The relationship between deformation microstructure and fatigue behaviours was established. The results showed that cyclic softening occurred and the softening degree decreased with increasing strain amplitude. The coarsening of γ" and the broadening of transverse channels of γ caused the movement of dislocation in the γ channel easily, and cyclic softening was resulted. Moreover, the dislocation recovery occurred at the low strain amplitude which also caused cyclic softening. Since the pilling-up of dislocation at the γ/γ" interfaces occurred as the degree of coarsen of γ" and broaden of transverse channels of γ decreased when the strain amplitude was large than 0.8%, resulting in decreasing in the degree of cyclic softening. The fatigue failure mode changed from normal fracture to shear fracture corresponding to a transferring of the crack stable propagation to the instant fracture. Our result is helpful for building the relationship of various blade fatigue failure modes, cyclic stress response and microstructure deformation under different strain amplitudes. It was benefited for the blade design and the strain amplitude allowable range.

Abstract:Effect of starting granule size and addition of WC on the microstructure and mechanical properties of double Ti(C,N) based cermets was investigated. Results show that the Ti(C,N) based cermets granules distribute in the matrix homogeneously. The amount of hard phases with the white core/grey rim and coreless structures in the matrix increases by increasing WC content. A new phase with the four layer composite structures was also found. With the increase of granules size, the fracture toughness increases, while the transverse rupture strength (TRS) and hardness have an opposite trend. With the increase of WC, the fracture toughness and TRS increase, while the hardness decreases. Higher fracture toughness of double Ti(C,N) based cermets is mainly owing to the branch, bridge and deflection of crack, the formation of micro-cracks at the nearby of the tip of main crack and the pull-out effect of granules.

Abstract:The solutionized Mg-3.52Sn-3.32Al(wt.%) alloy was processed by equal channel angular pressing (ECAP) via route Bc for 1, 4, and 8 passes, respectively. The microstructure and phase composition of the alloy were analyzed by optical microscope, scanning electron microscopy, transmission electron microscopy and X-ray diffraction, and the room-temperature mechanical properties were measured. The results show that many fine Mg2Sn particles and a few Mg17Al12 phases precipitate in the alloy after ECAP. The mechanical properties of the alloy first increase and then decrease gradually with increasing extrusion passes. The alloy possesses better mechanical properties after ECAP for four passes, the ultimate tensile strength, elongation and hardness increase to 250 MPa, 20.5% and 61.3 HV9.8 respectively, which is increased by 43.7%, 105% and 26.9% compared with the solutionized alloy. The room temperature fractograph of the ECAP processed alloy is ductile-fractured morphology under tensile condition.The mechanical properties of the ECAP processed Mg alloy is dependent on the grain size, precipitate and texture.

Abstract:A catalyst preparation method using dielectric barrier discharge (DBD) plasma was investigated in this paper. The results indicated that DBD plasma is good method to prepare Mo/Co/K/ZSM-5 catalysts in a rapid and efficient way. The DBD plasma method has similar performance with the traditional roasting method using X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), however, the former could obtained smaller size of particles and low agglomeration degrees. The activity tests also showed that the catalysts prepared by DBD plasma have higher activities towards synthesis of hydrocarbon (C5+) directly from synthesis gas than those obtained by the traditional roasting method.

Abstract:The effect of Y2O3 crucible on the purification of Ni3Al-based superalloy IC21 scraps during Vacuum Induction Melting was investigated. Different purification results were compared when using MgO crucible and Y2O3 crucible. The results indicated that Y2O3 crucible was more effective for reducing the content of hydrogen, nitrogen and oxygen. Hydrogen, nitrogen, and oxygen content using Y2O3 were about 50%, 80%, and 80% lower compared with MgO crucible, to 0.5 wppm, 1 wppm and 2 wppm in IC21 scraps, respectively. When melting temperature was above 1550°C or reaction time exceeded 5 minutes, it had limited impact on dehydrogenation and denitrification process when using Y2O3 crucible. Melting for 5 minutes at 1750°C or melting for 30 minutes at 1650°C, the content of oxygen reached the highest level, which was 6 wppm.

Abstract:Micro-B₄C/nano-Ti hybrid particulates reinforced copper matrix composites (CTBCs) were successfully prepared by high energy ball milling (HEBM) and spark plasma sintering (SPS). The microstructures and morphologies were characterized by X-ray diffraction (XRD), optical microscopy (OM), and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The results demonstrate that presence of uniformly distributed (B₄C+Ti) particles and a good interfacial bond between reinforcement and the Cu matrix. Besides, the interface bondingSmechanism was metallurgical bonding and mechanical bonding. The relative density of the as-SPSed samples was tested by Archimedes drainage method. Mechanical properties (microhardness, tensile yield strength, ultimate tensile strength and elongation to fracture) of CTBCs were significantly improved in comparison to the pure copper, which was mainly due to the load transfer, grain refinement and thermal. Finally, the fracture surface of the tensile sample presented ductile fractures.

