Abstract:In order to investigate the effect of strain rate on the tension behavior of TC11 titanium alloy, uniaxial tensile tests were conducted on this material over a wide range of strain rate. The results demonstrate that as the strain rate increases from quasistatic to dynamic, the yield strength of the TC11 titanium alloy increases slightly. The reduction of the strain hardening modulus is found under dynamic tension. Furthermore, the TC11 titanium alloy fails in shear under both the quasistatic and dynamic tension. However, the dimple size under dynamic fracture is smaller than that under quasistatic loading. By analyzing the temperature rise in the material during deformation, it is found that the easier strain softening and the smaller dimple size on the fracture surface at high strain rate may be attributed to the higher temperature rise.

Abstract:A broad range of Ta₂O₅-Y₂O₃ doped ZrO₂ (TYSZ) compounds were synthesized. The effects of dopant content on phase structure, phase stability, fracture toughness, coefficient of thermal expansion (CTE), and thermal conductivity were investigated. The TYSZ response mechanism under stress conditions was also explored. Result suggests that the lattice distortion caused by Ta₂O₅ and Y₂O₃ doping favors t phase stabilization. However, as the doping content increases, the high-temperature stability and fracture toughness decrease due to the suppressed stress-induced phase transformation and precipitation. The variation in CTE and thermal conductivity is due to the chaotic and expansive crystal structure. The 16TYSZ might be the potential candidate for advanced thermal barrier coating materials for its good phase stability, stress-sensitive phase transferability, and thermophysical properties.

Abstract:Molecular dynamics simulations were performed to study the deposition of the thermal spraying material under different process parameters. The effects of temperatures, cluster size, and spraying speed on the deposition of Ni clusters on the Fe substrate were examined. The morphology of clusters and the subsurface damage of the substrate were analyzed. The results show that in the heating-up process of Ni cluster, the melting point becomes higher with the increase of cluster size, and the complete melting temperature of Ni cluster is about 1800 K. During the spraying process, the matrix shows a “mountain” shape due to the impact force to disordered atoms. Furthermore, it is also found that spraying speed plays an important role in the deposition process. At lower spraying speed, the flattening ratio decreases again, but at higher spraying speed, the substrate has defects, such as vacancy and atomic cluster after the impact of clusters. Thus, there is a critical spraying speed mechanism in thermal spraying.

Abstract:Improving the hydrolysis resistance of AlN ceramic powder is crucial to the powder storage and shaping processing. In order to improve the hydrolysis resistance of AlN powder, a hydrolysis-resistant coating was used to act as a barrier layer to prevent water from contacting with the AlN surface. An amorphous Y₂O₃ coating was uniformly deposited and fully wrapped on the surface of AlN powder via a chemical precipitation process. The coating effectiveness and integrity were investigated by TEM, XPS and Zeta potential measurements. The hydrolytic behavior of AlN powder in an aqueous suspension was studied by following the pH vs. time at room temperature. The results show that the coated AlN powder is stable in water within 48 h, indicating that the surface coating treatment with Y₂O₃ can effectively passivate AlN powder against hydrolysis. Moreover, as a way to introduce the sintering additives, the chemical precipitation process can favor an improvement of thermal conductivity of the sintered AlN ceramic, compared with the conventional ball-milling process.

Abstract:The effect of efficiency of power dissipation on hot workability and corrosion behavior of AZ31 alloy was investigated. The results indicate that minor Ca-addition can significantly improve the hot workability and corrosion resistance due to grain refinement by facilitating recrystallization and formation of a more protective corrosion product layer doped with a trace amount of Ca(OH)₂. The instability zone exhibits worse corrosion resistance than dynamic recrystallization (DRX) domain due to heterogeneous microstructure and obvious wedge cracks. Moreover, wedge cracks caused by flow localization band can serve as channels for the diffusion of aggressive Cl^- and accelerate further corrosion of Mg matrix. The DRX domain with homogeneous fine grain microstructure and high efficiency of power dissipation obtained by hot deformation at 400 ℃/0.001 s^-1 of Mg-Al-Zn-Mn-Ca alloy simultaneously performs superior corrosion resistance and good hot workability.

Abstract:The microstructure, mechanical and anticorrosion properties of Mg-0.5Zr-1.8Zn-xGd (x=0, 0.5, 1.0, 1.5, 2.0, 2.5, wt%) alloys were investigated after a solution treatment at 470 ℃ for 10 h. Results indicate that the grain size of the alloy decreases with increasing the Gd content in the range of 0wt%~2.5wt%. When the Gd content is less than 1.5wt%, the alloy elements are more completely dissolved into the alloy matrix, and the second phase is mainly composed of nanoscale (Mg, Zn)₃Gd precipitated particle. At the range of 1.5wt%~2.5wt%, the insoluble micron-scale (Mg, Zn)₃Gd phase emerges in the alloy, and the number and size of the (Mg, Zn)₃Gd phase increase with the Gd content. The Mg-0.5Zr-1.8Zn-1.5Gd alloy shows excellent mechanical properties and anticorrosive ability, which can be attributed to a more homogeneous microstructure and the presence of nanometric secondary phase particles. In the 120 h immersion experiment, the average corrosion rate of the Mg-0.5Zr-1.8Zn-1.5Gd alloy deceases at first, then increases, and then decreases slowly. At last, with the increase of immersion time, it eventually becomes stable.

Abstract:The wheel casting-extrusion method was employed to produce high-quality SAL5356 Al alloy welding wire, which was used to weld 6061-type Al alloy plates. The performance of SAL5356 welding wire was compared with that of the ER5356 welding wire by mechanical characterization, metallographic observation, microhardness and nanoindentation. The results reveal that under the same metal inertia gas (MIG) welding parameters, the SAL5356 welding wire endows superior tensile strength and yield strength to the weld joint, meeting the requirements of GB-2006-3880.2 standard (T general industrial aluminum and aluminum alloy plate and strip part 2: mechanical properties). Moreover, SAL5356 welding wire renders better stability than the ER5356 welding wire, which can be ascribed to the relaxed diameter and pitch of welding wire. Though further research is required to optimize the composition, microstructure and performance of SAL5356 welding wire, the current results demonstrate the potential of using local technology to produce 5356 Al alloy wire for high-end applications.

