Abstract:Three kinds of γ′ phases with different morphologies and sizes were obtained by changing the primary aging temperature (1150, 1180 and 1200 °C) in the heat treatment process. Then, the samples with different γ′ morphologies were tested under condition of intermediate temperature and high stress (760 °C/800 MPa). The results show that the size of γ′ phase plays an important role in the stress rupture property. Increasing the size of γ′ phase appropriately can promote the uniform deformation of the alloy, thus improving the stress rupture life of the alloy.

Abstract:Morphotropic phase boundary (MPB) is very important for enhancing piezoelectric properties of piezoceramics. In general, the MPB of BiFeO₃-BaTiO₃ system ceramics locates near the composition of 0.70BiFeO₃-0.30BaTiO₃. However, higher content of BaTiO₃ will lead to lower Curie temperature of BiFeO₃-BaTiO₃ ceramics. Therefore, constructing an MPB for BiFeO₃-BaTiO₃ ceramics with lower BaTiO₃ content is a reasonable strategy to obtain both the good piezoelectric property and high Curie temperature. 0.74BiFe_1-xGa_xO₃-0.26BaTiO₃ (x=0~0.05) lead-free piezoceramics were fabricated by traditional sintering methods, and effect of Ga content on the structures and electrical performances was investigated. Results show that a composition-driven phase transition from rhombohedral (R) to pseudocubic (pC) is identified as x increases from 0 to 0.05. The ceramics show symmetries of R at x≤0.01 and pC at 0.04≤x≤0.05, and the MPB with R-pC coexistence is detected in the composition range of 0.02≤x≤0.03. The Curie temperature of the piezoceramics decreases slightly owing to increased tolerance factor t with the increment of Ga content. In particular, the high Curie temperature ~515 °C and improved piezoelectric property of piezoelectric coefficient d₃₃ of ~127 pC/N are obtained in the ceramics near MPB.

Abstract:Amorphous Ti-9.5Cu-8Ni-8Nb-7Al-2.5Zr-1.8Hf (wt%) filler alloy was employed to vacuum braze Ti₅₀Al₅₀ (at%) alloy at the brazing temperatures ranging from 1140 to 1220 °C for 30 min. The effect of brazing temperature on the microstructure and shear strength of the brazed joints was investigated. Results show that all the brazed joints are mainly divided into three reaction layers regardless of the brazing temperature, and both of α₂-Ti₃Al and Ti₂Cu(Ni) phases exist in each reaction layer, but their size and distribution change significantly with brazing temperature, especially the Ti₂Cu(Ni) phase in isothermal solidification layer Ⅱ. The continuous α₂-Ti₃Al layer Ⅰ is stable below 1200 °C but breaks and loses its barrier effect above 1200 °C. It is notable that the α₂-Ti₃Al precipitated in the brazed seam can act as a nucleation inhibitor and refine the crystal grain. Shear test results show that the average shear strength of Ti₅₀Al₅₀ brazed joints first increases and then decreases with brazing temperature and the maximum shear strength of 184 MPa is obtained at 1180 °C. α₂-Ti₃Al mainly occupies the fracture surface with cleavage characteristics.

Abstract:To understand the deformation mechanism and microstructure evolution of TC16 titanium alloy during cold heading, cold compression tests were conducted using a Gleeble 3800 thermo-mechanical simulator. The effects of strains (0.2, 0.4, 0.6, 0.8 and 1.0) and strain rates (0.1, 1.0 and 10.0 s^-1) on the deformation behavior and microstructure evolution of the alloys were investigated. Results show that larger true strain and higher strain rate are prone to cause local grain coarsening and adiabatic shear bands within the material. True strain should be selected in the range from 0.2 to 0.6. Uniform structure and fine grains that are suitable for cold forming can be achieved at a strain rate of 1.0 s^-1. The deformation softening observed during cold deformation is caused mainly by adiabatic temperature rise and local grain coarsening at larger true strains and higher strain rates.

Abstract:Al_xCuFeNiCoCr high-entropy alloys were prepared by powder metallurgy method. The effect of Al content on the properties and microstructure of the alloys was studied, and the change in the grain properties during the preparation of the alloys was discussed. The results show that the alloy grains are refined during the milling process, and the grain size of the alloy increases with the increase of Al content. New grains are generated in the alloy during the sintering process, and an intermetallic compound containing Al is initially formed by absorbing a certain amount of heat. A phase with simple crystal structure is obtained after heating at 1200 °C for 2 h, which confirms the formation of high-entropy alloy. Based on the obtained energy spectrum, the alloy composition is uniform, and the alloying degree is high. However, with the increase in Al content, a small number of high-contrast areas with high Al content emerge. The alloys exhibit a good high-temperature oxidation resistance and electrochemical corrosion resistance. The oxidation resistance at high temperature increases with the increase of Al content. The self-corrosion voltage is -235 mV when x=1.0. With the increase in Al content, the hardness also increases. The best overall properties of the alloy are achieved when x=1.0.

Abstract:The hot deformation behavior of Cu-bearing 304L stainless steel was studied by performing hot compression on Gleeble-3800 thermo mechanical simulator in the temperatures of 900~1150 ℃ and strain rates of 0.01~20 s^-1, and the processing maps were established by stress-strain curves. Results show that the better processing temperature range is narrowed from 200 °C to 75 °C with the increase of copper content in the alloy (0wt%Cu-304L, 2.42wt%Cu-304L, 3.60wt%Cu-304L). The alloy microstructure characteri-zation reveals that the main causes of instability are local flow instability, shear zone, void and cracking. At the same time, it is found that the plastic deformation can be converted into heat in a short time, leading to the local temperature rise of the deformed materials, which makes the copper segregation area with relatively low melting point easy to form holes and to become the source of cracking, and then reduces the hot workability.

Abstract:A method was developed for preparing silver/multi-wall carbon nanotubes (Ag/MWCNTs) composites after iodination of the MWCNTs. The MWCNTs were functionalized by ball milling in the presence of iodine, and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and thermogravimetric analysis (TG). The results show that the silver-nanoparticles (Ag-NPs) adhere better to the surface of the MWCNTs after iodination, which can improve the connection between the Ag-NPs and the MWCNTs. The hydroxyl (-OH) group stretching vibration is clearly enhanced, which activates the surface of the MWCNTs and increases the number of Ag⁺ nucleation sites on the surface of the MWCNTs. At temperatures lower than 260 °C, the mass loss of Ag/MWCNTs composite is less than that of MWCNTs. Finally, three silver-epoxy resin pastes were separately prepared, and the paste prepared using the Ag/MWCNTs composites has the lowest resistivity and the highest thermal conductivity.

