The traditional catalytic alloy materials are mostly precious metals, while the high-entropy alloy catalytic materials reported in recent years are mostly cheap metal materials, and some of them have better catalytic properties than the traditional precious metals. This paper will systematically review the five aspects of electrocatalytic hydrogen evolution reaction（HER）, electrocatalytic oxygen evolution reaction（OER）, ammonia decomposition reaction（NH₃）, electrocatalytic oxygen reduction reaction（ORR）, electrocatalytic carbon monoxide reduction（CORR） and electrocatalytic carbon dioxide reduction（CO₂RR）. Finally, the catalytic properties of the high-entropy alloys are summarized and the future research directions are prospected.

Polyether ether ketone(PEEK) has excellent comprehensive properties such as good self-lubricating property, high temperature resistance and hydrolysis resistance due to its unique structure. However, as one of the representatives of special engineering plastics, due to its high molding temperature, the ordinary plastic molding methods and cavity grinding tools are difficult to meet the preparation requirements of PEEK. In view of this, pure PEEK material was prepared by vacuum hot pressing sintering technology at different sintering temperatures. The structure, mechanical properties and thermal properties of the material were characterized by means of X-ray diffraction, infrared(IR) spectra and thermogravimetry(TG) analysis, and the friction and wear properties of the material were analyzed by multifunctional friction and wear testing machine, three-dimensional profilometer and scanning electron microscopy. The results show that the sintering temperature does not change the structure of the PEEK material, and has little effect on its thermal properties. With the increase of sintering temperature, the hardness of the PEEK material slightly increases and its thermal stability improves to a certain extent. When the sintering temperature is 350℃, the PEEK material has the best tensile and friction and wear properties, with tensile strength, elastic modulus and wear rate of 65.15 MPa, 6.42 GPa, and 0.513×10^-4 mm³/(N·m), respectively.

Magnesium-air batteries have attracted much attention in green and clean energy due to their advantages such as low cost, high energy density and high electrochemical equivalence. The research and development of magnesium-air batteries are still greatly hindered, mainly due to the problems of low battery discharge voltage, low anode utilization efficiency and high self corrosion rate in the application process of magnesium alloys. The reasons for these problems lie in the negative difference effect, passivation of discharge products and uneven microstructure of magnesium alloys themselves. Focusing on the anode materials of magnesium-air batteries, the anodic reaction mechanism and existing problems of magnesium alloys are summarized, and then the improvement methods for the electrochemical performance of magnesium alloys are reviewed from three aspects:alloying, processing technology and heat treatment process. Finally, the future development direction of magnesium-air battery anode materials is prospected.

Microstructure, mechanical properties and impact toughness of 42CrMoVRE steel after heat treatment by different processes were studied by means of scanning electron microscopy, tensile and impact testing machines. The results show that the microstructure of the experimental steel after oil quenching+high temperature tempering is tempered sorbite, the microstructure after normalizing+oil quenching+high temperature tempering is tempered sorbite+a small amount of acicular ferrite, and the microstructure after normalizing+oil quenching+low temperature tempering is tempered martensite. The normalizing treatment before quenching can effectively refine the ferrite grains and carbides, thus improving the contribution of fine grain strengthening and precipitation strengthening to strength. The lower tempering temperature significantly increases the strength of the experimental steel, and the main strengthening mechanism is fine grain strengthening and dislocation strengthening, but seriously reduces the impact toughness. The polygonal ferrite in the experimental steel after oil quenching+high temperature tempering can better inhibit the crack growth, and the impact toughness is high. The acicular ferrite in the experimental steel after normalizing+oil quenching+high temperature tempering has a small crack propagation resistance, resulting in a reduction in the impact toughness. The tempered martensite in the experimental steel after normalizing+oil quenching+low temperature tempering has a high residual stress, resulting in easy crack initiation and propagation, so the impact toughness is the lowest.

With the rapid development of computer technology, the methods of first-principles calculation and molecular dynamics simulation play an important role in material design and mechanism research. This paper summarizes the application of first-principles calculation in magnesium alloys, such as generalized stacking fault energy, lattice constant, elastic constant and crack formation energy. It also summarizes the application of molecular dynamics simulation in magnesium alloys, such as the evolution and migration of twin boundaries, the interaction between twin boundaries and dislocations and grain boundaries, the influence of element segregation on the interface, and the interaction behavior between precipitates and twin boundaries. The application status and limitations of first-principles calculation and molecular dynamics simulation in the magnesium alloys research are discussed, and the development prospect of atomic scale calculation and simulation research of the magnesium alloys is prospected.

As one of the most promising lightweight structural materials, magnesium alloys have excellent castability, machinability, biocompatibility and excellent mechanical properties, and have been widely used in many fields such as automotive manufacturing, aerospace, and biomedicine. With the demand onlightweight, the development of magnesium alloy integral components has become an emerging trend. However, the integral components usually have the characteristics of large scale and complex structure. Compared with traditional manufacturing processes, wire and arc additive manufacturing has the characteristics of high deposition rate, low cost, and high material utilization rate, providing the possibility to prepare large magnesium alloy components. Therefore, the wire and arc additive manufacturing of magnesium alloy has received a lot of attentions. This article mainly summarizes the research progress in wire and arc additive manufacturing of magnesium alloy from three aspects. Firstly, different process methods of wire and arc additive manufacturing technology are introduced; secondly, the research status of wire and arc additive manufacturing of magnesium alloy is introduced, including molding quality, microstructure and properties; finally, the possible challenges faced by magnesium alloy wire and arc additive manufacturing are summarized, providing a reference for further research and applications of magnesium alloy wire and arc additive manufacturing technology.