Abstract:The nucleation of rapidly solidified Au-19.25Ag-12.80Ge ternary eutectic alloy was analyzed and discussed according to the classical nucleation theory. Then the relationship between the incubation period of each phase and the melting temperature was obtained. The results show that for rapidly solidified Au-19.25Ag-12.80Ge brazing filler, the incubation period of AuAg solid solution is much shorter than that of Ge phase, and AuAg phase is precipitated preferentially as the main nucleation phase in the rapid solidification process. According to the time-dependent transient nucleation theory, the critical nucleation temperature, critical nucleation undercooling and critical nucleation number of the brazing filler were calculated under continuous cooling conditions. It can be seen that with increase of the cooling rate, the initial nucleation undercooling required to trigger melt nucleation increases, and the critical nucleation number increases substantially too.

Abstract:Effects of ion beam irradiation defects on electrical and optical properties of CdZnTe (CZT) crystals were studied. CZT crystals grown by the modified vertical Bridgman method were irradiated by Ar heavy ions with fluences ranging from 10¹⁴ cm^-2 to 10¹⁵ cm^-2. Results show that IR transmittance spectra vary from the high-straight type (before radiation) to the ascending type (after radiation), and light absorption by radiation induced free charge carriers occurs significantly in the mid-infrared light range. Current-voltage (I-V) characteristic curve of the irradiated CZT crystals becomes extremely asymmetrical and current increases sharply with the increase of negative voltage due to single-surface irradiation in the near-surface area. Hall measurements show that the net carrier concentration largely increases from ~10⁶ cm^-3 (before radiation) to ~10¹⁶ cm^-3 (after radiation), and the conduction type remains unchanged, since donor levels are considered to be the dominant among all the radiation-induced crystal defects.

Abstract:The interface properties of Zr-Si-N/hydrogen-terminated diamond (H-diamond) metal insulator semiconductor field transistors (MISFETs) with and without Al₂O₃ protective layer were studied. The Al₂O₃ protection layer and Zr-Si-N insulation layer were deposited by atomic layer deposition (ALD) and radio frequency (RF) sputter methods, respectively. The transfer characteristics of the MISFETs show that the gate threshold voltage varies from -2.5 V to 3 V with and without Al₂O₃ layer, which indicates that the devices switch from normally off to normally on operation. The output and transfer properties reveal the preservation of hydrogen termination because of the Al₂O₃ layer.

Abstract:The complete amorphous phase transformation of Sm-Fe-Zr-Nb alloy powders during high-energy ball milling process was investigated. The effects of milling time on the phase transformation and morphology of the Sm-Fe-Zr-Nb alloy powders were analyzed by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The result shows that complete amorphous microstructure is obtained after milling for about 2.5 h, and α-Fe phase (~5 nm) is precipitated from the amorphous matrix when the milling time is over 3 h. The number of short-range ordered structure increases. The uniform microstructure and the TbCu₇-type single phase are obtained by crystallizing the amorphous precursors milled for 2.5 h. The size of equiaxed grain is ~30 nm. This kind of micro-regulation plays a key role in improving the magnetic properties after nitriding.

Abstract:The band structures, lattice parameters, densities of states and bond characteristics of two different Li₇La₃Zr₂O₁₂ (LLZO) solid electrolyte materials in tetragonal and cubic phases were calculated by the first-principles method based on density functional theory (DFT). The reason why the ionic conductivity of the tetrahedral phase is lower than that of cubic phase was explained by the electronic structural characteristics based on the theoretical calculation results. Two kinds of crystalline structure LLZO materials were designed based on first principles calculation of LLZO and prepared by the high temperature solid phase method, and the properties of LLZO pellets with different sintering time were analysed. The effect of the synthesis process parameters on the properties of Li₇La₃Zr₂O₁₂ was explored. Results show that the average lattice size of cubic Li₇La₃Zr₂O₁₂ (C-LLZO) is a=b=c= 1.302 246 nm, while that of tetragonal Li₇La₃Zr₂O₁₂ (T-LLZO) is a=b=1.313 064 nm, c=1.266 024 nm. The C-LLZO sintered at 1000 ℃ for 12 h has a pure cubic phase and a maximum ionic conductivity of 9.8×10^-5 S·cm^-1 is realized at room temperature (25 ℃). The ionic conductivity of T-LLZO at room temperature (25 ℃) is 5.96×10^-8 S·cm^-1, which has a pure tetragonal phase structure after sintering at 800 ℃ for 6 h, basically in agreement with the calculation results.

Abstract:The valence electron structure and cohesive energy of α-Al, AlB₂ and (Al-Si)B₂ crystals were calculated using the empirical electron theory (EET) of solids and molecules. The calculated results indicate that Al-Al atomic layer on outermost surface of AlB₂ is relatively unstable and the cohesive energy of both α-Al and AlB₂ decrease with increase of Si content in Al-Si melt. According to the calculated results, a novel atomic mechanism of α-Al heterogeneously nucleating on AlB₂ in Al-Si alloy is explored. After adding additional Si, a certain amount of Si atoms enter into AlB₂, which results in formation of a stable Al-Si binary atomic structure layer on AlB₂ surface and finally improves the stability of AlB₂. This two-dimensional Al-Si atomic layer plays an important transition role in the subsequent heterogeneous nucleation process, which is responsible for the atomic mechanism of nucleation of α-Al attached to AlB₂.

Abstract:Commercial pure titanium (CP-Ti) sheets were cold rolled to different amounts, then annealed, and then re-rolled by 20%. Microstructure changes were investigated via electron backscatter diffraction (EBSD). After re-rolling, {112} <23> contraction twins and {102}<101> extension twins proliferate. A twin lamellas structure can be observed, caused by tangle of deformation twins and the generation of secondary and tertiary twins. There is no simple correlation between the average grain size and the amount of twinning. The grain size significantly decreases with the increase of pre-deformation degree, for 0.5 h annealed sample. Re-rolling tends to re-orient the lattice closer to ND. While the texture change and twin volume fraction are small and the {100}//RD fiber remains.

Abstract:The high-temperature deformation behavior of Ti600 alloy with a lamellar initial microstructure was investigated in the temperature range of 800~960 ℃ and the strain rate range of 10^-3~1 s^-1. Subsequently, the strain hardening exponent (n) was proposed to characterize the competition of flow softening and work hardening. The softening behavior of this alloy was also studied according to flow curve analysis and microstructure observation. The results indicate that deformation parameters have significant influences on the flow behavior of Ti600 alloy. The n-value gradually decreases after the peak strain, which indicates that the dynamic softening begins to take dominant. The dynamic softening behavior of Ti600 alloy mainly attributes to the bending, fragmentation, dynamic recovery and recrystallization of α phase during the high-temperature deformation according to the microstructure characterization. Based on experimental data, original strain-compensated Arrhenius, Hensel-Spittel and modified Arrhenius constitutive models are established to describe the deformation behavior of Ti600 alloy. The flow stresses predicted by three models are compared with experimental results, and the calculated correlation coefficients are 0.965, 0.989, and 0.997. Also, the values of average absolute relative error are 12.86%, 9.74%, and 3.26%. These results suggest that three models can descript the flow behavior of Ti600 alloy, and the modified Arrhenius model exhibits the highest prediction accuracy.

