Dynamic mechanical properties of C72900 copper alloy and 15-5PH stainless steel at different strain rates were studied by Hopkinson pressure bar test. The strain-stress curve was fitted on the basis of Johnson-Cook constitutive equation to determine material parameters. The compression test was simulated by ABAQUS software to verify the accuracy of the constitutive equation. The results show that the flow stresses of C72900 copper alloy and 15-5PH stainless steel increased significantly with increasing strain rate by tests, and both the materials had the similar flow stress behavior. The simulated true stress-true strain curves of C72900 copper alloy and 15-5PH stainless steel in the plastic deformation stage were consistent with the test results, and the relative errors were less than 3%, indicating that the established Johnson-Cook constitutive equations could describe the flow stress characteristics of C72900 copper alloy and 15-5PH stainless steel well. The application of C72900 copper alloy instead of 15-5PH stainless steel on the gasket of C919 aircraft safety pin was feasible and reliable.

The progressive failure model of fiber reinforced plastics and the continuous damage model of composite laminate of the Ls-Dyna software were applied to simulate the mechanical response and damage modes of carbon fiber reinforced plastic laminates under in-plane shear loads, with the mechanical parameters obtained by quasi-static uniaxial tensile and in-plane shear tests. The applicability of the two models was compared. The results show that in the initial linear elastic stage during in-plane shearing, the two models could simulate the mechanical characteristics of the carbon fiber reinforced plastic laminates. As the load continued to increase, the load-displacement simulation curve obtained by the progressive failure model still rose linearly, and dropped rapidly after reaching the load peak; the simulation curve had a large deviation from the test curve. When the material was damaged, because of the introduction of damage parameters, the load-displacement simulation curve obtained by the continuous damage model was nonlinear, which was in good agreement with the test curve.

With the continuous development of intelligent society, piezoelectric sensors are increasingly used. The types, structures, measurement principles and application scenarios of piezoelectric sensors are described. The research progress on sensitive element materials is reviewed, and the application of high-temperature piezoelectric materials and lead-free piezoelectric materials is summarized. Finally, the future development direction of piezoelectric sensors is prospected.

Plasma sprayed coatings have been widely used in surface protection engineering due to the excellent properties such as wear resistance, high temperature resistance and corrosion resistance. Pores are an important structural defect of plasma sprayed coatings. Excessive pores can lead to premature detachment failure of the coatings and shorten the service life, and therefore porosity is an important indicator to evaluate the coating quality. The pore formation mechanism, influencing factors, and the effect of the pores on the coating performance are briefly discribed. The research status of the porosity reduction of plasma sprayed coatings is reviewed from the aspects such as spraying process parameter optimization, laser remelting treatment, and modification of spraying materials. Moreover, the problems and development directions in the development of plasma sprayed coatings are summarized.

6063 aluminum alloy was prepared by pressure forming process, and then was treated by solution at 535 ℃ and aging. The effects of solution time (15-120 min), aging temperature (160-200 ℃) and aging time (1-24 h) on the microstructure, tensile properties and hardness of the aluminum alloy were studied. The results show that with increasing solution time, the grain size of 6063 aluminum alloy increased, and the primary Mg ₂Si phase gradually disappeard and redissolved in the matrix; but the solution time had no effect on the content and morphology of α-Al ₈Fe ₂Si phase and β-Al ₅FeSi phase. After solution treatment, with increasing aging temperature or aging time, the number of second phase Mg ₂Si increased, but a higher temperature or a longer aging time resulted in the coarse of the Mg ₂Si phase. With increasing solution time, aging time or aging temperature, the strength and hardness of the alloy increased first and then decreased, and the precentage elongation after fracture decreased first and then increased. The appropriate solution and aging treatment system for 6063 aluminum alloy was 535 ℃×60 min + 180 ℃×7 h; at this time the Mg ₂Si phase precipitated in the alloy was the smallest and dispersed, and the alloy had the highest strength and hardness and the appropriate precentage elongation after fracture.

Additive manufacturing is an important development direction of advanced manufacturing technique for metal parts, but the metal powder for additive manufacturing has some problems such as insufficient research and development, weak stability and incomplete standards, which seriously restrict its development. The basic principles of common spherical metal powder preparation techniques including centrifugal atomization method, two-stream atomization method and spheroidization method are summarized, and their advantages, disadvantages and development status are introduced. It is proposed that the development of domestic additive manufacturing powder preparation technique can start from two aspects. One is to carry out process and equipment improvement and standardization research on traditional methods, and build automated factories; the other is to strengthen the research on basic theories of powdering and explore new processes.