As one of the earliest used materials in the world, ceramics have excellent comprehensive properties and are widely used in aerospace, industrial production and so on. However, due to its poor processability, hard and brittleness, it is often connected with metal to form a composite structure in practical production and application. Choosing a suitable connection technology becomes the key to determine the good or poor performance of ceramics/metals. The progress of human society has also made great progress in the methods of welding ceramics/metals. Among many welding methods, diffusion welding is recognized as one of the best methods to connect ceramics and metals. This paper mainly summarizes the research status of diffusion welding of ceramics/metals at home and abroad, and puts forward the problems existing in diffusion welding of ceramics/metals and some improved methods.

The research progress in the preparation of foam glass, glass-ceramics and foam glass-ceramics from domestic metal tailings and metallurgical waste slag is reviewed. Among metal tailings, iron tailings have been widely studied in the field of preparing new types of glass due to their high SiO₂ content and huge reserves. Among metallurgical waste slag, blast furnace slag, steel slag, and nickel slag have been studied extensively. These three types of waste slag have large reserves and contain foaming agents(such as S) and crystal nucleation agents(such as TiO₂), which are beneficial for the preparation of new types of glass. The prospects for the preparation of new types of glass from metallurgical solid waste are prospected. Metallurgical solid waste has great raw material advantages in the preparation of new types of glass, and the prepared new type of glass products also have some special properties(such as the shape memory effect of tungsten tailings glass-ceramics, the wave absorption performance of iron tailings glass-ceramics, etc.), which can broaden its application range. The research is expected to solve the problem of metallurgical solid waste treatment, and achieve resource recycling.

The plasma enhanced chemical vapor deposition method was used to deposit silicon nitride thin films on p-type<100>silicon wafers. The uniformity and compactness of the films were characterized through spectroscopic ellipsometry(SE) and buffered oxide etching(BOE) solution dissolution experiments. The effects of four process parameters, including radio frequency(RF) power, chamber pressure, gas flow ratio and substrate temperature, on the properties of the silicon nitride thin films were studied. The results show that in the range of 60-100 W, the higher the RF power, the faster the growth rate of the silicon nitride thin films. A chamber pressure of 130 Pa is conducive to the formation of uniform and dense silicon nitride thin films. When the flow rate ratio of silane/ammonia gas is low, increasing the flow rate ratio can increase the compactness of the film, but the compactness hardly changes when the ratio exceeds 1.4. When the substrate temperature is between 200-300℃, the higher the substrate temperature, the lower the growth rate of the thin films and the higher the compactness. The optimal process parameters are:RF power of 100 W, chamber pressure of 130 Pa, silane flow rate of 280 mL/min, ammonia flow rate of 10 mL/min, substrate temperature of 300℃. The growth rate of the silicon nitride thin films prepared by the optimal process parameters is 16.3 nm/min, uniformity is 0.07%, refractive index is 2.1, and dissolution rate is 0.42 nm/s.

In the working process of hot working die, the upper and lower limit temperature cycle is subjected to cyclic mechanical stress at the same time, which results in plastic deformation of the surface metal of the die, and leads to the initiation and propagation of hot cracks and the formation of thermal fatigue. Thermal fatigue failure is widely concerned as one of the most important failure modes of the hot working die. Therefore, this paper presents the testing method, research progress, failure mechanism and evaluation standard of thermal fatigue crack of the hot working die steel, and summarizes the prediction model of thermal fatigue life of the hot working die steel. The research direction of thermal fatigue behavior of hot working die steel is prospected, which is expected to promote the accurate prediction of thermal fatigue life of the hot working die steel.

Effect of different welding heat input on corrosion resistance of heat affected zone(HAZ) of ultra-low Ni duplex stainless steel was studied by potentiodynamic polarization and double-loop electrochemical potentiodynamic reactivation(DL-EPR) method, and microstructure of the HAZ was characterized by means of optical microscope(OM) and transmission electron microscopy(TEM). The results show that after heat input, the corrosion resistant elements Cr and Mo in the heat affected zone can not fully diffuse to ferrite(δ) due to the faster cooling rate, resulting in the pitting equivalent value(PREN) of δ phase is lower than that of austenite(γ). In the range of heat input from 8.48 to 25.42 kJ/cm, the pitting resistance of the HAZ is reduced due to the appearance of Widmanstatten austenite(WA) and the precipitation of Cr₂N in the δ phase, and the pitting corrosion is mainly concentrated in the δ phase. When the heat input is 29.35 kJ/cm, the cooling rate decreases, resulting in the decrease of WA in the heat affected zone and Cr₂N in δ phase, and the maximum pitting potential E_b of 0.26 V is obtained. The increase of the content of intracrystalline grain boundary austenite(IGA) and grain boundary austenite(GBA) in the heat affected zone and the coarsening of its size reduce the number of γ/δ two-phase interfaces and cover part of δ/δ grain boundary, so that the minimum intergranular sensitivity value R_a of 58.3% is obtained in the heat affected zone, which has good resistance to intergranular corrosion.