Abstract:Copper matrix composites reinforced with graphene nanoplatelets (GNPs) were prepared by low-energy ball milling and spark plasma sintering (SPS). The effects of graphene content on the microstructure and the properties of such composites were studied. The results show that as the graphene content increases, the mechanical properties of the composite first improve and then gradually deteriorate. When the graphene content is 0.25wt%, the ultimate compressive strength of the composite is 409 MPa and its electrical conductivity is as high as 90% International Annealed Copper Standard (IACS). Further addition of graphene in the composite produces a larger cluster of GNPs within the copper matrix and results in the deterioration of the aforementioned properties. However, as the graphene content continues to increase, the wear rate of the composite declines steadily. The uniform distribution of graphene amongst the copper particles enables the transformation of the external applied load from the copper matrix to the chromium particles and graphene, effectively blocking internal dislocation motion, and thus improving the strength and other tribological properties of the composites.

Abstract:Ni coating was prepared on the surface of Al₂O₃ by chemical deposition method. Ni coated Al₂O₃ particles (Al₂O₃p@Ni) was used as particle-reinforcement for iron matrix. The Al₂O₃p@Ni/Fe composites were prepared by SPS. Results show that by optimizing electroless plating process, the surface of Al₂O₃ is uniformly covered by Ni. Ni coating presents a typical cauliflower structure with the size of 1~4 μm, which is deposited in pits and holes on the surface of Al₂O₃ and then gradually extends outwardly. The thickness of Ni layer is up to 100.55 μm, and Ni coating is closely bounded to Al₂O₃. In the process of sintering, Ni coatings not only improve the wettability between Al₂O₃ and iron matrix, but also promote the diffusion and reaction of Al₂O₃ and iron matrix at the interface. Finally, Al₂O₃/NiAl₂O₄/(Al_0.8Cr_0.2)₂O₃/NiFe₂O₄/Ni/iron matrix interface layer is formed by mechanical bonding, interdiffusion and chemical reactions, which can improve interface bonding strength greatly. The wear tests of Al₂O₃p@Ni/Fe composites and Al₂O₃p/Fe composites were carried out. Compared with Al₂O₃p/Fe composites, the wear mass loss of Al₂O₃p@Ni/Fe composites is decreased by 50%, and the friction coefficient is decreased by 12.5%. The wear resistance of Al₂O₃p@Ni/Fe composites is greatly improved.

Abstract:The flow behavior of a medium entropy alloy with a nominal composition of Fe_0.25Cr_0.25Ni_0.25Mn_0.25 was analyzed by isothermal compression performed in the temperature range of 900~1050 °C and strain rate range of 1~0.001 s^-1. The results show that the hot deformation is predominated by dynamic recrystallization, so that the flow curves exhibit a single-peak shape as those of other alloys with low stacking-fault energy. Particular emphasis was paid to develop a simple constitutive model which can describe the entire deformation history. For this purpose, the work-hardening behavior as well as the dynamic softening regime were analyzed. With the aid of Kocks-Mecking plots, it is found that the hardening rate of the present alloy is linearly decreased with stress in the work-hardening stage, and hence the stress-strain behavior can be described by the conventional dislocation density-based model. Meanwhile, the softening regime, which is caused by dynamic recrystallization, can be modelled by the classic JMAK equation. Besides, the model is further modified to reduce the number of parameters and simplify the regression analysis. The proposed semi-physical based model can not only accurately predict the stress-strain behavior to strain levels outside the experimental strain range, but can also be promoted to other alloys with low stacking-fault energy.

Abstract:Composite structure with amorphous layer and crystalline substrate is important for nano-machining. In order to study the influence of amorphous layer structure on the nano-cutting mechanism and mechanical properties of single crystal germanium (Ge), molecular dynamics (MD) simulations were carried out on the nano-cutting process of amorphous-crystalline layered structure (A-C model) with different amorphous layer thicknesses. Cutting force fluctuation, stress status, subsurface damage characteristics and material removal, which are the key issues in nano-machining were analyzed. The result shows that as the thickness of amorphous germanium (A-Ge) increases, the cutting force and stress decrease, and the cutting temperature increases. The plasticity of the material is enhanced as the thickness of A-Ge increases, which is due to the softening of A-Ge when the cutting temperature rises. When the thickness of A-Ge is the same as the cutting depth, the material has lower subsurface damage and higher material removal rate, so it has excellent mechanical properties.

Abstract:Given the lack of thermodynamic data on Li_1+xM_1-xO₂ materials, LiAlO₂ was split in accordance with the principle of the group contribution method. Mathematical models for estimating the ?G^θ_f,298, ?H^θ_f,298, and C_p of LiAlO₂ were proposed on the basis of thermodynamic principles. The group contribution method was used to estimate the ?G^θ_f,298, and ?H^θ_f,298 of 56 solid inorganic compounds and the C_p,298 of 54 solid inorganic compounds to test the reliability and applicability of the model. The group contribution method was used to estimate the mathematical model of solid inorganic compounds. Results show that the experimental data selected by fitting group parameters are accurate and reliable, and the group division method is appropriate. Mathematical models for estimating the ?G^θ_f,298, ?H^θ_f,298, and C_p of three types of Li_1+xM_1-xO₂ materials were constructed on the basis of the satisfactory results. The ?G^θ_f,298, ?H^θ_f,298, and C_p,298 of the 63 common Li_1+xM_1-xO₂ materials were also estimated.

Abstract:Metastable α?-phase U-Nb shape memory alloys exhibit outstanding corrosion resistance and mechanical property, in which multi-level twinning martensite is the typical microstructure. Phase-field method was used to simulate the formation process of α? thermoelastic martensite. Results show that driven by minimization of elastic strain energy, various self-accommodated martensite clusters are obtained, and several self-accommodation modes are found. Comparing the simulated results with experimental results, it is suggested that the asymmetric deformation gradient tensor and interface compatibility notably influence the variant pair and twinning plane. In addition, the texture development upon deformation was predicted based on the variant rearrangement process.