Abstract:In order to investigate the phenomenon that the affecting mechanism of high-titanium vanadium-titanium magnetite is caused by separate TiO₂ or by CaTiO₃ formed from TiO₂ and CaO, calcium ferrite was synthetized by pure reagents of Fe₂O₃ and CaO, and the effect of TiO₂ and CaTiO₃ on the formation mechanism of titanium calcium ferrite (FCT) was researched. Different samples were sintered at the temperatures of 1023~1423 K for different time under air atmosphere based on thermodynamics calculations with Factsage 7.0. The phase transformation and microstructure changes in sintered samples were examined through different characterization means including X-ray diffraction and scanning electron microscope-energy disperse spectroscopy. It is found that the formation process of calcium ferrite can be mainly divided into two stages. The synthesized product is Ca₂Fe₂O₅ with the reaction “Fe₂O₃ (s) + 2CaO (s) = Ca₂Fe₂O₅ (s)” between Fe₂O₃ and CaO at 1023~1223 K in the former stage, and the predominant product is CaFe₂O₄ with the reaction “Ca₂Fe₂O₅ (s) + Fe₂O₃ (s) = 2CaFe₂O₄ (s)” between Ca₂Fe₂O₅ and Fe₂O₃ at 1223~1423 K in the latter stage, in which the reaction rate is accelerated especially at 1423 K. It is observed that CaTiO₃ increases with increasing the temperature. However, the solid solution of Ti element in calcium ferrite is greatly difficult to realize and the reaction between TiO₂ and calcium ferrite is not an effective way to generate FCT. It is also observed that the amount of Fe element in the phase boundary of CaTiO₃ and FCT increases with the extension of the thermal insulation time. FCT is predominantly formed through the solid solution of Fe component in CaTiO₃, and the main reaction is “Fe₂O₃ (s) + CaTiO₃ (s) = FCT (s)”.

Abstract:The utilization of hydrogen energy has attracted great attention, while the storage and transportation of hydrogen restrict its wide practical application. As a solid hydrogen storage material, Mg-based alloys show great potential in the field of hydrogen storage. However, the high temperature of hydrogen absorption and release, and the slow rate of hydrogen release cast a shadow on its engineering application. To improve the hydrogen storage capacity of Mg-based alloys, the researches mainly focus on the optimization of alloy composition and the improvement of processing technology, and nano refinement is one of the most promising methods. In this study, all the processing technologies of nanostructured Mg are introduced, including high energy ball milling, physical vapor deposition, hydriding chemical vapor deposition, liquid-phase chemical synthesis and template method. The advantages and disadvantages of each method are also analyzed. The effect of nanostructure and element doping on the hydrogen storage property of Mg-based alloys is summarized. This study provides a reference for the research of the material development and improvement of preparation technology in hydrogen storage field.

Abstract:In order to acquire the mechanism of surface oxidation corrosion of plutonium (Pu) and its compounds and explore the environmental system that can effectively alleviate the oxidation corrosion of plutonium materials, some research results on surface chemistry of plutonium and its compounds were reviewed, which deepen the understanding of the corrosion behavior of plutonium and its compounds in the air. The adsorption behavior of active gases such as H₂, O₂, CO, CO₂ and H₂O (gaseous) and rare gases such as Xe on different surfaces of plutonium and its compounds was compared and analyzed, and some useful conclusions were obtained. It is concluded that the interaction of plutonium with various active gases and rare gases is accompanied by charge transfer, and the mechanism of reaction is mainly that the new chemical bonds are formed because of the interaction between the different hybrid orbitals of gas atoms (or molecules) and plutonium atoms such as Pu7s, Pu6p, Pu6d and Pu5f, which leads to related reactions and phenomena. The research work prospect on the surface corrosion of plutonium and its compounds is also taken from three aspects including improving research methods, carrying out research on other surface adsorption behavior of plutonium atoms and exploring new systems for protecting plutonium materials from oxidative corrosion.

Abstract:The effect of adhesion and electronic structure of TiN(111)/DLC interface is studied by the first-principles plane wave pseudopotential method within the density functional theory, and the inherent properties of the TiN transition layer to improve the adhesion performance of the metal substrate and DLC film were clarified. According to different surface terminations (Ti terminations and N terminations) of TiN(111) and the atomic coordination types of the interface (top, center and hollow), six possible interfaces models of TiN(111)/DLC have been constructed and calculated. The results show that Ti-center interface has the maximum adhesion energy；When TiN is terminated by N atom, the N-top interface is the most stable interface model, and the relaxed adhesion energy is 8.281 J/m_². The calculation results of the electron density, the partial density of states and Mulliken overlap population all suggest that Ti-C bond formed at Ti-center interface contains covalent and ionic properties, while N atom and C atom at N-top interface are mainly C-N covalent bond. In contrast, the N-top model is more likely to appear in the TiN/DLC interface.

Abstract:The forged Ti6242s titanium alloy was subjected to a thermal compression simulation experiment with 75% deformation at a temperature of 950~1010℃ and a strain rate of 0.01~10s-1 by Gleeble-3800. Based on the true stress-true strain curve obtained from the experiment, the artificial neural network (ANN) and Arrhenius equation were used to establish the constitutive model of Ti6242s alloy, and study its thermal deformation behavior. The results show that the flow stress rapidly rises to the peak stress after the deformation begins, and then the hardening and softening reach a dynamic balance. After the true strain reaches 0.6, the work hardening gradually dominates, and the hardening amplitude increases with the increase of the strain rate; artificial neural network The average relative error (AARE) of the predicted value of the constitutive model is 2.5%, and the correlation coefficient (R) is 0.999; the AARE of the predicted value of the Arrhenius equation constitutive model is 14.5%, R is 0.955, and the accuracy fluctuates greatly within the parameter range; The accuracy of the ANN constitutive model is much higher than that of the Arrhenius constitutive model, and it has consistent accuracy across the entire parameter range; the ANN constitutive model has good generalization ability, and it still has high accuracy in predicting flow stress outside the range of experimental parameters.