Sn3.0Ag0.5Cu solder balls with different diameters(300,500 and 760 μm) were soldered onto electroless nickel electroless palladium immersion gold(ENEPIG)/Cu by three reflows to form SAC305/ENEPIG/Cu solder joints, and then the solder joints were aged at 185℃ for 0-1000 h. The effect of solder ball diameter on reaction and evolution of interfacial intermetallic compound of the solder joints after reflow and aging was investigated. The shear strength and fracture modes of the solder joints with different solder ball diameters at different shear speeds(0.2 mm/s and 20 mm/s) were analyzed. The results show that with the diameter of the solder ball decreases and the aging time increases, the intermetallic compound(IMC) at the solder joints interface changes from single-phase(Cu, Ni)₆Sn₅ to double-phase(Cu, Ni)₃Sn₄ and(Cu, Ni)₆Sn₅. The growth rate of IMC decreases with the increase of solder joint size, showing obvious size effect. The shear strength of the solder joints decreases with the decrease of shear speed and the increase of aging time, and the decrease of shear strength of large size solder joints is significantly smaller than that of small size solder joints. Under the high-speed(20 mm/s) shear condition, the fracture surface of all size solder joints presents ductile fracture after aging for 300 h.

Friction stir welding of 6005A-T6 aluminum with thickness of 2.5 mm and S420MC steel plate with thickness of 3 mm was carried out. The microstructure, morphology and mechanical properties of the welding interface were studied by means of scanning electron microscopy, X-ray diffraction (XRD) and microhardness test. The results show that there is a special flash structure at the interface of steel/aluminum friction stir welding, and the steel/aluminum in the welding nugget zone presents a layered structure composed of intermetallic compounds of AlFe, AlFe₃ and Al₁₃Fe₄. The steel/aluminum interface bond is mechanical and metallurgical, and the average tensile shear load is 5.024 kN. The tensile fracture of the aluminum side is ductile fracture and the steel side is tough-brittle mixing fracture. The microhardness of the interface is 393 HV, which is much higher than that of the base metal, and the wear rate of the stirring head is 1.18 mm/m.

It is particularly important to improve the morphology and particle size of carbides in the high wear resistant Cr12Mo1V1 cold working die steel to improve its mechanical properties. The dissolution, size and morphology of carbides in the Cr12Mo1V1 steel during high temperature heating were studied by means of optical microscope(OM), scanning electron microscopy(SEM), Image-proplus 6.0 analysis, and laser confocal microscopy. The results show that the carbides of the Cr12Mo1V1 cold working die steel will dissolve and change in shape during high temperature heating. With the increase of heating temperature, the proportion of large sized carbides gradually decreases, and the proportion of small sized carbides gradually increases, resulting in the refinement of carbides. When the heating temperature is high enough, the morphology of large eutectic carbides will change obviously. When heated at 1200 ℃, the large eutectic carbide particles break into relatively smaller particles, and it is more obvious with the increase of holding time. Thermodynamic analysis shows that the dissolution and morphology change of carbides are spontaneous processes driven by surface energy reduction, and the kinetic analysis shows that due to the existence of concentration difference at different curvature radii on the carbide surface, alloy elements will diffuse from places with smaller curvature radii(such as thin necks and sharp corners) to places with larger curvature radii(such as flat interfaces), resulting in spontaneous disconnection and spheroidization of carbides.

In order to investigate the influence of laser power on microstructure and properties of cladding layer, FeCoNiCrMo high entropy alloy cladding layer was prepared on the surface of 42CrMo steel by using six kinds of laser power. Microstructure, phase, mechanical properties and corrosion resistance of the cladding layer were studied by means of X-ray diffractometer(XRD), scanning electron microscopy(SEM), energy dispersive spectrometer(EDS) analysis, Vickers microhardness tester, stress analyzer, friction and wear tester and electrochemical workstation. The results show that the microstructure of the FeCoNiCrMo layer prepared by laser cladding is mainly FCC solid solution phase. When the laser power is greater than 1.6 kW, BCC phase(α-Fe) structure appears in the cladding layer, showing dendrite microstructure with martensite in the dendrite and Cr-and Mo-containing ferrite located between dendrites. With the increase of laser power, the hardness of the cladding layer first increases and then decreases, reaching a maximum of 522 HV0.3 at 1.6 kW. When the laser power is 1.8 kW, the wear resistance and corrosion resistance of the cladding layer are the best, and the wear rate and self corrosion current density are 0.71×10^-5 g·N^-1·m^-1 and 1.69×10^-9 A·cm^-2, respectively. Laser power is an important factor that affects the microstructure and properties of the FeCoNiCrMo high entropy alloy layer. Increasing laser power is conducive to promoting the formation of BCC phase, significantly improving the mechanical properties and anti-corrosion properties of the cladding layer.

