Abstract:High-entropy alloy (HEA), as a class of new alloy materials characterized by high stability, excellent specific strength and corrosion resistance, has attracted much attention in the field of aluminum matrix composites (AMCs). To study the effect on microstructure and mechanical properties of aluminum alloys, AlCoCrFeNi HEA particles reinforced ADC12 composites were fabricated by high energy ultrasonic casting process. Subsequently, the effect of HEAs addition on the microstructure and mechanical properties of ADC12 alloys was investigated. Results show that the added HEA particles are tightly bonded to the aluminum matrix. The Al₂Cu phase in the matrix is refined. Meanwhile, the tensile strength and microhardness of the alloys with the addition of HEA particles are significantly improved. The yield strength and ultimate tensile strength of as-prepared composites with 12wt% HEAs are increased by 16.9% and 21.9% compared with those of the matrix, respectively. The wear rate of the composites is also decreased due to the enhancement of microhardness under applied load of 20 N. It is mainly attributed to the load transfer strengthening, dislocation proliferation and the optimization of the microstructure.

Abstract:In this study, FeCrMnxAlCu (x = 0, 0.5, 1.0, 1.5, 2.0) high-entropy alloys were prepared using a vacuum arc melting furnace. The microstructure and chemical composition of the alloys were analyzed using equipment such as XRD, SEM, and EDS. Additionally, the corrosion resistance of the alloys in 3.5 wt.% NaCl solution was evaluated through electrochemical polarization curve tests and immersion experiments. After corrosion, the alloy surfaces were analyzed using XPS equipment.The results of microstructure characterization showed that the prepared high-entropy alloys exhibited typical dendritic and interdendritic structures and possessed a dual-phase structure of FCC and BCC . Corrosion test results indicated that the corrosion resistance of the high-entropy alloys increased initially and then decreased with an increase in Mn content. However, compared to the alloy without Mn, alloys containing Mn still exhibited better corrosion resistance. Among them, the FeCrMnAlCu high-entropy alloy demonstrated the best corrosion resistance, with a more positive corrosion potential (Ecorr = -0.417 V) and a smaller corrosion current density (Icorr = 2.120×10-6 A?cm-2). Furthermore, the FeCrMnxAlCu high-entropy alloys activated and formed discontinuous and loose corrosion product films.

Abstract:CrMoNbTiVx (x=0, 0.2, 0.4, 0.6, 0.8) refractory high entropy alloys with different addition of vanadium were prepared, and the phase constitution, microstructure characteristics and oxidation properties at elevated temperature were investigated. Results show that the as-cast CrMoNbTiVx alloys with different addition of vanadium exhibit single body-centered cubic (BCC) crystal and form dendrite structure. After oxidation at 800 ℃ for 20 h and 100 h, weight gains of CrMoNbTi alloy are 0.25 mg/cm2 and 0.50 mg/cm2, respectively, while weight gains of CrMoNbTiV0.8 alloy are 1.49 mg/cm2 and 3.36 mg/cm2, respectively. Weight gains of CrMoNbTiVx alloys are decreased with decreasing of vanadium, and the surface of oxidation layer gets smoother with decreasing of vanadium. Height differences of CrMoNbTiV0.8 and CrMoNbTi after oxidation for 100h are 24.80 μm and 3.37 μm, respectively. The oxidation products of alloys with different addition of vanadium are different, and the V2Nb6O19 needle shape oxidation products can obviously reduce the oxidation properties of CrMoNbTiVx alloys. Reducing the addition of vanadium can promote formation of compact oxidation products of TiO2, CrVNbO6 and Ti4Cr3Nb3O2, and therefore improve oxidation properties of CrMoNbTiVx alloys. V2Nb6O19, CrVNbO6 and V2O5 in oxidation layer of CrMoNbTiVx alloys are reduced with decreasing of vanadium. The oxidation layer of CrMoNbTi without addition of vanadium is consisted of compact TiO2 and Ti4Cr3Nb3O2, and therefore the oxidation resistance is significantly improved.

