Abstract:Four types of Y₂O₃ partially stabilized ZrO₂ (YSZ)-based agglomerated powder containing no bonding phase, Al₂O₃, yttrium aluminum garnet (YAG), and MgAl₂O, labeled as B0, B1, B2, and B3, respectively, were prepared by spray granulation. And, the flow ability, apparent density and particle size distribution of those powders were investigated. Besides, the deposition efficiency (DE) and bonding mechanism of the four types of agglomerated powder prepared by atmospheric plasma spraying (APS) were analyzed. The results show that, compared with B0 powder, the flowability of B1, B2 and B3 powder is reduced by 6.94%, 5.15% and 25.2%, respectively, the apparent density is reduced by 2.85%, 2.19% and 7.67%, respectively, and the proportion of large-size agglomerated powder is increased by 15.82%, 6.65% and 29.75%, respectively. The DE of B1, B2 and B3 powder is increased by 75.80%, 181.49% and 59.21%, respectively, and the main reason for the improvement of DE is the adhesion and wrapping effect of the bonding phase. Because YAG has the lowest melting point and moderate particle size, B2 powder has the best flowability, the maximum apparent density, and the smallest proportion of large particles, which accordingly results in the strongest adhesion and wrapping effect and eventually leads to the highest DE.

Abstract:To improve the corrosion resistance of magnesium alloys, super-hydrophobic (SH) coating was fabricated on the surface of ZK60 magnesium alloy coated with layered double hydroxides (LDHs) film. The electric field was introduced in the coating preparation process, and the influences of working current density on the characteristics of the coatings were researched. The results indicate that the working current densities significantly affect the microstructure of the LDHs films, which has an important impact on the hydrophobicity of the SH coatings. When the working current density is 25 mA/cm², the SH coating presents a homogenous micro-nano structure and super-hydrophobicity. The corrosion current density of the SH coating (I_corr =9×10^-7 A·cm^-2) is two orders of magnitude lower than that of the ZK60 substrate (I_corr =3×10^-5 A·cm^-2), indicating excellent corrosion resistance.

Abstract:The pure Ti with different initial grain sizes which was annealed at 923 and 1023 K for 1 h was processed by ECAP at room temperature. The influence of initial grain size on microstructure and properties of ECAPed pure Ti was investigated by TEM, EBSD, tensile tests and microhardness tests at room temperature. The twinning behavior and deformation mechanism of pure Ti were also discussed during the ECAP. The results show that the initial grain size of pure Ti increases with increasing the annealing temperature. The grain refinement effect of pure Ti annealed at 1023 K is more significant than that of pure Ti annealed at 923 K after 1 pass of ECAP, while the microstructure of pure Ti annealed at 923 K is finer and more uniform than that of pure Ti annealed at 1023 K after 4 passes of ECAP. With the increase of ECAP pass, the yield stress increases, especially after 1 pass with more than 100% implication. The larger the initial grain size, the greater the stress increase. The deformation mechanisms of pure Ti during the ECAP include dislocation slips and deformation twinning, and with the increase of the initial grain size, the number of twins increases.

Abstract:The effect of cooling medium on microstructure evolution, variant selection and texture inheritance along with mechanical properties in a recrystallized commercially pure Ti sheet after β-solution treatment was investigated by combined use of optical microscopy (OM), electron channeling contrast (ECC) imaging, electron backscatter diffraction (EBSD) techniques, transmission electron microscopy (TEM) and micro-hardness test. It is found that with the decrease of cooling rate, fine needle-like α′ martensite (in water and liquid nitrogen), Widmanst?tten (in air), and coarse-grain microstructures (in furnace) are observed in turn. Additionally, the faster cooling rate results in a finer transformed structure accompanied with an attendant higher hardness value. Analyses for crystallographic orientations reveal that the Burgers orientation relationship (BOR) is strictly obeyed during the β→α cooling except for the β-furnace-cooled specimen with appearance of other misorientations disobeying the BOR. As for texture characteristics, firstly, the texture distribution is largely scattered compared with the initial one and new orientation components of <0001>//TD and <>//ND appear upon the water and liquid nitrogen quenching. Secondly, the texture inheritance phenomenon occurs in furnace cooling condition because of stronger variant selection, then leading to a stronger transformation texture. Results suggest that raising cooling rates can be more feasible to weaken the transformation texture by suppressing the variant selection.

Abstract:The pure titanium prepared by selective laser melting (SLM) was modified by equal channel angular pressing (ECAP). The pure titanium prepared by SLM was subjected to single-pass deformation modification at room temperature by a die with the angle of Φ=120° and ψ=20° between two channels, and its microstructure and mechanical properties were evaluated. The results show that the microstructure of SLM+ECAP pure Ti sample is refined, the grain size decreases from 13 μm to 7 μm, and the dislocation density increases. During the ECAP deformation process, twinning and continuous dynamic recrystallization (CDRX) occur simultaneously. The appearance of tensile and compression twin and the increase of dislocation density together promote the microhardness of SLM+ECAP pure Ti samples, increased by 13%, and YS and UTS are increased by 18% and 20.4% respectively, while the elongation decreases slightly.

Abstract:The corrosion, wear and tribocorrosion behavior of a new biomedical Ti-20Zr-10Nb alloy was investigated using electrochemical measurements, tribological tests and scanning electron microscopy (SEM). Potentiodynamic polarization tests show that the corrosion potential (E_corr) shifts towards negative values and that the corrosion current density (i_corr) is increased by two orders of magnitude; these trends differ from those observed with static corrosion. The wear and tribocorrosion results indicate that the wear volume of the Ti-20Zr-10Nb alloy increases with increasing applied load. The contribution of mechanical wear to the material loss of tribocorrosion is greater than that of corrosion. However, the friction coefficients obtained under conditions of electrochemical corrosion are lower than that obtained only under wear. Through observation of the wear crack, it is determined that abrasive wear mechanism is the main mechanism of tribocorrosion. The effect of abrasive particles on the wear and tribocorrosion behavior is considered, and it is found that material loss increases due to particle damage.