The numerical simulation of welding can realize the simulation of complex welding phenomena, reveal the essence and laws of welding phenomena, optimize the structure and process design, reduce the actual workload and improve the quality of welded joints by quantitative analysis of complex or unobservable phenomena and prediction of the laws that are not known under extreme conditions. However, due to the increasingly complex welding situation faced by welding technology in engineering, and the heat source model as the "soul" of welding numerical simulation, the reasonable selection and development of new welding heat source model is particularly important. Therefore, research on the development of welding simulation heat source model, secondary development and determination of heat source parameters have guiding significance for future engineering applications. In this paper, the development of heat source model in numerical simulation of gas shielded metal arc welding, plasma arc welding and laser-arc hybrid welding in recent years is systematically reviewed, the research progress of heat source model based on secondary development is introduced, the determination method of heat source parameters is summarized, and the future research focus of welding heat source model is pointed out.

Using CO₂ gas shielded welding method, YD212 type welding wire was deposited on the surface of Q345B steel substrate to form a composite plate. The effects of three heat treatment processes, namely quenching, normalizing, and spray quenching+tempering, on microstructure and mechanical properties of the composite plate were studied, and compared with untreated composite plate. The results show that the microstructure of fusion zone and surfacing layer of the composite plate are changed by three heat treatment process, in addition, the pearlite content of the substrate layer is also changed. The hardness of each layer of the composite plate is improved by heat treatment in varying degrees, among them, the increment of the normalized composite plate is smaller. The composite plate treated by spray quenching and tempering heat treatment has a higher content of pearlite in the substrate layer, significantly improves hardness and toughness, and significantly improves toughness in the fusion zone. The hardness of the surfacing layer is excellent, and its impact absorbed energy is 1.57 times that of the untreated composite plate.

Because of its high mixing entropy, high entropy alloy with multi-principal elements has the advantages of simple structure solid solution, excellent wear resistance, corrosion resistance and mechanical properties, as well as good ductility, therefore its plastic deformation behavior and deformation mechanism have attracted wide attention. The microstructure, mechanical properties, friction and wear properties and corrosion resistance of high entropy alloy were discussed. The research status of plastic deformation properties, deformation mechanism and grain refinement mechanism of high entropy alloy under quasi-static and dynamic deformation conditions was reviewed. Finally, the existing problems in the study of plastic deformation behavior of high entropy alloy are pointed out and the research direction of plastic deformation theory is prospected, which provides a reference for expanding the application field of high entropy alloy.

Evolution of microstructure and properties of reduced activation steel containing yttrium and titanium after intermediate heat treatment and that after aging at 550℃ for 500, 1250, 2500, 4000 and 5000 h were studied by means of optical microscope, scanning electron microscopy(SEM), transmission electron microscopy(TEM) and mechanical properties testing. The influence of microstructure evolution on mechanical properties was analyzed. The results show that the microstructure of the experimental steel remains stable martensite during aging, the grain coarsens, and the growth rate of M₂₃C₆ and MX phases, yield strength, tensile strength and impact properties of the experimental steel gradually decrease and tend to be stable. When the aging time increases to 4000 h, the coarsening speed of Laves phase decreases. When the aging time reaches 5000 h, the grain size of the experimental steel is 9.1 μm, the growth rate of M₂₃C₆ is 0.0072 nm/h, the growth rate of MX is 0.0004 nm/h, the yield strength and tensile strength of the experimental steel at room temperature are 632 and 755 MPa, respectively, the impact absorption energy at room temperature is 307 J, the ductile-brittle transition temperature is-64℃, and the yield strength and tensile strength of the experimental steel at 650℃ are 313 and 337 MPa, respectively. Grain coarsening is the main reason for the decrease in impact toughness of the experimental steel.

In view of the problems of coarse grain size and poor tensile properties of 304 stainless steel narrow gap TIG(tungsten inert gas welding) welded joint, the ultrasonic vibration head was applied to the test plate, and the ultrasonic vibration was introduced into the TIG welding process to weld it. Microstructure and mechanical properties of the welded joint were studied. The results show that after the introduction of ultrasonic vibration, under the combined effect of thermodynamics and dynamics, the weld penetration increases, the transformation rate of columnar crystal to equiaxed crystal in the weld zone increases, the proportion of equiaxed crystal increases, and the grain is refined. Compared with conventional TIG, the introduction of ultrasonic vibration improves the weld microstructure of the 304 stainless steel narrow gap welded joint, improves its mechanical properties, significantly improves the hardness of the weld zone, close to the base metal, and the tensile strength and yield strength of the welded joint are also higher than that of conventional TIG welded joint, and the elongation is also improved. When the ultrasonic amplitude is 40 μm, the tensile strength of the welded joint is the highest of 674 MPa, the yield strength is 376 MPa, and the elongation is 25%.

