Abstract:To improve the hot workability of hard-deformed superalloy U720Li, the effect of holding time before deformation (5 and 10 min) on hot deformation behavior was investigated by hot compression tests. Results show that the flow stress increases with increase in strain rate, while decreases with increase in deformation temperature and holding time. Based on the obtained Arrhenius-type constitutive models, the calculated peak stresses are in good agreement with experimental values, indicating that this model can accurately predict the hot deformation behavior of U720Li alloy, and the deformation activation energies for the holding time of 5 and 10 min were calculated to be 992.006 and 850.996 kJ·mol^-1, respectively. Moreover, processing maps of U720Li alloy with these two holding durations were constructed. Through observation of deformation microstructures in each domain of the processing maps, the optimal hot working conditions for the holding time of 5 min are determined to be 1090?1110 °C/ 1?10 s^-1 and 1146?1180 °C/1?10 s^-1, and the optimal hot working conditions for the holding time of 10 min are 1080?1090 °C/1?10 s^-1 and 1153?1160 °C/1?10 s^-1, indicating that the safe processing window can be obviously enlarged by shortening the holding time reasonably. In the absence of cracking, the dynamic recrystallization (DRX) grain size increases gradually with increasing the deformation temperature and holding time, but it first decreases and then increases with the increase in strain rate. When the deformation temperature is below 1100 °C, the DRX mechanism is mainly the particle-induced continuous DRX. As the temperature is raised to above 1130 °C, the main DRX mechanism changes to discontinuous DRX.

Abstract:Low-cycle fatigue crack initiation behavior of nickel-based single crystal superalloy at 530 °C was investigated. Results show that the behavior of crack initiation is closely related to the maximum strain. When the maximum strain is 2.0%, the fatigue crack is originated at the position of persistent slip bands on the surface of specimen, which is located on the {111} slip plane. No defects are observed at the crack initiation position. When the maximum strain is lower than 1.6%, the cracks are initiated at the casting defects on sub-surface or at interior of the specimen. The casting defects are located on the {100} slip plane vertical to the axial force. The crack is initiated along the {100} slip plane and then expanded along different {111} slip planes after a short stage of expansion. As the maximum strain decreases, the position of crack initiation gradually changes from the surface to the interior. Moreover, the secondary cracks extending inward along the fracture surface appear in the crack initiation area, and there is obvious stress concentration near the secondary cracks. The dislocation density is high near the fracture surface in the crack initiation zone, where a lot of dislocations cutting into the γ' phase exist. An oxide layer of 50?100 nm is presented on the fracture surface, and Ni, Al, Cr and Co elements are mainly segregated into the oxide layer of the surface.

Abstract:Defects such as cracks and micropores exist in nickel-based superalloy during laser powder bed fusion (LPBF), hindering their application in various fields. Hot isostatic pressing (HIP) was combined with conventional heat treatment (HT) to obtain LPBF nickel-based superalloy parts with ideal properties and fewer defects. The results show that HIP process can improve the densification, while the conventional HT can eliminate the micro-defects to improve the mechanical properties. After HIP treatment, the defect volume fraction of LPBF specimens decreases. After HT, the defect content of HIP+HT specimens increases slightly. After post-treatment, the hardness shows a decreasing trend, and the tensile strength and post-break elongation of HIP+HT specimens increase to 1326 MPa and 21.3%, respectively, at room temperature.

Abstract:The solidification process of polycrystalline nickel base superalloy can effectively reduce the porosity defects. The microstructure and mechanical properties of K417G alloy were studied at four different pouring temperatures of 1360 ℃, 1380 ℃, 1400 ℃ and 1420 ℃. The results show that with the increase of pouring temperature, the porosity decreased significantly, the γ" phase size and the (γ+γ") eutectic content increased slightly, while the MC carbide is not obvious. The overall mechanical properties at 1360 ℃ are significantly lower, the tensile strength and elongation of at 900℃, 10-3s-1 are only 656 MPa and 4.2 %, respectively, and the stress rupture life at 760 ℃ / 645 MPa is only 18 h. At 1380 ℃ to 1420 ℃, the difference of tensile properties at 900 ℃, 10-3s-1 is relatively small, and the average tensile strength and elongation are 761 MPa and 5.7 %, respectively, while the stress rupture property at 760 ℃ / 645 MPa tends to decline with increasing temperature. The stress rupture life of 1380 ℃, 1400 ℃ and 1420 ℃ are 88 h, 80 h and 74 h, respectively.