Abstract:The dynamic recrystallization behavior, grain orientation and texture formation of magnesium alloy under different deformation conditions (temperature, strain rate and deformation degree) were studied by using electron backscattering diffraction (EBSD) in the thermal compression experiment of AZ31 magnesium alloy. The results show that the greater the deformation temperature, the more adequate the degree of recrystallization and the more uniform the grain structure. The greater the degree of deformation or the smaller the strain rate, the greater the degree of recrystallization. During the hot deformation of magnesium alloys, the deformation temperature is the biggest factor influencing the dynamic recrystallization mechanism. At 300℃, the recrystallized grains of AZ31 magnesium alloy nucleate at the original grain boundary and sub-grain boundary. The recrystallization behavior is mainly formed by the rotation of sub-grain boundary, which shows the typical continuous dynamic recrystallization (CDRX) characteristics. At 400°C, the orientation of the recrystallized grains is deflected during local shear deformation, showing the typical characteristics of rotational dynamic recrystallization (RDRX). During the thermal compression process, {10-12} tensile twins are generated, and the grains re-rotate the basal plane orientation to form a fiber texture with the basal plane perpendicular to the compression direction.

Abstract:38CrMoAl steels were subjected to quasi-static and impact tensile tests with strain rates from 0.001 to 3000 s-1 after salt spray corrosion at different periods to investigate the effect of salt spray corrosion environment on the dynamic mechanical properties of 38CrMoAl steel materials under high strain rate conditions . The surface morphology, corrosion pit depth, corrosion product composition and fracture morphology of 38CrMoAl steel after salt spray corrosion were analyzed by means of digital microscope, FT-IR, SEM and EDS. The results show that the corrosion rate is positively correlated with the salt spray corrosion time, the corrosion acceleration process follows the power function characteristic, and the corrosion product layer promotes the corrosion of 38CrMoAl steel. The yield strength of 38CrMoAl steel increases with the increase of strain rate and decreases with the increase of corrosion cycle. The fracture of 38CrMoAl steel after salt spray corrosion shows many tear-like features. The longer the corrosion time, the more tear-like marks. The tear-shaped fracture makes the fracture necking of the specimen no longer develop uniformly, resulting in a decrease in the tensile strength and yield ratio after yielding. The strain rate strengthening term and adiabatic softening term in the J-C constitutive model were corrected, and corrosion correction parameters were added, so that the new model can accurately characterize the dynamic mechanical behavior of 38CrMoAl steel in a salt spray corrosion environment.

Abstract:To study the effect of grain size on the mechanical properties and deformation behavior of γ-TiAl Alloy in nanoindentation process, a polycrystalline γ-TiAl model was established by Voronoi method, and the nanoindentation process for different grain sizes was simulated by molecular dynamics method. According to the simulation results, the Load-depth curves of different grain sizes were obtained, and the hardness of γ-TiAl alloy with 7 kinds of grain sizes was calculated. The results show that the relationship between grain size and hardness exhibits an inverse Hall-Petch when the grain size is less than 9.9 nm. Meanwhile, the grain boundary activity and dislocation sliding promote the plastic deformation of matrix, and the grain boundary activity plays a major role. However, the relationship between grain size and hardness conforms to Hall-Petch when the grain size exceeds 9.9 nm. The grain boundary has little effect on the plastic deformation, and the plastic deformation of matrix is dominated by dislocation. In addition, the stress transfer and deformation recovery of γ-TiAl were analyzed in the nanoindentation process, it was found that the dense grain boundary grid can effectively inhibit the indentation defects and the internal stress transfer to the matrix. When the grain size becomes smaller, the stress distribution would be more uniform under the indenter and the elastic recovery ratio would be smaller along the indentation direction.

Abstract:In this paper, the effects of deformation temperature and strain rate on flow stress of Ti-555 titanium alloy during hot deformation are studied by hot compression tests at high temperature. The constitutive equation of Ti-555 is derived by Arrhenius hyperbolic sine function model, and the processing map of Ti-555 alloy at= 0.6 is established according to the dynamic material model. The results show that the flow stress of Ti-555 alloy is sensitive to strain rate and deformation temperature. The flow stress decreases with the increase of deformation temperature or the decrease of strain rate during hot deformation According to the processing map, the parameters of two hot working safety zones are determined as follows: (1) deformation temperature is 850 ~ 950 ℃, strain rate is 0.6 ~ 10s_^-1; (2) deformation temperature is 950 ~ 1150 ℃ and strain rate is 0.36 ~ 0.9s_^-1.

Abstract:In this paper, the high temperature oxidation behavior of a new metal interconnects material Fe-Cr-Co alloy in SOFC anodic atmosphere (N₂+2%H₂+60%H₂O) was studied by cyclic oxidation at 750C, and then the thermal stress analysis was carried out based on the interface morphology of the real oxide and the alloy. The phase structure, cross-sectional morphology and composition of the alloy oxide were characterized by X-ray diffractometer (XRD) and field emission electron microscope (SEM) equipped with energy spectrometer (EDS), and the thermal stress extreme distribution of the alloy oxide was simulated by image processing and finite element simulation technology. The characterization results show that 2 μ m oxide is formed by cyclic oxidation of Fe-Cr-Co alloy in 750C anode for 600h, which is composed of Fe-doped Cr₂O₃ inner layer and MnCr₂O₄ outer layer, and the simulation analysis shows that the maximum shear stress at the interface is distributed in the region between the peak and trough, which makes the oxide in this area easy to peel off first.

Abstract:The static coarsening behavior of Ti14 alloy with Ti2Cu phase during long term exposure at 500°C was investigated. The growth of precipitated phase is determined to be controlled by the diffusion mechanism revealed by the morphology variation during thermal exposure. The static coarsening processes are uncovered to be composed of rapid coarsening stage and stable coarsening stage, which are controlled by volume diffusion with LSW model. The rapid coarsening stage is mainly dominated by the terminal migration mechanism, and the stable coarsening stage is proceeded mainly by Oswald ripening mechanism. The rapid coarsening of the Ti2Cu phase initiates the strengthening of the second phase and effectively improves the plasticity in the rapid coarsening stage. But in the stage of stable coarsening, the increase in Ti2Cu phase increases the effective slip length and further affect the crack nucleation resistance, thereby reducing the tensile plasticity of the Ti14 alloy.

