Abstract:We proposed an efficient method to fabricate superhydrophobic, wear and corrosion resistant groove-textured surfaces based on TB6 (Ti-10V-2Fe-3Al) titanium alloy substrates. The smooth surface of the titanium alloy was ablated using a nanosecond laser to create a surface with a parallel groove pattern. In order to further improve the surface hydrophobicity, the laser treated surface was irradiated by an ultraviolet lamp for 1 h and subsequently immersed in a 3wt% octadecyltrichlorosilane solution for 2 h for chemical modification. The wettability of the groove-textured surfaces with varying groove spacing was investigated by analyzing surface morphology and chemical composition. Results show that the average coefficient of friction (COF) of the superhydrophobic surface is reduced by 34%, 56%, and 59% compared with that of the original hydrophilic surface under dry, water, and oil lubrication conditions, respectively. The mechanism variation of the CoF was also discussed. Potentiokinetic polarization testing demonstrates that the prepared superhydrophobic surface provides corrosion protection for the titanium alloy substrate.

Abstract:A high-hardness, wear-resistant gradient ceramic coating was prepared by laser cladding TiC particle-reinforced iron-based powder onto a 40Cr steel substrate to achieve the coating's gradient effect. Scanning electron microscope (SEM), energy dispersive spectroscope (EDS), X-ray diffractometer (XRD), micro-hardness tester, and friction and wear tester were used to investigate the microstructure, phase, hardness, and wear resistance of the cladding layer. Results show that the phase of the cladding layer is mostly austenite, some TiC strengthening phase, and a trace amount of ferrite phase. The cermet coating made of laser cladding TiC particle-reinforced powder has a compact microstructure, and the coating phase composition is essentially the same as the powder composition. The TiC phase, which is responsible for the strengthening effect, is dispersed across the molten pool following a gradient from the bottom to the top. The TiC phase reinforcing the molten pool is partly dissolved, and thus the size of the pool shrinks. Under the laser's intense heat, some TiC strengthening phases develop into shapes like squares, snowflakes, and fish bones. At the base of the molten pool, the TiC phase may develop in three ways, while the TiC strengthening phase is less widely dispersed. The TiC strengthening phase in the center of the molten pool is progressively expanded, and enriched and bridged in the top portion of the molten pool. The cladding layer has a Vickers hardness HV up to 19 602.94 MPa, and under the same circumstances, the friction and wear depth of the coating is only one-fifth of that of the substrate. This results in a considerable improvement in the wear resistance of the substrate.

Abstract:Zirconium is an excellent hydrogen absorption material and has been regarded as a candidate material in the deuterium storage field. However, due to its higher hydrogen absorption temperature and slower hydrogen absorption kinetics, it cannot be applied at present. Palladium electroplating was used as a surface modification to improve the property. The results show that after the palladium electroplating and annealing, the zirconium alloy can absorb hydrogen at room temperature with an appropriate incubation period. With the increase in temperature, the hydrogen absorption rate becomes faster with a shorter incubation period. A transition zone forms between the palladium layer and zirconium substrate, and PdH_1.33 and H_0.62Zr_0.38 are found in the transition zone after hydrogenation. These hydride phases in the transition zone play an important role in improving the hydrogen absorption property of zirconium. For the kinetics mechanism, it is determined to be 1-D diffusion at room temperature and 2-D diffusion at 250 °C.

Abstract:ZrC strengthened CoCrNi-based laser cladded coatings with different content of ZrC were prepared on the surface of low carbon steel. The effects of ZrC addition on microstructure, hardness and wear resistance of CoCrni-based medium entropy alloy coating were investigated. The results show that there is a good metallurgical bond between the cladding layer and the matrix without obvious cracks and defects. The CoCrNi alloy coating without ZrC is composed of single-phase FCC structure. With the addition of ZrC in the coating, the coating phase compositions change to FCC+ ZrC0.7+Cr23C6+ZrO2 multiple phase structures. The grains of the coating were significantly refined, and the combination of grain boundary strengthening, solution strengthening and dispersion strengthening (Orowan) was realized, which effectively improved the hardness and wear resistance of the coating. However, ZrO2 produced by the combination of Zr in ZrC and O in the air also has an adverse effect on the performance of the coating, mainly because the presence of ZrO2 will cause the uneven distribution of particles in the coating and weaken the effect of dispersion strengthening. Therefore, when the content of ZrC is small, the performance of the coating is not improved. However, when ZrC content in the coating increases to 5wt.%, more ZrC0.7 phase is separated out from the coating, which can effectively improve the performance of the material. The hardness is 651±15 HV_0.1 and the friction coefficient is 0.161 which is much lower owing to the synergetic strengthening effect.