Abstract:To solve the problems of processing Inconel 617 alloy at high temperatures, the hot deformation behavior of forged Inconel 617 at high temperature was studied. A Gleeble-3500 instrument was used to analyze the thermoplastic behavior in the temperature range of 900~1200 °C and strain rate range of 0.001~10 s^-1. The constitutive equation in this temperature and strain rate range was deduced, and the thermal processing map was obtained. The dynamic recrystallization after compression was studied by electron backscatter diffraction. The location of the instability zone was determined. Results show that under the conditions of thermal deformation, dynamic recrystallization occurs, and fine grains are obtained. The optimal temperature range for Inconel 617 thermal processing is identified as 1075~1175 °C, and this temperature range is in the stable zone for the material.

Abstract:Due to the excellent biodegradability, biocompatibility and mechanical properties of magnesium alloy, the possibility of magnesium alloy as intravascular stent was studied. Firstly, based on our previous work, a compact fluoride conversion coating was prepared on the surface of AZ31B magnesium alloy. The hemolytic tests, blood coagulation tests and platelet adhesion tests were carried out to evaluate the hemocompatibility of the fluoride treated AZ31B magnesium alloy. The surface energy was measured to analyze the mechanism of the hemocompatibility of the samples. Results show that the fluoride treated AZ31B magnesium alloy has potential application value in intravascular stenting.

Abstract:The effects of extrusion temperature on dynamic recrystallization, texture and tensile properties of biodegradable Mg-2Zn-1Y-0.5Zr alloys were studied, and the corrosion mechanisms of as-extruded alloys in SBF solution were elaborated. The results show that the extruded alloy at 440 ℃ (E440) has a bimodal structure with coarse unrecrystallized (unDRXed) grains and fine recrystallized (DRXed) grains. The deformed grains from unDRXed region make the greatest contribution to the texture strength. The extruded alloy at 460 ℃ (E460) has uniform DRXed grains, and its excellent tensile properties reveal a dominance of fine grain strengthening. Simultaneously, the uniform DRXed grains are good for the weakening of texture strength. The E460 sample exhibits the best corrosion resistance with a corrosion rate of 0.669 ± 0.017 mm·a^-1.

Abstract:Microstructure analysis, EDS analysis, mass loss experiment and electrochemical test were used to detect the corrosion performance of WE43 alloy after solution and solution-aging treatment. The result shows that heat treatment changes the second phase in the matrix to obtain different corrosion properties. The corrosion rate of solution-aging samples immersed for 0 and 6 h is higher than that of solution samples, and lower than that of solution sample immersed for 24 h. It is also found that during the corrosion process of WE43 alloy, the corrosion rate decreases first and then increases. Mathematical model was used to explain the relationship between the second phase and corrosion performance, and the reason why the corrosion rate changes with time.

Abstract:Equal channel angular pressing (ECAP) is an effective and efficient severe plastic deformation (SPD) technique used to produce ultrafine grained (UFG) materials with improved properties. This review highlights a comprehensive summary of the mechanical property of various Mg-Li alloys subjected to ECAP processing, the effect of the processing parameters as well as the mechanism involved. This research can also provide directions and supports for the mechanical property improvement of Mg-Li alloys in the future.

Abstract:ZrO2-doped (Bi0.5Na0.5)0.91Pr0.02Ba0.07TiO3 lead-free ferroelectric ceramics were synthesized by solid-phase sintering method. The influence of Zr substitution on the phase structure, microstructure, energy storage behavior and dielectric behavior of (Bi0.5Na0.5)0.91Pr0.02Ba0.07TiO3 were systematically investigated. All samples formed a single perovskite phase with fine and uniform crystal grains. The doping of Zr effectively increased the breakdown field strength. When the doping amount is 0.03 mol, the maximum effective energy storage density of the ceramic reaches 1.38 J/cm3 at a field strength of 138 kV/cm, and the energy storage efficiency reaches 52.44%. At the same time, it exhibits stable high-temperature ferroelectric characteristics. A large dielectric constant of 1150 is obtained and remains stable.

Abstract:Because of the special heterojunction structure, SnO2-NiO has been used as gas sensing material and supercapacitor electrode addition material.But it has been studied less in electrocatalytic oxidation of industrial wastewater. The effect of SnO2-NiO-IrO2 electrode on the electrocatalytic methyl orange solution was studied by adding active oxide IrO2. SnO2-NiO-IrO2/Ti electrodes were prepared by thermal decomposition method. SEM, XRD, XPS, BET, CV, EIS, LSV, TOC, UV, and strongthen life were used to test the microstructure and the catalytic performance.It’s shown that IrO2 changeg the concentration of oxygen vacancies in the SnO2 lattice, resulting in forming the impurity defects in the crystal structure, refining the grains, and then increasing the specific surface area and conductivity of the composite oxide coatings. The diffusion rate of the active matter to the inner layer was increased too. Thus, the catalytic activity and stability of the electrode were optimized.The electrode with IrO2 content of 23.1% had the best degradation effect on methyl orange, which had a maximum degradation rate of 93% and a maximum service life of 678 hs.

Abstract:The second phase particles in aluminum alloy are produced in the casting process and have a significant effect on the physical and chemical properties of the material. At present, the commonly used quantitative characterization methods of the second phase have the problems of too much manual work and time consumption. In this paper, a fast extraction and quantitative statistical characterization method of the second phase in large-scale aluminum alloy based on deep learning is proposed. This method can achieve multi angle refined quantitative statistics by fast and intelligent extraction of the second phase features in the image. The results show that the image processing time of this method is the same as that of software batch processing, which is only 0.4s/sheet, but the image segmentation accuracy is improved from 42.74% to 91.12%. In order to meet the requirements of fine characterization, 110000 full field sem images of 7B05 aluminum alloy, including four types, were segmented and extracted. The new characterization parameters of the second phase, such as aspect ratio, shortest distance, surface distribution and line distribution, were calculated. The results of line distribution show that the full field multi angle method used in this paper is better than the traditional statistical results of randomly selected field of view. This method shows that the error of statistical representation is smaller and the feature information is more comprehensive. The quantitative statistical results show that the average area of the second phase is the smallest at the nearest upper and lower surface of the cast rolled 7b05-t4 aluminum alloy section with a thickness of 6 mm, and there is a trough value near the thickness of 3 mm; The average area of the second phase is 1.99 μ m2, 1.84 μ m2 and 2.18 μ m2, the average aspect ratio is 1.89, 1.95 and 1.84, and the number of the second phase is 33574, 33207 and 42035, respectively. The above results show that the rapid extraction and quantitative statistical characterization method of the second phase in aluminum alloy based on deep learning can carry out multi angle data analysis and mining, and provide the basis for the study of microstructure and properties.