The cobalt-doped manganese oxide for aqueous zinc-ion battery cathode material was prepared by solvothermal, hydrolyzing and annealing with cobalt nitrate and manganese nitrate as raw materials. The microstructure and electrochemical performance of cobalt-doped manganese oxide was investigated. The results show that the prepared cobalt-doped manganese oxide h-CoMn _3.2O _x had a hierarchical yolk-shell structure, and the porous shell surface was decorated with petal-like nanosheets with radial dimension of more than 100 nm. Both of the shell and nanosheets were composed of primary nanoparticles with average size of 5 nm. Cobalt-doping endowed manganese oxides with small size and delicate structure. h-CoMn _3.2O _x had the manganosite MnO crystal structure. Compared with monometallic manganese oxide, h-CoMn _3.2O _x exhibited relatively large specific surface areas and specific capacities, and had good cyclic stability. The energy-storage behavior of h-CoMn _3.2O _x was attributed to sequent co-insertion of H ⁺ and Zn ²⁺.

Ferroelectric materials have unique photovoltaic properties due to their polarized electric field, and are widely used in many fields, especially in photovoltaic power generation. The generation mechanism of internal electric field (photovoltaic mechanism) in ferroelectric materials, and the effects of electric field regulation mechanism on photovoltaic properties of ferroelectric materials are reviewed from aspects of the preparation of narrow band gap ferroelectric materials, enhancing visible light absorption by self-doping of oxygen deficiency constructing composite heterojunction, preparing multipole axial molecular ferroelectrics, and regulating the domain orientation and distribution in ferroelectric materials by external polarization field. The research direction of improving photovoltaic performance by regulating internal electric field is pointed out.

Powder bed fusion additive manufacturing technique can quickly form complex structural parts with high dimensional accuracy, and has received extensive attention in many fields. However, compared with traditional manufacturing methods, its cost is higher. The recycling of metal powder can effectively reduce manufacturing costs. Combined with the research progress on additive manufacturing metal powders, changes of the chemical properties, physical properties and parts properties of commonly used 316L stainless steel, Ti6Al4V alloy and IN718 alloy powders in the recycling process are summarized. On the basis of demand for additive manufacturing of civil aviation parts, several problems existing in metal powders recycling are analyzed, and solutions are proposed.

Under the background of increasing demand for lightweight, liquid die forging technique with excellent formability has been widely concerned. The lightweight design criteria and key points of lightweight design of equipments are summarized, and the application of liquid die forging aluminum alloy in equipments is introduced. The research progress on liquid die forging technique of aluminum alloy from the aspects of process principle and characteristics, forming materials, forming die and forming equipment is reviewed. Finally, the research and development direction of this technique in the future is put forward.

The wire and arc additive manufacturing (WAAM) has gained more and more attention because of its unique advantages in forming large-scale components, and has become one of the most widely used metal additive manufacturing technology. The development history of WAAM is described. The influence of process parameters on the morphology of deposited layer and the evolution mechanism of microstructure is analyzed from the perspective of “shape and property control”. The numerical simulation methods for residual stress and their advantages and disadvantages are discussed, and it is pointed out that the combination of computational fluid dynamics and finite element method is one future research trend. The common methods for controling the residual stress and deformation, as well as the problems and challenges in wire and arc additive manufacturing, are summarized.

The 304 stainless steel substrate was grinded to 1200 ^# (1 ^# process), 2000 ^# (2 ^# process) by sandpaper in sequence and grinded to 2000 ^# and polished by diamond polishing paste with size of 0.5 μm (3 ^# process), respectively, and then the CrMoN coating was deposited on the surface. The phase composition, surface and cross-section morphology, hardness, surface hydrophobicity, corrosion resistance and conductivity of the coating were studied. The results show that the roughness of the coating surface deposited on the substrate surface pretreated with 1 ^# process was the largest, followed by that pretreated with 2 ^# process, and the roughness that pretreated with 3 ^# process was smallest. The phase of the coating consisted of CrN, Cr ₂N and Mo ₂N. With decreasing substrate surface roughness, the microhardness, free corrosion potential and water contact angle of the coating increased, and the corrosion current density and interface contact resistance after polarization decreased. The comprehensive properties of the CrMoN coating deposited on the substrate surface pretreated with 2 ^# process were excellent, which were close to those pretreated with 3 ^# process.