Graphite/silicon carbide composite high-temperature molten salt packaging materials were prepared by selective laser sintering（SLS）, impregnation densification and liquid-phase melting siliconizing. Microstructure, phase composition, compressive strength and thermal conductivity of the packaging materials were studied by means of scanning electron microscopy（SEM）, X-ray diffraction（XRD）, universal testing machine and thermal conductivity tester. The results show that the addition of high-purity silicon powder in the material formula will result in in-situ sintering reaction to generate silicon carbide reinforcing phases, fill the internal pores of the packaging material, and improve its compressive strength and thermal conductivity. The coating treatment of high-purity silicon powder can aggravate this reaction, and the maximum performance improvement is achieved when the addition amount of high-purity silicon powder is 20 mass%. On this basis, adding 20 mass% mesophase carbon microspheres can maximize the compressive strength and thermal conductivity of the packaging material, and reduce porosity. After graphitization and liquid-phase melting siliconizing treatment, the surface layer of the packaging material is dense and has the best performance, with the compressive strength of 30.328 MPa, the thermal conductivity of 103.582 W/（m·K）, and the overall open porosity of 8.43%, which can realize the packaging and heat exchange enhancement of high temperature molten salt.

TZM alloy has the characteristics of high melting point, high strength, low linear expansion coefficient, good corrosion resistance, and good high-temperature mechanical properties.It is one of the most widely used molybdenum alloys and plays an irreplaceable role in many fields.Based on the research status of TZM alloy and on the basis of molybdenum alloy hot working forming and strengthening theory, the preparation methods, mechanical properties control methods, microstructure control methods and the latest research progress of TZM alloy are reviewed in this paper.The control strategies, such as changing doping and sintering processes, and alloy elements and second phases control, are introduced.In addition, the relationship between these interfaces and the properties of TZM alloy is also discussed.Finally, the future research direction and development of TZM alloy are prospected based on the strengthening and toughening mechanism.

The A5052 aluminum alloy and Q235 low carbon steel were welded by resistance rivet-welding. Effect of hardness of self piercing rivets and welding parameters on macro morphology and mechanical properties of resistance riveted joints and the joint state between rivet leg end and lower plate were analyzed. The results show that the holes formed in the resistance riveted joints with high hardness rivets(HRC of 42±1) are less, and its macro morphology is better than that of the welded joints with medium hardness rivets(HRC of 36±1) and low hardness rivets(HRC of 33±1). When high hardness rivets are used for welding, with the increase of welding current, the aluminum alloy remaining between the end of rivet leg and the lower plate becomes thinner. When the welding current is 10 kA and the welding time is 400 ms, the maximum shear resistance of the high hardness rivet welded joint is 7.67 kN.

First, the extruded Cu-15Ni-8Sn alloy was solution treated at different temperatures for 1 h, and the optimum solution temperature was optimized. On this basis, the alloy was aged at 400 ℃ for 2 h. Microstructure, fracture morphology, tensile strength and hardness of the extruded, solution treated and aged alloy were analyzed by means of optical microscope, scanning electron microscopy, tensile test and Rockwell hardness tester. The results show that a large number of Sn rich phases are distributed at the grain boundaries and in grains of the extruded alloy, the hardness of the alloy is 81.5 HRB, and the tensile strength is 597 MPa. With the increase of solution temperature, the grain size of the alloy begins to grow, and the second phase particles gradually dissolve into the matrix. When the solution temperature is 840 ℃, the second phase particles are almost completely dissolved into the matrix, and the grain size of the alloy is 75-180 μm; when the solution temperature reaches 860 ℃, the grains appear overburning, indicating that the optimum solution temperature of the alloy is 840 ℃, at this time, the hardness of the alloy is 55.6 HRB, and the tensile strength is 396.5 MPa. After aging, the mechanical properties of the alloy are significantly improved: the hardness is 105.4 HRB, and the tensile strength is 839.8 MPa, which are 89.6% and 112% higher than those of the alloy solution treated at 840 ℃.

Corrosion and passivation behavior of 2507 duplex stainless steel in electrolytic seawater antifouling environment was studied by means of open circuit potential, potentiodynamic polarization curve, potentiostatic polarization curve, Mott-Schottky curve and corrosion morphology observation. The results show that the corrosion form of the 2507 duplex stainless steel in electrolytic seawater antifouling environment is pitting corrosion; With the increase of NaClO mass concentration, the hydrolysis of NaClO leads to the increase of solution pH value, hinders the cathodic depolarization process of dissolved oxygen, slows down the anodic oxidation dissolution rate, increases the open circuit potential and self corrosion potential, and decreases the corrosion tendency. However, the NaClO hinders the formation process of the passive film, the passivation area decreases, the carrier density increases, the shielding performance of the passive film decreases, the impedance radius decreases, the corrosion current density increases, the number of pitting holes increases, the hole depth increases, and the corrosion resistance decreases.