Abstract:The effect of the shot peening intensity on the surface integrity of TA15 titanium alloy hot extruded profile was numerically and experimentally studied. The surface roughness and residual stress distribution obtained by the numerical simulation were compared with the shot peening experimental results, and the reliability of the established finite element model was verified. The effects of shot peening intensity on the microhardness and microstructure of the material surface were investigated. The experimental results show that the compressive residual stress layer with a maximum value of 558~764 MPa and a depth of 115~151 μm was introduced into the surface of TA15 titanium alloy profile after shot peening. The plastic deformation occurs on the material surface, the grain is refined, the dislocation density and the hardness of the material surface increase. The hardened layer with a depth of 100~150 μm forms, and the surface roughness increases. The increase of the shot peening intensity increases the maximum compressive residual stress, the depth of the compressive residual stress layer and the surface hardness. However, the increase is not obvious when the intensity exceeds 0.188 mmA, and the cracks might appear on the material surface. Moreover, at the intensity of 0.222 mmA, the residual stress relaxation occurs on the material surface due to the folding defect, which reduces the surface integrity of the material.

Abstract:3D through-hole Pb-Ca-Sn anode was prepared which may be a promising anode with excellent performance for copper electrowinning. And the electrochemical properties of 3D through-hole Pb-Ca-Sn anode and Pb-Ca-Sn anode were studied by galvanostatic polarization, electrochemical impedance spectroscopy, anodic polarization and double-Slope Tafel carried out in 160 g/L H₂SO₄ solution at 45 °C. Besides, the micro-morphology, element distribution and phase composition of the oxide layer were investigated. Results show that compared with the traditional Pb-Ca-Sn, 3D through-hole Pb-Ca-Sn anode shows much lower anodic potential, higher exchange current density and better electrocatalytic activity. These characteristics are related to its excellent 3D through-hole structure, which increases the oxygen evolution surface area of the anode. Furthermore, the content of β-PbO₂ and PbSO₄ in the oxide layer of 3D through-hole Pb-Ca-Sn is higher and lower than those of Pb-Ca-Sn, respectively.

Abstract:Heterojunction solar cells (HSCs) with the structure of p-Si/n-ZnO nanorod (NR) arrays were prepared by synthesizing a ZnO NR array film on patterned p-type silicon substrate through a low temperature hydrothermal method. ITO and Al films as the front and back contact electrode layers were deposited by DC-magnetron sputtering, respectively. The influences of various factors, such as annealing temperature for seed layer and hydrothermal synthesis time for ZnO NR arrays, on the crystal structure, surface morphology, and optical property of the ZnO NR array film were investigated. Results show that the optimized short-circuit current density and allover energy conversion efficiency of the p-Si/n-ZnO nanorod array HSCs are 11.475 mA·cm^-2 and 2.0%, respectively. Compared with those of p-Si/n-thin film ZnO solar cell, the photovoltaic properties of the p-Si/n-ZnO nanorod array HSCs are improved significantly.

Abstract:TiC/Hastelloy composite has been proposed as one of promising intermediate temperature solid oxide fuel cell interconnects, and the oxidation resistance is one key property for its application. TiC/Hastelloy composites with 50vol% and 58vol% metal matrix were prepared by reactive infiltration method. Results show that high metal content results in the increase in Cr content, which optimizes the oxidation resistance of TiC/Hastelloy composites by promoting formation of continuous Cr₂O₃ layer to inhibit external diffusion of Ni and Ti. The content of Ti and Ni oxides in oxide scale obviously decreases. The mass gain reduces from 2.03 to 0.55 mg·cm^-2. Meanwhile, in order to inhibit the migration of Cr, Co is extra introduced into the composites with 58vol% metal. During the oxidation process, Co and Fe (in metal matrix) show high external diffusion rate through Cr₂O₃, and generate in-situ CoFe₂O₄ layer outmost the oxide scale.

Abstract:The possible activated slip systems and slip traces of pure coarse-grained magnesium were investigated during cyclic deformation at room temperature. Results show that numerous criss-cross slip traces are observed on the surface of the specimens after cyclic loading. Based on the results of a combinatory analysis for the unit cell orientation and direction of the slip traces, it is determined that the criss-cross slip traces are formed by the intersection of the basal slip traces in the former matrix and the subsequent {} twinning area during the reversed cyclic loading. Moreover, the most likely pyramidal slip mode is the sliding of <> pyramidal dislocations on {} pyramidal planes, while the basal slip traces are denser than the pyramidal slip traces, suggesting that there is limited pyramidal slip activity.

Abstract:The effect of minor Gd element on the microstructure and properties of Mg-8Zn-1Mn-3Sn alloy was studied. The results show that Mg-8Zn-1Mn-3Sn-xGd is mainly composed of α-Mg matrix, MgZn₂, MgZn, Mg₇Zn₃, Mg₂Sn phase and MgSnGd phase. The MgSnGd phase is a high temperature phase, which is formed firstly during the solidification and changes the solidification process, causing the semi-continuous second phase at the grain boundary to transform into a discontinuous network. The MgSnGd phase has a coherent orientation relationship with the α-Mg matrix, which can be used as a heterogeneous nucleation core to refine grains. The Mg-8Zn-1Mn-3Sn-0.5Gd alloy has the best comprehensive mechanical properties. The mechanical properties of the alloy are significantly improved by adding Gd elements to refine the grains, and the MgSnGd phase pins the grain boundary to hinder the movement of dislocations and the transformation of the second phase of the grain boundary.

Abstract:Based on electron backscattered diffraction (EBSD) and grain growth model of thin film materials, grain sizes and growth thermo-kinetics were investigated during annealing with different heating rates in high-voltage anode aluminum foil. Results show that the grain growth exponent n=4, activation energy Q_g=129 kJ/mol and rate constant K=1.28×10^-8 m⁴·s^-1 are calculated by the typical isothermal grain growth equation. Based on grain growth model of thin film materials and energy anisotropy, the reasons for the rapid growth of (001) oriented grains are well explained, and a typical 40°<111> misorientation relationship with S-grains is found.

Abstract:The arc characteristics and droplet transfer behavior in plasma-GMAW-P hybrid welding were investigated. The effect of plasma arc current on GMAW-P arc shape and metal transfer was discussed. The results indicate that the plasma arc will change the electrical conductivity and stress state of GMAW arc to affect the morphology of GMAW arc and droplet transfer behavior. When the plasma arc current is small, the GMAW arc in the base current period basically burns along the wire axis, and the bell-shaped GMAW arc in the peak current period is compressed due to two opposite forces (the electromagnetic force generated by the plasma arc and the wire) in the welding direction. At this time, the drag force of plasma flow and its downward component increase, the droplet transition is promoted, and the detached time of droplet is shortened. When the plasma arc current reaches a certain value, the metal vapor in the atmosphere near the plasma arc increases, and the conductive path of the GMAW arc will be changed to bias the GMAW arc to the plasma arc. At this time, the downward component of the drag force of the plasma flow on the droplet decreases, the promotion of the droplet transition is weakened, and the detached time of droplet is increased.