Abstract:In order to clarify the performance of 625 alloy during 10000 h long term thermal aging at 750℃, the mechanical behavior and microstructure evolution were investigated by means of Scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as tensile and hardness tests. Results show that a phase transition from the metastable γ" phase to the steady-state δ phase occurs in 625 alloy at 750℃. At the initial stage γ" phase rapidly precipitates and grows in matrix, and then decreases and disappears with the extension of thermal aging. While the transformed δ phase gradually nucleates and grows in size, and turns to be the main strengthening phase in 625 alloy in the long run. With the prolonging of the thermal aging time, tensile strength, yield strength and hardness of the alloy are continuously improved, with the elongation constantly reducing. After 3000 h’s thermal aging treatment, the mechanical properties tend to keep stable. There was no significant difference between the two types of δ phase in the reinforcement of 625 alloy.

Abstract:C-HRA-5(22Cr25Ni3Cu4W2Co) is a new kind of austenitic heat-resistant steel with excellent combination of high temperature strength and resistance to high temperature steam oxidation, can be used for the superheaters and reheaters (with the highest temperature 700℃) in the advanced ultra supercritical (A-USC) boilers. Compared with the existing austenitic steels, as HR3C, Super304H, TP347, the alloy design of the investigated steel is more complex. The precipitation of second phases will affect the mechanical properties of the steel. As known, the Cu element precipitated as Cu-rich phase in the Super304H steel; the Nb element precipitated as Z phase in the HR3C steel, but as Nb-rich MX phase in the Super304H steel. However, the precipitation and evolution of second phases in the C-HRA-5 steel has not been investigated clearly. In this work, the C-HRA-5 steel specimens were aged at 700℃ for 0~15627 h. OM was used to observe the changes of grain size and twins, and the evolution of the second phases in aged specimens was analyzed by SEM+EDS and TEM+EDS+SAED. The results are as follows. The grain size of the investigated steel was stable, and the second phases precipitated during 700℃/15627 h aging, including Z phase, Cu-rich phase, Laves phase, and M23C6 carbide. M23C6 mainly precipitated on the grain boundaries, the others in the grains, but σ phase was not founded. During aging, the Z phase and Cu-rich phase were relatively stable, especially the average diameter of the Cu-rich phase was less than 10 nm after aged for 15627 h. These phases are the main factors increasing the strength. The coarsening rate of M23C6 carbide on grain boundaries was fast. After aging for 817 h, the network of M23C6 carbide was observed on grain boundaries. After 15627 h, the width of M23C6 carbide was about 550 nm. However, the coarsening rate of the M23C6 inside grains was slow. In the late-stage of aging, due to the addition of W, a large number of needle-shaped Laves phases precipitated inside grains. And the coarsening of Laves phase was apparent in length but slight in width. A small amount of granular Laves phase precipitated near or in the M23C6 carbides that on grain boundaries and its size was stable. During the long-term of aging, no σ phase was found. It is because that the high content of Ni and addition of Co could inhibit or delay the precipitation of the σ phase in the C-HRA-5 steel.

Abstract:The welded joint of industrial pure zirconium (R60702) was treated by surface high energy shot peening (HESP). The microstructure, surface grain size, micro distortion, gradient structure and crystal orientation were characterized by optical microscope (OM), X-ray diffraction (XRD) and electron back scattered diffraction (EBSD). A surface roughness measuring instrument was used to measure and evaluate the surface roughness, and an electrochemical workstation was used to study the corrosion resistance of R60702 welded joints. The results showed that after HESP treatment, a gradient structure was formed on the surface layer of the industrial pure zirconium welded joints with a thickness of about 110 μm, and the grains of top layer reached the nanometer level; In the process of surface nanocrystallization, twins and dislocation slip were the main deformation methods; After HESP treatment, the self-corrosion potential of R60702 welded joints was positively shifted, and the corrosion current density was reduced; HESP treatment made the surface structure of the three areas of the welded joints uniform, and the self-corrosion potential tended to be uniform, which effectively inhibited galvanic corrosio.

Abstract:Ti6Al4V titanium alloy was prepared by selective laser melting technology. The effects of different forming surfaces (XOY, XOZ) and different loads (20N, 40N, 60N, 80N) on the friction and wear properties of Ti6Al4V alloy were studied. The friction and wear properties of different forming surfaces were evaluated by friction coefficient (COF) combined with wear volume loss, and the wear track morphology and wear mechanism were characterized by optical microscope (OM) and three-dimensional profile measuring instrument. The results show that compared to the XOZ surface, the wear volume of the XOY surface is reduced by 0.27×10-5mm3 when the normal load is 20N, and the average friction coefficient is smaller. However, when the load is greater than 20N, the wear volume and average friction coefficient of XOY surface are larger than those of XOZ surface. The depth and width of the plough groove of the worn track increase with the increase of the load. The plough groove exhibits obvious peeling behavior, and there is a blocky "adhesive" distributed on the track, causing adhesive wear and oxidative wear. From the aspects of friction coefficient, wear volume and micro-morphology, it is quantitatively reflected that XOZ surface of Ti6Al4V alloy formed by SLM has better friction and wear performance than XOY surface, and XOY surface shows more wear resistance only under low load.

Abstract:The forming of TC4-ELI thick-walled pipe was studied by using finite element numerical simulation and actual extrusion. The differences and the reasons for the differences were explored in microstructure and mechanical properties of different areas in thick-walled pipes. The results show that during the external temperature and equivalent stress of the pipe are relatively high during the extrusion process. More α grains are elongated along the ED direction, and the elongated α grains grow to a higher degree. Base texture with relatively high strength is generated. However, the internal stress of the pipe is relatively low. The preferred orientation of the grains is not obvious, and only weak {-12-10}<20-21> plate texture is generated. Mechanical properties are affected by the combined effect of grain size and crystallographic orientation. Although the exterior of the pipe has coarse grains, the schmid factor between the axial tensile stress and base texture are small. It causes that the exterior of the pipe has higher strength.

Abstract:The effects of strain rate on quasi-static and dynamic mechanical properties and fracture behavior of 6005A-T6 aluminum alloy were studied by quasi-static tensile test and dynamic tensile test.The strength of 6005A-T6 aluminum alloy increased with the increase of the strain rate, the tensile strength and yield strength of the strain rate of 200/s increased by 30MPa and 25MPa, respectively, compared with the quasi-static tensile strength. In the process from the quasi-static to the strain rate of 10/s, the tensile strength and yield strength of the material increased most obviously. The plasticity of 6005A-T6 aluminum alloy increases with the increase of strain, but decreases when the strain rate reaches 200/s.Under the condition of high speed tension, the increase of dislocation density and the increase of slip band are the major reasons for the increase of strength and elongation. When the strain rate reaches 200/s, the main reason for the decrease of elongation after fracture is that the grain has no time for large deformation due to the too fast tensile rate.