Effect of solution treatment at different temperatures and solution and double aging treatment on impact properties of GH4151 alloy was studied by impact test. Microstructure, precipitates and fracture surface morphology of the GH4151 alloy treated by different processes were observed by means of optical microscope, scanning electron microscopy and transmission electron microscopy. The results show that for the alloy subjected to only solution treatment, when the solution treatment temperature is lower than 1140 ℃, the impact toughness of the alloy has little change, and when the solution temperature is higher than 1140 ℃, the impact toughness increases with the increase of solution temperature. The fracture process is dominated by the stable crack propagation zone, and the fracture surface is ductile fracture. For the alloy treated by solution treatment and aging, when the solution temperature is lower than 1160 ℃, the change of impact toughness is relatively stable, and when the solution temperature is higher than 1160 ℃, the impact toughness decreases with the increase of solution temperature. There is no stable crack propagation zone in the fracture process, and the fracture surface is a typical intergranular brittle fracture. This is mainly because when the solution temperature is lower than 1140 ℃, the grain size of the alloy does not change much, but when the temperature is higher than 1140 ℃, the grain size increases obviously. After two-stage aging, when the solution temperature is higher than 1160 ℃, the continuous or discontinuous second phase on the grain boundary significantly reduces the impact toughness of the alloy.

Effect of secondary tempering temperature on microstructure, mechanical properties and residual stress of 42CrMo4M steel was studied by means of optical microscope, scanning electron microscopy, transmission electron microscopy and X-ray diffractometer. The results show that after secondary tempering, the martensite lath in the 42CrMo4M steel further recovers and recrystallizes, and the dislocation density decreases significantly. The long strip shape carbides gradually spheroidize and coarsen, transforming into granular morphology. With the secondary tempering temperature increases, the yield strength and tensile strength of the 42CrMo4M steel show a trend of first increasing and then significantly decreasing, while the change in plasticity and toughness is relatively small. After secondary tempering at 660℃, the impact absorbed energy of the 42CrMo4M steel at-20℃ slightly increases from 111 J after quenching and tempering treatment to 120 J, with an increase of only 9 J. In addition, with the increase of secondary tempering temperature, the residual stress in the 42CrMo4M steel shows a trend of first decreasing and then increasing. After secondary tempering at 640℃, the residual stress in the 42CrMo4M steel is the lowest of 111.7 MPa, which is about 26.75% lower than that of 152.5 MPa after quenching and tempering treatment.

In order to control the microstructure of 40CrMnMoA alloy steel after hot deformation, the dynamic recrystallization behavior of the alloy steel was studied. The high temperature compression test of the 40CrMnMoA alloy steel was carried out by using Gleeble-1500D thermo-mechanical simulation compression tester at the conditions of deformation temperature of 900-1200℃ and strain rate of 0.005-5 s^-1, and the stress-strain curves of the alloy steel were obtained. Based on the experimental data, the Zener-Hollomon parameter(Z parameter) and deformation activation energy Q(325397.448 J/mol) of the alloy steel were determined. The results show that the stress-strain curves of the 40CrMnMoA alloy steel has an obvious downward trend under the condition of low lnZ(<30), the smaller the lnZ is, the more obvious the characteristic is, which is a typical dynamic recrystallization curve. Under the condition of high lnZ(>30), the stress of the 40CrMnMoA alloy steel increases with the increase of strain, showing typical dynamic recovery characteristics. Based on the experimental data, the work hardening rate θ of the 40CrMnMoA alloy steel is calculated, by analyzing the θ-σ curve under the condition of low lnZ, the critical strain and peak strain of the 40CrMnMoA alloy steel are obtained, and the corresponding dynamic recrystallization critical strain model is established:ε_c=0.0010988Z^0.19324.

There is metastable phase structure in TC4 titanium alloy manufactured by additive, which has obvious influence on microstructure and corrosion resistance of the alloy. Based on this, the heat treatment of the TC4 titanium alloy manufactured by additive was carried out by different processes. The effects of heat treatment on the microstructure, residual stress and corrosion resistance of the TC4 titanium alloy manufactured by additive were studied by means of scanning electron microscopy(SEM), X-ray diffraction(XRD), residual stress measurement and electrochemical analysis. The results show that the heat treatment process has an important influence on the microstructure of the TC4 titanium alloy. When the titanium alloy is heat treated at above 940℃ for 1 h and cooled, the microstructure changes from metastable α' phase to α+β phase and a small amount of secondary α phase, and compared with furnace cooling, titanium alloy under water cooling condition has higher β phase content. When the heat treatment temperature is 800, 940 and 1080℃, the residual stress on the surface of the titanium alloy is relatively low. The corrosion resistance of the titanium alloy is closely related to the microstructure and residual stress. The finer the α phase grain, the higher the β phase content, the greater the residual compressive stress and the better the corrosion resistance of the alloy. When the heat treatment temperature is 1020℃, the residual compressive stress on the surface of the titanium alloy is 470 MPa, and the corrosion resistance is good.

Effect of different heat treatment processes on microstructure and properties of S31803 duplex stainless steel was studied by means of optical microscope, microhardness tester and electrochemical workstation. The results show that the microstructure of the S31803 duplex stainless steel is mainly composed of ferrite(α) and austenite(γ), and the content is 41% and 59% respectively. With the increase of heat treatment temperature, the content of the α phase increases. When the heat treatment temperature reaches 1000 ℃, the content of the α phase increases to 49.26%, but decreases with the increase of holding time, and the change trend of the γ phase content is opposite. With the increase of heat treatment temperature, the hardness of the S31803 duplex stainless steel increases due to the increase of the α phase content, and with the increase of holding time, the hardness decreases due to the decrease of the α phase content. The corrosion resistance of the S31803 duplex stainless steel is mainly affected by the proportion of two phases and the precipitated phase content. With the increase of heat treatment temperature, the α/γ phase ratio increases, the corrosion resistance decreases, but the increase of holding time will change the α/γ phase ratio and the content of precipitates at the same time, and its corrosion resistance has no obvious change rule.