Abstract:The hot deformation behavior of as-extruded GH4710 alloy prepared by vacuum induction melting(VIM)+electroslag remelting(ESR)+vacuum arc remelting(VAR) triple smelt process was studied by hot compression tests at temperatures of 1050~1150℃ and strain rates of 0.01~5 s-1. The results show that the stress-strain curves have obvious dynamic recrystallization characteristics, and the stress decreases significantly with increasing temperature and decreasing strain rate. Base on the compressive true stress vs. true strain curves, the critical strain model of dynamic recrystallization was developed. At the same time, the Arrhenius constitutive model considering the influence of strain is established to accurately describe the dependence of alloy stress, strain rate and temperature. Finally, based on the dynamic material model, the thermal processing diagram of the alloy was constructed, and combined with the microstructure analysis, the rheological instability of the alloy was clarified as the uneven microstructure , and the hot working parameters of the as-extruded-trip-smelted GH4710 alloy are suggested to be the deformation temperatures of about 1050~1100 ℃ and the strain rate of about 0.01~0.1 s-1.

Abstract:In this work, temperature range,microstructure evolution and corresponding mechnanical properties of sub-solvus and super-solvus were studied through experiment specimens; Thermal mechanical boundary conditions for simulation calculation were obtained through experiments; A method for designing heat treatment process of full-sized turbine disk components based on experiment and finite element analysis was proposed. The heat treatment process developed and implemented using this method has successfully prepared a full-sized dual-microstructure turbine disk, its microstructure and mechanical properties of different parts have been verified.

Abstract:Selective laser melting (SLM) is one of the most widely used technologies for additive manufacturing of metallic materials, and its forming accuracy still cannot meet the requirements of practical applications due to the complex thermo-physical processes in the forming process. Therefore, in order to improve the dimensional accuracy of SLM formed parts, this study proposes an integrated Response Surface Methodology (RSM) and Non-dominated Sorting Genetic Algorithm-II (NSGA-II) approach to optimize the dimensional accuracy of SLM formed GH3265 superalloy. Firstly, a model of SLM process parameters with dimensional errors in X, Y and Z directions was developed using response surface methodology, and then the model was optimized by NSGA-II for multi-objective optimization. The results show that: the model constructed by the response surface method has high prediction accuracy, and the correlation coefficients R2 are 0.9456, 0.9842, and 0.9704 in order; The optimization algorithm is able to obtain the optimal interval of the processing parameters at 1500 iterations: the laser power is 250.8-310W, the scanning speed is 1028-1400mm/s, the hatching space is 0.071-0.084 mm; The experimental validation results show the high reliability of the integrated method with ARE of 5.95%, 4.92%, and 3.97% for dimensional errors in X, Y, and Z directions, in that order.

Abstract:In this work, the macro-micro coupled finite element simulation of the FGH4113A P/M superalloy during the forging process was carried out and systematically studied. The effects of workpiece temperature, die temperature, height-diameter-ratio of the workpiece, and strain rate on the microscopic average grain size (d_ave) and its distribution uniformity of the forged turbine disks were analyzed by single factor simulation. Based on the orthogonal experimental design and response surface method, the mapping relationship between processing parameters and microstructure state variables was established. The d_ave and the standard deviation of grain size distribution were taken as the optimization targets of processing parameters to achieve microstructural control. Then the optimal processing parameters can be obtained by multi-objective optimization of the established response surface model, listed as: the workpiece temperature of 1097℃, the die temperature of 976℃, height-diameter-ratio of 2.4, and strain rate of 0.021s^_-1. The validated finite simulation under this deformation condition was carried out to verify the reliability of the optimization results. The results show that the forged turbine disk depicts the characteristics of the finer d_ave and uniform grain size distribution. This study can provide the guidelines and reference for process formulation in the production process of high-performance superalloy turbine disks.

Abstract:The high temperature fire retardancy of titanium alloy is an important factor restricting its application in aero-engine, and the laser ignition method can accurately reflect the fire retardancy of titanium alloy under local heating. Due to the limitations of laser ignition experiments on the microscopic boundary and the transient propagation mechanism of the temperature field, molecular dynamics (MD) simulations and JMatPro calculation were applied to study the temperature field of Ti-6Al and Ti-48Al alloys. The results show that a molten pool is formed on the surface of Ti-Al alloys under continuous laser irradiation, and the temperature field of the molten pool is normally distributed from the center to the edge. When the center temperature reaches the critical point of ignition, the extended combustion occurs, and the extended combustion path advances along the direction of the air flow. Compared with Ti-6Al alloy, Ti-48Al alloy has higher fire retardancy under laser ablation. This is due to the better heat transfer performance of Ti-48Al, which leads to the weakening of the heat concentration effect near the boundary of the spot temperature field. So it is necessary to increase the partial pressure of oxygen, and thus to reduce the ignition point of the alloy in order to achieve the ignition boundary condition of Ti-48Al alloy under the same laser heat source. In the aspect of extended combustion path, the boundary heat collection effect of specimens shown by MD models reveals another mechanism affecting combustion expansion path besides the direction of air flow. That is, the heat generated by the laser spot is interrupted when it is transmitted to the boundary of the specimen along the short side direction, resulting in a concentration of heat near the boundary. So the combustion path also tends to expand along this direction.