Abstract:To investigate the influence of cooling rate on the solidification structure of Al-Cu binary alloy, the ingot of Al-6%Cu alloy was produced by the wedge-shaped copper mode casting. The results indicate that when the cooling rate decreases from 100 K/s to 2 K/s, the grain morphology transformation of ingot is as follows: columnar grains→mixing of columnar grains with equiaxed grains→equiaxed grains. Meanwhile, the width of columnar crystal at the ingot edge increases from 244.7 μm to 408.2 μm, the average grain size of equiaxed crystal at the ingot core decreases from 629.8 μm to 152.8 μm, and the average dendrite arm spacing increases from 10.1 μm to 52.8 μm. The parameters A and n of Al-6%Cu alloy in the empirical formula of average dendrite arm spacing and cooling rate are 78.75 and 0.41, respectively. When the cooling rate decreases from 100 K/s to 25 K/s, the morphology of eutectic Al₂Cu changes from skeletal to lamellar, and α-Al near the eutectic Al₂Cu is cellular. With the cooling rate increases from 2 K/s to 100 K/s, the hardness of Al-6%Cu alloy is increased from 618 MPa to 726 MPa.

Abstract:Conductive SrVO₃ powders were synthesized by sol-gel method combined with subsequent heat treatment. The molar ratio of Sr:V was adjusted during the sol process. The thermal behavior of the gel was analyzed to figure out the calcination temperature in order to get the precursors without residual carbon, and then the gel was reduced in H₂ to obtain the final products. The influence of temperature and molar ratio of Sr:V on the morphologies, structures and compositions was researched. The conductivity of the samples was tested by standard dc four-probe technology. The results show that when the molar ratio of Sr:V=1:1.06, the calcination temperature is 500 °C and reduction temperature is 850 °C in H₂, the SrVO₃ powers without the impurities of residual carbon or vanadium oxides can be obtained. The electrical conductivity of SrVO₃ powders reaches 714.3 S/cm, while that of graphite powders is about 500 S/cm.

Abstract:The hot deformation behavior of Al-xMg-2.8Zn alloys at deformation temperature of 300~490 °C, strain rate of 0.001~5 s^-1 was studied by isothermal hot compression tests. After correcting the flow softening from deformation heating in stress-strain curves, Arrhenius-type constitutive equations and processing maps were used to predict and analyze the hot deformation behavior of Al-xMg-2.8Zn alloys. The results show that the flow stress increases with increasing Mg content and strain rate or decreasing temperature. According to the processing maps and corresponding microstructure of alloys, the range of optimum hot deformation parameters of alloys is determined. The range of hot deformation temperature and strain rate both extend and the instability domains extend to the zone of higher temperature and lower strain rate with increasing the Mg content.

Abstract:Based on the first-principles method of density functional theory (DFT), the segregation behavior of Si, Ni, Mn, Cr, and Mo at the NbC/fcc-Fe interface was studied, and the influence of B on the segregation behavior of alloying elements was analyzed. The results show that Cr and Mo can stably exist in the interface and NbC. Mo tends to segregate in the interface and NbC; Ni and Mn have a slight tendency to interface segregation. Mo is easy to segregate into NbC to form composite carbides. When the Mo/Nb content ratio is less than 2/3, the (Nb, Mo)C composite carbide is more stable and the binding energy is greater, which should be related to the strong electronic interaction between Mo and C and between Mo and Fe. When B is doped to the interface, the tendency of Mo and Cr to segregate to the interface is suppressed, expecially the segregation of Mo at the interface, thereby improving the corrosion resistance of the material. In addition, B can make Ni and Mn tend to be uniformly distributed in the matrix.

Abstract:The hot deformation behavior of Incoloy 825 alloy under 60% deformation,950 ~ 1150 ℃ temperature and 0.001 ~ 1s-1 strain rate was studied by hot compression test. Based on Arrhenius equation and Zener Hollomen parameter model, the constitutive equation model of the alloy was established. The microstructure evolution of the alloy was studied by means of metallographic microscope (OM) and electron backscattering diffraction (EBSD). The results show that the percentage of DRX increases with the increase of deformation temperature or the decrease of strain rate. DRX includes both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) during hot deformation. With the increase of deformation temperature or the decrease of strain rate DDRX increases and CDRX decreases. In addition, with the increase of temperature or the decrease of strain rate, the low angle grain boundary gradually transforms to the high angle grain boundary. Simultaneous random distribution Σ3 twin boundaries tend to homogenize, It also promotes the dynamic recrystallization.

Abstract:SiCp/Al composites are composed of SiC particles and aluminum alloy matrix with great performance differences. The cutting process is complex, and there are many factors affecting the processing quality, and the material simulation modeling is difficult. In this paper, a parametric modeling method of SiCp/Al composites is proposed considering the random distribution of particles, particle size, volume fraction and other factors. The removal process, cutting force, surface morphology and damage of SiCp/Al composites with different volume fraction are studied and verified by experiments. The simulation analysis and experimental results show that the parametric modeling is effective. SiCp/Al composites are characterized by severe surface damage, high cutting force, surface defects covered by substrate coating, and small actual cutting depth. The processing quality of SiCp/Al composites can not be evaluated by surface roughness alone. SiCp/Al with large particle size and high volume fraction has lower cutting force, lower specific grinding energy, worse surface quality, smaller actual cutting depth, more serious coating phenomenon and easier coating falling off. SiC particle size has an important influence on surface damage, cutting force and specific grinding energy. This paper can provide some references for the surface removal characteristics research and engineering application of SiCp/Al composite.

Abstract:In this paper, a triangle of complex characteristic temperature parameters derived from glass transition temperature Tg is constructed from two perspectives of the glass-forming ability (GFA) in cooling process and glass stability (GS) in heating process. According to two complex characteristic temperature parameters, a GFA & GS criterion is derived and modified from the perspective of balanced contribution of two temperature parameters Tg/Tl and Tx/Tg, and the three temperature parameter (Tx-Tg)/(Tl-Tg) to the evaluation criterion: GTg=Tg/Tl+Tx/Tg+(Tx-Tg)/(Tl-Tg) and GTgm=Tg/Tl+(Tx/Tg)/2+((Tx-Tg)/(Tl-Tg))^0.3. Through a large number of metallic glasses, oxide glasses and cryoprotectants, the reliability and efficiency of the criteria are verified and elaborated from GFA and GS in comparison with the current criteria based on characteristic temperatures. The results show that the new criteria have wide application in the evaluation of GFA & GS, especially the modified criterion has the best performance in the evaluation of GFA & GS of metallic glasses, and can be used as a reliable criterion.