Abstract:The martensitic microstructure of Zr-Cr-Fe alloy after β-quenching are investigated by a combination of electron channeling contrast imaging (ECC), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques. All of theoretical 12 α variants inherited from one single β phase have been obtained in the current study that revealed strict Burgers orientation relationship (BOR) with respect to β parent phase. The entire martensitic microstructure consisting of these 12 α variants in the as-quenched Zr-Cr-Fe alloy can be divided into four sub-regions or morphological groups. Each sub-region, in turn, is dominated by only one type of three-variant cluster (one crystallographic group composed of three α variants) showing the self-accommodation triangular morphologies. These three variants from individual cluster share a common pole of β parent phase and are related to each other by an angle/axis pair . The preferred formation of such three-variant cluster is ascribed to the elastic interaction between variants to achieve the largest degree of self-accommodation.

Abstract:Many theoretical and experimental studies showed that stress triaxiality has an important influence on ductile fracture. However, recent studies showed that Lode parameter, which can be linked to normalized third stress invariant, is also an essential factor. In the present study, round notched bar and flat grooved plate specimens made of 7075 aluminum alloy were used to assess the effect of stress triaxiality and Lode parameter on ductile fracture and on theScorresponding microscopicSmechanism. Quasi-static tensile experiments and parallel numerical simulations were conducted to obtain stress triaxiality, Lode parameter and failure locus. A fractographical analysis was performed to determine the rules of void evolution under different stress states. Stress triaxiality and Lode parameter have an important influence on failure strain. The effect of Lode parameter decreased with the increases in stress triaxiality. The fractographs showed that the size of the void decreased with the increase of stress triaxiality, and the morphologies of the voids of different Lode parameters were obviously different. TheSnucleation rate and growth degree of secondary voids were also affected by Lode parameter.

Abstract:In this thesis, Fe-Si system metal magnetic powder core was prepared from flaky Fe₉₅Si₁B₂P_0.5Cu_1.5 alloy powders instead of the spherical Fe-6.5%Si alloy powders. Firstly, the preparation of Fe₉₅Si₁B₂P_0.5Cu_1.5 alloy powders and Fe₉₅Si₁B₂P_0.5Cu_1.5 magnetic powder core were studied, and then the influences of annealing temperature and forming pressures on soft magnetic properties of the magnetic powder core were systematically investigated. Research showed that the permeability (μe) of Fe₉₅Si₁B₂P_0.5Cu_1.5 magnetic powder core had optimal stability of frequency in the frequency range of 1~200kHz. Residual internal stress produced in the pressing process was fully released after annealing at 450℃ for 1h, which could significantly improve the permeability (μe) of the magnetic powder core, and the maximum value was 53 with a forming pressure of 1.74GPa. With the increase of the applied DC magnetic field level, the permeability of the magnetic powder core decreased gradually. When DC magnetic field levels(H) was 50Oe, the percentage permeability of the magnetic powder core remain higher than 70%, As H increase to 130Oe, the permeability of magnetic powder core was still greater than 20. This showed that Fe₉₅Si₁B₂P_0.5Cu_1.5 magnetic power core had optimal DC-bias property.

Abstract:In this paper,the relationship between additive particle size and the properties of AgSnO2 contact materials was studied.Bi2O3,TiO2 and CeO2 were chosen as additives,and four kinds of particle sizes were selected.Meanwhile, the proportion of additives was selected through wetting ability tests.And AgSnO2 contact materials are prepared by powder metallurgy technology.The physical and electrical contact properties of AgSnO2 contact materials doped with different kinds and particle sizes additive were studied,the results showed that the influence of particle sizes of three additives(Bi2O3,TiO2 and CeO2) on the properties of AgSnO2 contact materials is consistent,and fine additive particle is beneficial for the improvement of the properties of AgSnO2 contact materials.With the decrease of additive particle size, the physical and electrical contact properties of AgSnO2 contact materials are improved,and the optimal particle size of additive is 200nm.The results indicate that the properties of AgSnO2 contact materials can be improved by selecting the optimal particle size of additive.