Abstract:The micro-arc oxidation ceramic film with wear resistance was prepared on the surface of A356 aluminum alloy using micro-arc oxidation technology (MAO). The investigation of the effect of micro-arc oxidation on the fretting wear mechanism of A356 aluminum alloy was explored on an SRV-V fretting friction and wear testing machine using sphere-plane point contact under variable normal loads and displacement amplitudes. The results show that the MAO film consists of a porous outer layer and a dense inner layer with good homogeneity, denseness and bonding strength. The friction coefficient and wear rate of MAO film are lower than those of A356 alloy when the normal load and displacement amplitude increases. It indicates that the MAO film has good friction reduction and wear resistance. The frictional dissipation energy coefficient of MAO film is lower than that of A356 alloy when the displacement amplitude increases, which can enhance the wear stability of fretting wear process of A356 aluminum alloy. The wear mechanism of A356 alloy changes from abrasive wear to adhesive wear when the normal load increases, accompanied by ploughing and fatigue peeling. The wear mechanism of MAO film changes from abrasive wear to adhesive wear and fatigue peeling when the normal load increases. The wear mechanism of A356 alloy changes from adhesive wear and fatigue peeling to adhesive wear and abrasive wear when displacement amplitude increases. The wear mechanism of MAO film changes from adhesive wear and fatigue peeling to adhesive wear and abrasive wear when displacement amplitude increases. The accumulated Fe and O elements are gathered within the A356 aluminum alloy wear scars, which indicates that there is material transfer and oxidation wear during the fretting wear process of GCr15/A356 frictional counterpart. The Fe elements are gathered within the MAO film wear scars, which indicates that there is material transfer of GCr15/MAO film frictional counterpart.

Abstract:The NiCrBSi-CrSi₂ composite coating was prepared by supersonic flame spraying (HVOF) technology on the 12CrMoVG substrate by using different kerosene flow rates. XRD, SEM, EDS, Raman, Vickers microhardness tester, electronic tensile testing machine and high temperature rotational friction and wear testing machine were used to characterize the coating phase, microstructure, mechanical properties and high temperature friction and wear properties at different kerosene flow rates. The results showed that the phase composition of coatings is basically the same, all of which have γ-Ni, Ni₃B, Cr₂B, CrSi₂ and Cr₅Si₃. But as the kerosene flow increases, the CrSi₂ and Cr₂B parts in the coating will be transformed into Cr₅Si₃ and CrB phases, respectively. The microhardness and bonding strength of the coating showed a trend of first increasing and then decreasing with the increase of kerosene flow, and the porosity and wear rate showed a trend of first decreasing and then increasing. When the kerosene flow rate is 30 L/h, the powder melting effect is the best, the porosity of the coating is as low as 0.17 %, the microhardness is higher to 569 HV_0.3, the bonding strength is higher to 59 MPa, and the wear rate is as low as 2.84×10_-14 ^m₃^{/(N.m). Oxides such as Cr}₂O₃, SiO₂ and NiCr₂O₄ generated on the surface of the wear mark and the high coating hardness make the coating 30 L/h show optimal high temperature friction and wear resistance. The wear mechanism of the coating is mainly oxidative wear and adhesive wear.

Abstract:In PEMFCs components, the bipolar plate is the most important part due to its high proportion of the cost, volume, and mass of PEMFC (45 %, 80 %, and 50 %).Because of the material and process problems of the bipolar plate, the volume and mass of the traditional graphite PEMFC are relatively large, which increases the weight of the vehicle, reduces the available space of the vehicle chassis, and affects the performance of the PEMFC vehicle. Therefore, the development of a lightweight, low-cost, simple preparation process for the bipolar plate is of great significance to promote its commercial application.The metal bipolar plate has attracted much attention in the PEMFC field because of its low cost, good mechanical properties, electrical conductivity, thermal conductivity, and relatively easy-to-control volume. However, in the PEMFC environment, the metal bipolar plate is easy to form a passivation film, which leads to an increase in its contact resistance. Therefore, improving the corrosion resistance of metal bipolar plates and maintaining good conductivity are the main focus of current research on PEMFC.Our review summarized the graphite, composite, and metal bipolar plate preparation process or surface modification methods, and discussed the advantages and disadvantages of bipolar plate or surface-covered carbide coatings, metal coatings, and nitride coatings. in addition, we compared the corrosion resistance and interfacial contact resistance performance of these coatings under the PEMFC environment.