Abstract:In this paper, βTitanium alloy was prepared by vacuum melting, cold deformation, and solution treatment. A six-anvil high press was used to perform high-pressure aging treatment on β-Titanium alloy, and the effects of high-pressure aging parameters on the microstructure, microhardness and elastic modulus of βTitanium alloy were studied, and the aging kinetics was analyzed. It is found that, aging pressure and time have significant effects on microstructure, hardness and elastic modulus. With the increase of pressure and time, the precipitation of α phase and martensite phase increases. The pressure and time of high-pressure aging have significant effects on the modulus of microhardness and elasticity. As the pressure increases, the microhardness first decreases and then increases, and the elastic modulus increases; as time increases, Vickers hardness and the elastic modulus first increase and then decrease.

Abstract:In this paper, a multi-material composite casting model with variable wall thickness structure is builded. Firstly, by simulating the filling and solidification process of A356 alloy in the multi-material composite casting mold, the filling time and temperature field results of the multi-material composite casting mold were obtained. The solidification time of zircon sand with silica sand, chromite sand with silica sand decreased progressively. The solidification time of casting is shorter at the Connection position of zircon sand with silica sand and chromite sand with silica sand, and the solidification speed of metal liquid is faster. Secondly, analysis the Electron Backscatter Diffraction Analysis (EBSD), electron microprobe analysis (EPMA), tensile strength and scanning fracture of A356 alloy casting with silica sand, chromite sand and zircon sand composite casting in gravity casting. The results show that at the same wall thickness, the grain size of chromite sand and zircon sand castings is better, the concentration ratio of Al, Mg, Si and other elements is lower, the mechanical properties are increased, and the fracture is characterized by ductile fracture. At the same time, with the decrease of wall thickness, the grain size of sand castings of the same material is fine, the concentration ratio of elements is reduce, the mechanical properties are increase, and the fracture surface presents the characteristics of ductile fracture.

Abstract:Based on Mo equivalent design, novel Ti-6Al-xMo(x = 2, 3, 4) titanium alloys was deposited by laser solid forming (LSF) from mixed Ti, Al and Mo elemental powders, and the microstructure and room temperature tensile properties of the alloys were investigated. The results showed that the solidification microstructure of the three alloys presents a coarse columnar grains growing along the direction of <100>, and the top is composed of equiaxed grains. With the increase of Mo content, the average width of the columnar grains decreases, and the thickness of the equiaxed grains layer increases gradually. The microstructure in primary β grains is composed of primary α lath and retained β phase, and there also exits grain boundary α and α colonies. With the increase of Mo content, the width and area ratio of primary α lath decrease. When the Mo content increases to 4 wt.%, the secondary α phase appears in the grain. Moreover, 12 α variants were found in all the three components by Electron Backscatter Diffraction (EBSD) analysis, and the variation was dominant. In terms of mechanical properties, the strength and hardness increase with the increase of Mo content while the elongation decreases. By contrast, Ti-6Al-2Mo and Ti-6Al-3Mo have the very good tensile properties of 962 MPa tensile strength and 11.5% elongation, and 982 MPa tensile strength and 9.2% elongation, respectively.

Abstract:The NiCrFeAl/h-BN.SiO₂ abradable sealing coatings were prepared by METCO 6P-Ⅱ flame spraying. With the addition of SiO₂, the abradability of the NiCrFeAl/h-BN coatings are improved. The anti-erosion performance of the abradable sealing coatings prepared with different flow-ratios of oxygen and acetylene (oxygen-acetylene ratio) were researched. The results show that the h-BN and SiO₂ particles are coated by NiCrFeAl during the spraying process. The metal phase adequately melted with the increase of oxygen-acetylene ratio, and the distribution of h-BN and SiO₂ are more homogenous. The Rockwell superficial hardness was raised from 50.8 HR15Y to 70.3 HR15Y, and the bonding strength was improved. The morphology of the wear tracks was characterized by adhesive wear and abrasive wear, and the roughness decreases with the increasing oxygen-acetylene ratio. The cohesive force of the coating was promoted deriving from the nonmetallic phase was coated by metal phase almost fully. The weight loss rate of the coatings decreases, and the anti-erosion performance are improved.

Abstract:Plastic deformation will be produced in the process of manufacture and service for the titanium bearing equipment, which will affect its fatigue resistance. In order to study the effect of pre-strain on the fatigue crack propagation behavior of commercial pure titanium TA2, fatigue crack propagation tests were carried out on the original material and the materials with 10%, 20% and 30% pre-strained value. Combined with the digital image correlation (DIC) technology, the strain fields at the crack tip were obtained, and the effect of pre-strain on the strain field at the crack tip was researched. The results show that, with the increase in pre-strained value, the propagation rate decreased during the steady-state fatigue crack propagation stage, meanwhile the crack opening displacement decreased and the crack opening load increased, and the plastic zone at the crack tip, the plastic deformation and the cyclic plastic strain accumulation decreased. Therefore, the pre-strain inhibits the plastic deformation and cyclic plastic accumulation at the crack tip, which leads to the more obvious crack closure effect, thus inhibiting the crack propagation. The research results have reference significance for the safety evaluation of titanium bearing equipment.

Abstract:The isothermal constant strain rate compression test of TA5 titanium alloy was carried out by Gleeble-3800 thermal simulator at temperature 850~1050℃, strain rate 0.001~10s_^-1 and maximum deformation of 60%. According to the experimental data, the flow stress curve of TA5 titanium alloy was analyzed, and the material parameters (deformation activation energy, Z parameter and power dissipation coefficient) were calculated under different process parameters. In addition, the prediction model of process parameters and material parameters was established by response surface method. Finally, the optimized process parameters were obtained by multi-objective visualization optimization. The results show that the flow stress of TA5 titanium alloy has negative temperature correlation and positive strain rate sensitivity. The prediction model based on the response surface methodology has high accuracy, and the optimized machining parameters range is (850~990℃/0.004~0.15s_^-1). The main deformation mechanisms of this region are dynamic recovery and dynamic recrystallization.