Abstract:The laser cladding technology successfully prepared Fe-based JG-8 alloy composite coatings with different La2O3 content on the surface of 27SiMn steel substrate, and systematically studied the effect of adding La2O3 on the structure and properties of Fe-based JG-8 alloy composite coatings. X-ray diffractometer (XRD) and scanning electron microscope (SEM) equipped with energy spectrometer (EDS) were used to analyze and test the phase structure and microstructure of Fe-based JG-8 alloy composite coating. The hardness and tribological properties of the Fe-based JG-8 alloy composite coating were analyzed and evaluated by a microhardness tester and a friction and wear tester at room temperature. The results show that the addition of La2O3 can effectively refine the structure and transform the crystal grains from the original columnar crystals to fine planar crystals. The hardness of the Fe-based JG-8 alloy composite coating shows a trend of first increasing and then decreasing with the increase of La2O3 content. Among them, the hardness (532.76Hv0.3) of the 0.8wt% La2O3 Fe-based JG-8 alloy composite coating is the highest. Compared with the Fe-based JG-8 coating without La2O3 added, the hardness of the 0.8wt% La2O3 Fe-based JG-8 alloy composite coating increased by 15%. In the friction and wear process, the main wear mechanism of the Fe-based JG-8 coating without La2O3 is adhesive wear and fatigue wear, and the main wear mechanism of the 0.8wt% La2O3 Fe-based JG-8 alloy composite coating is abrasive wear. The 0.8wt% La2O3 Fe-based JG-8 alloy composite coating has the lowest volume wear, which is 37.1% lower than that of the Fe-based JG-8 coating without La2O3.

Abstract:The microstructure evolution in Al-Si-Cu foam during foaming process was studied using the scanning electron microscope. Through mixing the powder to the composition of Al-6Si-5Cu-2TiH₂-1.5MnO₂ wt%, and using the hot pressure process at 500℃, the Al foam could be foamed homogeneously at 640℃ for 12-20min. The corresponding microstructure analysis showed that the sample before foaming contained spherical Si, Al₂Cu, lump-shaped TiH₂ and flat MnO₂ phase. After foaming, the sample showed the millimeter-scale main hole with the sparse micrometer-scale pores inside the hole wall. The precipitates in hole wall were intragrain small Si and Al₂Cu particles, and grain boundary eutectic Si and Al₂Cu phases, as well as randomly distributed lump-like Al-Mn phase, MnO₂ phase and spherical Ti-rich phase. Therein, the Ti-rich phase, formed by the reaction of liquid Al and TiH₂ after release H₂, exhibited two types of morphology. The first one consisted of a Ti core, a thin layer of τ₂(Al₁₄Ti₃₃Si₅₃) inner shell, and the mixed dendrite-like τ₁(Al₂₀Ti₃₂Si₄₈) and τ₂ phases outer shell. The second type of morphology consisted of Ti core, and a mixed lump-like τ₁and (Al,Si)₃Ti shell. The composition of Si in the first type was much higher than that of the second type. That was mainly because the Si composition in liquid Al was not uniform due to the inheritance of the original microstructure of solid Al and Si, and the two types of Ti-rich phase formed in the Si rich and Si poor regions. The microstructure analysis of foaming process could be the foundation for designing the aging strengthening aluminum foam.

Abstract:In this paper, the biomimetic micro- and nanotopography was fabricated in one step on the micron scale spherical "template" of SLM-Ti substrate by anodic oxidation technology. The results show that the TiO₂ nanotubes arrays on SLM-Ti substrate without UV irradiation or high-temperature treatment exhibit superhydrophilic property after being modified with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane molecules. The morphology and static/dynamic water contact angle of POTS modified CP-TiO₂ and SLM-TiO₂ were compared and analyzed. The measured static contact angles of CP-TiO₂ and SLM-TiO₂ are ?149° and ?163.8° respectively, indicating that both of them are close to the superhydrophobic standard. However, the dynamic contact angle is the more important factor when self-cleaning, waterproof and anti-fouling characteristics are required. The results show that the water droplet was pinned on the CP-TiO₂ surface when the surface was tilted vertically, while the droplet on SLM- TiO₂ surface rolled off quickly within 155ms when the surface was tilted less than 1°.

Abstract:TC20 titanium alloy was subjected to different solution aging treatments. The effects of different solution aging treatment parameters on microstructure, mechanical properties and fracture morphology of TC20 titanium alloy were analyzed by tensile test at room temperature and plane strain fracture toughness test, combined with optical microscope, scanning electron microscope and micro Vickers hardness tester. The results show that when the solution temperature is constant, the strength and hardness of the alloy increase, while the plasticity and toughness decrease with the aging temperature increasing. When the solution aging process is at 950 ℃ for 0.5 h with water quenching, and then aging at 500 ℃ for 4 h with air cooling, the alloy can achieve a good strength and toughness match. At this time, the tensile strength of the alloy is 1106 MPa, the yield strength is 1019 MPa, and the fracture toughness is as high as 87.6 MPa?m^1/2.The fractures of the forged TC20 titanium alloy tensile and compact tensile (CT) specimens without solution aging treatment show typical ductile fracture morphology characteristics, while the fractures of the specimens treated with different solution aging treatments are mainly quasi-cleavage fracture and cleavage fracture. As the aging temperature increases, secondary cracks and voids on the fracture surface of the tensile specimen gradually appear, the plasticity gradually decreases, the size of the dimples of the CT specimen gradually becomes smaller and shallower, and the fracture toughness gradually decreases.

Abstract:The effects of solution and aging at different temperatures on the microstructure and hardness of Ti2041 alloy were studied. The results show that: at the solution temperature of 700℃, the content of primary α phase and the grain size increase gradually, with the increase of holding time; At the solution temperature of 750℃, with the increase of holding time, it can be seen that there are secondary α phases in the microstructure and static recrystallization occurs. The grain size increases gradually; At the solution temperature of 800℃, α′ martensite appears in the microstructure, and the morphology changes from equiaxed to lath. The change of hardness value is also different under different solution temperature. At the solution temperature of 700℃,with the increase of holding time, the hardness value decreases from 301.6HV to 285.2HV;At the solution temperature of 750℃,with the increase of holding time, the hardness value increases first and then decreases. The maximum value is 308.2HV;At the solution temperature of 800℃,with the increase of holding time, the hardness value increases gradually and the maximum value is 331.4HV. After aging treatment, secondary α phase appeared in the microstructure at different aging temperatures. With the increase of aging temperature, the size of secondary α phase decreases. The hardness value increases gradually and the maximum value is 451.75HV.The main strengthening mechanism is the second phase(secondary α phase) dispersion strengthening.