Abstract:Based on this "cluster plus connected atoms" model and the ideal composition formula of nickel-based superalloys, the element content of Cr/Mo/W of DD98M alloy was reduced, and the DD98MC alloy was obtained. The parent alloys of the two alloys were prepared by vacuum induction melting. Then they were subjected to solution aging and long-term aging at 1273k. The as-cast microstructure of the two alloys after aging was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The effects of long-term aging at high temperature and Cr/Mo/W on the as-cast microstructure and properties of the alloys were analyzed. The results show that long-term aging causes partial decomposition of γ" phase, promotes element diffusion and intensifies element segregation. With the extension of long-term aging time, γ" phase coarsen or even becomes rafting, the hardness decreases, the absolute value of misfit decreases, and the cubic degree of γ" phase decreases. As the content of Cr/Mo/W elements decreases, the absolute value of misfit decreases, the cubic degree of γ" phase decreases and the hardness decreases. Under long-term aging, the γ" phase of DD98M alloy becomes rafting. Meanwhile, there are coarse γ" phase formation and a large moment of σ phase precipitation in grain boundaries and grains. Under long-term aging, for the DD98MC alloy, only σ phase and MC carbide precipitate in grain boundaries. Compared with the DD98M, the DD98MC has better structural stability and mechanical properties.

Abstract:718 alloys have become key materials in nuclear power and aerospace fields because of their excellent mechanical properties and good high-temperature processing performance. Nuclear grade 718 alloys need to meet special requirements such as strong irradiation resistance and small thermal neutron absorption cross-section, therefore, the elemental content of Ni, Nb, and C in alloys is generally controlled at low levels, however, there is less research on the thermal deformation structures and properties of such low Ni, Nb, and C nuclear grade 718 alloys. This work investigated the effects of different hot rolling process parameters and post-rolling heat treatment on the structures and tensile properties of nuclear grade 718 alloys by designing different initial rolling temperatures and deformation amounts. The results show that, under the condition that the initial rolling temperature is below 1150℃ and the heat deformation is lower than 90%, a large number of elongated grains appear in the structure and the elongation of the alloy is reduced; when the initial rolling temperature achieves 1150℃ or the heat deformation reaches 90%, a uniform equiaxed grain structure can be obtained. After the solid solution treatment of the rolled plate at 990℃, δ phases are precipitated and pinned to grain boundaries, forming a mixed grain microstructure, as well as the average values of yield and tensile strength at 315°C after standard aging treatment can reach 1050MPa and 1238MPa, accompanied by an elongation after the fracture as high as 26%; Upon solid solution treatment at 1020°C, the grown equiaxed grains are obtained, whereas the average yield and tensile strength at 315°C can attain 985MPa and 1175MPa after standard aging treatment, respectively, and the elongation after the break is up to 29%, showing good strength and toughness.

Abstract:The microstructure of hot-corrosion resistant single crystal superalloy with different Ta and Co contents and the microstructure stability during long-term aging at 1000 ℃ was investigated. The results show that in the single crystal superalloy of the experiment, the dissolution temperature of γ" phase increases with the increase of Ta content, the size of γ" phase first increases and then decreases after complete heat treatment. The dissolution temperature of γ" phase decreases and the size of γ" phase and the content of γ" phase reduces with the increase of Co content. During the long-term aging process at 1000 ℃, the coarsening rate of γ" phase first decreases and then increases with the increase of Ta content, while the coarsening rate of γ" phase decreases with the increase of Co content. The mismatch degree of γ/γ" phase and the diffusion of elements in matrix are the main factors affecting the coarsening rate of γ" phase in the four alloys. In addition, Ta increases the content of γ" phase, promotes the distribution of Re, W, Mo and Cr in γ matrix, and promotes the precipitation of TCP phase, while Co reduces the distribution of Re, W, Mo and Cr in γ matrix, reduces the supersaturation of matrix and inhibits the precipitation of TCP phase.

Abstract:The effect of solidification cooling rate on microstructure and room temperature tensile properties of equiaxed nickel-based cast superalloy K4750 were studied by designing shell insulation methods. Four types of insulation methods were designed, including: sand-filled, test bars without insulation felt, wrapped single-layer insulation felt and wrapped double-layer insulation felt, and the order of solidification cooling rate at the test bar of the shell is: test bars without insulation felt ≥ sand-filled > > wrapped single-layer insulation felt ≥ wrapped double-layer insulation felt. After standard heat treatment, the test bar with sand-filled shell has the highest room temperature tensile strength (1115MPa), the test bar without insulation felt is the seconed highest (1095MPa), and the single-layer insulation felt and the double-layer insulation felt are the worst (950MP and 952.5MPa respectively). OM, SEM and EBSD were used to characterise the microstructure of the alloy. The results show that the grains of sand-filled, test bars without insulation felt, single-layer insulation felt and double-layer insulation felt are equiaxed crystals, and the average grain sizes were 176μm, 167μm, 325μm and 315μm, respectively. Sand-filled and test bars without insulation felt alloys solidification cooling rate is faster, the formation of small equiaxed crystals more easily coordinated deformation in the stress conditions, solidification process to form the MC type primary carbide is finer and mainly in the form of blocks, which is conducive to inhibit the expansion of microvoids and cracks during deformation, significantly improving the tensile properties of the alloy at room temperature. On the contrary, single-layer insulation felt and double-layer insulation felt alloys solidification cooling rate is slower, the formation of large-size equiaxed crystals are not conducive to the coordinated deformation between the grains, and the precipitation of MC type primary carbide with large size and long strip shape promotes the emergence and expansion of holes and microcracks, which significantly reduces the strength and plasticity of the alloy at room temperature.