Abstract:Sm-Co based alloys are best candidate materials in high-temperature applications, such as national defense industry, aerospace engineering, and microwave communications, etc. The addition of appropriate alloying elements may help to improve the performance of Sm-Co alloys, thereby meeting the acquirements in the above-mentioned fields. The first-principles calculation method is suitable for screening candidate doping elements and it can provide a theoretical basis for the design of Sm-Co alloys. In this work, a first-principles calculation model of SmCo5 alloy with main group doping elements is established. Taking Al, Ga, In, and Sn as examples, the influence of intrinsic characteristics of doping elements, doping concentration and temperature on the phase stability and magnetic properties of SmCo5 alloy are studied. The bonding interactions between the doping elements and Co atoms are revealed based on the electronic structures. Combined with the analysis of electronic structures, such as bond population, charge density, differential charge density and density of states, the microscopic mechanism of the effect of different elements on the stability of SmCo5 was clarified. The calculation indicates that the physical and chemical properties of doped main group elements and the size of the vacant space in the doping systems are two main factors that influence the occupation site of the doping elements. Al and Ga are beneficial to the stability of SmCo5 system. Moreover, the occupation sites probability of Al varies insignificantly with temperature, which indicates that the SmCo5 system doped with Al may be applied in applications with a wide temperature range. Regarding to the magnetic properties, the SmCo5 system doped with In has a relatively high magnetic moment, although the total magnetic moment of the SmCo5 system always decreases with the addition of the studied main group elements. The main reason is that In has a relatively large atomic radius, which may induce lattice distortion and result in the increase of magnetic moment between Co atoms. Therefore, the decrease of the total magnetic moment of the doping system can be compensated. Based on the above calculations, Al and In are selected as the candidate elements which are beneficial to the stability and magnetic properties of SmCo5 based alloys. Moreover, the optimal doping concentration ranges of Al and In are predicted.

Abstract:Thermal barrier coatings are one of the most important materials in gas turbine to protect the high temperature components. The SmTaO4 ceramics have excellent high-temperature phase stability and mechanical properties and show great potential for use as next-generation thermal barrier coating materials. In this paper, the TiO2-SmTaO4 ceramics have been prepared via high temperature solid-state reaction. The results show that that TiO2 doped SmTaO4 did not change the crystal structure of the SmTaO4 itself and its phase structure was still a single monoclinic phase. The TiO2-SmTaO4 ceramics doped with 2% mol have a second phase, which is inferred to as Sm0.33TaO7. The TiO2-SmTaO4 ceramics have a lower thermal conductivity (1.42 W?m?1?K?1 at 900 ℃) than 7–8-YSZ and SmTaO4（1.59W?m-1?K-1，900℃）, with a minimum nearly 30% lower than YSZ. The highest thermal expansion coefficient is detected in 2% TiO2-doped SmTaO4 ceramics (10.8×10-6K-1), which is much higher than that of YSZ (10.0×10-6K-1). Compared with pure SmTaO4, TiO2 doping increased the thermal expansion coefficient of TiO2-SmTaO4 ceramics. This indicates that TiO2-SmTaO4 ceramics have the potential to be employed as thermal barrier coatings.

Abstract:Bismuth stannate (Bi2Sn2O7) synthesized by chemical coprecipitation was used as modified component. The effect of Bi2Sn2O7 doping on the wetting angle of Ag/SnO2 interface was studied by the sessile drop method. The Ag/SnO2(x)-Bi2Sn2O7(y) electrical contact materials were prepared by mechanical alloying technique combined with molding sintering process. The phase structure, electrical and mechanical properties of the materials were characterized by SEM, XRD, OCA, resistance tester, hardness tester and densimeter. The results showed that Bi2Sn2O7 doping can significantly improve the interfacial wettability between Ag and SnO2, and the minimum wetting angle is 82 ° when the mass ratio of Bi2Sn2O7 to SnO2 was 2:10. The lower resistivity of Ag/SnO2(x)-Bi2Sn2O7(y) electrical contact materials were achieved with a decreased wetting angle between Ag and SnO2. Especially when the content of Bi2Sn2O7 is 2wt.%, the resistivity reaches the lowest value2.28 (μΩ·cm), and the relative density (96.96%)and hardness(90.0 HV0.3) reach the maximum value.

Abstract:Three-dimensional meso-structural finite element models of TiBw/Cu, (TiB2p + TiBw)/Cu and TiB2p /Cu composites were built. Based on the Abaqus uncoupled thermoelectric analysis theory, the quantitative relationship between the microstructure characteristic parameters and the macroscopic electrical conductivity of the composites was revealed by simulation method.The results show that the volume fraction of TiB2 particles is the main factor affecting the electrical conductivity, and the electrical conductivity gradually decreases with the increase of the volume fraction,while the particle size has no significant effect on the electrical conductivity. The volume fraction and the orientation Angle of TiB whisker are the main factors affecting the electrical conductivity. When the whisker orientation Angle is parallel to the current direction, the electrical conductivity is the best, and when the whisker orientation Angle is perpendicular to the current direction, the electrical conductivity is the worst. In the (TiB2p+TiBw)/Cu composites,the volume fraction of the whisker and the whisker orientation Angle are the main factors affecting the electrical conductivity, and the type of the whisker has little effect on the conductivity.This paper provides a new idea and method for the electrical conductivity prediction of (TiB2p + TiBw)/Cu composites, and provides a basis for the hybrid design of the composite with particles and whiskers.

Abstract:_{: Due to the poor deformability of Mg alloys, the microstructure obtained by the conventional hot-rolling processes generally contained coarse grains. This could lead to inferior mechanical properties. To enhance the toughness, surface mechanical attrition treatment (SMAT) was utilized in this work to produce gradient structure in a hot-rolled (HR) Mg-Gd-Y alloy. The underlying mechanisms for toughening were disclosed. After peak-ageing (PA), the strength of the HR alloy increased obviously while the ductility decreased sharply. This was because the precipitates blocked dislocations and generated stress concentration, resulting in cleavage fracture as a brittle rupture. The HR-SMAT-PA sample showed comparable strength with the HR-PA sample, while the ductility was enhanced, exhibiting better toughness. The ultrafine grains in the near-surface layer led to uniform deformation and ductile fracture. Thus, the cleavage fracture in the deep layer could not go through the entire cross-section of the sample. As a result, the premature failure was inhibited and the ductility was increased}.