Abstract:Removal of milling marks at the root fillet of titanium alloy blade is a tough work because of the interference between the polishing tool and the workpiece. A polishing method based on elastic magnetic tool was proposed. The software ANSYS Maxwell was used to simulate the effect of different pole orientation arrangements on the magnetic field distribution. A comparison of polishing effect was made between elastic and inelastic magnetic pole carriers. The processing parameters of the elastic magnetic tool polishing for the blade root were optimized by orthogonal experiment (Taguchi) method. Results show that compared with the inelastic magnetic polishing tool, the elastic magnetic polishing tool with polyurethane as the pole carrier can effectively improve the surface quality of the polished workpiece. Under the optimal processing parameters (rotational speed=900 r/min, feeding rate=6 mm/min, machining gap=1.5 mm and abrasive size=10?14 μm), the original milling marks at the blade root are effectively removed and the average surface roughness R_a is dropped from 0.95 μm to 0.12 μm, which verifies the feasibility of the elastic magnetic polishing tool in the surface finishing of the titanium alloy blade root.

Abstract:The effect of die forging on the microstructure evolution and deformation behavior of metastable β-titanium alloy Ti55511 was investigated by electron backscatter diffraction. Before die forging, the alloy Ti55511 was subjected to multi-pass forging to optimize the microstructural heterogeneity (texture) which can cause mechanical behavior anisotropy of titanium alloys. Results show that after die forging, Ti55511 components exhibit different microstructures and textures in different local areas. No <100> fiber texture is found in all areas with different degrees of deformation. Dynamic recrystallization occurs in the area where large strain occurs during the early stage of die forging. Basket-weave microstructure forms in most local areas.

Abstract:To study the relationship between the microstructure and tensile properties of the novel metastable β titanium alloy Ti-5.5Cr-5Al-4Mo-3Nb-2Zr, a heat treatment process of ABFCA (solid solution in α+β region with subsequent furnace cooling followed by aging treatment finally) was designed, by which α phases of different sizes can be precipitated in the β matrix. The results show that the microstructure obtained by this heat treatment process is composed of primary α (α_p) phase, submicro rod-like α (α_r) phase and secondary α (α_s) phase. The alloy with multi-scale α phase has an excellent balance between strength and ductility. The elongation is about 18.3% at the ultimate tensile strength of 1125.4 MPa. The relationship between the strength of the alloy and the α phase was established. The strength of the alloy is proportional to the power of ?1/2 of the average spacing and width of α phase. The α_s phase with a smaller size and phase spacing can greatly improve the strength of the alloy by hindering dislocation slip. The transmission electron microscope analysis shows that there is a large amount of dislocation accumulation at the α/β interfaces, and many deformation twins are found in the α_p phase after tensile deformation. When the dislocation slip is hindered, twins occur at the stress concentration location, and twins can initiate some dislocations that are difficult to slip. Meanwhile, the plastic strain is distributed uniformly among the α_p, α_r, α_s phases and β matrix, thereby enhancing the ductility of the alloy.

Abstract:In order to improve the low cycle fatigue property of selective laser melting Ti-6Al-4V alloy,the effects of heat treatment on the microstructure and properties of selective laser melting Ti-6Al-4V alloy were studied by using OM,SEM,TEM,room temperature tensile and low cycle fatigue tests.The results show that the as-built microstructure is characterized by epitaxially grown β columnar grains and acicular martensite α" with a certain orientation in the grains.After annealing,α" decomposes and transforms into basket-weave α+β.After cyclic heat treatment,lath α becomes globularized,and the microstructure is composed of equiaxed α, lath α and residual β.After heat treatment,the low cycle fatigue property of the annealed state reaches more than 87% of the forgings,which reaches more than 90% of the forgings for the cylic heat treated state.

Abstract:The β-solidifying γ-TiAl alloys have higher strength and service temperatures than that of conventional γ-TiAl alloys, but currently there is still a lack of systematic and in-depth understanding of the tribological properties and wear mechanisms of this type of alloy. In this study, the dry-sliding tribological behavior of a β-solidifying γ-TiAl alloy with the chemical composition of Ti-44Al-3Mn-0.4Mo-0.4W(at.%, named as TMMW) was investigated. For comparative purposes, the tribological behavior of a common 40CrMo steel was also examined under the same conditions. It was found that there is a significant difference in the friction coefficient values between TMMW and 40CrMo, and they exhibit different patterns as the load changes. The friction coefficient of TMMW alloy first increases and then remains relatively stable, while that of 42CrMo steel increases continuously with the raise of load. The wear resistance of the TMMW alloy is superior to that of the 40CrMo steel as the load increases from 2N to 10N, and the wear rate decreases from 6.97×10-3 mm3/(N·m) to 1.88×10-4 mm3/(N·m) under the 10N load. The wear mechanisms of TMMW alloy are mainly abrasive wear, accompanied by some adhesive wear and plastic deformation caused by abrasive wear, while that of 40CrMo steel is mainly adhesive wear, accompanied by certain abrasive wear and oxidation wear. It is observed that these phases are followed by βo,α2 and γ in decreasing order of hardness. Therefore, the wear resistance of the βo phase may be superior to that of α2 and γ phases under the present conditions. Meanwhile, the presence of βo phase makes the alloy prone to plastic deformation during grinding, thereby maintaining a relatively stable friction coefficient value even under a high load of 5~10N.