Abstract:High-entropy bulk metallic glasses (HE-BMGs) are novel bulk alloys combined the multi-principal component characteristics of high-entropy alloys with the long-range disordered atomic stacking characteristics of metallic glass. HE-BMGs, like conventional BMGs, are thermodynamically in a metastable state. However, the crystallization processing of HE-BMGs is different from the conventional BMGs. In this paper, non-equiatomic ZrxTiNiCuBe (x=1.5, 2, 2.5, 3, 3.5at.%) HE-BMGs are prepared by copper mold casting method, and their crystallization kinetics was studied by differential scanning calorimeter (DSC) under both non-isochronal and isothermal conditions. The non-isothermal crystallization kinetics of Zrx HE-BMGs showed a multiple-stage processing. The characteristic temperatures increased with the increase of the heating rate, showing obvious kinetics effects. The activation energy calculated by the Kissinger equation showed Eg>Ex>Ep1,indicating that the overcoming the energy barrier for the rearrangement of was more difficult than atoms nucleation process and the grain growth process of crystallization. The activation energy of crystallization event is Ep1

Abstract:The influence of pre-deformation on phase transformations, microstructures and hardening response in near β Ti alloy Ti-5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe (wt%) during aging treatment was studied. The results show that obvious α phase refinement and stronger age hardening effect can be achieved when the alloy is slightly deformed before aging treatment. Because the formation of intermediate phases (O′, ω and O′′) suppresses long-range stress induced martensitic transformation and mechanical twinning, the alloy is mainly deformed via dislocation slipping during loading. Large numbers of crystal defects are generated during pre-deformation. With increasing the pre-deformation, the number density of dislocations increases gradually. These crystal defects generated by pre-deformation may partly annihilate upon early aging, but the precipitation of α can also be promoted, resulting in refined α precipitates. In the sample with 5% pre-strain, the average thickness of α precipitates decreases by 57% after aging at 600 °C compared with the sample without pre-strain, and the number density increases from 7.0±1 laths/μm² to 22.0±3 laths/μm². Some platelet-shaped α phases form when the samples experience comparably large pre-strains such as 12% and 20%. It proves that the refined α precipitates and better hardening effect can be achieved by pre-deformation plus aging treatment for titanium alloy.

Abstract:Three-point bending fatigue experiments were conducted on a typical Zr-based bulk metallic glass (BMG) at ambient temperature to investigate the fatigue behavior under cyclic loading conditions. Results show that the stress amplitude-cycles to failure (S-N) curve of the Zr-based BMG is determined, and the fatigue endurance limit is 442 MPa (stress amplitude). To evaluate the probability-stress amplitude-cycles to failure (P-S-N) curve, an estimation method based on maximum likelihood was proposed, which relies on statistical principles to estimate the fatigue life of the material and allows for a reduction in the number of samples required, offering a cost-effective and efficient alternative to traditional testing methods. The experimental results align with the American Society for Testing and Materials (ASTM) standard, indicating the reliability and accuracy of this estimation method in evaluating the fatigue behavior of Zr-based BMG.

Abstract:Machine learning prediction models for thin wire-based metal additive manufacturing (MAM) process were proposed, aiming at the complex relationship between the process parameters and the geometric characteristics of single track of the deposition layer and surface roughness. The effects of laser power, wire feeding speed and scanning speed on the width and height of the single track and surface roughness were experimentally studied. The results show that laser power has a significant impact on the width of the single track but little effect on the height. As the wire feeding speed increases, the width and height of the single track increase, especially the height. The faster the scanning speed, the smaller the width of the single track, while the height does not change much. Then, support vector regression (SVR) and artificial neural network (ANN) regression methods were employed to set up prediction models. The SVR and ANN regression models perform well in predicting the width, with a smaller root mean square error and a higher correlation coefficient R². Compared with the ANN model, the SVR model performs better both in predicting geometric characteristics of single track and surface roughness. Multi-layer thin-walled parts were manufactured to verify the accuracy of the models.

Abstract:SiC particle (SiCp)/Al composite materials were fabricated via powder packed resistance seam welding additive manufacturing. The influence of welding speed on microstructure and mechanical properties of the specimen was investigated, elucidating the formation and fracture mechanism of single-pass multi-layer deposition. The results demonstrate that a dense internal structure of the specimen characterized by uniformly dispersed SiCp embedded within the Al matrix is formed. However, particle agglomeration and porosity defects are observed. The porosity increases with the increase in welding speed, and the microstructure of the RSAM-24 specimen has the highest density, characterized by a density of 2.706 g/cm³ and a porosity of 1.672%. The mechanical properties of the specimens decrease as the welding speed increases. Optimal mechanical properties are obtained when the welding speed is set as 24 cm/min. Specifically, the average hardness, tensile strength and elongation values are 463.736 MPa, 52.16 MPa and 2.2%, respectively. The tensile specimens predominantly exhibit fracture along the interlayer bonding interface and the interface between the Al matrix and SiC particles, and the damage mode is ductile fracture.