Metallographic examination and tensile test were carried out on the long-term service radiation section tube of ethylene cracking furnace, and the microstructure, carbide size, room temperature and high temperature mechanical properties of carburized and non-carburized zone were studied. The quantitative relationship between carbide width and tensile properties of furnace tube was established. The results show that the grain morphology and size of non-carburized zone and carburized zone of the furnace tube were similar. The former was composed of austenite matrix, primary carbides, G phase and NbC phase; the latter had no G phase, and its primary carbides were obviously coarsened. The carburized zone had more creep holes and microcracks. The room temperature strength and plasticity of the furnace tube were seriously deteriorated. The high temperature tensile properties of the non-carburized zone basically met the requirements, and the carburized zone was obviously embrittled. The carbide width increased with the distance from outer surface of furnace tube. The tensile strength and yield strength of the furnace tube were positively related to the carbide width, and the percentage elongation after fracture was negatively related to it.

Magnetic field-controlled directional solidification provides a new route to prepare high-quality alloys and castings, and is of great significance for improving the metallurgical quality of products and developing new preparation techniques. The main research progress on the directional solidification of nickel-based superalloys under magnetic field in recent years is summarized. Several typical effects between magnetic field and metal conductive melt are described. The revolution of the directional solidification structures of nickel-based superalloys under static magnetic field, alternating magnetic field, pulsed magnetic field and traveling magnetic field, and the influence of magnetic field on typical solidification defects such as stray grains and on the creep properties of superalloys are systematically summarized. The formation mechanisms of solidification structures and defects under different types of magnetic fields are discussed. Finally, the development trend and breakthrough points of directional solidification of superalloys under magnetic field are prospected.

Mechanical and physical parameters and curing residual strain of epoxy resin potting material with curing temperature of 60℃ were tested at environmental temperatures of -30-60℃. Taking it as an input condition, the thermal strain of the epoxy resin potting structure was simulated by the finite element simulation, and the results were compared with the test results, and the thermal coupling characteristics of the epoxy resin potting structures were studied. The results show that the relative errors of the simulated thermal strain and the experimental thermal strain of the epoxy resin potting structure were both within the allowable range of the project, the finite element simulation results was accurate. The thermal stress in the range of -30-60℃ was far less than its fracture strength, and it would not crack due to thermal stress in the range of temperature.

During the fire, different temperatures, fire duration and extinguishing methods, and different equipment materials result in different damage degrees and types of post-fire equipment, and changes of the microstructure and properties of equipment material. The damage evaluation method of the post-fire equipment commonly fabricated from carbon steel, low-alloyed steel and stainless steel and the research status at home and abroad of damage evaluation of mechanical properties and corrosion resistance of its material are summarized. The existing problems in the damage evaluation of the post-fire equipment and the future research direction are discussed.

Selective laser melting technique is a widely used laser additive manufacturing technology in preparation of precise and complex parts, which could realize the near net forming of complex parts. Through the forming process parameters, and solution and aging treatment methods, the research progress of microstructure and mechanical properties control of TC4 alloy formed by selective laser melting in the current stage is reviewed, and the future development direction is prospected.

Development in recent years of hot stamping steels, including ordinary hot stamping steel, hot stamping steel with high hardenability and oxidation resistance, high strength ductile hot stamping steel, ultra high strength hot stamping steel, high hydrogen embrittlement sensitivity hot stamping steel and ultra high strength hot stamping steel reinforced by nanoparticles, is summarized. The relation between lightweight and functionality of hot stamping steel parts, the relation between strength and hydrogen embrittlement and the influence mechanism of microstructure refinement on strength and toughness are analyzed. The suggestions for the further development direction of hot stamping steels are put forward.

A U-shaped thin-walled structure part model of T300 carbon fiber reinforced AG80 epoxy resin (T300/AG80) composite was established by ABAQUS finite element software. The stress and springback amount (synchronous demolding by simulation) changes during hot-press curing molding and the residual stress distribution after demolding were studied. The simulation of residual stress was verified by the small-hole test method. The results show that during the molding process, the stress and springback amount of the side wall and bottom surface of the U-shaped structure part increased with time. The stress and springback amount increased with the distance from the bottom surface or the distance from the center of symmetry. After demolding, the residual stress at the center of symmetry of the U-shaped structure part was the smallest, and the residual stress increased with the distance from the bottom surface or the distance from the center of symmetry. The greater the residual stress released before and after demolding, the greater the springback amount. The relative error between the residual stress measured by the small-hole method and the simulation was less than 10%, indicating the simulation was accurate.