Abstract:W-3.5Nb alloy was prepared by selective electron beam melting technology (SEBM). The influence of linear energy density on the formation of pore defects was studied. Different types of pore defects were analyzed. The results show that: With the increase of the linear energy density, the defect content decreased, the volume of defects was the lowest (0.01%) at the linear energy density of 1.44 J/mm. When the linear energy density continued to increase, the volume and quantity of defects increased. There were four types of pore defects in SEBM W-3.5Nb alloy: lack of fusion defects, micron dendritic pores, micron spherical pores and nano spherical pores. At the low linear energy density, the large defect (>5000 μm_³) which was the lack of fusion caused by insufficient energy input and insufficient melting depth was dominant; when the energy density increased, the defect size was smaller (< 2000 μm_³), among which the low sphericity defects were the dendrites defect caused by the dynamic flow of molten pool, and the high sphericity defects were micro and nano spherical pores caused by the shrinkage of the melting pool and micro shrinkage between dendrites during solidification.

Abstract:The effect of laser peening on vibration fatigue performance of electrochemically hydrogenated 316L austenitic stainless steel was studied. The residual stress, microhardness and microstructure of laser peened specimens with different power densities followed by hydrogen charging were tested and analyzed, and the vibration fatigue life and fracture morphology of the corresponding specimens were compared and studied. The results show that laser peening induces an increase in dislocation density on the surface of material and effectively refine the grains, which inhibits the invasion of the hydrogen atom. At the same time, the complex grain boundary and high density dislocation multiplication structure hinder the aggregation and diffusion of hydrogen atoms, reduce the degree of the martensitic transformation of 316L austenitic stainless steel, which helps to suppress micro-crack initiation. On the other hand, the high residual compressive stress induced by laser peening not only inhibits hydrogen penetration, but also increases the fatigue crack growth threshold and slows down the crack growth rate. Vibration fatigue test results show that the fatigue life of laser peened specimens with different power densities followed by hydrogen charging has been significantly improved, and the maximum amplitude can be up to 79.36%. The fracture morphology analysis further proves that laser peening can effectively reduce the fatigue crack growth rate of hydrogen-charged specimens, increase the fracture toughness of the material, and then improve the vibration fatigue properties of materials.

Abstract:Stem from high specific strength, low density, low elastic modulus, excellent mechanical properties, high temperature resistance and corrosion resistance, titanium alloy has become a promising candidate material to solve the high casing damage rate under heavy oil thermal recovery conditions. However, the study of titanium alloy slotted screens under thermal recovery conditions is still lacking. In this paper, the physical and chemical properties, axial thermal deformation, axial thermal stress, the change law of screen and slot shape of titanium alloy screen pipe under typical working conditions of heavy oil thermal recovery in Liaohe Oilfield were systematically investigated by finite element assistance (FEA) calculation and Full-size test, the results showed that titanium alloy screen had good strength and toughness properties under thermal recovery condition, the thermal stress of titanium alloy screen under 350 °C thermal recovery temperature was only 19.3 % and 20.4 % of that of CMS screen and composite screen. After seven cycles of thermal recovery temperature, the axial elongation of titanium alloy screen at 350 °C was only 58.7 % – 60.4 % of that of steel screen, under the large bending degree of 20° / 30 m and the high temperature of 350 °C, the titanium alloy screen had excellent deformation resistance, and the maximum ovality was only 4.13 %, the parallel slit remains intact and the sand control ability was better than that of the steel screen of the same specification. Based on this study, it can be considered that the titanium alloy screen and casing can effectively reduce the axial thermal stress and elongation of the thermal recovery pipe string in the thermal recovery condition, and had high temperature resistance and fatigue resistance, titanium alloy screen had good deformation resistance under the extreme bending condition of thermal recovery, which is one of the effective methods and development directions to solve the problem of high casing damage rate in heavy oil thermal recovery field in China, this study also provided technical reference for the design, use and management of titanium alloy screen.

Abstract:As a new high-temperature material design with higher strength and lighter weight, researchers have paid attention to the SiCf reinforced nickel matrix composite. However, the severe interface reaction hinders the further development of this material. Since a long-time preparation could reduce the severe reaction, hence, in present work the Ni/SiCf composite system is prepared by spark plasma sintering which is characterized by shorter preparation time. SEM and EDS are used to analyze the interface morphology and element distribution. The results show that Ni reacts with SiCf and Ni3Si and carbon particles are formed. The reaction zone further reacts with Ni to generate Ni(Si,C) solid solution. There exist strong thermodynamic and kinetic conditions between Ni/SiCf system and Ni/Ni3Si system, which induce violent interface reaction. Raising sintering temperature and prolonging holding time could prompt Ni3Si and carbon particles to further dissolve. The dissolution process will shrink the reaction zone and expand the solid solution zone.

Abstract:Nano-TiC reinforced AlcoCrFeNi high entropy alloy coating was prepared on 304 stainless steel surface by laser cladding technique. The microstructure, phase structure and element distribution of the coating were systematically studied by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The hardness distribution, wear characteristics and corrosion resistance of the coatings were characterized by microhardness tester, friction and wear tester, ultra-depth of field microscope and electrochemical workstation. The results show that the quasi-spherical nano-TiC and rod-like micron TiC precipitates are uniformly distributed in the coated BCC (B2) matrix. The hardness of Alcocrfeni high entropy alloy coating increased by 15% after the addition of TiC phase compared with that without the addition of TiC. The surface wear rate and surface roughness per unit area (SA) decreased by 42% and 18%, respectively, compared with that of AlcoCrFeNi high entropy alloy coating. The dispersion strengthening effect of TiC reinforcing phase in the coating was the main reason for the improvement of coating hardness and wear resistance. The self-corrosion current of Alcocrfeni high entropy alloy coating with TiC is about one order of magnitude lower than that without TiC coating. The dense passivation film formed on the surface of the coating by TiC reinforcing phase is the main reason for its good corrosion resistance.