Abstract:The local structure and dynamics of impurities Fe, Al and Mn in beryllium were investigated on an atomic scale using ab initio molecular dynamics and statistical physics methods. The analysis of the radial distribution function centered on impurity atoms shows that the density of beryllium atoms around Fe and Mn is 8.4% and 8.6% higher than that around Al, respectively. The statistics of the measure square displacement of impurity atoms show that the diffusion coefficients of Al atoms are 114% and 133% larger than that of Fe and Mn atoms in the melt beryllium, respectively. Statistical analysis of velocity autocorrelation function of impurity atom shows that Fe and Mn atoms collide strongly with beryllium atoms in the first coordination layer, indicating that they are tightly surrounded and bound by the surrounding beryllium atoms in the central position, while the beryllium atoms around Al are loosely arranged and have weak binding forces with Al. The analysis of the activity coefficients of the impurities shows that when Fe or Mn enters the melt beryllium, it reduces the free energy of the system, whereas when Al enters, it increases the system energy. In summary, the interatomic force of BeAl is weak, so they do not form intermetallic compounds, and Al diffuses quickly in beryllium. While BeFe and BeMn have strong interatomic forces, and tend to form more BeFe and BeMn bonds to reduce the free energy of the system, so Fe and Mn diffuse slowly in beryllium. Ab initio molecular dynamics can be used to forecast the best experimental temperature for the vacuum distillation of beryllium.

Abstract:Core-shell MoSi₂@Nb powder was prepared by electrostatic layer self-assembly method. The surfactants SDS (CHSO₄Na) and CTAB (C₁₉H₄₂BrN) were used to modify the surface of the two particles to make them charged, and the Zeta potential of the suspension was tested by the Zeta potentiometer. Scanning electron microscope, transmission electron microscope and energy dispersive spectrometer were used to characterize the phase, morphology, microstructure and element distribution of synthetic materials. The results show that when the SDS concentration is 2 mmol/L, the CTAB concentration is 3mmol/L and the pH value of Nb suspension is 5, the coating effect is better after secondary cladding. NbSi₂ phase is found at the interface between Nb and MoSi₂ after calcination at 200 °C for 2 h in Ar atmosphere, indicating that Nb is highly active and reacts with Si. Core-shell structure is still retained in MoSi₂@Nb material after spark plasma sintering at 1450 °C for 2 h under uniaxial pressure of 40 MPa. However, it is found that Nb reacts strongly with MoSi₂, and most of the Nb phase is reacted. This issue needs to be addressed in subsequent studies. The fracture toughness (K_IC) of MoSi₂@Nb material is significantly improved to 5.75 MPa·m^0.5 compared with that of MoSi₂ material (3.32 MPa·m^0.5).

Abstract:The production of deep well-shaped WC-Co cemented carbide blocks via industrial powder pressing remains a challenging technical problem, primarily due to the unsuitability of the forming agent. The forming agent paraffin wax was modified through four types of modifiers, including organic high-molecular-mass resins, plasticizers, surfactants and lubricants. The qualitative screening of resin types was explored and an orthogonal experiment involving the combination of these four paraffin wax modifiers was conducted to obtain an optimized quantitative ratio of modifiers. The results reveal that the insertion of the small molecule chain of resin into the interstitial spaces of paraffin wax crystals is likely a crucial factor for improving the compatibility between the resin and paraffin wax. Through orthogonal experiments, the optimized formulation for the forming agent is determined: 100 parts of 58# paraffin wax, 15 parts of EVA-2, 4 parts of DPHP, 4 parts of oleic acid amide and 2 parts of stearic acid. This optimized formulation is applied to industrial production at one Chinese company, and qualified deep well-shaped cemented carbide products are achieved, which contain 90wt% WC and 10wt% Co.