Abstract:The effect of two-step sub-solvus heat treatment process on the γ "phase microstructure of a novel nickel-based powder metallurgy superalloy FGH4113A (WZ-A3) was studied. The cooling rate of large-size forged turbine disc is lower after forging, and the size distribution of γ" phases is from about 100nm to 4500nm. Small samples were taken from the disc for heat treatment experiments. When the samples were heated to 1000 ℃ and 1050 ℃, the total proportion of γ "phases decreased, and the evolution mechanism showed signs of Oswald coarsening mechanism and PAM mechanism. When the sample was heated to 1100 ℃, the intracrystalline γ" phase was completely dissolved. If two-step sub-solid solution heat treatment process was used, the sample was first heated to 1120 ℃ for 2h followed by rapid cooling, and then heated to 1000 ℃, 1050 ℃ or 1100 ℃, the total proportion of γ "phases decreased. The evolution of intracrystalline γ" phases was dominated by the Oswald coarsening mechanism, and its morphology and size were relatively stable during the heating process. The testing rods were cut from the disc and went through as forged state + 1000 ℃ (without heat preservation) + aging heat treatment and as forged state + 1120 ℃ (2h) + aging heat treatment respectively, and followed by tensile test at 550 ℃. The yield and tensile strengths of the latter one are significantly higher than the first one, and this can be treated as a reference for dual-performance heat treatment process design of large-size turbine discs.

Abstract:In this paper, the effects of different heat treatment processes on the microstructure and properties of a new type of Ni-based superalloy ZGH451 were studied. The results show that the as-deposited microstructure is mainly composed of epitaxial micro-columnar grains, and there is γ/γ＇ eutectic exists among the interdendritic region. The segregation of element in the alloy results in the size difference of γ＇ phase between dendritic region and interdendritic region, which are 100 nm and 250 nm, respectively. The microstructure and properties of alloy with varying heat treatment processes are different: as the solution temperature increases from 1180 ℃ to 1350 ℃, the segregation degree of the alloy decreases gradually until the initial melting microstructure is found at 1350 ℃. With the first aging temperature increasing from 1050 ℃ to 1150 ℃, the size of γ＇ phase increases gradually, and its shape changes from spherical and other irregular shape to cube shape. In summary, the heat treatment process (HT2) suitable for the alloy is optimized. Compared with the as-deposited alloy, the grain size of alloy is significantly increased after the complete heat treatment, and the segregation and γ/γ＇ eutectic of the alloy are eliminated. The denser dislocation network is formed at the γ/γ＇ interface during tensile deformation at 1000 ℃. The tensile strength and yield strength are 520 MPa and 269 MPa, respectively, and the elongation is 11%.

Abstract:Carbides transformation during heat-treatment process has a significant effect on the mechanical properties of superalloys. XRD, SEM, EPMA, and TEM were used to investigate the distribution and evolution mechanism of carbides and their effects on high-temperature tensile properties of Co-Cr-Nb-W wear-resistant alloy during heat-treatment process. There are two carbides transformation processes in the Co-Cr-Nb-W alloy during brazing simulation and aging: MC+matrix=M₆C and M₂₃C₆+matrix=M₆C. The fracture mechanism of the Co-Cr-Nb-W alloy under high temperature tensile stress is a hybrid mechanism of ductile fracture and brittle fracture, and the interface between the bulk primary carbide and the matrix is easy to become the source of crack source. The heat treatment process eliminates the lamellar M₂₃C₆ which is easy to cause grain boundary migration, induces the precipitation of fine M₆C particles around the skeleton MC, improves the interdendritic element segregation, promotes the formation of high-density overlapping stacking fault (SF) bands in the matrix, and increases the tensile strength of the alloy at 1000℃ by about 20 MPa.

Abstract:The influence of stress on the recrystallization process of pure titanium was investigated. Bending stress was applied during the annealing process of a pure titanium plate to observe the recrystallization process under tensile and compressive stresses on one section. Industrial pure titanium TA1 rolled plates with different deformation levels of 20%, 40%, and 60% were prepared. These samples were then subjected to a temperature of 600 °C and a stress of 30 MPa for 10 min. It is found that in the samples with 20% and 40% deformation levels, only a few recrystallized grains are observed. Additionally, the average grain size in the region under stress becomes larger than that in the region without stress. To further investigate the grain growth, the rolled sheet with 40% deformation level was kept at 600 °C and 30 MPa for 60 and 120 min. It is observed that the abnormal growth of grains in the tensile stress area continues until the critical size is reached, after which they stop growing. The increased grain growth during recrystallization can be attributed to the stress-promoting dislocation adjustment. The grains with favorable conditions tend to grow abnormally along the direction of the applied stress. However, the high density of residual dislocations within the titanium plate results in a reduction in the driving force for grain growth, leading to the existence of critical size. These findings provide an explanation for different recrystallization behavior observed in titanium under tensile and compressive stresses.