Abstract:This paper aimed to explore the effect of micro-alloyed Nb on the tribology performance of hypoeutectic gray cast iron. Four disc samples containing different contents of Nb (0, 0.12wt.%, 0.21wt.%, and 0.33wt.%) were fabricated. Non-asbestos resin-based friction materials were selected as counterface. The friction test was performed on a constant speed friction machine under different temperature conditions. Prior to test, the microstructure of discs was observed by SEM and metalloscope. After test, the worn surfaces of friction couples were characterized through SEM. Results showed that the friction coefficient increases firstly and then decreases with the increasing Nb addition. This was determined by the refining effect of Nb on the pearlite matrix. The friction efficiency was adversely influenced by the Nb addition. This was because the as-refined graphite by Nb weakened the heat dissipation capacity. Additionally, the wear resistance of disc increased with the increase of Nb concentration in the range of 0~0.21wt.%, but an obvious decrease at 0.33wt.%. This was closely related to the transformation of wear mechanisms.

Abstract:Using VC and WC-8Co composite powder, prepared by in-situ reduction carbonization, as raw materials, ultrafine WC-Co cemented carbide was prepared by sinter-HIP technology. The influences of the contents of the VC addition and the carbon of the composite powder on the phase composition, microstructure, and mechanical properties of the cemented carbides were investigated. The results showed that the grain size, hardness and fracture toughness of cemented carbides were mainly affected by the content of VC addition. These properties changed monotonically with the increase of VC content. The change of transverse rupture strength with VC content was related to carbon content. The compression strength decreased first and then increased with the increase of temperature. With the optimized carbon content of WC-8Co composite powder in the range of 5.60-5.68wt.% and the VC addition no more than 0.5wt.%, the high comprehensive performance ultrafine cemented carbides were prepared, with the highest value of TRS at room temperature and compression strength at 600oC as 4482MPa and 4914MPa, respectively. Based on the characteristics of the microstructure and the stress distribution, simulated by the elastic-plastic finite element model, the law of performance change and the mechanism of its performance were analyzed.

Abstract:Creep tests of high Nb containing TiAl alloy were carried out at different temperatures and various stresses, combining with scanning electron microscope (SEM), transmission electron microscope(TEM) and other analytical methods, the effect of nano Y₂O₃ on high temperature creep performance of Ti-45Al-6Nb-2.5V alloy was explored. The microstructure of the as-cast high Nb containing TiAl alloy consists of α₂/γ lamellar feature. In addition, the microstructure was refined significantly and the high temperature tensile properties were improved with the addition of Y₂O₃. According to results from creep tests, the creep resistance of Ti-45Al-6Nb-2.5V alloy is considerably improved after adding 0.15at.% nano Y₂O₃, the steady-state creep rate at 800℃/300MPa decreases from 2.389×10^_-7s^_-1 to 1.500×10^_-7s^_-1; and the creep life of Ti-45Al-6Nb-2.5V alloy at 850℃/250MPa increases from 14.10h to 61.50h. The mechanism of adding nano Y₂O₃ to improve creep resistance is that Y₂O₃ has high bonding strength with the matrix, which can effectively hinder the movement of dislocations and weaken the tendency of cavities to initiate. After analysis, the creep behaviors of the two alloys at 800℃/300MPa are mainly controlled by dislocation climbing and twinning, and the creep damage and fracture mechanism is initiation of voids and propagation of cracks.

Abstract:Amorphous alloy has a unique short-range ordered, long-range disordered atomic arrangement structure, with high strength, high hardness and excellent corrosion and wear resistance and other properties, has a strong application potential in the field of protective coating. The preparation technology of cold spraying layer, which is characterized by low temperature solid deposition, can effectively avoid the oxidation and crystallization of non-crystalline alloy materials in the spraying process, but the cold spraying technology depends heavily on the plastic deformation ability of powder. In order to improve the deposition and deformation performance of amorphous alloy particles under high speed impact, this paper innovated the liquid nitrogen-room temperature cycle cryogenic treatment method to pretreatment the Fe87.4Cr2.5Si6.8B2.4C0.9 amorphous alloy powder, and prepared the embedded composite coating of amorphous alloy particles on the 6061 aluminum alloy substrate surface by adjusting the technological parameters of cold spraying. The influence mechanism of cryogenic treatment on the deposition behavior of amorphous powder and the microstructure of coating was studied. The results showed that the coating thickness was only 6μm, and the amorphous particles were discontinuously distributed on the surface of the substrate. Only the amorphous particles with smaller particle size could have effective plastic deformation, but the crystallization rate was low during the deposition of the powder. The average thickness of the coating prepared by cryogenic amorphous powder was 67μm, and the amorphous alloy particles in the coating were uniformly distributed. The amorphous particles with larger particle size could also undergo effective plastic deformation, but the crystallization rate was higher during the powder deposition.6061 aluminum alloy substrate in the process of friction and wear of the main wear mechanism is adhesive wear and fatigue wear. Amorphous coating, the main wear mechanism of abrasive wear and use the original amorphous powder and cycle cryogenic processing powder preparation of amorphous coating is low, the quality of the wear of 6061 aluminum alloy substrate respectively quality wear rate of 15.7%, 11.8%.

Abstract:In this paper, the morphology of discontinuous precipitates at the grain boundary of Cu-2.0wt% Be alloy and the relationship between the discontinuous precipitates and heat treatment parameters were studied. The heat treatment parameters were selected by orthogonal experimental design, and the samples with a large difference in microstructure were prepared. The discontinuous precipitates mainly exist at the grain boundary and are mainly composed of γ phase and α matrix phase. According to the results of range analysis, the main heat treatment parameters affecting grain boundary reaction amount are secondary aging temperature, followed by primary aging time and secondary aging time. The analysis of anelastic behavior shows that the grain boundary reaction amount has a great influence on the deformation of the sample during loading. This is due to the non coherent relationship between the γ phase formed by discontinuous precipitation and the matrix. There is a disordered region around the γ phase, where the annihilation of dislocations causes the rearrangement of atoms, resulting in crystal slip and plastic deformation of the alloy. However, the two sides of the grain boundary without boundary reactants are crisscrossed with γ "phase, where dislocations are easy to pile up and hinder the crystal sliding.