Abstract:The size, morphology and distribution of the secondary α phase were observed by EBSD, SEM and TEM. Tensile properties at room temperature of aged alloys were measured. The effect of secondary α phase on strength and ductility of novel near β titanium alloy, Ti-6Mo-5V-3Al-2Fe-2Zr, has been studied. The results show that with the increase of aging temperature from 520℃ to 560℃, the size of the intragranular αi phase changes little but the spacing decrease. With further increase of aging temperature, the width and spacing of the αi phase increase. As the increase of aging time from 4h to 8h, the width of the αi phase increases but the spacing changes little. When the aging time is 12h, there is no significant change in the αi phase. A relationship equation between secondary α phase and alloy strength has been established, which shows a good agreement with the calculated values of strength change induced by secondary α phase. It can be indicated that the spacing of the αi phase determines the alloy strength. The spacing of αi phase is the smallest and the ultimate tensile strength is the highest 1502MPa after aged at 560℃ for 8h. The alloy ductility is affected by both intragranular α phase and grain boundaries α phase. The continuous αGB phase and αi phase with smallest spacing form after aged at 560℃ for 8h, resulting in poor alloy ductility. The αWGB phase, which is distributed along the grain boundaries and grows parallel into the grains, as well as discontinuous αGB phase and αi phase with largest spacing, form after aged at 680℃ for 8h, resulting in significant improvement of alloy ductility.

Abstract:The SEM, EBSD and TEM were used for analyze the microstructure morphology and distribution characteristics of inertial friction welded joint in welding state and post-welding heat treatment state. In addition, the mechanical properties of the joint in post-welding heat treatment state were studied. The results showed that the weld zone was single equiaxed α grains, which is composed of lamellar martensite α" phase + grain boundary lamellar αP phase + metastable β phase in welding state, and with (0001)//ND fiber texture. The microstructure was consisted of grain boundary lamellar αP phase + intragranular lamellar αS +β phase after post-weld heat treatment. The (21 ?1 ?3)[21 ?1 ?9] orientation texture was also formed on the basis of the original fiber texture. Under the effect of welding pressure and thermal cycling, the equiaxed αP phase in thermo-mechanically affected zone had been transformed into a rod and approximately paralleled to the welding interface. The equiaxed αP phase in thermal affected zone still maintained original shape. The weld zone had the highest microhardness, which gradually decreased from weld zone to base metal. The post-weld heat treatment can reduce the hardness of the weld zone and obtain uniform hardness distribution in welded joint. The tensile specimens at room temperature failed in the base metal away from weld center line.

Abstract:In this study, the Ti6Al4V alloys were fabricated by selective laser melting (SLM) technology. The effect of laser energy density (LED) on the relative density, micorhardness, compression strength and plasticity of the Ti6Al4V alloys was systematically studied. The optimum LED processing window for SLM of Ti6Al4V alloys was in the range of 84.8–163.6 J/mm_³. In the optimum LED window, the TiN reinforced Ti6Al4V matrix composites were fabricated by SLM in different N₂ concentration (3 vol.%, 10 vol.% and 30 vol.%) atmospheres based on gas–liquid reaction. The principle of the novel technology for fabricating of the composites is as follows: decomposition of N₂ near the Ti6Al4V melt pool generates N atoms/ions, the gaseous N atoms/ions react with liquid Ti atoms to in-situ synthesize uniformly distributed TiN reinforcements which combine with the Ti6Al4V matrix during melting–solidification, finally, the TiN reinforced Ti6Al4V matrix composites are built by SLM layer-by-layer. Effect of N₂ concentration on the microstructure and mechanical properties of the Ti6Al4V matrix composites was researched. The composite fabricated by SLM in 3 vol.% N₂ atmosphere exhibited a good combination of high strength and high plasticity. The strengthening and toughening mechanisms were studied.

Abstract:Porous titanium orthopedic implants fabricated by 3D printing have golden prospects. As one of the surface technologies, electrolytic plasma polishing can effectively remove the powder particles attached to the surface of 3D printed porous titanium parts and can reduce the surface roughness. In this paper, the surface morphology and surface roughness of the external and inner surface were analyzed and tested at different plasma polishing times. Electrolytic plasma polishing is effective to improve surface roughness. The longer the polishing time is, the smoother the surface is and the lower the surface roughness is. The polishing time is an important factor affecting the surface roughness. By the fitting curve, the surface roughness of the external and inner surface can be guaranteed to be within a reasonable range by the control of polishing time.

Abstract:Magnesium alloy is an ideal bone implant material with high specific strength and good biocompatibility.SDue to the limitation of rapid degradation rate of magnesium alloy in clinical application, SLM can be used to alloyed magnesium alloy and improve its corrosion resistance.SMg-1zn-xGd (x=0, 0.25, 0.5, 1, 2 wt%) alloy was formed by SLM, and the average corrosion rate of magnesium alloy soaked in simulated body fluid for 72 h was tested. The corrosion mechanism was analyzed by SEM, EDS and TEM.SThe experimental results show that Gd content has a significant effect on the corrosion rate of magnesium alloy, and the degradation rate of magnesium alloy decreases first and then increases with the addition of 0~2 wt% Gd, and the magnesium alloy has the best corrosion resistance with the addition of 0.5 wt% Gd.SThe surface passivation film produced by the corrosion reaction can slow down the corrosion process to a certain extent, and the Mg₅Gd phase precipitated along the grain boundary increases after the addition of excessive Gd, resulting in intensified corrosion of magnesium alloy.

Abstract:In this paper, an ultra-fine-grained Mg-2.5Zn-1Ca alloy was prepared by extrusion + equal channel angular extrusion (ECAP) composite processing technology. The microstructure evolution characteristics during the deformation process were analyzed by OM, SEM, XRD, EBSD etc., combined with mechanics performance changes, study alloy strengthening mechanism during deformation. The results show that after extrusion + ECAP deformation, the grains and the second phase grains are significantly refined, and the uniform fine grain structure is obtained after extrusion + 2 passes ECAP, with an average grain size of about 1.1μm; At the same time, the fine Ca₂Mg₆Zn₃ particles are dispersed distributed in the matrix. The grain refinement is the result of the combined effect of severe plastic deformation, dynamic recrystallization, and the finely dispersed Ca₂Mg₆Zn₃ phases. ECAP deformation significantly improves the mechanical properties of the alloy. The two passes have the highest tensile strength and elongation, which are 275MPa and 17% respectively. With the increase of ECAP deformation passes, the texture strength gradually weakens, and the basal texture gradually changes into a new texture. Moreover, ECAP deformation alloy has higher non-basal Schmid factor, and the microstructure is uniformly refined, which makes the material have better elongation.