Abstract:Explosion welding was carried out on the basis of vacuum hot melt W/CuCrZr composite plate. Metallurgical microscope, scanning electron microscope and energy dispersive X-ray spectroscope were used to observe the microscopic morphology of the bonding interface. At the same time, combined with finite element calculations, the evolution mechanism of the interface of the hot melt explosion welded W/CuCrZr composite plate was explored. The results show that the interface bonding of the hot melt explosion welded W/CuCrZr composite plate is good and there is a cross-melting zone with 3–8 μm in thickness, but cracks are developed on the W side. The numerical simulation reproduces the changes of pressure, stress, strain and internal energy at the bonding interface in the process of hot melt explosion welding. The location of the crack generated in the experiment coincides with the high stress position calculated by numerical simulation. The high pressure and high temperature near the hot melt explosion welding interface further promote the bonding of the interface.

Abstract:The sub-stable β-type TB18 titanium alloy exhibits a significant strengthening effect through solutionizing-ageing and possesses excellent potential for achieving a balanced combination of strength and toughness. As a result, it has emerged as a favoured material for manufacturing high-end aviation components. This work aimed to investigate the impact of solid solution treatment on the microstructure and mechanical properties of TB18 titanium alloy. Specifically, the effects of different solution temperatures, solution times, and slow cooling rates after solutionizing on the alloy"s microstructure and mechanical properties were illustrated. The goal is to understand the mechanism behind the interaction between solution treatment and the microstructure-mechanical properties of TB18 titanium alloy. The results indicated that following the solutionizing and aging treatment within the β single-phase region, lamellar and needle-like αs phases precipitated within the β matrix. The presence of lamellar αs phases contributed to the improvement of the toughness of the TB18 titanium alloy. Furthermore, it was observed that the fracture toughness of the TB18 titanium alloy improved with an increase in the thickness of the lamellar αsphases. Elevated solutionizing temperature or prolonged solid solution holding time can result in the coarsening of β grains in TB18 titanium alloy, leading to a decrease in material strength and plasticity. When increasing the cooling rate from 0.25 ℃/min to 1 ℃/min after solutionizing, the fine α_s phases uniformly distributed within the TB18 titanium alloy after aging treatment, and the tensile strength increased to 1343 MPa while the elongation was 5 %. By subjecting the TB18 titanium alloy to a solutionizing regime at a temperature of 870 ℃ for 2 hours, followed by air cooling, it achieved a favorable combination of strength and toughness. Further aging at 530 ℃ for 4 hours, again with air cooling, results in a tensile strength of 1315 MPa, yield strength of 1225 MPa, elongation of 8.5%, impact toughness of 29.2 J/cm2, and fracture toughness value of 88.4 MPa . m1/2.

Abstract:The hot deformation behaviour and microstructural evolution of a kind of Ni-Mo alloy (Hastelloy B3) were investigated by Gleeble-3500 thermal simulation tester in the temperature range of 950°C~1250°C, and in the strain rate range of 0.01~5 s-1. Electron backscatter diffraction (EBSD) was used to analyze the microstructure evolution. Arrhenius constitutive model of this alloy was developed on the basis of peak stresses. The microstructural evolution of Hastelloy B3 alloy during deformation was observed via an optical microscope. The critical strain of dynamic recrystallization (DRX) of Hastelloy B3 is identified based on the work hardening rate versus flow stress curves. The DRX kinetics for Hastelloy B3 alloy can be represented in the form of Avrami equation. The results show that DRX behaviour tends to occur at high temperatures and low rates of deformation parameters. According to the EBSD analysis of the grain boundary angle and dislocation density of the deformed organisation of the alloy, dislocations tend to accumulate at the original grain boundaries to form low-angle grain boundaries and then evolve into High-angle grain boundaries. Thus, the main DRX mechanism for Hastelloy B3 alloy is identified as discontinuous dynamic recrystallisation (DDRX) dominated by continuous dynamic recrystallisation (CDRX).