Abstract:In this paper, the numerical simulation method is used to analyze the key factors affecting the metallurgical quality of the ingot back-end from the perspective of energy input ( and heat dissipation ) at the start-up stage during VAR process. The start up stage process parameters of the third smelting process are studied and verified by experiments. The results show that the surface temperature of the ingot gradually increases with the remelting time during the start-up stage, and the surface temperature reaches the highest at the height of 30 mm ingot. By controling the appropriate time to increase the arc current and accelerate the current rise rate, the surface temperature of the molten pool can be significantly increased. The arc current of Φ720mm TC17 titanium alloy increases by 4kA in the third remelting, and rapidly rises to a large current in 1min, then the holding time of the large current is extended by 6min, which can accelerat to bulid the molten pool, and the weight of the molten metal is reduced by about half. The numerical simulation and experimental results are in good agreement.

Abstract:Four kinds of Ni-xCr alloy laser cladding layers (x=20, 40, 60 and 80, wt%) were prepared by high-speed laser cladding technique, and the relationship between microstructure and wear resistance of Ni-Cr alloy laser cladding layers with different Cr contents was investigated. The results show that the four Ni-Cr alloy laser cladding layers all have reticulated dendritic structures. Among them, Ni-20Cr and Ni-40Cr are single-phase γ-(Ni, Cr) solid solutions, and their wear mechanisms are adhesive wear and abrasive wear. With the increase in Cr content, Ni-60Cr and Ni-80Cr are γ-(Ni, Cr) phase and Cr phase, as well as Cr-rich precipitates, and their wear mechanisms are adhesive wear, abrasive wear and fatigue wear. A moderate increase in Cr content can enhance the hardness and wear resistance of Ni-Cr alloy laser cladding layer. However, excessive addition of Cr results in the precipitation of Cr-rich precipitates. The hardness of these precipitates is 2430.4 MPa, which is lower than the hardness of the Ni-60Cr matrix (4024.86 MPa) and Ni-80Cr matrix (7022.68 MPa). A hardness transition zone exists between the Cr-rich precipitates and the matrix. Cracks are likely to initiate and expand in this zone, leading to deep spalling, which is not conducive to the wear-resistant properties of the laser cladding layer. Ni-80Cr has the highest hardness, but its high Cr content leads to a large number of penetrating cracks and Cr-rich precipitates on the surface, ultimately resulting in the worst wear resistance. Ni-60Cr exhibits the best wear resistance due to its high hardness and dense microstructure.

Abstract:The recent progress and future prospects for ultra-centrifugal sedimentation in solids are described, mainly involving equipment, miscible systems and compounds. Almost 90% ultracentrifugation experiments were performed on the 1st and 2nd high-temperature ultracentrifuge which is typically operated at temperatures below 500 °C under the maximum centrifugal acceleration up to 10⁶ g. The strong gravitational and temperature fields induce atomic-scale graded structure, grain growth and refinement, and voids accumulation caused by the atomic sedimentation in miscible systems. New structures, properties and substances are produced in some compounds. A new cantilever high-temperature ultracentrifuge with a test temperature up to 1200 °C is under construction at Zhejiang University, making it possible to simulate the composition, microstructure and property evolution of superalloys in the operating environment of aircraft engines.

Abstract:The formation mechanism of porous anodic oxides remains unclear till now. The classical field-assisted dissolution (FAD) theory cannot explain the relationship between the current curve and FAD reaction, and the influence of the electrode potential on anodization is rarely reported. The electrode potential theory, oxygen bubble model and the ionic current and electronic current theories were introduced to explain the growth of porous anodic oxides of three metals (Ti, Zr and Fe). Taking the anodization of Ti in aqueous solution containing 0.5wt% NH₄F as an example, the electrode potential was calculated, and the morphology of porous anodic oxides was investigated at low voltages. Results show that the growth of porous anodic oxides is determined by the ratio of the ionic current to the electronic current. During the anodization, metals are classified into two groups: one is easy to form the compact oxide layer, and the other is easy to induce oxygen releasing, thus forming oxygen bubbles. The electrolyte is also classified into two groups correspondingly: compact oxide layer-assisted electrolyte and releasing oxygen-assisted electrolyte.