Abstract:To investigate the effects of double-scaled reinforcements on the tensile properties and failure behavior of aluminium matrix composites, Ni-Co-P coated carbon fibers reinforced 7075Al matrix composites (CF/Al), FeCoCrNiAl high-entropy alloy particles reinforced 7075Al matrix composites (HEA_p/Al) and Ni-Co-P coated carbon fibers and FeCoCrNiAl high-entropy alloy particles hybrid reinforced 7075Al matrix composites (CF-HEA_p/Al) were fabricated by vacuum hot pressing sintering under the pressure of 30 MPa at 580 °C for 10 min. The microstructure and the fracture morphologies of the composites were observed, and the tensile properties of composites were characterized. Results show that the yield strength (YS) and ultimate tensile strength (UTS) of CF-HEA_p/Al composites are firstly increased and subsequently decreased with increasing the CFs content from 0vol% to 40vol%, while the elongation is decreased. Owing to the hybrid reinforcing effects of Ni-Co-P coated carbon fibers and FeCoCrNiAl high-entropy alloy particles, the YS and UTS of CF-HEA_p/Al composites have larger improvement compared with those of CF/Al and HEA_p/Al composites, and the fracture morphology is characterized by mixed rupture modes of ductile rupture of 7075Al matrix and fiber pull-out and fracture.

Abstract:The influence of Hf element on enthalpy and hardness relaxation behavior of Zr₇₀Al_7.5Ni₈Cu_14.5 (70Zr), Zr₅₅Al₁₀Ni₅Cu₃₀ (55Zr) and (Zr_0.75Hf_0.25)₆₅Al_7.5Ni₁₀Cu_17.5 (65Zr_0.75Hf_0.25) bulk glass-type alloys with large diameters of centimeter-level was examined by measuring the temperature dependence of apparent specific heats in as-spun and annealed states. Results show that the structural relaxation of 70Zr and 55Zr alloys occurs through a single-stage mode where the relaxation peak is observed at the annealing temperature (T_a) near glass transition temperature (T_g), while 65Zr_0.75Hf_0.25 alloy shows a double-stage reaction with enthalpy relaxation peaks appearing at 523 and 648 K near T_g. The single-stage relaxation mode for 70Zr and 55Zr alloys indicates that these alloys have high resistance to annealing-induced relaxation over the whole temperature range up to T_g, because the distinct relaxation occurs only around the temperature of T_g. 65Zr_0.75Hf_0.25 glassy alloy shows a relaxation sub-peak around 523 K presumably due to the weaker bonding nature of Zr-Hf atomic pair with nearly zero in heat of mixing, and the distinct main relaxation occurs near T_g. The Vickers hardness also shows the similar double-stage peak behavior as a function of T_a for 65Zr_0.75Hf_0.25 as well as (Zr_0.5Hf_0.5)₆₅-Al_7.5Ni₁₀Cu_17.5 (65Zr_0.5Hf_0.5) alloys, so the T_a for the first-stage hardness peak agrees with that for the enthalpy relaxation. These results imply that icosahedral-like medium range ordered structure consisting of Zr, Al, Ni and Cu elements with the three components rule for stabilization of supercooled liquid remains stable during the low T_a relaxation. The double-stage enthalpy and hardness relaxation only appear in 65Zr_0.75Hf_0.25 and 65Zr_0.5Hf_0.5 glassy alloys which deviate from the three components rule, implying that the unnecessary multiplication for the formation of bulk glassy alloys leads to an increase in structural instability during low-temperature annealing.

Abstract:In order to reduce the RE-Fe-B material cost and to balance the utilization of rare earth sources, [(Pr, Nd)_1?xMM_x]_30.3(Fe, Co)_bal- M_0.73B_0.98 (x =0.3, 0.5, 0.7, wt%) magnets were prepared by double main phase (DMP) and single main phase (SMP) processes. DMP magnets are superior to SMP magnets with the same nominal composition in magnetic properties and corrosion resistance. For x=0.5, the magnetic properties of DMP magnets are B_r=1.308 T, H_cj=799.980 kA/m and (BH)_max=325.6436 kJ/m³, which are higher than those for SMP magnets (B_r=1.297 T, H_cj=746.8868 kA/m and (BH)_max=317.8428 kJ/m³) with the same nominal composition, and the impro-ved RE-rich phase distribution and REs heterogeneity distribution are the main reasons. When DMP magnets are exposed to a hygro-thermal environment, there is not only RE-rich phase corrosion, but also pulverized main phase grain due to hydrogenation behavior difference between LaCe-rich and LaCe-lean shell-core within one individual grain. As a result, it is demonstrated that DMP techni-que is an effective approach to improve the permanent magnetic properties and corrosion resistance of MM-based sintered magnets.