Abstract:Effect of the addition of trace CaO particles (0.1 and 0.3wt. %) into Mg-2Zn-0.5Sr on the microstructure, mechanical properties, and bio-corrosion behaviors was investigated. Microstructures and the composition and distribution of the second phases of Mg-2Zn-0.5Sr-xCaO composites (x=0, 0.1 and 0.3wt. %) were characterized by optical microscope (OM), X-ray diffraction (XRD), electron probe microanalyzer (EPMA), which indicated that the addition of CaO particles can lead to grain refinement and the CaO particles were mostly enriched between the second phases at grain boundaries and the α-Mg matrix. Results of mechanical properties investigated by tensile tests at room temperature show that the addition of CaO particles can improve the strength. However when adding 0.1 wt.% CaO particles, the plasticity decreases, but when adding 0.3 wt.% CaO particles, the plasticity increases. Electrochemical tests show that the corrosion potential (E_corr) of Mg-2Zn-0.5Sr/CaO composites significantly shifts toward a more positive direction when CaO particles were added into Mg-2Zn-0.5Sr. Immersion tests show that the average corrosion rate of Mg-2Zn-0.5Sr is 7.55 mm/year. And when adding 0.1 wt.% CaO, the corrosion rate decreases by about 18.3%, and when adding 0.1 wt.% CaO, the corrosion rate increases by about 52%. Both the microstructure and mechanical properties can be attributed to grain refinement and the mechanical bonding of CaO particles with the second phases and the α-Mg matrix. The bio-corrosion behaviors can be attributed to grain refinement and the formation of table and dense CaHPO₄ protective film due to the reaction of CaO.

Abstract:In order to improve the wear resistance of stainless steel surface, WC-10Co-4Cr coating with two grain sizes was prepared by plasma spraying. The phase structure of the coating was characterized by SEM and XRD. Friction and wear test, the influence of grain on the microstructure and friction properties of the coating was studied. The results show that the microstructure of nano-WC-10Co-4Cr coating contains WC and W₂C, and there is also γ phase of Co/Cr(W, C). It is not found that the W2C precipitated in the micron coating will follow the surface of WC particles Epitaxial growth of the coating structure, and nano-agglomerated particles more easily along the flattened particle boundary contraction, significantly reducing the particles within the vertical through cracks. At room temperature and 200℃, nano-WC-10Co-4Cr coating friction coefficient and the average wear rate are better than the micron coating. Compared with the micron coating, nano-WC-10Co-4Cr coating at room temperature wear is rooted in the hard particles induced plow wear, at 200℃ for the wear-resistant micro-domain plowing combined wear mode The And the corrosion potential of 1Cr18Ni9Ti matrix increased from -617mV to -335 ~ -290mV in 3.5% NaCl solution, which decreased the tendency of corrosion.

Abstract:In present work, the relationships between electrical conductivity, hardness and microstructures of 7050 alloy during isothermal quenching in 180℃~250℃ following solid-solution treatment were investigated. Results show that in the initial stage of isothermal quenching at 180℃ and 200℃, electrical conductivity of isothermal specimens is lower than that of the specimen direct water quenching following solid-solution treatment and with the increase of isothermal time, hardness of isothermal specimens in natural aging temper increases at first and then decreases. With isothermal quenching at 180℃ for 128 min GPΙ zones and η’ phases are formed in matrix, with isothermal quenching at 200℃ for 32 min GPΙ and GPΙΙ zones are formed in matrix, and with isothermal quenching at 250℃ for 32 min η’ and S phases are formed in matrix. The formation of strengthening phases during isothermal quenching is the main reason for the hardness of specimens increase in natural aging temper. When 7050 alloy plates are isothermal quenching at 200℃ for 16 min following solid-solution treatment, their T6 temper hardness is only 3.4% lower than that of the direct water quenching plates and their conductivity increases by 9.2%, which are close to the properties of RRA treated plates with the regression regime of 180℃ for 32 min. Therefore, taking isothermal quenching at 200℃ for 16 min as a pre-treatment process following solid-solution treatment it will make 7050 alloy plates obtain excellent comprehensive properties.

Abstract:HEC solutions of varying concentration were used as lubricant, which were introduced into friction pairs of Ti-6Al-4V plates and Si₃N₄ balls. Optical Surface Profiler and 3D Measuring Laser Microscope were used to measure the surface of plates and balls, respectively. The EDS and Raman spectroscopy were used to analysis the chemical composition on the resulting wear scars. The friction tests for the effect of speed and concentration of solution on tribology properties of Ti-6Al-4V were carried out on UMT-2. The results showed that a super-low friction state (μ≈0.005) was ahiceved after a long running-in stage. The COF decreases with the increasing rotational speed (80~630 r/min). The water will evaporate under high speed (> 630 r/min), which is owing to the heat by friction. In addition, the COF decreases with the increasing concentration (0.25%-2.00%). However, the kinematic viscosity of lubricant takes significant negative effect on COF when the concentration is larger than 2.00%. The surfaces of Ti-6Al-4V were worn down with smoothed flats under appropriate speeds and solutions, which was conducive for forming lubrication films. TiO₂ was detected on the scar by Raman spectrum. On the basis of these experimental results, a lubrication model was proposed.