Abstract:NiTiNb shape memory alloy ingots were prepared by means of cold crucible vacuum induction melting method. Influence of this melting method on chemical composition and solidification microstructure of the alloy were studied. Losses of alloying elements during vacuum induction melting were evluated. Method for improving the accuracy of alloying element content was also advanced. The results show that higher heating power and repeated melting are benefit to sufficient alloying of different elements. The content of C and O increases with melting time and decreases with vacuum level, the influence of vacuum level is more notable than melting time. Lower cooling rate of the melt lead to the appearance of columnar zone. Besides, the size of columnar zone and shell zone in the ingt will continuously increase with the decrease of cooling rate. The splash which caused by the severe reaction of Ni and Ti during early period of melting will lead to heavier losses of the alloying elements. However, the accuracy of element content can be remarkably improved by adjustment of the weight for raw materials.

Abstract:_{: By arranging the Carbon nanotubes (CNTs) macrofilm (CMF) on the meta copper foil evenly,which is made into compositecurrent collector (Cu-CMF),to improve the associativity of active substance with current collector, reduce the interfacial resistance of the battery. Mingle the reduced graphene oxide(rGO)in active substance graphite to increase the contact point between graphite particles of active substance, which help obtain the high specific capacity and chemical stability battery. Characterization was executed by scanning electron microscopy(SEM) and electrochemical testing. The results show that the graphite electrode has a specific capacity of 102.7 mAh g^-1 at a ratio of 2 C based on Cu-CMF composite collector mingle with rGO, which is the 3.7 times(27.4 mAh g^-1) of the undoped graphite electrode based on copper foil collector. It shows the excellent rate capability.}

Abstract:AlCoCrFeNiSix(x=0.1，0.2，0.3，0.4，0.5) high-entropy alloy coatings were prepared on the surface of AISI 304 stainless steel. The effect of Si element on the microstructure and properties of the high-entropy alloy was investigated using X-ray diffractometer (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS), transmission electron microscope (TEM), Vickers hardness tester, and electrochemical workstation. The results show that the high-entropy alloy coatings consist of solid-solution grains with body-centered cubic (BCC) lattice. With the increase of the Si element content, the substitutional solid solution of Si element causes the crystal lattice to shrink, and the crystal grains are gradually refined. Besides, the AlNi phase with nano-scale spherical shape is dissolved in the crystal grains, and a small amount of Cr23C6 carbides are precipitated along the grain boundaries. The evolution of the microstructure leads to an increase in the microhardness of the coating, with the maximum hardness reaching 848.1 HV0.3. The thermodynamic corrosion tendency and uniform corrosion rate of AlCoCrFeNiSix high-entropy alloy coating are lower than the AISI 304 stainless steel. The doping of Si element improves the repair ability and stability of the passivation film, and promotes the corrosion mechanism to transform from pitting corrosion developed by autocatalysis to intergranular corrosion.

Abstract:The microstructure and mechanical properties of Mg/Al alloy dissimilar metal resistance lap joints were studied by adding an interlayer of titanium foil. The research results show that adding a 0.2mm thick titanium interlayer can greatly increase the strength of Mg/Al dissimilar metal resistance spot welding joints. The maximum tensile shear force of the joint first increases and then decreases with the increase of welding current.; The maximum tensile shear force reaches the maximum of 2.2kN while the welding current is 14kA. TiAl3 is formed at the aluminum-titanium interface, and the joint fractures in the heat-affected zone on the magnesium side. After conversion, the shear strength of the joint can reach 156MPa. Through SEM and EDS analysis, the addition of a titanium interlayer blocks the mutual diffusion of magnesium alloy and aluminum alloy, and the titanium interlayer hinders the formation of Mg-Al intermetallic compounds, thereby greatly improving the bonding strength of the joint.

Abstract:A series of hot extrusion tests were carried out for a novel powder metallurgy superalloy WZ-A3. The effects of extrusion temperature, extrusion speed, and extrusion ratio on the microstructure and the microstructure uniformity of the extruded bar were investigated. The results show that under the conditions of a constant extrusion speed of 35 mm/s, an extrusion ratio of 4.7:1, and an extrusion temperature of 1110 ℃, completely dynamic recrystallization of the extruded bar occurs. With the increase of the extrusion temperature, the grain coarsens. Under the conditions of a constant extrusion temperature of 1110 ℃, an extrusion speed of 35 mm/s, and an extrusion ratio of 2.1:1, the recrystallization is incomplete and there are more PPB left. When the extrusion ratio increased to 4:1~4.7:1, complete recrystallization is achieved, PPB can also be completely eliminated. At an extrusion temperature of 1130 ℃ and an extrusion ratio of 4.7:1, in the range of 20-50 mm/s extrusion speed, the grains tend to grow much larger. At an extrusion temperature of 1110 ℃, an extrusion speed of 35 mm/s, and an extrusion ratio of 4.7:1, the microstructure of the entire extruded bar is rather uniform. From the head of the bar to the tail, the grains are slightly refined. The grains at the edge of the extruded bar are smaller than that at the core and 1/2R.

Abstract:Film cooling is a common cooling design in aerospace high temperature components, and it is also a typical fatigue risk point of the whole structure. To optimize designs of film cooling holes, an experimental and numerical study was conducted to investigatred fatigue properties of GH4169 alloy film cooling holes with different shapes. Results showed that the fatigue life of the circular shaped hole was obviously lower than those of both the oval shaped hole and the dust-pan shaped hole, and the hole shape exhibited a few influence on the fatigue life of the specimens corresponding to the same skew angle of holes. The specimens of the circular shaped hole failed with only one fracture surface, and the fracture surface was perpendicular to the loading direction. However, the specimens of the oval shaped hole and the dust-pan shaped hole failed with master fracture surface and slave master fracture surface, and the fracture surface was along the hole axis direction. Fatigue crack initiation occurred at the middle region of the circular shaped hole, while fatigue crack initiation occurred at both the entrance and the exit of the oval shaped and the dust-pan shaped hole. The crack initiation zone was flat and smooth, moreover, more dimples were observed on the fracture surface with fatigue crack propagating. Both the skew angle of holes and the shape hole orifice exhibited significant influence on the tress distribution and the peak stress of the hole under quasi-static loading.