Abstract:Aluminum foam bar (AFB) with thin outer wall was prepared by melt foaming method. The effect of span, diameter and porosity on its bending deformation behavior was investigated by cantilever beam bending experiment and finite element simulation. Bending deformation behavior was recorded by high-speed camera and the relationship between load and displacement was obtained. X-ray micro-computer tomography (Micro-CT) technique based on 3D finite elements was selected to scan and to reconstruct AFB, by which numerical simulation was carried out. The results show that span has important effect on the failure behavior and the increased span leads to decreased energy absorption capacity. In addition, increased diameter and relative density contribute to peak load improvement. Finite element simulation results match well with the experimental results, which clarifies that cell walls fail due to different types of stress during the bending process. Crack propagation follows the weakest cell walls path link during the failure process.

Abstract:The influence of Ti addition into Al-based alloy fabricated by laser powder bed fusion (LPBF) technique was demonstrated. The microstructure characteristics, phase identification and nano-hardness of the LPBF-processed samples without or with 3wt% Ti addition were investigated by scanning electron microscope, electron backscatter diffraction, X-ray diffraction, transmission electron microscope and nano-indentation tests. The results reveal that a refined grain microstructure and lower average grain sizes can be obtained. Due to the heterogeneous nucleation provided by Al₃Ti precipitated phases, the ranges of grain sizes are reduced within 2.5 μm. As the low angle grain boundary increases, higher crystal lattice distortion energy contributes to the increase in average nano-hardness (to 2.36 GPa) and Young's modulus (to 92.72 GPa) values. The <100> texture of LPBF-processed Al-based alloy with 3wt% Ti addition is slightly enhanced, while there is still a random crystal orientation. The phase transformation from α-Al to Al₃Ti can be obtained.

Abstract:K-TIG is a welding process based on traditional TIG welding, which increases the welding current to 300 A or even higher value and forms the“keyhole”effect by the feat of tungsten electrode cooling system to achieve the ultimate deep penetration welding. The welding width of K-TIG welding is wider than that of plasma and laser weld, and the weld pool is larger. The traditional heat source model is not suitable for the characteristics of heat source distribution in K-TIG weld. Based on the SYSWELD simulation platform and the experimental results of K-TIG welding for titanium alloy, a combined heat source model for numerical simulation of K-TIG deep penetration welding of titanium alloy was developed. The results show that when the distribution coefficient of double ellipsoidal heat source is 0.75 and the acting depth is 4 mm, the simulation weld pool is consistent with the actual joint cross section, and the front weld width is 12 mm and the back weld width is 5 mm. The finite element simulation results of temperature loop curve and residual stress are basically consistent with the experimental results, verifying the accuracy of the established K-TIG heat source model.

Abstract:Vacuum Arc Remelting (VAR) is one of the most commonly used methods for the production of titanium alloy ingots. Due to the high temperature and opacity of the melting process, it is difficult to experimentally study the fluid flow behavior and macrosegregation during the melting process. Based on this, the VAR melting process of Ti60 high-temperature titanium alloy was studied by numerical simulation method. The effects of melting current and magnetic field stirring intensity on fluid flow behavior and macrosegregation were also discussed. The results show that the molten pool shape changes gradually from "flat" to "V-shaped" when VAR melts titanium alloy. At the end of solidification, the content of Zr elements in the bottom and edges of the ingot is low, and the content in the center and shrinkage cavity is high. The Lorentz force generated by the melting current makes the melt flow counterclockwise, and the larger the melting current is, the more intense the melt flow is. At the same time, it also leads to more severe macrosegregation at the ingot center and riser. The Lorentz force generated by the stirring magnetic field is applied to the whole molten pool, which not only promotes the flow of melt in the upper part of the molten pool, but also facilitates the flow of melt in the lower part of the molten pool, and also leads to more serious macrosegregation in the ingot center and shrinkage cavity. When there is no stirring magnetic field and the stirring magnetic field is large, the Zr element will produce more serious macrosegregation in the ingot. In order to effectively control the occurrence of macrosegregation defects in VAR melting titanium alloy, small melting current and appropriate stirring intensity should be adopted.