With DX56D+Z, HC220BD+Z, HC420LA and HC420/780DP automobile steel sheets as research materials, flow stresses and plastic strains obtained by uniaxial tensile testing were fitted by Ludwik, Swift, Hockett-Sherby, Voce, Swift-Hockett-Sherby and Swift-Voce hardening models, and the fitting accuracy of the six hardening models was compared and analyzed. With HC420/780DP steel sheet as an example, the fitting effect of the six hardening models was analyzed for predicting flow stresses in a large strain range (after necking).The results show that in the plastic deformation stage, the growth mode of flow stresses described by Hockett-Sherby hardening model was the closest to the test results, and the fitted flow stresses coincided with the measured results at the highest degree. The difference of flow stresses in the large strain range of HC420/780DP steel obtained by extrapolation with the six hardening models was relatively large. Swift-Hockett-Sherby and Swift-Voce mixed model had higher degrees of freedom of fitting, and had more significant fitting effect.

The effects of wear time, load, rolling speed, and relative humidity on the number of wear particles on surface of soft styrene-butadiene rubber wheel and the rubber wheel temperature were studied with a self-designed friction and wear testing machine. The wear mechanism under different working conditions was analyzed. The influence degree of each factor was analyzed by orthogonal experiment. The results show that the number of wear particles increased with the increase of wear time and load, and decreased with the increase of rolling speed and relative humidity. The number of wear particles with particle size of 2.5 μm and the temperature of the rubber wheel had the same changing trend with various factors. The amount of the small wear particles could be predicted by temperature changes. The wear mode was fatigue wear under low load, and was fatigue wear and abrasive wear under high load. The order of the influence degree of each factor was load, rolling speed, relative humidity, type of grinding wheel. When the load was 100 N, the rolling speed was 8 m·s ^-1, the relative humidity was 60% and the grinding wheel was a cement wheel, the number of wear particles was the least.

Ti-6Al-4V alloy was prepared by selective laser melting (SLM) technique, and the effect of laser scanning speed (705, 805, 905, 1 005, 1 105 mm·s ^-1) on internal defects, microstructure and mechanical properties of the alloy was studied. The results show that the pore defects and the porosity of Ti-6Al-4V alloy formed by SLM increased with the scanning speed. The alloy microstructure was composed of needle-like α' martensite, and the scanning speed had little effect on the microstructure morphology. With the increase of laser scanning speed, the tensile strength, yield strength and microhardness of the alloy decreased, and the elongation did not change much. The tensile fracture form of the alloy was ductile fracture, and there were deeper tensile cracks and more unmelted particles and spheroidization in the fracture at higher scanning speed.

Laminated structures designed by bionics principle can better solve intrinsic brittleness problems of carbide ceramics. It is now one of the most effective ways to strengthen and toughen carbide ceramics, and has good application prospects. The structural design features of laminar ceramics are described. The preparation, performance and main toughening mechanisms of SiC and B ₄C laminar ceramics are reviewed. The development of carbide laminar ceramic materials is summarized and prospected.

The hydrothermal parameters were optimized by orthogonal tests to prepare WO ₃ nanowires with sodium tungstate as tungsten source, hydrochloric acid as regulator, ammonium sulfate as auxiliary agent, and then the reticular WO ₃/poly 3,4-ethylenedioxythiophene (PEDOT) nanowire hybrid structure film was prepared by electrodeposition method. The structure and electrochromic properties of the film were studied. The results show that the electrochromic performance of WO ₃ was optimal under hydrothermal reaction temperature of 190 ℃, time of 4 h and pH of 2, and the contrast was 80.6%. The WO ₃/PEDOT film with hybrid structure of score-shell nanowire was successfully prepared by electrochemical deposition under optimal hydrothermal conditions, and the outer side of the WO ₃ monocrystalline nucleus was covered by an amorphous thin shell. Compared with WO ₃ nanowire and PEDOT, WO ₃/PEDOT film showed excellent electrochromic and optical modulation properties, fast response speed and good cycling stability. The contrast of the film was 89.1% wth the coloring time of 3.4 s and the fading time of 2.2 s, and after 1 000 cycles, the contrast was retained 98.8%.