Abstract:A series of high-speed Impact tests,with 7.5 mm projectiles,were performed on new-type Ti-Mo-V based α+β dual-phase titanium alloy with equiaxed grains.The penetration damage was analyzed by optical microscope and scanning electron microscope.The results show that there is no obvious zoning phenomenon in the macro crater whether the plates are perforated or not. At the impact point,the change of the projectile penetration angle results in the change of the penetration shape. The protective property of the plates will decrease when the projectile penetrates obliquely, and the asymmetric shape crater can be seen by side-cutting along the central axis of the crater. There are two kinds of adiabatic shear bands which are distributed in the center and two sides of the impact crater: (1) semi-arc distribution in the center of the impact crater; (2) on both sides of the crater center, the distribution is about 45° along the direction of penetration. The maximum shear stress is in the direction of 45°, and the adiabatic shear band is easy to expand and extend along the direction of the maximum shear stress.The connection and growth of the micro-hole and the micro-crack are the main reason for the failure of the protection.

Abstract:In order to prevent and control electromagnetic pollution, it is urgent to develop effective electromagnetic shielding materials. In this paper, The Fe_73.2Si_16.2B_6.6Nb₃Cu₁ alloy was designed and amorphous ribbons were prepared. After high-energy ball milling, amorphous alloy powder was obtained. The effects of ball-milling time on soft magnetic properties, microstructure, morphology and electromagnetic wave absorption properties of alloy powders were studied. The results showed that the crystalline phases α- (Fe, Si) was formed after ball milling, which improved the soft magnetic properties. The maximum saturation magnetization was 137.94emu/g. The morphology of the amorphous alloy powder was elliptical and the minimum average particle size is 8.42μm. The alloys showed excellent electromagnetic absorption performance. The loss mechanism of electromagnetic waves was mainly magnetic loss. After ball-milling for 50h, the amorphous alloy powder had the best electromagnetic absorption performance. The minimum reflection loss was -42.26dB at the frequency of 4.57GHz, and the maximum effective absorption bandwidth (<-10dB) was up to 5.78GHz when the thickness of the absorber was 2.5mm.

Abstract:In order to investigate the effects of lamellar thickness and γ/α2 interface on the deformation and mechanical properties of dual-phase TiAl alloy during nano-indentation process, molecular dynamics method was used to simulate the nano-indentation process of γ and α2 phases with diamond indentation perpendicular to γ/α2 interface for five kinds of dual-phase TiAl alloy models. The results show that the hardness of the material increase with the decrease of the lamellar thickness. When the lamellar thickness decreases to 7nm, the hardness of the material reach the maximum value. However, when the lamellar thickness further decreases, the hardness of the material decrease. The elastic modulus of the material changes with the thickness of lamellar and is proportional to the hardness. In addition, the deformation behavior of γ phase in the nano-indentation process is mainly the stacking fault of {111} plane, and the γ/α2 interface can effectively hinder the dislocation movement. The deformation behavior of α2 phase is mainly the stacking fault of (0001) base plane. The Schockley partial dislocation motion formed on the base plane lead to the phase transformation on the material surface. The prismatic plane slip system is activated.

Abstract:In this paper, lotus-type porous Mg-Mn and Mg-Mn-Zn alloys were fabricated successfully by metal-gas eutectic unidirectional solidification (the Gasar method). Effects of elements on the mechanical properties and corrosion properties of porous Mg alloy was studied. The results showed that the addition of 1 wt.% Mn could increase the compressive strength of pure Mg from 64 MPa (porosity~36%) to 74 MPa (porosity~37%), and the compressive strength of the porous material could be increased to 115 MPa (porosity~37%) by adding 1 wt.% Zn to Mg- wt.% Mn alloy. Addition of Zn can effectively improve the corrosion resistance of Gasar Mg-Mn alloy. Conical solute enrichment area near the pore bottom of Gasar Mg-1wt.%Mn-1wt.%Zn alloy showed good corrosion resistance. Pore structure can affect the corrosion resistance of Gasar materials. When the average pore diameter was 1026 μ m, the corrosion of the pore wall in Mg-1wt.%Mn alloy was more serious. While the average pore diameter was decreased to 306 μ m, the pore of the samples would be blocked by corrosion products, and the corrosion of pore walls was less.

Abstract:Abstract: The near-stoichiometric ratio SiC fiber and polycarbosilane were used as fiber reinforced phase and matrix precursor to prepare SiC/SiC composites by polymer precursor impregnation cracking process through polymer precursor infiltration and pyrolysis (PIP) method. The morphology of SiC fiber and SiC/SiC composite was analyzed by SEM technology, and the mechanical properties of the material were tested by three-point bending method. Result showed that the near-stoichiometric ratio SiC fiber had the characteristics of high strength and high modulus,?and the pyrolytic carbon interfacial layer occupied important influence on mechanical properties and fracture behavior of SiC/SiC composites. The mechanical properties of SiC/SiC composites first increased and then decreased with the increase of the thickness of the pyrolytic carbon interfacial layer. For the polymer precursor infiltration and pyrolysis method based on the intrinsic characteristics of the near-stoichiometric ratio SiC fiber, the suitable interface layer thickness of the SiC/SiC composite is 0.10μm-0.15μm.

Abstract:The microstructure, the thermal deformation behavior and the microstructure evolution during the thermal deformation of a novel Ni-based Powder Metallurgy(PM) superalloy under different initial conditions（1150℃ Hot Isostatic Pressing，1150℃ Hot Isostatic Pressing+1150℃ Hot Extrusion，1150℃ Hot Isostatic Pressing+1130℃ Hot Extrusion）were investigated by means of the Scanning Electron Microscope(SEM), the Optical Microscope(OM), the Thermal Compression Testing Machine, and the Electron Backscatter Diffractive (EBSD). The results show that the PPBs and the coarse γ′still remains in the HIP samples and the PPBs disappeared in the 1130℃ and 1150℃ hot Extrusion samples, which are equiaxed Grains. During the thermal deformation process, the Work Hardening-Recrystallization Softening phenomenon was observed in these three samples under different conditions. The thermal deformation activation energies of peak stress are 861kJ/mol, 858kJ /mol and 489kJ/mol, respectively. The deformation temperature had an obvious effect on the deformation microstructure of the samples. The abnormal grain growth appeared in both the hot isostatic pressing and hot isostatic pressing+1130℃ hot extruded samples under the condition of 1150℃-0.001/s. Compared with the other two conditions, the sample of 1150℃ Hot Isostatic Pressing+1130℃ Hot Extrusion showed the best deformation behavior.