Abstract:A novel process named Expansion Equal Channel Angular Pressing (Exp-ECAP) which couples multiple forms of deformation such as upsetting, shearing, and extrusion into one was proposed. Ti/Al bimetallic composite rod was successfully fabricated by a single pass of Exp-ECAP process at 450 ℃ combined with post annealing heat treatment. The interface microstructure and bonding properties of Ti/Al bimetallic composite rod were investigated using SEM, EDS, XRD, EBSD and shear test. The results show that under the severe shear stress of Exp-ECAP process and the high-temperature annealing conditions, the Ti/Al bimetallic composite rod achieves good interfacial bonding quality, and a metallurgical bonding layer of approximately 1.27μm thickness is appeared through mutual diffusion of the titanium and aluminum matrix elements. New phases generated in the bonding interface layer are mainly intermetallic compound TiAl, and a small amount of inhomogeneous distributed Ti3Al (near the titanium side) and TiAl3 (near the aluminum side) are also contained. Moreover, a large number of equiaxed ultrafine grains are obtained in the Ti/Al interface bonding layer through phase transformation reactions and partial recrystallization, and the grains grow randomly without obvious preferred orientation. The shear strength of Ti/Al bimetallic composite rod is about 66.29 MPa, and shear failure mainly occurs in the TiAl phase layer, exhibiting brittle fracture characteristics.

Abstract:In this research, the effects of solution time and long-term aging on microstructure evolution and mechanical properties of a traditional nickel-based single crystal superalloy under different heat treatment conditions were studied. The obtained results demonstrate that the best heat treatment regime is “1310℃/4h (AC)+1130℃/4h (AC)+899℃/16h (AC)”. After the solution treatment, the participating of adverse phase of TCP has been avoided to obtain the preferable microstructure with small size and a high degree of cubic of strengtheningγ′phase. The difference in creep rupture life and percentage of elongation is slight under different heat treatment regimes. During the deformation, the brittle TCP phase was broken first, demonstrating that it is not the crack initiation. However, the weak carbide/matrix interface in inter-dendrites is the source of the crack.

Abstract:The state of stress concentration in a concave-convex self-expanding bracket with a structure that has a negative Poisson ratio was studied using NiTi UMAT program. It has been found that the support performance of the concave and convex bracket changes completely with the variation in the number of units (Nc) and the angle (θ) between the inclined bar and the horizontal direction of the support ring. The change in the axial distance of the support is primarily influenced by the parameters h/l and θ, and it exhibits a negative correlation. The dilation rate of a concave-convex stent in a diseased femoral artery can reach 90.3%, which is generally higher than that of existing self-dilation medical stents. The concave-convex stent can achieve uniform expansion when working in the femoral artery, thereby avoiding the issue of a narrow middle and wide ends. The Goodman fatigue curve and fatigue factor were evaluated, meeting the national requirements for medical stents.

Abstract:12Cr12Mo stainless steel is an important material for static blade ring of steam turbine. The heterogeneous microstructure and properties of welded joints of thick 12Cr12Mo stainless steel are often occurred. In this paper, 12Cr12Mo butt joint of thick plate was prepared by electronic welding. The microstructure and mechanical properties of the joint were studied. The results show that the inhomogeneity of microstructure and mechanical properties along with thickness are found. The fusion zone is mainly quenched martensite, the heat affected zone is the mixed microstructure of martensite and tempered sortensite, and the microstructure of base material is tempered sortensite. The grain size of the fusion zone decreases with the increase of the penetration depth while the grain size of the fusion zone decreases with the increase of the penetration depth. The grain size of the heat affected zone at different thickness positions is the same. However, the grain sizes of the heat affected zone are smaller than that of the fusion zone and the base metal. The tensile strength and hardness increase gradually as the penetration depth increase while the elongation decreases continuously. The fracture location of the layered tensile specimens appears in the fusion zone, and the fracture dimple becomes smaller and shallower with the increase of penetration depth. The difference of microstructure evolution caused by heat input and cooling rate along with thickness of the weld is the main reason for the inhomogeneity of microstructure and mechanical properties.

Abstract:The main problem of SLM additive preparation of thermoelectric material Cu₂Se is that Se element is easy to burn under the action of high energy density heat source of laser. At present, there is no commercially available Cu₂Se powder for 3d printing, and no scholars have used SLM to prepare medium temperature thermoelectric material Cu₂Se. In this study, laser-induced high-temperature self-propagating reaction + ball milling method was used to prepare Cu₂Se powder with good fluidity for SLM additive manufacturing for the first time. Under the optimized process parameters, Cu₂Se thermoelectric material additive parts with smooth surface, good mechanical properties and excellent thermoelectric properties were obtained. The grain growth of Cu₂Se bulks prepared by SLM has obvious anisotropy in the horizontal and vertical directions. The grains in the vertical section are mainly slender columnar crystals with a length of about hundreds of microns growing along the deposition direction, and the horizontal section is an equiaxed crystal with a size of about tens of microns. There are nano-scale micropore defects at the grain boundaries on the horizontal section. The ZT values measured in the vertical and horizontal directions at 673 K are 0.74 and 0.33, respectively. The maximum compressive strength along the vertical and horizontal directions is 125.08 MPa and 42.69 MPa, respectively. The average microhardness of the additive is 62.5 HV. The thermoelectric properties of Cu₂Se prepared in this study are comparable to those of Cu₂Se prepared by traditional methods in the vertical direction, and the mechanical properties are good, indicating that it is feasible to prepare Cu₂Se thermoelectric materials by SLM. This study opens up a new way for the preparation of medium temperature thermoelectric materials.