Silicon carbide ceramic has high strength and thermal conductivity, and good chemical stability, and is widely used in aerospace, petrochemical, integrated circuits and other fields; however, defects are easy to form in the silicon carbide ceramic during processing because of its high hardness and brittleness, which restricts the application of silicon carbide ceramic with complex structures. The preparation processes of silicon carbide ceramic with complex structures are described, and the advantages and disadvantages of the commonly used preparation technologies, such as cold isostatic pressing combined with pressure-free sintering, gel injection molding combined with reactive sintering, slip casting combined with reactive sintering, 3D printing combined with reactive sintering, are analyzed in order to provide a certain theoretical reference for the preparation of silicon carbide ceramic with complex structures.

Shaft parts are prone to failing such as friction, wear, corrosion and fatigue during service, which seriously affect the normal operation of construction machinery equipment. Laser cladding technique, as a common technical means for repairing and remanufacturing shaft parts, can effectively extend service lives of parts. The application of laser cladding technique in the remanufacturing of shaft parts is summarized. The influence of laser cladding process parameters (laser power, cladding speed, overlap rate and powder feeding amount) and cladding material selection on the repairing performance of shaft parts and the auxiliary application of simulation software are focused on. The development trend of laser cladding remanufacturing technique is prospected.

Two kinds of Al ₂O ₃ powder with average grain size of 0.31, 0.77 μm (named as 1 ^# and 2 ^#, respectively) was molded by low solid content (volume fraction of 45%) gelcasting, and then was cold isostaticly pressed (CIP) and pressurelessly sintered to obtain Al ₂O ₃ ceramics. Effects of powder and CIP pressure on densification of Al ₂O ₃ green body and ceramics were studied. The results show that the Al ₂O ₃ powder with smaller grain size was more difficult to disperse, and required higher addition amount of polyacrylate ammonium dispersant; the obtained green body and sintered ceramics had lower relative density. With increasing CIP pressure, the relative densities of the two Al ₂O ₃ green bodies increased, and the pores decreased; the relative densities of the two sintered ceramics showed a trend of increase first, then decrease, and then being stable. When the CIP pressures were 350-400 MPa, the two ceramics had the maximum relative densities and less intercrystalline pores.

In simulated wet desulfurization slurry flow environment, the effect of impact angle of NaCl solution+quartz sand acid slurry with sample impact surface on the erosion behavior of Cr30A high chromium cast iron was studied. The results show that the mass loss of the cast iron was relatively large under the interaction of corrosion and abrasion after the slurry impacted the cast iron at angles of 60° and 30°. The mass loss of the cast iron was relatively small after the slurry impacted the cast iron vertically, and the main cause of the mass loss was impact abrasion. The mass loss of the cast iron was the smallest after the slurry impacted cast iron parallelly, and the main cause of the mass loss was pitting. When the cast iron was subjected to the paralled impact of the slurry, its erosion mechanism was mainly micro-cutting. When subjected to the 30° angle impact of the slurry, the erosion mechanism was mainly cutting and plowing, and extrusion edges, impact pits and shallow flaky fatigue peeling existed on the cast iron surface. When subjected to the 60° angle impact of the slurry, the erosion mechanism was mainly deep material layer peeling and severe corrosion abrasion. When subjected to the vertical impact of the slurry, the erosion mechanism was mainly the shedding of surface material, accompanied by slight corrosion abrasion.

Considering the effects of coating, and the effects of tensile time, tensile rate, viscoelastic stress and reaction force on initial stress, the improved hyperelastic constitutive and viscoelastic constitutive model of thermoplastic polyurethane composite fabric and a single fiber bundle were established by tensile test. The stress-strain and stress relaxation curves during the tensile process were predicted and compared with the test results. The results show that the established hyperelastic constitive model could accurately predict the stress-strain curve of the fabric and the single fiber bundle, and the realtive errors were less than 3.5%. The viscoelastic constitutive model could accurately predict the stress relaxation curve of the fabric, and the relative error was less than 3.21%.

The mixture of Ti powder, Sn powder and C powder with mass ratio of 2:1:1 was mechanically alloyed in a simoloyer mill, and then was treated by aging at room temperature. The phase composition, microstructure and formation mechanism of Sn whiskers in the mechanical alloying powder were studied. The results show that flocs appeared in the power mixture after mechanical alloying and aging at room temperature, and were composed of Sn whiskers. The Sn whiskers were columnar, collicular-shaped or nodular, knotted or curved, and needle-shaped single crystal β-Sn with body centered tetragonal structure. The whisker had a diameter of about 100 nm, and the zone axis was[011] zone axis of β-Sn. Under heat and huge stresses produced by mechanical alloying, the recrystallization and direct growth of Sn occurred, and then Sn whiskers were obtained.