Abstract:W-ZrC materials were prepared by ordinary consolidation sintering. The effects of ZrC addition on the mechanical properties and microstructure of the materials at room temperature and high temperature were studied, and the damage behavior under high heat flux shock was studied. The results show that ZrC is beneficial to densification and grain refinement, and improve the strength and toughness of W materials. The relative density and tensile strength of W-3wt%ZrC can reach 99.7% and 472MPa. The relative density and room temperature tensile strength of W-3wt%ZrC were 99.7% and 472MPa, respectively, and the tensile strength at 400 to 1000 C did not decrease at 420MPa, but the strain increased from 3.4% at room temperature to 11% at 1000 C. High heat flux shock show that high strength can improve the impact resistance of materials against high heat load. The surface of W-3wt%ZrC material has no cracks load under high heat flux shock of 200 MW/m2 (5 ms). The main crack spacing of W-3ZrC is smaller than W-0.7wt%ZrC at 300-400MW/m2. With the increase of the high heat load energy, the cracks gradually expand along the longitudinal direction. Microstructure shows that ZrC can consume the crack propagation energy and hinder crack propagation.

Abstract:ZCuSn10P1 copper alloy was formed by using thixo-extrude process. The mechanical properties with tensile strength, elongation, Brinell hardness and Vickers hardness were measured by using uniaxial tensile test and hardness test. The fracture morphology was observed by scanning electron microscope and the fracture mode was analyzed. The influence of forming specific pressure on the mechanical properties of thixo-extruded copper alloy was investigated. The tensile strength increases first and then decreases with increasing forming specific pressure. While the elongation decreases with increasing forming specific pressure. The functional relationships between forming specific pressure and the tensile strength and elongation are parabolic and exponential, respectively. The tensile fracture mode of thixo-extruded copper alloy is hybrid fracture including intergranular fracture and ductile fracture. The variation of Brinell hardness increases first and then decreases with increasing forming specific pressure. The Vickers hardness of liquid is highest, followed by the solid-liquid interface, the lowest solid phase at the same process. The microhardness of the solid phase, the solid-liquid interface and the liquid phase both increases first and then decreases as the forming specific pressure increases. The mechanical properties of thixo-extruded copper alloy are higher than that of conventional casting. The process parameter at forming specific pressure of 250 MPa and extrusion rate of 15 mm/s is fine. And the tensile strength is 387 MPa, the elongation is 2.8%, the Brinell hardness is 128 HBW, respectively.

Abstract:Three-dimensional small crack propagation behavior of deforming TiAl alloy at 650℃ is studied by in-situ observation fatigue testing, and then long crack propagation behavior of the alloy in temperature range from 650℃ to 800℃ is studied by fatigue crack propagation tests. It shows that, the three-dimensional small cracks can still grow even though in the stress intensity factor region that below the long crack propagation threshold value, furthermore, the growth rates of small cracks are higher than long cracks in this region; The sample edge straight horizontal manufacturing nick is one of the main positions of three-dimensional small crack initiation of the alloy. Small cracks merge at the position of bends that occur during the fatigue testing. The fatigue life of the alloy is not sensitive to irregular strip manufacturing defects on the surface of the sample; The steady propagation rates of long fatigue cracks of the alloy are not sensitive to temperature changes in temperature range from 650℃ to 800℃. All the long crack propagation processes exhibit the cleavage fracture. Crack propagation threshold values are related to ductile-brittle transition temperature, the temperatures below the ductile-brittle transition temperature have lower threshold values.

Abstract:The creep behavior of the as-extruded Mg-8Gd-1Er-0.5Zr alloy was studied in the present paper under various temperatures (150-200 ℃) and stresses (50-70 MPa) for 100 h. The microstructure evolution during creep was investigated by optical microscopy (OM) and transmission electron microscopy (TEM), and the creep mechanism was analyzed. The results show that the alloy exhibited good creep properties under the experimental conditions. The creep curves can divide into two stages: the deceleration creep stage and the steady creep stage. The steady-state creep rate is 6.48×10_-11 s_-1, and the creep strain is 0.007% at the temperature of 150℃ and the stress of 50 MPa; The steady-state creep rate is 4.26×10_-9 s_-1, and the creep strain is 0.226% at the temperature of 200 ℃ and the stress of 50 MPa. In the case of lower temperature (150 ℃), diffusion mechanism acts as the main control mechanism, whereas dislocation mechanism controls the creep behavior at the higher temperature(175 ℃, 200 ℃). Furthermore, the precipitates of β′ phase in grains and the β phase at grain boundaries are formed during the creep process. The orientation relationship between the β′ phase and α-Mg matrix is (020)_β′∥_Mg, [001] _β′∥[0001]_Mg. The β′ phase can effectively inhibit the dislocation gliding, and the β phase can pin gain boundaries, both of them play an important role in improving the high temperature creep performance of the alloy.