Abstract:To investigate the influence of longitudinal wave rolling (LR) on the microscopic orientation of AZ31B magnesium alloy, this paper studied the heat treatment of AZ31B magnesium alloy sheet at 400 ℃/20 min and 450℃/20 min. Wave-flat and flat-flat rolling was carried out in wave-flat and flat-flat rolling, the amplitude of the corrugated roll is 4mm and the period is 0.35mm. The grain size and orientation at wave trough, wave waist and wave peak were analyzed by EBSD. The results show that both the basal texture strength and average grain size decrease after heat treatment, and the basal texture strength decreases significantly after heat treatment at 450℃/20min, but the average grain size increases. After 400℃/20min+LR, the average grain size of the plate decreases significantly, the basal texture strength at wave peaks and troughs increases compared with that at heat treated samples, and the basal texture strength of the wave lumbar is almost unchanged. However, due to the deflection of a large number of grains at wave peaks and troughs along the opposite direction of RD, the overall macro-texture strength decreases significantly. After the second pass, the surface basal texture strength at the peak and trough of 400℃/20min+LFR is significantly lower than that at the corresponding position after 400℃/20min+LR, while the wave waist strength is significantly enhanced, and the average grain size is further reduced. Compared with 400℃/20min+FFR, the texture strength of base plane is weaker than that of wave waist but stronger than that of wave peak and trough. Therefore, the overall base texture strength of LFR and FFR plates is close to each other at 400℃. The substrate texture strength of the plate after 450℃/20min+FFR is significantly lower than that after 400℃/20min+FFR, and the texture proportion of {0001}<11-20> type is lower, the average grain size increases.

Abstract:When welding aluminum-steel joints using continuous drive friction welding, the welding end face has the characteristic of rotating around the axis, and the phenomenon of uneven linear velocity along the radius direction will occur during welding, resulting in uneven friction torque and heat production. At the same time, because the dissolution rate between aluminum and steel is low, this will lead to the formation of a non-uniform aluminum-steel intermetallic compound at the joint interface, which affects the overall mechanical performance of the joint. The cold spray deposition Si interlayer can achieve good bonding with aluminum and steel, reduce the production of brittle Fe-Al intermetallic compounds, form a good performance Fe-Al-Si intermetallic compound, and change the joint bonding method. In this paper, cold spraying method was used to deposit Si powder on the end face of Q235 steel rod to form a 20um thick interlayer, and then continuous drive friction welding was used to weld with a 1060 aluminum rod. The effect of adding the Si interlayer on the friction torque, welding temperature, mechanical properties of the joint, and the morphology and properties of the interface intermetallic compound was compared and analyzed. The results showed that the addition of the Si interlayer reduced the friction coefficient of the aluminum/steel interface, reduced the friction torque and peak temperature of the welded joint, and further reduced the thickness of the intermetallic compound layer. The interface morphology was interlaced with each other, and the joint had mechanical interlocking, which increased the contact area. The intermetallic compound was mainly composed of Fe₂Al₅ and Fe₃Al replaced by Al₂Fe₂Si₃, Al_0.5Fe₃Si_0.5 with better mechanical properties. The average bending angle of the joint increased by 59°, and its toughness was significantly improved, and the uniformity of the mechanical properties was reduced.

Abstract:In this study, the effects of zirconium (Zr) and chromium (Cr) elements doping on the structure and properties of Copper (Cu) interconnection thin films were investigated. Cu, Cu (Zr), Cu (Cr), and Cu (ZrCr) interconnection films were deposited on SiO₂/Si substrates by direct current (DC) magnetron sputtering technology, and the films were annealed under vacuum condition at different temperatures from 400 ℃ to 800 ℃ for 1 hour. The surface morphologies, microstructure, and electrical properties of the films were tested and analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and four probes method. The results showed that single element doping of Zr or Cr improved the thermal stability of Cu interconnect films. The precipitation of Zr or Cr elements prevented mutual diffusion between Cu film and Si substrate, and suppressed the growth and aggregation of the grain, which made the films maintain good properties. After vacuum annealing at 700 ℃, the resistivity of the Cu(Zr) or Cu(Cr) film was less than 10 μΩ ? cm (pure Cu film was 74.70 μΩ ? cm). The co-doping of Zr and Cr elements further improved the thermal stability of Cu interconnection films while maintaining low resistivity and interconnect reliability. Especially after vacuum annealing at 800 ℃, the resistivity of Cu(ZrCr) film as low as 3.23 μΩ ? cm (pure Cu film was 103.50 μ Ω ? cm).