Abstract:For continuous carbon fiber reinforced aluminum matrix composites (CF/Al composites), the thermal shrinkage behavior and thermal residual stress distribution in the vacuum pressure infiltration preparation process were studied by combining the numerical simulation with the thermal performance test. The results show that the transverse thermal shrinkage strain of the composite is much larger than that the axial thermal shrinkage strain, and it is transversely isotropic. The radom fiber arrangement RVE model can accurately predict the axial and transverse thermal shrinkage behavior curves of the composite. In the prepared composite, the fiber and matrix alloy are in compressive stress state and tensile stress state, respectively. The transverse residual stresses of the matrix alloy and fiber is less than their axial residual stresses, and both show the transverse isotropic. The matrix alloy will appear different degrees of damage under the action of axial residual tensile stress. Especially, the high residual stress at the small fiber spacing will cause local interfacial failure, which is not conducive to the bearing capacity of the composite. It is an important technical approach to reduce the local segregation of fibers in order to improve the mechanical properties of the composite.

Abstract:Cu/SSZ-13 catalysts with the nearly same content of copper species were prepared by ion exchange technology with copper acetate, copper chloride, copper nitrate and copper sulfate as precursors, respectively. The effects of copper source on NH₃ selective catalytic reduction (NH₃-SCR) were probed detailedly. The physicochemical properties of the catalysts were investigated by XRD, ICP, N₂ absorption-desorption, SEM, H₂-TPR, XPS and NH₃-TPD. The results of activity test display that the performance of Cu/SSZ-13 zeolite for ammonia selective catalytic reduction at low temperature is significantly different. The light off temperature T50 (the temperature when conversion efficiency ≥ 50 %) follows the order of Cu (copper acetate) / SSZ-13 < Cu (copper chloride) / SSZ-13 < Cu (copper sulfate) / SSZ-13 < Cu (copper nitrate) / SSZ-13. The characterization results manifest that the distribution and quantity of copper species and the acidity of zeolite catalysts are affected by copper source. The Cu/SSZ-13 catalyst prepared with copper acetate as precursor possesses the largest number of isolated Cu^₂₊ and strong L acid sites, which are conducive to the low-temperature NH₃-SCR reaction.

Abstract:In order to take full advantage of Incoloy800H alloy, the creep behavior of Incoloy800H alloy tubes at temperatures ranging from 600℃to 1050℃ was investigated based on creep character-temperature parameter models. The reliability equations of steady creep rate, rupture time and initiation time of tertiary creep were obtained by multiple linear regression. The effective relationships among allowable stress, service temperature and reliability were established. The results demonstrate that the creep reliability equations make the prediction for creep behavior of Incoloy800H alloy tubes more accurately. The long-term creep data are completely located in the 0.997 confidence band of predicted results by corresponding reliability equations. In comparison with recommended allowable stresses by ASME, the creep reliability equations can provide more reasonable evaluated results.

Abstract:Tungsten films have excellent characteristics such as high melting point, high conductivity，stable chemical properties, and strong radiation resistance, and are widely used in microelectronics, nuclear energy engineering and other fields. Since the structure and performance of the film have a strong dependence on the deposition parameters, it is essential to control the process parameters of the deposition process to obtain a tungsten film with excellent properties. This paper studies the effects of sputtering power and sputtering pressure on the deposition rate, microstructure, and phase structure of tungsten films. Using DC magnetron sputtering technology, a tungsten film is prepared on a Si substrate at room temperature. Atomic force microscope, XRD, four-probe resistance measurement, profiler, etc. were used to characterize the structure and electrical properties of the film. The results show that the deposition rate of the film is affected by the sputtering power and the gas pressure. The deposition rate increases linearly with the increase of the power, and first increases to a peak and then decreases with the increase of the gas pressure. The resistivity and surface roughness of the film depend on the sputtering pressure, and increase with the increase of the sputtering pressure. The increase in the resistivity of the film may be caused by the increase in the surface roughness. Under constant sputtering power, the formation of α-W mainly depends on the sputtering gas pressure. All β-W phases are formed under high pressure, but for the sputtering power is large enough, under higher pressure, the formation of some α-W phases will also be observed. The formation of the specific phase structure (α-W/β-W) in the tungsten film is not only dependent on the deposition pressure, but also related to the sputtering power, which may be related to the energy of the atoms incident on the substrate.

Abstract:In previous superheavy force field gradient materials on the basis of optimizing the process parameters of preparation, we prepared TiB₂-TiC-Fe component a continuous gradient variation of TiB2/42CrMo composite materials.By XRD, SEM observation of the gradient layer of ceramic/metal alloy phase boundary between a continuous gradient variation.Through hardness testing, the hardness of the ceramic to metal parts are diminishing gradient change, the elastic modulus variation of intermediate gradient layer form closer to trigonometric functions.In the related parameters based on the study of the extraction, laminar strength analytical model is established.After adopting ANSYS finite element simulation method, the simulation analysis of the displacement in applying external loading conditions, a layered model of normal stress and shear stress distribution, the gradient materials is obtained at the bottom of the maximum tensile stress of the metal on the type of material damage, the main reasons for the failure and the actual material corresponding to the three point bending experiment phenomenon.Finally, research materials long thick ratio on the stress distribution, it is concluded that in a certain scale, gradient material mechanical properties not increases with the increase of the ratio of long thick linear infinite, for engineering materials design has certain guiding significance to the next.

Abstract:A new kind of equiatomic AlNiZrCuY high entropy amorphous composite material (denoted as HEACM) ribbons was prepared by vacuum arc melting technology and rapid quenching system. The microstructure and phase stability of HEACM were characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and differential scanning calorimetry (DSC), and the hardness was measured by Vickers microhardness test methods. All tests were performed in simulated seawater (3.5 wt.% NaCl corrosive solution) at room temperature by CHI660E electrochemical workstation. The corrosion resistance of Al20Ni20Zr20Cu20Y20 was investigated by potentiodynamic polarization curve (Tafel) and electrochemical impedance spectroscopy (EIS). The results show that Al20Ni20Zr20Cu20Y20 HEACM is composed of amorphous phase and intermetallic compounds. The actual density measured by Archimedes method is about 5.792 g/cm3. The Vickers microhardness of this composite material is 461 HV0.1. Its breakdown potential (Eb) is -0.215 V and maintaining passivity current density (ipass) is 29.44 μA/cm2. The equiatomic AlNiZrCuY high entropy amorphous composite material has broad application prospect in the field of corrosion resistance and wear resistance on metal surface.