Abstract:In this study, the synthesized WC-8Co composite powder with the particle size of 100nm, 250nm, and 400nm were added to the coarse WC/Co powder respectively. The mixture was sintered at different temperature with Ar atmosphere. The morphology, grain size and its distribution of the sintered bulk were studied. The WC grain growth mechanism of the samples with composite powder additives at different sintering stage was analyzed. It was found that the ultra-coarse cemented carbide was prepared by WC/Co mixed powder with nanometer or submicron particle size composite powder additives. Especially, the cemented carbide with a grain size 9.3μm was prepared using the mixed powder with the nanocomposite powder additives as raw material. At the initial sintering stage, the addtion of the namometer and ultrafine composited powders increases the surface energy of the mixed powders obviously, which is benefit to promote the growth of WC grains effectively. During the liquid sintering temperature, the sintered bulks with the nanocomposite powder have a larger dissolution driving force, which causes the small grains to dissolve and precipitate on the surrounding large grains, further increasing the grain size of the sintered bulks. In the bulks where the ultrafine composite powder was added, the small grains WC are concentrated and the dissolution driving force is small, and the precipitation mainly occurs in the surrounding small grains between, the dissolved precipitation to achieve a dynamic equilibrium, so that the average grain size of sintered bulk grows slowly.

Abstract:Self-assembly layered rare-earth hydroxide (LRH) nanosheets of ternary Y/Gd/Eu system were synthesized at freezing temperature by a chemical precipitation route. The anion-exchange behaviors and optical properties of the LRHs were studied. At the SO42-/Ln3+ molar ratio (R) of 0.25, the SO42- almost repalces the NO3- located in the interlayer of the LRH via anion exchange, however, the photoluminescence (PL) intensity decreases. Gd3+ substitution for Y3+ has significantly changed the coordination environment of Eu3+, leading to different intensities for the splitting bands of 5D0→7FJ transition peaking at ~590 and 595 nm. Sulfate exchange inhibits surface diffusion and inter-particle sintering during calcination and well-dispersed oxide powders that exhibit typical Eu3+ red emission were hence obtained. Gd3+ addition sensitizes Eu3+ emission to enhance the PL intensity of the phosphors. Improved PL intensity and external quantum efficiency and decreasing fluorescence lifetime were observed at a higher calcination temperature.

Abstract:Nano SiC particles dispersion strengthened WC-10Ni cemented carbide composites were fabricated by high energy ball milling(HEBM) and vacuum sintering(VS). The effects of the SiC content and vacuum sintering temperature on the microstructure and the room temperature mechanical properties of the SiC doped WC-10Ni cemented carbide composites were investigated in this paper. The results showed that the well-combined and highly-densified (nearly 99.2%) WC-10Ni-SiC composites can be obtained by the VS technology at 1 450 ℃ and 1 500 ℃, respectively. The addition of the SiC can not only restrain the growth of WC grains, but also play a role in refining grains, but also accelerate densification of the WC grains sintering. Also the vickers hardness of the prepared composite materials is improved with the increase of SiC content, up to 1 649 HV. Their fracture toughness and flexural strength increased with the increase of the SiC addition and then decreased. The fracture toughness and flexural strength of the WC-10Ni-SiC cemented carbide composites are 12.7 MPa?m_1/2 and 1 126.1 MPa, respectively when the content of the SiC is 0.5wt %.

Abstract:[001] oriented DD11 single-crystal superalloy (SC) was shot-peened perpendicular to [001] to induce pre-deformation. Pre-deformed micro-structure was investigated using elecron backscatter diffraction (EBSD), scanning electron microscopy (SEM) and micro-hardness tester (HT). After subsequent thermal exposure (TE), the effect of the temperature and pre-deformation degree on surface structure was researched by SEM and HT, moreover, high-temperature fatigue performance after peening-exposure was tested. The results show that after pre-deformation, [110] and [111] oriented subgrains were observed on the surface, and that surface strain hardening effect occured. The greater the deformation degree was, the larger the subgrain orientation angle, the depth of the rotating subgrain layer and the hardening effect were. With the increase of exposure temperature, the pre-deformed surface micro-structure showed a relaxion of micro-hardness and a dynamic recovery process of spheroidization, fragmentation-discontinuous cellular organization and continuous cellular organization. Furthermore, the greater the deformation degree was, the lower temperature the recovery process occured at. However, the recrystallization was not observed at the condition of shot peening and 1060℃/2h. Compared with grinding and TE, the 1060℃ fatigue cycles increased while peening and TE. For fatigue condition 1060℃/350MPa/r=-1/axic, the main source of fatigue is sprouting inside, while secondary source is born on the surface.