Abstract:The hot-rolled Zr-2.5 Nb alloy plate are heated in the high temperature region (750 ~ 850℃) of α + β two-phase region for different holding time (1 ~ 10 h), and then cooled to room temperature in different ways, the effects of different heat treatment conditions on the microstructure type, microstructure characteristic(phase content、grain size , etc.) and mechanical properties of the alloy are studied.The results show that there are two different diffusion transformation in the air-cooling and furnace-cooling process compared with water-cooling. In the air-cooling process, nano-scale lath αs phase is precipitated inside the β phase to form the bimodal microstructure. During the furnace cooling process, α_p phase directly consumes β phase and grows up to form equiaxed microstructure.With the increase of heat treatment temperature and the holding time, the volume fraction of α_p phase decreased, the continuity of β_trans phase increased and α_s phase coarsening in air-cooling process, The volume fraction of α_p phase in the equiaxed microstructure in furnace-cooling process remains basically unchanged, the average grain size increases, and the continuity of the residual β phase is enhanced. Compared with the equiaxed microstructure, the nano-α_s phase in the bimodal microstructure improves the strength of the alloy and the α_p phase ensures that the alloy has good plasticity. Reducing the heat treatment temperature and holding time can make the bimodal structure alloy have excellent combination of strength and plasticity.

Abstract:Filtered cathodic vacuum arc deposition has an ultra-high ionization rate (nearly 100%), which can effectively suppress micro defects in the coatings optimize the microstructure of the coatings, and improve the performance of the coatings. In response to the poor corrosion resistance of metal bipolar plates in hydrogen fuel cells and their tendency to dissolve in acidic environments during long-term operation of proton exchange membrane fuel cells , we used a filtered cathodic vacuum arc deposition process to deposite a series of high conductivity and strong corrosion resistant nc-TiC/a-C: H coatings on the surface of metal bipolar plates in proton exchange membrane fuel cells In this paper, the effects of deposited ion energy on the conductivity and corrosion resistance of TiC/a-C: H coatings deposited on the surface of metal bipolar plates in hydrogen fuel cells were investigated. Nc-TiC/a-C: H nanocomposite coatings with a thickness of 0.52-1.05 μm were deposited on the surfaces of SS 304 stainless steel and monocrystalline silicon at negative substrate bias voltages of -100~-500 V with acetylene gas flow rate of 30 sccm by a dual bend filtered cathodic vacuum arc deposition process. The phase structure of the coatings were analyzed using X-ray diffraction (X pert pro MPD); The cross-section and surface microstructures of the coatings were characterized by field emission scanning electron microscopy (S-4800, Hitachi); Observation of high-resolution morphology of coatings using transmission electron microscopy (FEI CM200, Philips); The chemical element composition and chemical bond structure of the coating were analyzed by X-ray photoelectron spectroscopy (ESCALAB 250Xi, Thermofish); Raman spectroscopy (LavRAM Aramis, Horiba Jobin Yvon) characterizes the chemical structure distribution of carbon elements in the coating; The electrochemical workstation (IM6ex, Zahner elektrik) evaluated the corrosion resistance of coatings under simulated hydrogen fuel cell operating conditions. The surface contact resistance tester tested the contact resistance under different pressures; The study analyzed the changes in microstructure, coating composition, phase structure, corrosion resistance, and conductivity of TiC/a-C: H coatings under different negative bias voltages. The results show that the TiC/a-C: H composite coatings deposited under negative bias voltage of -100~-500 V exhibit dense low defect characteristics. The coatings are nanocrystalline/amorphous composite structure constructed by amorphous carbon coated nc-TiC nanocrystals. As the negative bias voltage increases, the size of nanocrystals in the coating increases from 3.3 nm to 7.9 nm. The optimal nc-TiC/a-C: H coating (coating deposited at negative bias -100 V) achieved an ultra-low corrosion current density of 0.0525 μA/cm_² in a simulated hydrogen fuel cell corrosion environment (80 ℃, 0.5 mol/L H₂SO₄+2 ppm HF aqueous solution), and achieved an extremely low ICR value of 1.49 mΩ/cm_² under a compression force of 1.4 MPa. Our results show that the nc-TiC/a-C:H coatings prepared by filtered cathodic vacuum arc deposition process can effectively improve the corrosion resistance and conductivity of SS 304 stainless steel bipolar plates within a wide negative bias range, meeting the performance requirements of DOE 2025 target for hydrogen fuel cell bipolar plates. This work open up a new avenue for the large-scale preparation of high-performance metal bipolar plate coatings.

Abstract:In order to study the role of P in super ferritic stainless steel, based on the composition of S44660 steel, the mass fraction of P was adjusted, and the P content was controlled to 0.004%, 0.009%, 0.033% and 0.055%, respectively, and the effect of P content change on the microstructure and mechanical properties of cast S44660 super ferritic stainless steel was studied. The results show that: P can expand the crystallization temperature range (ΔT), reduce the grain size and increase the equiaxed crystal rate when the P content is 0.009% and 0.033%, but when the P content is 0.055%, the grain size increases and the equiaxed crystal rate decreases; The right amount of P can improve the room temperature tensile properties and hardness of the material; P has a dual effect on the impact toughness of the material, on the one hand, P has a refinement effect on the grain, thereby improving the impact absorption work of the material, on the other hand, excess P will promote its deflection at grain boundaries, which in turn affects the toughness of the material.