Abstract:The development of high-power space electric propulsion technology has a very urgent requirement of LaB6 cathode material with low work function. In this paper, rare earth Ce was selected as doping element to reduce work function of LaB6. Firstly, La1-xCexB6 solid solution nanopowders（x=0.2, 0.4, 0.6, 0.8）were prepared by a molten salt route, and then they were used as raw materials to fabricate La1-xCexB6 cathode materials by hot pressing sintering. XRD and SEM technology were used to investigate microstructures of La1-xCexB6 cathode materials. The effect of Ce doping on work function of LaB6 cathode material was studied. Results show that the La1-xCexB6 cathode materials fabricated by hot pressing sintering of La1-xCexB6 nanopowders are single phase solid solution, their relative densities range from 98.49%~98.98%. The work functions of La1-xCexB6 cathode materials are between 1.85 eV and 2.54 eV, all lower than that of LaB6 without Ce doping. Besides, work function of La1-xCexB6 cathode materials decreases at first and then increases with Ce content increasing. La0.6Ce0.4B6 cathode material has the lowest work function of 1.85 eV. Solid solution doping of rare earth Ce is an effective way to reduce work function of LaB6 cathode material.

Abstract:High entropy shape memory alloy ia a novel type of high temperature shape memory alloy developed on the basis of NiTi alloy with equal atomic ratio and the concept of high entropy alloy. In recent years, the (TiZrHf)₅₀(NiCoCu)₅₀ and (TiZrHf)₅₀(NiCuPd)₅₀ series high entropy shape memory alloys with excellent comprehensive properties have been developed, which has attracted extensive attention and research interest. In this paper, the research progress of high entropy shape memory alloy is reviewed from the aspects of phase composition, microstructure, martensitic phase transformation behavior, shape memory effect and superelasticity. Simultaneously, the future inveatigate keynote of high entropy shape memory alloy is also prospected.

Abstract:In order to deal with the sensitive damage failure of heavy equipment in severe service environment for a long time, it is urgent to develop new engineering materials with outstanding performance. High-entropy metallic glasses (denoted as HE-MGs) is a new type of structural and functional material that has attracted much attention from scholars in recent years. With the special composition design concept, it takes into account the structural advantages of traditional amorphous alloys and the excellent comprehensive performance of high-entropy alloys. Although HE-MGs are barely 10 years old, its related research and exploration have made considerable headway. In view of the above-mentioned facts, the related concepts and evolution process are recapitulated. Herein, the factors affecting the phase stabilities of high entropy alloys and the rules of phase selection are summarized. In the meantime, the existing HE-MGs composition patterns and main characteristics and properties are concluded. The latest research progress on the room-temperature mechanical properties, serrated flow behavior, friction and wear properties as well as thermal stability are summarized. In the end, the research trend and application prospect of HE-MGs are put forward.

Abstract:In recent years, material design approach is being changed from trial and error experiments to integrated calculation based on computational models in synergy with the rapid development of Materials Genome Initiative and Integrated Computational Materials Engineering (ICME). High specific strength, outstanding corrosion resistance and good fatigue properties make titanium alloys widely used as structural material for aerospace and implants for biomedical area. This paper reviews the development history and alloying methodology of ? titanium alloys. The near ? alloys with addition of multi elements such as Al, Zr, Mo, V, Cr and Fe is becoming more and more attractive. Several design approaches are summarized in this paper where include Mo equivalent method, e/a method and “cluster- plus-glue-atom” model based on empirical methodology, and also include some method based on computational thermodynamics or first principles. Finally, the integrated calculation model of computational design used for hierarchically structured materials is discussed in detail and the potential application of this approach in titanium alloy design is analyzed.

Abstract:Owning to high melting temperature, refractory metals possess excellent properties under high temperature, hence they are crucial materials in parts bearing extreme thermal conditions such as engine, gas turbine, rocket, missile, etc. So refractory metal parts are very important in military equipment and civil life. However, it is very difficult to fabricate due to the high melting temperature and good thermal conductivity. Additive manufacturing is a new technique developed in recent years, it possess unique advantages thus providing a possible fabrication route for refractory metals. In this paper, research progress on additive manufacturing of tungsten and tungsten alloy, porous tantalum, niobium alloy, molybdenum alloy and refractory high entropy alloys were summarized. It may be helpful for researchers dedicated in related field.

Abstract:Surface nanocrystallization treatment can change the surface structure of the material and improve the surface properties of the material. Titanium alloy has excellent comprehensive resistance and has a wide range of applications. Surface nanocrystallization technology can be used to prepare a certain thickness of nanolayer on the surface of the titanium alloy, which can further enhance the corrosion resistance of titanium alloys. This article introduces the surface nanotechnology and the mechanism of surface nanocrystallization of titanium alloy, and reviews the current research progress on the effect of surface nanocrystallization on the electrochemical corrosion of titanium alloy at home and abroad. The effects of the surface state, composition, residual stress and microstructure of the titanium alloy on the corrosion resistance of the nanolayer after surface nanocrystallization are mainly explained. And the future research direction of surface nanocrystallization of titanium alloy is explored.

Abstract:In view of the status quo of huge reserves of low-grade titaniferous polymetallic ore that could not use directly, a gradient magnetic separation-vortex reduction method for preparation of Ti-Si-Fe alloy was proposed. The low-grade titaniferous polymetallic ore was processed by dry flux weakening magnetic separation to obtain the magnet powder products. And the medium magnetic titanium concentrate was obtained by medium magnetic separation. The medium magnetic titanium concentrate was used to prepara the Ti-Si-Fe alloy by vortex smelting reduction method. The results showed that the reduction temperature of silica and carbon could be reduced effectively by the generated iron. In the process of direct carbothermal reduction of titanium dioxide, the restrictive link was the reduction of low-valence titanium oxide (TiO→Ti). The generated silicon and iron could reduce the carbothermal reduction temperature of titanium dioxide to realize the successful preparation of Ti-Si-Fe alloy.

Abstract:The decomposition of TiH2 at high temperature was studied, and it was applied in the manufacture of high purity WTi alloy. The effect of hot pressing sintering process on the purity of WTi10 speicmen was investigaed. Microstructures by different raw material ratios were investigated, too. Optical microscope, Scanning electron microscope (SEM), CS analyzer, ONH analyzer and Glow discharge mass spectrometry (GDMS) were used to analyze the microstructure and impurities of the WTi10 specimens. The results indicate that with the increase of the ratio of TiH2 to Ti, the lower impurity of C,S,O,N,H more uniform distributed microstructure, and much less diffusion of W to Ti matrix. The purity of WTi10 products is up to 99.9993%.