Abstract:In this study, multi-pass spinning of AZ91 magnesium alloy tube was conducted by power forward spinning. The microstructural evolution, phaseStransformation and micro mechanical properties were examined by opticalSmicroscope, SEM-EBSD-EDS, and nano-indentation tests. The results show that when the wall thickness of AZ91 magnesium alloy tube reduced by 88.33%, the surface was well formed without cracks or folds. In the initial stage of spinning, plastic deformation mainly occurred on the outer surface of magnesium alloy. With the spinning deformation increased, the deformation of inner and outer surface tended to be consistent. The brittle phase Mg₁₇Al₁₂ broke down and distributed with a streamline shape in magnesium alloy. At the same time, the grain of magnesium alloy refined and dynamic recrystallization occurred. With the increase of deformation, the strength of tubular parts increased, and the hardness was up to 1.036 GPa. The strengthening modes mainly include second phase dispersion strengthening and fine grain strengthening.

Abstract:Ni0.6Co0.2Mn0.2(OH)2 as precursor of lithium-ion batteries ternary cathode material was prepared for batch preparation by a hydroxyl co-precipitation method in the system of CSTR (continuous stirred tank reactor). Then, the Ni0.6Co0.2Mn0.2(OH)2 was roasted with Li2CO3 to receive Li[Ni0.6Co0.2Mn0.2]O2 under high temperature in the air. Scanning electron microscope (SEM), X-ray diffraction (XRD) and Transmission electron microscope (TEM) were used to examine the morphology and structure of the obtained Li[Ni0.6Co0.2Mn0.2]O2. The resulting Li[Ni0.6Co0.2Mn0.2]O2 powders have a type of spherical structure composed of secondary particles with a typical α-NaFeO2 lamellar structure. The electrochemical tests indicate that this cathode material have a good electrochemical reversibility and much better cycling stability in the voltage range of 2.8 and 4.3 V. Its initial charge and discharge specific capacity are as high as 206 mAh g-1 and 176 mAh g-1 at 0.2 C, with a capacity retention rate of 85% after 100 cycles．

Abstract:The effects of different cold rolling reduction ratio(ε=7%，14%，20%，27%) prior to aging on pricipitation hardening of the 1460 alloy have been studied. Some dense dislocation walls (DDW) have developed in the Al matrix in the ε= 20% sample.The matrix dislocations provide nucleation sites for the T1 phase, thus the pricipitation of the T1 is enhanced and its size remians about 100 nm, furthermore the samples reach the peak strength in a shorter time. The preferable process is 27% cold rolling reduction + 160 ℃/12 h. The results show that the tensile strength and elongation of the samples could be increased to 590 MPa and 8.0%.

Abstract:Porous tungsten matrix for Ba-W cathode was prepared by plasma spheroidization process combined with spark plasma sintering (SPS). The effect of plasma spheroidization process parameters on the spheroidization efficiency and properties of the W powders, microstructure of the porous W matrix sintered by SPS as well as the emission performance of the corresponding Ba-W cathode were investigated. The results show that spherical W powders with smooth surfaces and good sphericity can be obtained when the powder feed rate and carrier gas flow rate is 2.4 g/min and 4.0 L/min, respectively. The spheroidization efficiency is above 98%. The apparent density and flowability of the spherical W powders are enhanced greatly after plasma spheroidization. In contrast to the raw W powders, the structure and distribution of pores within the porous W matrix prepared by the spherical W powders are improved significantly after SPS, and the open porosity increases from 18.3% to 19.7%. The saturation pulse current density of the Ba-W cathode prepared with spherical W powders is 11.2 A/cm₂, which is higher than that of 8.7 A/cm₂ for the Ba-W cathode prepared by the raw W powders. The emission performance of Ba-W cathode can be highly improved by modifying the properties of W powders and microstructure of the porous W matrix.

Abstract:High-entropy alloy with high hardness, high strength, wear resistance, corrosion resistance, high temperature heat stability and other excellent performance owing to the metal - metal interface between the natural characteristics of high entropy alloy and aluminum alloy ,has a good wetting interface. In this paper, AlSiTiCrNiCu high-entropy alloy particles were used as the reinforced phase to reinforce aluminum alloy in order to study the effect of high-entropy alloy volume fraction and sintering temperature on the thermal conductivity of the composites. The result shows that the thermal conductivity of (AlSiTiCrNiCu) p / 6061Al composites decreases with the increase of the volume fraction of AlSiTiCrNiCu particles, and the thermal conductivity of (AlSiTiCrNiCu) p / 6061Al composites is 61.59 W / (m ? K) , Compared to the matrix 6061Al alloy decreased by 52%. When the volume fraction is 10%, the thermal conductivity of the composites decreases with the sintering temperature, and the thermal conductivity of the composites is 65.80 W / (m ? K) when the sintering temperature is 540 ℃. By TEM analysis, the type of the interface between high-entropy alloy and aluminum alloy is the diffusion interface and it doesn’t occur any interface product , which contributes to the reduction of thermal conductivity.