Abstract:The effect of Fe content on NdFe_10.25TiNb_0.25/Xwt.%α-Fe permanent magnet alloy was studied in terms of microstructure and magnetic properties. Alloy ingot is composed of α-Fe phase, 1:12 phase and Nd-rich phase, Fe content increases, α-Fe phase content increases, and 1:12 phase content decreases. The grain size of the thin strip decreases gradually with the increase of Fe content, and Fe2Ti phase is produced. The contents of Fe₂Ti phase and Nd-rich phase decrease gradually with the increase of Fe content. When X≥15, the thin strip only has 1:12 phase and a-Fe phase, and the average grain size is reduced to less than 60 nm. After nitriding, the average grain size is reduced by 15%-20%, and the magnetic properties are obviously improved. When X=15, the obtained nitrided alloy thin strip has better magnetic properties, coercivity is 1010 Oe, saturation magnetization is 130.7 emu/g, which is 25% higher than that when X=0, and saturation magnetization is 12% higher. After bonding, the maximum magnetic energy product decreases first and then increases, and reaches the highest value at X=15, reaching 4.03 MGOe, which increases by 40% compared with 2.88 MGOe at X=0. The nitriding alloy thin strip at X=15 has good structural stability at high temperature, and maintains structural stability below 360℃, which has great application potential at high temperature.

Abstract:In the study, the twinning behavior of VW53 magnesium alloy in solid solution was studied by compression experiments under different strains at room temperature, and the effects of twinning on microstructure and properties were investigated. The microstructure of VW53 magnesium alloy was observed and analyzed by optical metallography (OM), scanning electron microscopy (SEM) and electron backscattering diffraction (EBSD). Vickers microhardness was tested. The results show that {10-12} tensile twins and {11-21} tensile twins are mainly produced during the compression process of VW53 magnesium alloy at room temperature. With the increase of strain {10-12} twins will nucleate, grow, merge, and even annex the entire grain {10-12} twins will nucleate, grow, merge, and even annex the entire grain, while {11-21} twins will not expand and merge significantly. With the increase of strain, the degree of cross-cutting of twin boundary and segmentation of refined grain increase, which can effectively improve the mechanical properties of VW53 magnesium alloy.

Abstract:To prolong the life of the desulfurization slurry circulating pump impeller. In this study, WC-reinforced CoCrFeNiTi-WCx(x=0, 5, 10, 15, and 20 wt%) high–entropy alloy (HEA) coatings were fabricated on the base material 30CrMnSiA steel surface of desulfurization slurry circulating pump impeller by laser cladding. The effects of WC content on the microstructure, phase composition, element distribution, microhardness, wear resistance, and corrosion resistance of the coatings were systematically studied. It was found that the phase composition of CoCrFeNiTi HEA coating was FCC (Fe-Ni), BCC (Fe-Cr), Laves (CoTi2), and AB-type (compounds of Ti) phases. With the increase of WC content, the diffraction peak intensity of Laves phase increased, and new phases carbides (WC, TiC, Cr7C3, and Fe3C) were formed. The microstructure of CoCrFeNiTi HEA coating was mainly composed of cellular crystals at the bottom and equiaxed dendrites at the top. With the increase of WC content, the coating microstructure was mainly equiaxed dendrites, and the grain size gradually refined. The addition of WC improved the performance of the coatings, among which the CoCrFeNiTi-20% WC coating had the largest microhardness of 654.955 HV0.2 and the smallest coefficient of friction (0.664) and wear quality(1.3×102 um^3?s^(-1)?N^(-1)), the best wear resistance, and the wear mechanism was mainly slight adhesive wear and abrasive wear. In addition, with the increase of WC content, the coating showed lower corrosion rate and corrosion current. Among them, CoCrFeNiTi-20%WC coating had the smallest corrosion current and the best corrosion resistance.

Abstract:In this paper, different cuprates of Mg-9Gd-4Y-2Zn-0.5Zr (wt.%) alloys were prepared using Conventional Backward Extrusion (CBE) and Rotational Backward Extrusion (RBE) processes. The corresponding regions of the different cuprates were characterized using OM, SEM, EBSD and other testing methods. The results show that the grain refining ability of RBE is much larger than that of CBE, and the grain refining effect in the heart of RBE is the best, and the content of Dynamic Recrystallization (DRX) in the RBE-III region can be up to 98.1%, with an average grain size of 2.5 μm. The texture weakening ability of RBE is also better than that of CBE, and the texture strength of the core can be weakened to 1.258. In the RBE cups, the degree of crushing of the LPSO phase is also larger than that of CBE, and the distribution of the second phase (β-phase) is more uniform, and the precipitated β-phase can promote DRX through the mechanism of Particles Simulated Nucleation (PSN) and restrain the growth of the grains through the pinning effect. In CBE and RBE cup molding processes, the dynamic recrystallization mechanism is the same, which is Continuous Dynamic Recrystallization (CDRX) and Discontinuous Dynamic Recrystallization (DDRX).