Abstract:In order to investigate the effect of hole expansion strengthening of split mandrel with different relative expansion amount on the fatigue properties of 7050 aluminum alloy, a finite element model of hole expansion strengthening of split mandrel was established, and hole expansion strengthening of split mandrel experimental was carried out. The residual stress on the hole wall of the hole expansion strengthening specimen and the distribution law of the stress on the hole wall of the loaded specimen were analyzed. In addition, the relationship among relative expansion amount, residual stress and fatigue life was explored. Finally, the resist fatigue effect of hole expansion strengthening of split mandrel was revealed. The results showed that, the relative expansion amount of 2%, 3%, and 4%, while the maximum residual compressive stress of the hole wall were 246.8, 338.6, and 367.7 MPa at the inlet area of the hole wall of the specimen. The relative expansion amount was positively correlated with the maximum residual compressive stress of the hole wall. Inlet area of the hole wall of the loaded specimen, the relative expansion amount of 2%, 3%, and 4%, and the maximum stress of the hole wall were 451.2, 368.7, and 321.6 MPa, the relative expansion amount was negatively correlated with the maximum stress of the hole wall. The median fatigue life of specimen with relative expansion amount of 2%, 3%, and 4% is 1.17, 1.52, and 1.71 times of that of with relative expansion amount of 0.

Abstract:Titanium alloys exhibit great potential for applications in various engineering fields due to their excellent comprehensive properties, whereas the lower elastic modulus significantly limits their usage in structural parts that require for high strength and high rigidity of materials. In order to develop high elastic modulus titanium alloy with good comprehensive mechanical properties, Ti-6Al-4Mo-xMn (x=0, 1, 2, 3, 4 wt.%) alloys were prepared by a cold crucible suspension melting method. The effect of Mn content on the microstructure and mechanical properties of the alloy was systematically investigated. The results demonstrated that the prepared Ti-6Al-4Mo-xMn alloys were composed of α and β phases without Ti-Mn phase impurity. With the increase of Mn content, the α→β phase transition temperature decreased, resulting in an increase in volume fraction of β phase. Moreover, the microstructure of the alloys gradually became finer and evolved toward Widmannstatten microstructure. The hardness of the alloy increasesd from 30 HRC to 46 HRC; and the tensile strength increased from 838 MPa to 1266 MPa, which is because solution strengthening and microstructure refinement caused by Mn atoms. With the increase of Mn content, the elastic modulus of the alloy increased first and then decreased. When the Mn content is 1%, the elastic modulus of the alloy exhibited a highest, value of 136 GPa, and the tensile strength was 916 MPa, which are 24.0% and 3% higher than those of Ti-6Al-4V alloy, respectively.

Abstract:To obtain titanium alloy porous structures with good mechanical properties and high permeability, a trade-off between the porosity of the porous structure and its strength needs to be maintained. Taking human knee tibial prosthesis as the research object, firstly, according to the stress state of the tibia, topology optimization is used to design and reconstruct the compressive and shear cell structures (TO-P1, TO-P2, TO-S1, TO-S2) under different loading conditions, and several common basic cell structures (BCC, FCC, RDC, DCC) are studied and compared; secondly, by performing different types of porous titanium alloys for compression and shear performance simulation, to research the mechanical properties of porous titanium alloys with different topologies regarding compression and shear resistance, and to verify the validity of the simulation analysis by forming porous titanium alloy compression specimens with SLM technology; finally, four porous titanium alloys with better mechanical properties were chosen for permeability analysis. The results show that the TO-S2 structure has the best compressive, shear mechanical properties and permeability, suitable for porous structures of compression-shear load type implants.

Abstract:Irradiation-induced generation of point defects accelerates the evolution of the microstructure of nuclear power plant materials and affects the reactor lifetime to a large extent. In this paper, based on the quadratic continuous phase field model of the phase field method with coupled vacancy and interstitial atoms, the phase separation of Fe-15at.%Cu-1at.%Ni-1at.%Mn alloy under the vacancy diffusion mechanism is simulated using this model, and the interaction mechanism between the vacancy diffusion-induced point defects and the Cu-rich phase is investigated. The results show that the presence of vacancy and interstitial atoms promotes the growth and coarsening of the Cu-rich phase, the increase of the initial concentration of point defects promotes the phase separation and accelerates the nucleation rate of the precipitated phase, and the elevated temperature delays the growth and coarsening of Cu atoms and vacancy rings, and the point defects can also increase the yield strength to a certain extent, which provides a new idea to investigate the effect of vacancy diffusion mechanism on the properties of irradiation-resistant materials.