Abstract:The dry sliding friction wear test of T6 treated Al-10Si-5Cu-0.75Mg alloy was performed with UMT-2 tribometer. The wear mechanisms of the alloy under different load and revolving speed were analyzed by means of SEM, XRD and EDS. The results reveal that the wear rate of Al-10Si-5Cu-0.75Mg alloy is increased with the increase of revolving speed and applied load. but under 800 r/min high revolving speed, Al-10Si-5Cu-0.75Mg alloy still has a good wear resistance. The wear rate of the Al-10Si-5Cu-0.75Mg alloy under 15N applied load is only increase by 291% compared with 5N applied load, this belongs to mild wear. The average friction coefficient changes within the range from 0.35 to 0.40, and the change is small over time, which indicates a strong stability. Meanwhile, as the applied load increases, the wear mechanism is changed from the abrasive wear and the adhesive wear of low applied speed to the delamination wear and the oxidative wear of high applied speed. Keywords: Al-10Si-5Cu-0.75Mg alloy; wear rate; friction coefficient; wear mechanism

Abstract:Graphene nanosheets (GNFs) reinforced aluminum composites were fabricated by spark plasma sintering (SPS) with different temperature and holding time. The microstructure and tensile properties of the composites were prepared and analyzed. Results show that the SPS process affects the mechanical properties of the composites by regulating the characteristic of GNFs/Al interface. When sintering at 500℃, the interfacial reaction of GNFs/Al is inhibited, but the interface bonding of graphene/aluminum is weak, which result in the low mechanical properties of the composite. When sintering temperature is increased to 560℃, the mechanical properties of composite significantly improved, which result from the GNFs/Al interface bonding force is obviously enhanced and the interface reactions is effectively control by rapid sintering. In addition, GNFs can also inhibit the coarsen of aluminum matrix grain with the sintering temperature increases.

Abstract:The different level microstructure (grains,colonies and lamellas)were obtained when TC4 titanium alloy was heat-treated at different cooling rates, and the Hall-Petch relation was established based on different level microstructure. With the increase of cooling rate, the lamellas were refined; the yield strength and tensile strength increased, whereas the ductility gradually decreased.The relationship between lamella size and mechanical properties was in line with Hall-Petch relation, therefore the lamella was the main characteristic parameter affecting the mechanical propertiesand.

Abstract:The (Ca_0.96D_0.04)MnO₃(D=Ca, Sr, Rb, Sm) oxide powders were prepared by sol-gel method firstly, and the CaMnO₃(CMO) bulk samples were prepared thereafter by spark plasma sintering in argon atmosphere and air atmospheric sintering at ordinary pressure respectively. After analyzing their phase compositions, the better preparation method of CaMnO₃ bulk samples are selected and then the (Ca_0.96D_0.04) MnO₃ (D=Sr, Rb, Sm) oxide bulks were prepared. Finally, the phase composition, microstructure and thermoelectric properties of (Ca_0.96D_0.04) MnO₃ (D=Ca, Sr, Rb, Sm) bulk samples are measured and analyzed. The results show that the CaMnO₃(CMO) bulk samples prepared by spark plasma sintering in argon atmosphere have occurred phase decomposition, which is due to the SPS poor oxygen sintering environment. High quality (Ca_0.96D_0.04)MnO₃(D=Ca, Sr, Rb, Sm) bulk samples with single phase can be prepared by atmospheric sintering at ordinary pressure. The dimensionless figure of merit ZT is improved with peak values of 0.11,0.08,0.07 at 873K for (Ca_0.96D_0.04)MnO₃(D= Sr, Rb, Sm) bulk samples respectively, which are about 1.3~2.2 times higher than that of the un-doped samples.

Abstract:The effect of ultrasonic impact treatment (UIT) on very high cycle fatigue properties of MB8 magnesium alloy welded joint was investigated by ultrasonic fatigue test. At the same time, the mechanism of UIT to improve the very high cycle fatigue properties of MB8 magnesium alloy welded joints was investigated from three factors, such as stress concentration, residual stress and grain refinement. The results show that the S-N curve of the fatigue life, in 1× 108 cycles, the fatigue strength of as-welded specimen is 31.62MPa , the fatigue strength of treated specimen is 39.81MPa, and the fatigue strength of treated specimen is 26% higher than that of the as-welded. This shows that UIT can obviously improve the very high cycle fatigue properties of MB8 magnesium alloy welded joint. The weld toe stress concentration factor of as-welded specimen Kt1 is equal to 1.95, the weld toe stress concentration factor of treated specimen Kt2 is equal to 1.67, and stress concentration factor is reduced by 14.4%. The UIT can reduce the stress concentration of the weld toe. After UIT, the stress at the toe of the specimen changes from residual tensile stress to residual compressive stress. UIT refine surface grain of welded toe to improve very high cycle fatigue properties of MB8 magnesium alloy welded joint.