Abstract:Different concentrations of La2NiO4+δ (LNO) nanoparticles were decorated on La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) surface through one-step infiltration. Scanning electron microscope showed that LNO nanoparticles were distributed uniformly on LSCF surface, with a size range 50–250 nm. Electrochemical test revealed that compared with the bare LSCF, polarization resistance of LSCF cathode decorated with LNO particles reduced by 41%~50%, and its stability was improved, where its polarization resistance has increased by 50.42% after annealing at 750℃ for about 125 h while that of bare one increased by 76.89%. Evidenced by X-ray powder diffraction, La2SrOx phase appeared in LNO-LSCF after 100 h annealing, which was one of the possible reasons for enhanced stability. X-ray photoelectron spectroscopy showed that after annealing for 100 h, the surface Sr content decreased by 3.66% compared to that before annealing, whereas that of the bare one increased by 27.95%, indicating that LNO modification can effectively suppress Sr surface segregation of LSCF.

Abstract:It was investigated that the effect of Ni on the electrochemical corrosion behavior of Zr-Cu-Al amorphous alloys in 3.5wt.% NaCl neutral solution by potentiometric polarization and electrochemical impedance spectroscopy.The results show that the Zr₅₅Cu₃₀Ni₅Al₁₀ amorphous alloy containing Ni element has better corrosion resistance than Zr₅₅Cu₃₅Al₁₀ amorphous alloy in NaCl solution.The Zr-Cu-Al amorphous alloys generated pitting corrosion in NaCl solution, and the circular corrosion pit is filled with foam-like holes.Compared with the elemental distribution of Zr-Cu-Al amorphous alloys before and after corrosion, the alloying elements were selectively dissolved because of Cl^_-.Amorphous alloys containing Ni elements form a dense passivation film, which inhibits the selective dissolution of metal elements, thereby improving corrosion resistance. The results can provide reference for the composition design and application of Cl^_- resistant amorphous alloys.

Abstract:The lifetime of traditional thermal barrier coating with one layer bond coating is limited by the insufficient oxidation resistance. A thermal barrier coating with a double-layer bond coating was prepared by HVOF and APS. Vacuum heat treatment was carried out prior to the top coating. Oxidation resistance of the thermal barrier coating was researched. The results show that the content of β-(Co, Ni)Al phase is raised from 13.91% to 27.78% by the 1050℃×3h vacuum heat treatment, and the distribution is more homogeneous. The roughness of HVOF sprayed bond coating is decreased by vacuum heat treatment. The roughness of vacuum heat treated bond coating is raised from Ra 7.2μm to Ra 10.4μm by the introduction of APS layer, and the bonding strength of thermal barrier coating is up to 39.4MPa. The wight gain rate of thermal barrier coating is 0.1719g/m_².h after oxidized at 1050℃ for 200h, which is consistent with antioxidant level of aviation industry standard. The bond coating sprayed by APS is sacrificed to oxidize prior to HVOF layer. The stress tolerance of bond coating/top coating interface is improved, and the lifetime will be extended.

Abstract:Mg-based hydrogen storage materials have attracted much attention because of their low price, high hydrogen storage capacity and fine safety. However, its higher temperature of hydrogen absorption and desorption and slow kinetic properties limit its further research and application in hydrogen storage. Recent research mainly focus on exploring different modification methods to obtain low cost, large quantities, small particles and high stability of MgH2 nanopowders, and some progress has been made; However, it is still a great challenge to obtain magnesium-based alloy hydrogen storage materials which have ideal thermodynamic properties and practical application value at ambient temperature. In this review, we summarized recent progress in the research on magnesium-based alloy hydrogen storage materials, and further categorized reported methods on changing thermodynamic and kinetic properties of magnesium-based alloy, to provide better empirical and theoretical support for obtaining magnesium-based hydrogen storage materials with high capacity and excellent kinetic & thermodynamic properties in hydrogen adsorption & desorption.

Abstract:With unique design concept, high entropy alloy coating has excellent mechanical properties and physical and chemical properties superior to traditional alloy coating, and has strong application potential in many fields, which has attracted extensive attention of researchers. In this paper, the recent research progress of main preparation technology of high entropy alloy coating was reviewed, including laser cladding technology, thermal spraying technology, cold spraying technology, magnetron sputtering technology, electrochemical deposition technology etc.. The advantages and disadvantages of each preparation technology and the performance characteristics of the high entropy alloy coating were analyzed in detail, and the problems in the research process of high entropy alloy coating at present were put forward, which provided reference and guidance for the follow-up research, application and development of high entropy alloy coating.

Abstract:High entropy alloys, a new type of hot-research alloy, have received extensive attention in the material industry. Taking equal atomic ratio CoCrFeNiMn as the prototype, numerous fcc-structure high-entropy alloys with excellent mechanical properties have been reported. Recently eutectic high-entropy alloys have attracted more and more attention of scientific researchers due to their excellent casting properties and comprehensive mechanical properties. In this paper, we selecte the CoCrFeNiNbx alloy system, focus on precipitation-strengthened high-entropy alloys and eutectic high-entropy alloys, and summarize the current research progress from the aspects of composition design, microstructure evolution, mechanical properties and strengthening and toughening mechanism. Finally, we analyze the shortcomings of current research and point out the direction of future research.

Abstract:Ultra-high temperature ceramics have the unique advantages of being able to maintain physical and chemical stability in ultra-high temperature environments (>2000°C) and in reactive atmospheres (e.g., atomic oxygen, plasma environments), and thus have great potential for applications in thermal protection systems for high-speed aircraft and hot-end components for rocket engines. In recent years, Ta_xHf_1-xC (x=0~1) ultra-high temperature ceramics have become a new hot topic in the field of ultra-high temperature ceramics due to their ultra-high melting points and excellent resistance to oxidation and ablation. Based on the available published reports, this paper presents a comprehensive review of the research progress on the composition, preparation, intrinsic properties and high-temperature oxidative ablation properties of Ta_xHf_1-xC (x=0~1) ultra-high-temperature ceramics in abroad and domestic. The relevant progresses in the preparation and properties of the material systems are highlighted, the shortcomings of the existing studies are summarized, and the future research trends are prospected, aiming to provide useful guidance for the theoretical, experimental and application studies of Ta_xHf_1-xC (x=0~1) ultra-high-temperature ceramics.