With Mo sheet as buffer layer, AgCuTi filler metal was used to braze quartz glass and TC4 titanium alloy, so as to control the difference of thermal expansion coefficient between the quartz glass and the TC4 alloy and reduce the stress of the brazing joint on the quartz glass side. The effect of Mo buffer layer on stress relief and microstructure and properties of the brazed joint was analyzed. The results show that the addition of Mo buffer layer can adjust the difference of thermal expansion coefficient between the quartz glass and the TC4, transfer the stress of the brazing joint on the quartz glass side to the Mo buffer layer, reduce the stress on the quartz glass side, and improve the performance of the brazing joint. At the same time, the addition of Mo buffer layer can prevent the diffusion of dissolved Ti element in TC4 base metal to the quartz glass side, weaken the reaction on the quartz glass side, and reduce the thickness of the thin reaction layer near the quartz glass side. When the brazing temperature is 900℃ and the holding time is 10 min, the shear strength of the brazed joint with Mo buffer layer is the highest, reaching 37 MPa.

Based on the coupling model of electromagnetic field, temperature field, microstructure field and stress/strain field, the induction hardening process of inner ring of double row spherical roller bearing was simulated by DEFORM software, and the quenching process of sectional current density was put forward. The temperature change, microstructure evolution, surface and subsurface hardness, residual stress and retained austenite during induction hardening of spherical roller bearing inner ring were studied. The results show that the induction hardening method of sectional current density can make the hardened layer of the inner ring of the bearing distribute uniformly, the heating efficiency increases with the increase of current density of coil, and the temperature at the cusp position changes sharply. After quenching, the retained austenite content on the raceway surface is about 6.97%, the martensite content is about 92.3%, the surface hardness is about 60.9 HRC, and the thickness of the raceway hardened layer is about 2.97 mm. After cryogenic treatment, the retained austenite content and residual stress decrease, the martensite content and hardness increase, the residual stress distributes symmetrically along the radial plane of the center of the inner ring, and the residual stress in the subsurface layer is the largest. The numerical simulation results are in good agreement with the experimental results.

Martensite and austenite（MA） islands thin film samples of acicular ferrite X65 pipeline steel were accurately prepared by focused ion beam（FIB） etching method. The substructure of MA islands was characterized by electron backscatter diffraction（EBSD） technique and transmission electron microscopy（TEM）, and the role of MA islands in fatigue crack propagation was studied. The results show that the MA content in the acicular ferrite X65 pipeline steel is about 5.7%, and MA islands are mainly distributed at grain boundary, with size ≤ 3 μm. The internal substructure of MA islands is divided into several blocks with different sizes by martensite and retained austenite. The retained austenite and martensite distribute alternately in the MA islands, and there is a coherent relationship between martensite and austenite in some areas. The alternately distribution of retained austenite and martensite in MA islands has a significant inhibition effect on fatigue crack propagation. When the fatigue crack propagation path encounters MA islands, the main crack propagation direction deflects and bypasses MA islands, while the branch crack is captured by MA islands and stops propagation.

Effect of different aging processes on microstructure, mechanical properties, conductivity and exfoliation corrosion resistance of 7A75 aluminum alloy was studied by means of optical microscope, transmission electron microscopy, tensile test at room temperature and electrical conductivity test. The results show that the conductivity of the alloy after two-stage+reaging and non-isothermal aging treatment can be increased from 36.9 %IACS of T73 to 39.8 %IACS and 39.4 %IACS, and the maximum exfoliation corrosion depth of the sample center can be reduced from 723 μm of T73 to 620 μm and 555 μm. This is mainly because the cooling process of two-stage+reaging and non-isothermal aging treatment can promote the precipitation of fine dispersed phase, which makes the area fraction of precipitation phase in the crystal of two-stage+reaging and non-isothermal aging have higher than that of T73 aging. At the same time, the content of Cu in the grain boundary precipitates is increased, the size is increased and the distribution is more discrete, which reduces the exfoliation corrosion sensitivity of the alloy.

Effect of final aging on microstructure and mechanical properties of 7475 aluminum alloy during two-stage aging treatment was studied by means of transmission electron microscopy and universal material testing machine. The results show that when the first aging process is 120℃×5 h and final aging process is 160℃×14 h, the amount of precipitated phases in the alloy matrix is large, the precipitates are fine and dispersed, the precipitation free zone at the grain boundary is relatively narrow, and the precipitated phases at the grain boundary are discontinuously distributed. At this time, the tensile strength, yield strength and elongation of the alloy are the best, which are 509 MPa, 463 MPa and 12.4%, respectively. Compared with the untreated alloy, the tensile strength, yield strength and elongation increase by 4.5%, 9.2% and 11.7%, respectively. When the final aging temperature is 160℃, with the increase of the final aging time, the strength of the alloy first increases and then decreases, but the change is not significant. When the final aging temperature is greater than or equal to 165℃, the strength of the alloy decreases significantly with the increase of the final aging time, which is due to the significant broadening of the width of the precipitate free zone at the grain boundary and the significant coarsening of the matrix precipitated phase.