Abstract:Dendritic nanospheres with unique three dimension (3D) center-radial channels possess excellent specific surface area and pore volume. Objects can be loaded into the nanochannels of dendritic nanospheres, developing novel carrier, delivery vehicle, or reaction platform. In the work, a novel kind of highly stable multifunctional composite material has been explored for the first time, i.e., dendritic mesoporous silica titania nanospheres (DMSTNs) supported gold (Au) nanoparticles. Even though DMSTNs have suffered series of chemical reactions and modifications, 3D center-radial textures are still unchanged. Anatase TiO2 and Au nanoparticles have been successfully decorated onto the channels. The as-prepared catalysts exhibit more outstanding multipurpose catalytic performances than those of a contrast sample, i.e., dendritic mesoporous silica nanospheres (DMSNs) supported gold (Au) nanoparticles. Under simulated sunlight for splitting water, the amount of produced H2 and the corresponding rate are 210.01 mmol.g-1, ca. ten-folds of the contrast sample. Without light irradiation, the apparent kinetic constant of p-nitrophenol reduction by our catalyst is 2.150×10-3 s-1, being about nineteen times than that of the reference (0.111×10-3 s-1).

Abstract:In this paper, CuSn10P1 copper alloy was formed by semi-solid thixotropic reverse extrusion. The effects of cold rolling deformation, isothermal temperature and isothermal time on microstructure evolution and mechanical properties of CuSn10P1 copper alloy were studied. The results show that the liquid phase segregation phenomenon in semi-solid copper alloy can be effectively improved by thixotropic reverse extrusion, and the cold rolling deformation and isothermal treatment process have a great influence on the microstructure and mechanical properties of semi-solid thixotropic reverse extrusion tin bronze. With the increase of cold rolling deformation, the average grain size decreases first and then increases, and the tensile strength increases first and then decreases. With the increase of isothermal temperature and the extension of isothermal time, the grain size increases gradually, and the tensile strength of the formed parts increases first and then decreases. Under the conditions of cold rolling deformation of 30%, isothermal temperature of 900℃ and isothermal time of 20min, the microstructure and properties of CuSn10P1 copper alloy formed by semi-solid thixotropic reverse extrusion are better and all parts are uniform. The liquid phase fraction of the forming parts were 14.41%, 14.37%, 14.33%, 14.30%, the grain size was 60.60 μm, 60.28 μm, 59.51 μm, 61.10 μm, the shape factor was 1.29, 1.24, 1.26, 1.27, the tensile strength was 407 MPa, the elongation was 7.6%, respectively.

Abstract:In order to investigate the effect of dissolved oxygen ( DO ) on the super-heated steam corrosion of Zr-0.75Sn-0.35Fe-0.15Cr-0.3Nb ( wt% ) alloy, the samples were put into a static autoclave and a dynamic autoclave for 400 °C/10.3 MPa/deoxygenation and 300 ppb DO super-heated steam corrosion tests, respectively. The corrosion resistance of the alloy was evaluated by corrosion weight gains. Scanning electron microscope and transmission electron microscope were used to analyze the microstructure of the oxide film and the characteristics of the oxide film/metal (O/M) interface. The results reveal that DO can accelerate the corrosion of Zr-0.75Sn-0.35Fe-0.15Cr-0.3Nb alloy, and the weight gain after 250 d exposure under 300 ppb DO is 17 % higher than that under deoxygenation condition. The transition layer at the O/M interface under the deoxygenation condition is thinner than that under the 300 ppb DO condition. In addition, a ZrO layer of about 100 nm is observed in the transition layer under the former condition but not observed under the latter condition. To some extent, the thicker transition layer and the existence of the ZrO layer can provide more time for the stress release in the oxidation process, inhibiting the generation of cracks and thus improving the corrosion resistance of zirconium alloys. This can explain the better corrosion property in the later stage of corrosion under the deoxygenation condition.

Abstract:In order to study the corrosion resistance of the SAF2507 duplex stainless steel (SAF2507 DSS) propeller blades in seawater containing sulfate-reducing bacteria (SRB) and iron oxidizing bacteria (IOB), a secondary quench stamping technology was proposed to stamping SAF2507 DSS propeller blades.The corrosion behavior of propeller blades in seawater containing SRB and IOB was studied according to the precipitated phases types and precipitation laws of the propeller blades at different secondary quench stamping temperatures.The results showed that when the secondary quench stamping temperature was 700℃,a small amount of χ phases was precipitated on the surface of the propeller blades;and when it reached 850℃, the χ phases is completely converted to the σ phases, and the precipitation of σ phases reach the peak value,and at 950 ° C only a small number of σ phases are precipitated.The variation laws of the corrosion current density,Ac impedance and other electrochemical properties of propeller blades at different secondary quench stamping temperatures was consistent with that of χ phases and σ phases in the surface layer of propeller blades and the corrosion resistance characteristics of χ phases and σ phases themselves.When the secondary quench stamping temperature was between 750 ° C and 1050 ° C, the corrosion resistance of propeller blades changes in the rule of "enhancement - reduction - enhancement" with the increase of the secondary quench stamping temperature, and the corrosion resistance of propeller blades was the worst at 850 ° C in seawater containing SRB and IOB.For the surface characteristics of the rich Fe on the surface layer of propeller blade after secondary quench stamping, the surface passivation film of propeller blade was damaged in seawater containing SRB and IO, which leads to the decrease of corrosion resistance.

Abstract:The (Zr0.55Cu0.3Al0.1Ni0.05)98Er2 amorphous alloy bars with diameter of 6 mm were prepared by copper mold suction casting method. The effects of isothermal temperature and time on the thermal stability in supercooled liquid region were investigated, and the crystallization kinetics behavior was studied by continuous heating and isothermal heating.The results show that with the increase of isothermal heat treatment temperature, the isothermal heat treatment time of (Zr0.55Cu0.3Al0.1Ni0.05)98Er2 amorphous alloy is shorter; According to Kissinger equation, the activation energy Ex of the amorphous alloy is 337.39 kJ/mol; The experimental data obtained by the two methods are very close, which can be proved by each other.