Abstract:Hot deformation experiments were carried out on homogenized industrial electrolytic nickel using a Gleeble-3500 hot simulation tester, and the hot deformation behaviors were investigated at deformation temperatures of 900, 1000, 1100, and 1200 °C, and at strain rates of 0.01, 0.1, 1, and 10s_-1 ^{at a deformation amount of 60%}.The true stress-true strain curves were obtained based on the compression data, the effects of deformation temperature and strain rate on the mechanical properties of electrolytic nickel were analyzed, and the rheological stress eigenstructure equations were obtained, and the thermal processing diagrams were established based on the dynamic material model and the Prassd instability criterio.The results show that electrolytic nickel exhibits strong sensitivity to deformation temperature and strain rate, and the rheological stress decreases gradually with the increase of deformation temperature and the decrease of strain rate;The rheological stress reaches a peak and decreases to a certain value and then tends to stabilize, showing the characteristics of rheological softening;According to the thermal processing diagram, the better thermal processing range of electrolytic nickel is obtained as follows: deformation temperature 980~1040 °C, strain rate 3.16~10s_-1^; deformation temperature 1100 °C, strain rate 1~4 s_-1^.

Abstract:Due to the metastable structure characteristics of long-range disorder and short-range order, amorphous alloys have excellent mechanical properties, superior corrosion resistance, outstanding magnetic and prominent catalytic properties. However, amorphous alloys often have poor glass-forming ability and are difficult to form large-size bulks, so their application range is limited and they are mostly presented in the form of amorphous alloy coatings. On account of the long period and high cost of preparing amorphous alloy powders, the selection and optimization of amorphous alloy coating composition are particularly important for the performance without considering the specific coating preparation process. Therefore, this paper mainly introduces the preparing chain of amorphous alloy coatings and the similarity of different forms of amorphous alloys. At the same time, taking Al-based amorphous alloys as an example, its composition design and optimization process are reviewed systematically. The research status and development of Al-based amorphous alloy powder preparation and Al-based amorphous alloy coatings by thermal spraying are summarized as well, so as to provide a new viewpoint and an enlightenment for the design and development of new-type amorphous alloy coating composition in the future.

Abstract:Owing to excellent fracture toughness, high specific strength and stiffness, stable high- and low-temperature performance, and good corrosion resistance, advanced lightweight aluminum-lithium (Al-Li) alloy has become one of the most competitive aerospace materials. Laser welding is the most promising process for welded Al-Li alloy thin sheet, which possesses the advantages of high energy density, narrow heat-affected zone, low deformation, and fast welding speed. For Al-Li alloy structure, welded connection instead of mechanical connection can effectively improve the utilization rate of materials, reduce the components, decrease manufacturing costs, and achieve weight loss. At present, there are still some key technical problems and issues in laser welded Al-Li alloy due to its own material properties. In this paper, the research status of Al-Li alloy, laser welding, and laser welded Al-Li alloy in aerospace field are summarized by reviewing the cryogenic progress. Furthermore, the main research trends of laser welded Al-Li alloy are prospected.

Abstract:Micro and nano copper powders, mainly on nano and sub-micron scales, are critical functional materials in the modern military, shipbuilding, aerospace, and cutting-edge science and technology fields due to their high electrical and thermal conductivity, low electrochemical mobility behavior, strong solderability, low price and easy availability of raw materials. For different applications, there are different requirements for the morphology, particle size, and surface properties of copper nanopowders, while smaller particle size distribution and higher activity, as well as easy oxidization, put forward higher requirements for the preparation and storage. Liquid-phase reduction method utilizes the mechanism of redox reaction to control the particle size and morphology of copper nanopowders by regulating the process conditions. On this basis, surface modification treatment can be carried out to improve the antioxidant ability to achieve better application characteristics. In this paper, the effects of different regulating factors (reducing agent, copper source, protective agent, solvent, reaction temperature, and pH) on the morphology, particle size, and dispersion of copper nanopowders in the liquid phase reduction process are reviewed, and the three treatments of copper nanopowders for antioxidant resistance (surface capping, surface crystal reconstruction, and surface transformation treatment) are further summarized, as well as the current status of the application of copper nanopowders in the fields of chemical catalysis, medical antimicrobial, lubrication friction and electronic pastes. The current status of the application of copper nanopowders in chemical catalysis, medical antimicrobials, lubricating friction, and electronic pastes is briefly described. The application dilemma and development direction of copper nanopowders are summarized. The development prospect is outlooked, to provide a reference for the development of copper nanopowders prepared by liquid phase reduction method.