Abstract:Low-density niobium alloys have characteristics such as low density, high melting point, and good corrosion resistance, and are widely used in aerospace, nuclear engineering, high-temperature structures, and other fields. To study the effect of different deformation processes on the microstructure and properties of low-density niobium alloys, rolling and extrusion deformations were carried out on the low-density niobium alloys in this study, and the effects were investigated through OM, SEM observation, mechanical property testing, and other methods. The results indicate that when rolling deformation is used, the deformation is large, the microstructure is uniform, the second phase is dispersed, the strength is high, and the plasticity is good, with an elongation after fracture of up to 37 %. When extrusion deformation is used, stress concentration can easily lead to cracking, and deformation is not easy to penetrate. The microstructure is not uniform, and the strength is high, but the plasticity is only 15 %, the impact of deformed microstructure on mechanical properties has been analyzed, which can guide the processing of niobium alloys.

Abstract:Al-Mg-Zn alloy has moderate strength, excellent corrosion resistance and an age-hardening response through precipitating T-Mg32(Al, Zn)49 phases and it is expected to be used as structural material in aerospace and various types of hulls. Sc is one of the most effective microalloying elements in aluminum alloys. The primary Al3Sc phase formed during solidification acts as a nucleating particle to effectively refine the as-cast microstructure of the alloy, and the secondary Al3Sc phase formed during homogenization significantly inhibits recrystallization. Al3Sc particles have excellent thermal stability and can effectively improve the weldability of alloys. Due to the high price of Sc, the method of Sc and Zr compound addition is widely used in industry. The Al3(Sc, Zr) phase formed by adding Sc and Zr at the same time has similar physical and chemical properties to Al3Sc and can greatly reduce the cost while retaining the strengthening effect. In this paper, four Al-Mg-Zn alloys with different Sc/Zr ratios were studied, and the influence of Sc/Zr ratio on the mechanical properties of Al-Mg-Zn alloys in aged state was studied. Transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the effect of Sc and Zr microalloying on the precipitation of T-Mg32(Al, Zn)49 phase, and the contribution of different strengthening mechanisms to yield strength was quantitatively calculated. The results showed that a large amount of T phase is dispersed in Al-Mg-Zn alloy with small size, and different Sc/Zr ratio has no significant effect on T phase. The main strengthening mechanism of Al-Mg-Zn alloy was the precipitation strengthening of T phase, which contributes 283~297MPa to the strength. The contribution of solid solution strengthening to the strength of the alloy was 33~40MPa. The mechanical properties of the alloy were improved by the addition of Sc and Zr, and the properties of the alloy were increased by about 30MPa through grain boundary strengthening. The tensile strength of 0.13Sc-0.14Zr alloys and 0.17Sc-0.1Zr alloys was 551~552MPa and the yield strength was 461~463MPa.

Abstract:TiN coatings are widely used in metal bipolar plate modification due to good corrosion resistance and electrical conductivity.The TiN deposition process is susceptible to formation non-metallic vacancies due to the preparation conditions, affecting the coating properties. Therefore, in this paper, the electronic structures of TiNx systems containing different amounts of nonmetallic vacancies are calculated using the first principle method, and a study of the effect of nonmetallic vacancies on the crystal structure, energy band structure, density of states, relative concentration of free electrons, and charge spreading of each TiNx system is carried out. The analytical results show that with the formation of nonmetallic vacancies, the stability of each TiNx system gradually decreases and the nonmetallic vacancy formation energy gradually increases. The relative concentration of free electrons of each TiNx system is calculated to be in the following order: TiN0.25＞TiN＞TiN0.5＞TiN0.75.The electrical conductivity of the TiNx system is mainly affected by the combination of three factors: the metallization of the 3d orbital state of the Ti atoms, the reduction of the contribution of the N atoms to the 2p orbitals, and the decrease in the volume of the crystal cell due to the deletion of the N atoms.