Abstract:As a method that can significantly improve the coercivity of sintered NdFeB magnets and realize the high-quality utilization of heavy rare earth, grain boundary diffusion has increasingly become a research hotspot in the field of rare earth permanent magnetism and industry. In this paper, the influence of substrate composition difference on the magnetic properties of the magnets after grain boundary diffusion during the batch preparation of the grain boundary diffusion sintered magnets has been studied by using the automatic spraying equipment system. The results of microstructure and EDS element analysis show that the difference in the growth range of the coercivity of the magnets after grain boundary diffusion is closely related to the adequacy of the formation of the grain core-shell structure in the magnets after diffusion, the uniform distribution of the grain boundary phase and the content of ferromagnetic elements in the grain boundary phase, At the same time, the temperature coefficient of the magnet prepared by the grain boundary diffusion process is better than that of the magnet of similar brand prepared by the traditional process. Keywords: Sintered NdFeB magnets; Grain boundary diffusion process; Magnetic properties

Abstract:With the continuous improvement of the requirements of advanced engineering technology on the performance of shape memory alloys, traditional shape memory alloys are increasingly difficult to meet the requirements. High entropy shape memory alloys have emerged as the times require, which has attracted great attention of researchers.Compared with traditional shape memory alloys, high entropy shape memory alloys have significantly improved recoverable strain, yield strength,high temperature phase stability and hyperelasticity, and have broad application prospects. In this paper, the research status, martensitic transformation and shape memory effect of high entropy shape memory alloys are briefly reviewed,and the existing shortcomings and future development of high entropy shape memory alloys are prospected.

Abstract:Wave-absorbing materials play a vital role in national defense and people"s livelihood, but traditional wave-absorbing materials are difficult to meet the increasingly complex electromagnetic environment due to their large mass and narrow frequency band. The integration of structural design ideas of wave-absorbing metamaterials with "thin, light, wide and strong" and dynamic tunable and insensitive polarization angles has contributed to the rapid development of the field of electromagnetic wave absorption. In this paper, we firstly clarify the principles and methods of metamaterial wave absorption and the important influence of geometric design on electromagnetic wave absorption performance. Secondly, the development status of wave-absorbing metamaterials in carbon, water, metal and inorganic compound-based material systems is discussed in detail, and the current development trend of active tuning, lightweight and broadband, and multi-band compatibility is indicated as the main line. Finally, the current development bottlenecks and future research directions are summarized, providing ideas for the optimal design of wave-absorbing metamaterials.

Abstract:Al-Si alloys prepared by selective laser melting (SLM) have great potential in the development of aerospace materials customization and lightweight. However, corrosion behavior affecting the life of SLM forming parts has not been widely concerned. Based on current literature reports, this paper analyzed the formation reasons for metallurgical defects and microstructure according to solidification characteristics in the SLM process. Combined with the corrosion mechanism of traditional casting Al-Si alloy in chlorine compounds, the corrosion mechanism of Al-Si alloy prepared by SLM was further discussed. The effects of metallurgical defects, microstructure, and heat treatment on corrosion behavior are summarized. It is found that the relative density, surface topography (roughness) of the sample, eutectic Si content, morphology, and distribution has important effects on corrosion performance. On this basis, it is pointed out that the existing technological parameters in the corrosion research of Al-Si alloy under the SLM process are not systematic, the effects of Mg, Fe, and other elements are ignored, the research methods and scope are not perfect, and the future development direction.

Abstract:Due to the restriction of strong basal texture, the formability of the thin magnesium alloy sheets at room temperature is insufficient, and its industrial application is greatly limited. Based on the mechanism of texture weakening of Mg alloy sheets, this paper highlights the feasibility and unclearly mechanism problems of shear induced twinning actviaiton to realize texture weakening of magnesium alloy sheets. Combined with the process development for activating twinning to weaken the texture of magnesium alloy sheets, the features and limations of shear contained technology in Mg alloy sheets are discussed. Given the undelying mechanism of slip and twinning actviaiton under complex stress and lacing of technology for shear-induced texture weakening of Mg alloys, An effective Schmid factor and an equal channel angular bending technology were proposed respectively, and the application of the new calculation theory and shear processing technology in Mg alloy sheets was presented.

Abstract:Hydrogenation station is a critical chain in the construction of hydrogen energy industry. The hydrogen compressor is one of the core and key monomer equipment of the hydrogenation station, and the high-density safe hydrogen compression material is the basis for the large-scale application of the hydrogen compressor in the hydrogenation station. This paper summarizes the research progress of high-density AB2 type hydrogen storage materials based on China"s resource advantages, and describes the static hydrogen compression materials with highly matched platform pressure. The hydrogen balance pressure at lower than 100℃ reaches 25, 45, and 85 MPa respectively, which corresponds to the primary, intermediate, and ultimate pressurization requirements, it can meet the application requirements of long-tube trailers, type III bottle passenger cars, and type IV bottle commercial vehicles. It has economic value and social significance to promote the engineering application of hydrogen compressor in hydrogenation station by multi-stage pressure matching of high efficiency hydrogen compressor and compatibility with existing hydrogenation system.