In order to study the effect of graphite morphology on wear process of cylinder liner cast iron, three cast iron materials with different graphite morphology, gray cast iron, vermicular graphite cast iron and ductile cast iron, were selected as the research objects, and the dry friction and wear experiments of the three cast iron materials were carried out at different temperatures. The results show that with the increase of the temperature, the friction coefficient and the wear mass loss of the gray cast iron increase, while the friction coefficient and the wear mass loss of the vermicular cast iron and the ductile cast iron increase first and then decrease. The friction coefficient and the wear mass loss of the gray cast iron at room temperature are the largest and the wear resistance is the worst; the friction coefficient and wear mass loss of the gray cast iron at high temperature are still the largest, and the friction coefficient of the vermicular cast iron is larger than that of the ductile cast iron, but the wear mass loss is the smallest and the wear resistance is the best.

The research status of lead-free solders reinforced with carbon-based nano-particles such as carbon nanotubes (CNTs) and graphene nanosheets (GNSs) for electronic micro-connection was reviewed. The effects of reinforced phases such as CNTs, GNSs, fullerenes (FNS), metal modified CNTs and GNSs on microstructure and properties of lead-free solders and brazing joints were introduced. The preparation method, melting characteristics, conductivity, wettability, mechanical properties and solder joint reliability of lead-free composite solders are briefly described. The existing problems, solving measures and development trend of lead-free composite solders reinforced by carbon-based nano-particles are pointed out.

In order to study the effect of composite small diameter shot peening on contact fatigue performance of gears, the effect of composite small diameter shot peening was analyzed by combining finite element simulation and shot peening strengthening test, and the effect of life improvement of composite small diameter shot peening gears was verified by gear contact fatigue life test. The results show that compared with the single small diameter shot peening, the composite small diameter shot peening can obtain greater residual compressive stress and smaller surface roughness. With the increase of shot peening intensity and shot peening coverage, the residual compressive stress increases, and the depth of the maximum residual compressive stress is basically unchanged. The rationality of the finite element model of shot peening is verified by shot peening strengthening test, and the composite small diameter shot peening can introduce high residual compressive stress on the surface of the gear and improve the surface hardness without changing the roughness. The results of gear contact fatigue life test show that the transmission efficiency between gear pairs is significantly increased after composite small diameter shot peening, and the fatigue life is 2.38 times of that of the gear without shot peening, and the effect of life improvement is obvious.

Electron backscatter diffraction(EBSD) and scanning electron microscopy(SEM) were used to analyze the texture, recrystallization and fatigue fracture surface of EH36 ship plate steel treated by normalizing process. The fatigue crack propagation behavior, fatigue fracture mechanism and the effect of external load and stress ratio on the stress intensity factor amplitude of the normalized EH36 ship plate steel were studied by means of tensile test, fatigue crack propagation rate test, fatigue fracture toughness test and numerical simulation. The results show that the EH36 ship plate steel has strong {110} and {111} plastic texture components, the average grain size is 8.2 μm, the proportion of deformed grains is 4.1%, and the elongation is 33.3%. The fatigue crack propagation life prediction formulas for stress ratios of 0.03 and 0.1 are obtained through double logarithmic linear fitting, which are da/dN=1.07×10^-9(ΔK)^3.49 and da/dN=1.96×10^-9(ΔK)^3.35, respectively. The fatigue fracture toughness K_J0.2BL(30) of the normalized EH36 ship plate steel is 387 MPa·m^1/2 calculated by J-integral method. The fatigue fracture mechanism of the experimental steel is a mixed fracture mechanism of cleavage transgranular fracture and microporous growth polymerization fracture. The multi-parameter simulation shows that under a constant maximum external load, the amplitude of stress intensity factor decreases with the increase of stress ratio under the same fatigue crack length. When the ratio of fatigue crack length to the length of the standard compact tensile specimen is 0.62, it can be used as a criterion for the experimental steel to enter the transient fracture zone.

The causes of crack formation in GH99 alloy during laser engineered net shaping were studied and discussed, and the solution to optimize process parameters was proposed. The results show that the internal cracks are short linear-needle-like, forming in columnar grain boundaries or secondary dendrites, perpendicular to the direction of deposition, and distributed and propagated along the fine oriented grain boundaries. The enrichment of Al and Ti elements at grain boundaries tends to precipitate γ'(Ni₃(AlTi) phase,which weakens grain boundary, melts the grain boundary and is difficult to be shrank during solidification, resulting in crack nucleation. In the process of rapid thermal cycling, the accumulation of residual stress causes the crack to propagate along the grain boundary. By optimizing the process parameters to reduce the heat input, the thermal crack formation of the GH99 alloy during laser engineered net shaping can be overcome, and the crack-free forming of the components can be realized.