Abstract:The present article focuses on the change of mechanical properties of oxide fiber reinforced ceramic matrix composites with temperature from room temperature (RT) to 1400 ℃. Alumina fiber reinforced silica composite (Al₂O_3f /SiO₂) and quartz fiber reinforced silica composite (SiO_2f/SiO₂) were prepared by sol-gel process with alumina fiber and quartz fiber as reinforcement respectively. The tensile strength and compressive strength of the composites at room temperature ~1400 ℃ were investigated, and the microstructure and crystal phase structure of the composites were characterized by electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the mechanical properties of alumina fiber reinforced SiO₂ composites are much higher than those of quartz fiber reinforced SiO₂ composites under RT~1000 ℃. However, while the temperature was raised to 1200^℃, the mechanical properties decrease sharply, and strong bonding occurs between silica particles and fibers. As the temperature was further increased to 1300~1400 ℃, mullite and α-quartzite phases were formed. The mechanical properties of composites are sharply decreased due to brittle fracture under the action of stress. The brittle fracture caused by the disappearance of interfaces is the main mechanism of high temperature failure of composites.

Abstract:Numerical simulation method was used to study material flow law of magnesium alloy variable curvature panel formed by progressive bending technology (PBT). The experimental is completed, and several types of magnesium alloy variable curvature panel are obtained. The curvature radius of panel range is from 205.7 mm to 72.56 mm. The suitable process parameters for progressive bending of magnesium alloy variable curvature panel are determined. The results show that curvature radius of panel is related to amount of press height. As press height increases, radius of curvature of panel decreases. With increase of press height, absolute deviation between simulation results and experimental results decreases, and relative error increases. With increase of curvature radius of panel, absolute error increases and relative error decreases. For internal grid panel of magnesium alloy, and maximum relative error is 5.22%. For outer grid panel of magnesium alloy, and maximum relative error is 5.51%. The generatrix straightness method was used to evaluate the degree of concave defects on surface of magnesium alloy panel. With the curvature radius of panel decreased, the generatrix straightness deviation increased, and the generatrix straightness coefficient increased. When curvature radius of panel is 72.56 mm, the maximum deviation of generatrix straightness is 0.083 mm, and the corresponding maximum value of generatrix straightness coefficient is 0.237%.

Abstract:The TiO₂ coatings were prepared by micro-arc oxidation coupled with a high and low-frequency pulse. The low-voltage and high-frequency pulse promoted the electrodeposition of nano-particles and effectively improved the anticorrosion performance of the coatings. The number of micropores on the surface of the coatings decreased, the porosity of the coatings decreased from 2.72% to 0.896%, the thickness increased to 23.76μm, and the Ti content increased from 30.02% to 42.48%. The high-frequency pulse was applied to the nanoparticle suspension, and the content of Nb increased to 10.62%. The coatings comprised anatase, rutile, Al₂TiO₅, Nb₂O₅, and Nb-Ti compounds. The Nb peak value increases significantly under the high-frequency pulse. The corrosion current density decreased from 7.995×10_-7 ^A/cm₂ ^{to 3.}249×10_-7 ^A/cm₂^.The high-frequency pulse accelerated the deposition of nano-particles into the coatings, and the low-voltage and high-frequency electromagnetic field accelerated the deposition of particles into the positive electrode electrophoresis, thus enhancing the performance of the coatings.

Abstract:The Bi2Sr2CaCu2Ox(Bi-2212) multifilament round wires were fabricated by the powder-in-tube technique. Open ends and closed ends wires were heat-treated in 1atm flowing O2. Several samples at various points of the partial-melt processing were prepared. The influences of the gas content inside wires on the diameters, microstructures and the phase compositions were systematically investigated. The results showed that large amount of bubbles were residual during the partial melting process of Bi-2212 filaments in pure O2 atmosphere. Porosity agglonerated large bubbles on melting of the Bi-2212 powders. These bubbles were partially retained inside the final wires. High internal gas pressure would cause the molten phase towards the Ag layer to fill the defects, resulting the filament-to-filament bonding and the worse texture.