Abstract:The effects of melt-spinning speed(v=15,20,25,30 and 35 m/s, respectively) and heat-treatment process on the magnetic properties and microstructure of melt-spun Nd26Pr3FebalCo4Ga0.42B0.92 ribbons were investigated. The ribbons show an obvious orientation when the speed v is less than 25m/s in the free side,which c-axis is perpendicular to the strip surface;the orientation decreases with the increase of melt-spinning speed. The grain can be refined by increasing the melt-spinning speed，when v < 25 m/s, the amorphous content increases obviously, the initial magnetization shows a one-step magnetization process，which demagnetization curve have good squareness；When v > 25 m / s, the initial magnetization changes to two-step magnetization process, and the demagnetization curve collapses obviously; The best magnetic properties are obtained when v=25 m/s,Br=0.91T，μ0Hcj=1.70 T，（BH）max=108.22 kJ/m3, After optimum crystallization annealing treatment, the amorphous content reduce significantly；all of the magnetic properties of ribbons have improved,the v>25 m/s imporve obviously, squareness and coercivity improve remarkable.The ribbon prepared at v=35m/s get the highest coercivity, μ0Hcj=2.10 T.The best magnetic properties are obtained when v=30 m/s,Br=0.91T，μ0Hcj=1.82 T，（BH）max=141.65 kJ/m3,The microstructure changes along with the thickness direction.The wheel side is composed of amorphous and fine grains,the free side is composed by larger grains.After the heat-treatment,the amorphous is reduced significantly.

Abstract:FSA powder is of crucial importance to microwave absorption material because of the higher magnetic permeability and saturation magnetization. However, poor resistance to salt spray corrosion limits its further application in extreme environment (marine and damp heat, etc.). Therefore, SiO2 and carbon layers are in situ deposited on FSA surface by using the St?ber process and catalytic chemical vapor deposition technology to form FSA@SiO2@C composite structure. Furthermore, the anti-corrosion electromagnetic properties of the composite mechanism are studied by network vector analyzer and electrochemical test. The SiO2 and carbon layers are uniformly coated on the surface of the FSA and tightly combined with it. The thickness of the SiO2 is about 100 nm, and the thickness of the carbon is about 5 nm. The SiO2@C reduces the corrosion rate of FSA from 2.66×10-12 to 1.52×10-12 m/s, which significantly improves the corrosion resistance of FSA in salt spray environment. When the matching thickness is 3 mm, the microwave absorption properties of FSA@SiO2@C is significantly improved compared with FSA. The absorption bandwidth is expanded from 4.2 GHz to 5.84 GHz, and the RLmin reach as low as -21.65dB (7.41GHz), which is less than -19.03 dB (5.93 GHz). of pure FSA. The multi-shell composite structure can significantly improve the corrosion resistance and microwave absorption performance of FSA, and provides a feasible design idea for the multi-functional magnetic metal microwave absorbing materials with anti-corrosion and high efficiency.

Abstract:Proton-conducting oxides show high proton conductivity operating below 600 °C, which offers a significant advantage in developing low cost and durable solid oxide cells (SOCs) at intermediate-to-low temperature. The ABO3 perovskites based on Ba, Ce, Zr, Y, and Yb are state-of-the-art proton conductors such as BaZr1-xYxO3-δ (BZY), BaCe0.7-xZrxY0.2O3-δ (BCZY), and BaCe0.7-xZrxY0.1Yb0.1O3-δ (BCZYYb). However, it is very difficult for these materials to balance the sinterability, conductivity and stability. To achieve dense electrolyte with high conductivity and long-term stability at the low sintering temperature, one of the most common approach is adding sintering aids in the fabrication processing of proton-conducting oxides. In recent researches, the effect of sintering additives on the electrical conductivity of proton conductors are still in the arguments. This review provides a comprehensive discussion of recent research developments on sintering additives modified proton conducting oxide. Moreover, we summary in detail the influence of different sintering additives on the relative density, grain growth, sintering behavior, and bulk and boundary conductivity of proton conducting oxides, as well as pointing out the potential research directions.

Abstract:Additive manufacturing (AM), i.e. 3D printing technology, is a rapid prototyping method (RP) developed in the 1980s, by which some complex structures can be efficiently manufactured. It also provides a platform for the development of complex geometrics, and is instrumental in cost-savings and time-savings of the production. Energy-absorbing materials and structures are used to absorb energy in collisions and to minimize the damage of the impact target, and their geometries are becoming increasingly complicated in order to achieve higher performances. Therefore, novel energy absorbers usually need the AM technology to produce. Meanwhile, their developments have received extensive attention in many research fields, as nearly all major industries are enjoying the benefits of them. This paper aims to provide a comprehensive overview of new energy absorbers characterized by cellular structures, which includes introductions of various lattice morphologies, design methods and the additive manufacturing technologies they used, supplemented by the summarization of advantages, challenges and the application prospect of the structure.

Abstract:TiAl-based alloys have become the key material for the update of aerospace engineering. However, the coarse as-cast grain size, low room temperature plasticity and strength limit their further engineering application. In this paper, the Ti-48Al-2Cr-2Nb ingot alloyed with TiB2 and Ni was prepared by the induction melting and the effects of TiB2 and Ni on the solidification microstructure and mechanical properties were studied systematically. The results showed that the addition of TiB2 and Ni exhibited little influence on the solidification path and primary phase. The grain size was refined from 700 μm to 100 μm, and the flake TiB2 and Ni-riched τ3 phase was determined. The room temperature tensile strength of T4822-(Ni, TiB2) alloy was similar to that of the matrix alloy, and the fracture elongation was increased by 30%. At 700 ℃-900 ℃, T4822-(Ni, TiB2) alloy showed the preferable tensile strength, and the tensile strength at 900 ℃ reached 365 MPa, 9% higher than that of the matrix alloy. At 800 ℃ and 900 ℃, the breaking elongation reached 25.3% and 36.1%, respectively, much higher than that of the matrix alloy. The refinement of grain size and the block γ phase at grain boundary are the main reasons for the plasticity improvement of T4822-(Ni, TiB2) alloy, and the outstanding high temperature strength can be attributed to the borides and Ni-riched τ3 phase at the inner and interface of the lamellar colony.

Abstract:This paper studies the evolution of the microstructure of the wire arc additive manufactured TC4 titanium alloy with a hydrogen content of 0.55wt.% after HVC hydrogen treatment. The conclusion shows that the microstructure of TC4 titanium alloy produced by wire arc additive manufacturing technology is coarse columnar β crystals, and the inside of the crystal grains is lamellar α clusters. After the hydrogenation treatment, due to the diffusion of hydrogen and the effect of the grain boundary corrosion, the inner layer of the β crystal becomes smaller and the hydride is produced. Subsequently, the hydrogenated titanium alloy was quenched at a temperature of 810℃, and α′, α″ and metastable phase βM were formed in the structure. In the process of aging and hydrogen removal, with the decomposition of martensite, metastable phase and hydride, the lamellar α grains in the columnar β crystals are significantly refined, forming a staggered fine needle-like microstructure.