Abstract:the exothermal agent KClO₃ was decomposed KCl as the diluent was added into the B₂O₃-CeO₂-Mg system to prepare ultra-fine CeB₆ powders via salt-assisted combustionSsynthesis. TheSproductsSwereSanalyzedSbySXRD,SSEM,SEDSSandSTEM,and theSformationSmechanism of the

Abstract:Particle refinement is the effective way to improve the coercive force without increasing the HRE content in Sintered Nd-Fe-B magnets. The magnetic properties and initial magnetization permeability has been investigated in order to correlate the particle refinement by traditional powder metallurgy method with nominal composition of (Pr₂₅Nd₇₅)₂₅Dy₆Al_0.5B₁Co₁Cu_0.2Fe_bal sintered Nd-Fe-B magnet. The particles with average size of 3.0 μm achieved the best Hcj, and the particles with average size of 3.5 μm obtained the best Br respectively. Refined particle size which made the morphology regular and uniform. But with further decreased the average particle size, Nd rich phase was in the form of oxide, and unevened distribution in the grain boundary, and the demagnetization coupling efficiency droped, results in the decrease of Hcj. The oxidation content increased with the average size becoming samller, the Br decreased with the impurity content increased. On the other hand,the initial permeability dramatically fallen with the impurity content.

Abstract:The pure molybdenum powder was consolidated to bulk material with the relative density of over 0.98 via high-pressure torsion (HPT) processing at 350 ℃. The deformation of particles and pores, the evolution of crystallite size and dislocation density, and the strengthening mechanism during HPT processing were analyzed through scaning electron microscopy (SEM), X-ray diffraction (XRD) and the Vickers microhardness. The influence of applied pressure during HPT on the microstructure evolution, mechanical properties and thermal stability were discussed. The results show that the relative density and average microhardness of the HPT processed sample were improved obviously with the increasing applied pressure from 2.0 GPa to 3.0 GPa. Also, the crystallite size and microstrain experience a decrease and an increase with the increasing applied preassure which leads to the increase of dislocation density. In addition, the grain size in the HPT processed sample has a finite increase during the DSC processing, which indicates the thermal stability of HPT processed microstructure.

Abstract:In this article, the Ni0.8Co0.15Al0.05(OH)2 precursor was prepared by co-precipitation method, which AlO2- as Al source used. The precursor was processed at 500 oC, followed by mixing with excess LiOH?H2O and calcined at 700 oC for 12h under O2 atmosphere. Finally, LiNi0.8Co0.15Al0.05O2(NCA) materials have been synthesized. X-ray diffraction (XRD) showed that the NCA material is a typical α-NaFeO2 layered structure and belongs to the R-3m space group. According to scanning electron microscopy (SEM), they were uniform spheroidal particles with 5~6 μm diameters. The results of electrochemical tests showed that the first discharge capacity of NCA is 167.1 mAh/g at 0.1C rate, and the capacity retention rate is 96.2% after 200 cycles. Rate capacity test indicated that its capacity at 0.1C and 10C is 184.0 mAh/g, 112.7 mAh/g, respectively. When restored to 0.1C, the capacity can reach 179.7 mAh/g, and has a good rate performance.

Abstract:This paper selects 316LN and Alloy 690, the structural materials with largest contact area with nuclear power plant primary circuit coolant as research objects. Under simulated Pressurized Water Reactor （PWR）primary circuit water chemistry condition, we use static autoclave immersion method and high temperature elec-trocchemistry to study the effect of zinc concentration on corrosion behavior of these two structural materials. The results show that zinc addition can inhibit corrosion rate of materials and corrosion product releasing rate obviously. Compare with Zn-free condition, zinc additioncan make corrosion rate of 316LN and Alloy 690 re-duce by 1.4 times and 1.5 times and reduce corrosion product release rate by 2.3 times at most，respectively. When zinc concentration is 10~50ppb, it can inhibit corrosion rate and corrosion product release rate effectively. When Zn concentration is above 50ppb, Zn concentration doesn’t have obvious effect on corrosion rate and corrosion product release rate.

Abstract:In this contribution, we present the preparation of high purity niobium ingot for RF superconducting cavities by more than three times electron beam melting under high vacuum. The purity of obtained high pure niobium ingots were more than 99.99%, and RRR value reached more than 300. High pure niobium ingots has reaches the standard specifications for RF superconducting cavities.The RRR value of high purity niobium ingot is mainly affected by the interstitial impurities such as H、N、O、C, while the standard of Ta content can be relaxed moderately. With increasing the number of electron beam melting, the interstitial impurities can be removed effectively, and RRR values grow steadily.The results show that, RRR value and impurity content should be combined to evaluate the quality of high purity niobium, while impurity content alone is insufficient.