Abstract:Since the magnesium and magnesium alloys have good load transmission, exceptional biosafety, unique biodegradability, etc, they have significant application possibilities in the field of medical implantation. Furthermore, excellent corrosion resistance is one of the paramount prerequisites for magnesium and magnesium alloys as medical implants. However, magnesium alloys exhibit poor corrosion resistance, leading to rapid degradation in physiological environments due to high corrosion rates. This premature degradation, before completing their intended service life, compromises their structural integrity, severely limiting their clinical applications. Surface modification treatment of magnesium alloy to improve corrosion resistance has become a research hotspot of medical magnesium alloy. This study primarily focused on the research advancements in the corrosion resistance enhancement of medical magnesium alloys. The developmental trajectory and characteristics of medical magnesium alloys were outlined. Additionally, surface modification techniques such as micro-arc oxidation and ion implantation, as well as microstructure and properties of magnesium alloy surfaces after surface modification were reviewed. The formation mechanisms of various coatings were discussed, and their structures and properties were analyzed. The impact of coatings on the degradation rate of magnesium alloys was elucidated, aiming to identify key issues and potential solutions in the implementation and application of surface modification for medical magnesium alloys. Recommendations were also provided, presenting the research directions for surface modification of medical magnesium alloys.

Abstract:With the further improvement of material fatigue life extension and processing of parts with complex shapes, laser shock processing has encountered more and more obstacles in practical applications and it is particularly urgent to improve and optimize the specific processing methods in laser shock treatments. Using the stress effect produced by pulsed lasers to process materials in various fields still has broad prospects. Given the specific needs of laser shock in different industrial applications, several processing improvement methods which get rid of the equipment dependence on high-performance laser units were proposed. The non-laser parameters referred to include adjustable indicators such as the absorption layer, constraint layer, and defocusing state between laser and material. The selected material, thickness, and other related attributes of the absorption layer and the constraint layer directly affect the intensity of laser-induced shock waves, while changes in defocusing amount lead to differences in physical or chemical effects on the material surface. The process setting range for the above non-laser indicators is wide and easy to control, and reflects good adaptability of irregular components. The development of new technologies for equal (unequal)-strength and high-strength surface strengthening based on changes in these indicators, as well as new green packaging technologies such as laser marking, are introduced in detail. The new ideas behind these new methods are expected to inspire researchers to further explore the application potential of green lasers.

Abstract:Owing to their multiple outstanding properties including low density, high thermal conductivity, good ablation and thermal-shock resistances, Cf/C composites have great potentials in various high-end structural application fields such as hypersonic aircraft, aircraft braking systems and rocket nozzles, etc. However, the high oxidation sensitivity of Cf/C composite generally causes some severe problems including serious chemical ablation and significant degradation of service performances. To address these problems, the preparation of ZrB2-SiC-based ultra-high temperature ceramics (UHTCs) coatings on the surface of Cf/C composites is the most effective solution so far. Consequently, this paper reviewed the recent progress in the topics of compositional/microstructural modifications of ZrB2-SiC-based coatings, their oxidation resistances and enhancement mechanisms. Moreover, the principles as well as advantages/disadvantages of popular preparation methods of ZrB2-SiC-based ceramic coatings were systematically summarized, respectively. Based on this, the prospects of the promising directions of research and the technique development of this field were forecasted.

Abstract:Accident-tolerant fuel can significantly enhance the capability of light-water nuclear reactors to withstand core melting under LOCA, is a revolutionary development of nuclear fuel technology and nuclear power safety. Cr-coating deposited on the current Zr-based nuclear fuel cladding demonstrates good adhesion, excellent corrosion resistance in high-temperature and high pressure water, and high-temperature oxidation resistance. Therefore, Cr-coated zirconium alloys emerge as the most promising ATF solution for practical engineering application in nearest future. The present paper reviews the research progress on oxidation behavior of Cr-coated zirconium alloy in high-temperature steam environment. The oxidation kinetics of the Cr coating, the effect of microstructure on the anti-oxidation performance of the Cr coating, the failure mechanism of the Cr coating after long-term oxidation and the Cr-Zr interdiffusion behavior are discussed. Additionally, strategies for enhancing the anti-oxidation performance of the Cr coating and suppressing Cr-Zr interdiffusion are summarized, and future development directions are prospected, aiming to provide references for the optimization design and engineering application of Cr-coated Zr-based nuclear fuel cladding.