Accelerated water bath moisture absorption tests at 25 ℃ and 50 ℃ were carried out on carbon fiber reinforced polymers (CFRP) laminates, and the uniaxial tension and three-point bending tests were performed. The rule of the moisture absorption, tensile strength and bending strength varying with the moisture absorption time and the bath temperature was studied. The failure mechanism of the CFRP laminates was discussed. A residual strength model of CFRP laminates was established by fitting the experimental data. On the basis of the environmental equivalent coefficient, the hygrothermal aging life of the laminates was predicted. The results show that the average saturation moisture absorption rate of CFRP laminates at 50 ℃ was 0.77%, and was larger than 0.33% at 25 ℃. At the same moisture absorption time, the moisture absorption rate at 50 ℃ was higher than that at 25 ℃. The tensile strength and bending strength decreased by 7.4% and 17.2% after moisture absorption saturation at 50 ℃ compared with that before moisture absorption, respectively, and the decrease degree was higher than those after moisture absorption saturation at 25 ℃. The higher the bath temperature, the more serious the interface damage between CFRP laminate carbon fiber and resin, and the more obvious the cracks. The real aging life prediction method on the basis of residual strength and environmental equivalent coefficient could provide evidence for the service reliability evaluation of CFRP laminates in hygrothermal environment.

CoCrFeNiTiCuMo _xV _x( x=0.5,1.0,1.5,2.0, atomic ratio) powder was mechanically alloyed in a high-energy planetary ball mill to prepare high entropy alloy powder, and influence of molybdenum and vanadium content on the phase composition, grain size and lattice strain of the alloy powder was studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the diffraction peaks of pure metal phases disappeared, and the alloy powder with a dual-phase structure of BCC+FCC was obtained after high-energy ball milling. The content of BCC phase increased, FCC phase decreased with the increase of molybdenum and vanadium content. The alloy powder particle size was between 100-200 nm, and the particles were flat. The grain size of the alloy powder decreased and the lattice strain increased as the content of molybdenum and vanadium increased.

The thick-wall parts of Inconel 625 alloy were prepared by additive manufacturing technique using cold metal transition (CMT) arc as heat source. The microstructure and properties of the parts under oscillating and two-pass multi-layer arc trajectories were comparatively studied. The results show that spatter appeared during the additive manufacturing with oscillating arc trajectory, and the surface of the thick-wall parts was rough; no obvious spatter appeared during additive manufacturing with two-pass multi-layer arc trajectory, and the surface was smooth. The growth mode of dendritic crystals in the thick-wall parts was epitaxial growth, and there were secondary and tertiary dendrites in the dendritic crystals; the dendrite spacing under oscillating arc trajectory was smaller than that under two-pass multi-layer arc trajectory. The average tensile strength of the thick-wall parts under two-pass multi-layer arc trajectory was higher than that under oscillating arc trajectory. The anisotropy percentages of the tensile strength of thick-wall parts under oscillating and two-pass multi-layer arc trajectory were very small, which were 4% and 4.5%,respectively. The fracture type of thick-wall parts was ductile fracture.

Surface texture technique is a new type surface modification technique, which can effectively improve the tribological properties of materials through machining patterns with a certain shape and size, and with regular arrangement on the surface of materials by micro-fabrication technique. Surface texture plays an important role in mechanical friction pairs because of its outstanding advantages in improving the tribological characteristics of materials. The common texture preparation methods are introduced; the wear reducation mechanism of surface texture under different working conditions is described; the influence of surface texture topography and its geometric parameters on the wear resistance is summarized. The development direction of surface texture technology is prospected.

Research progress on four piezoelectric application materials in the field of energy harvesting, including piezoelectric ceramics, multi-stacked piezoelectric ceramics, piezoelectric polymers and piezoelectric composites, is reviewed. The structural characteristics, preparation methods, and application occasions are highlighted, and the research trends of the piezoelectric materials in future is proposed.

12 groups of welding process parameters (welding current at 60, 70, 80, 90, 100, 110 A, welding speed at 1.96, 2.88 mm·s ^-1) were set by uniform experimental design. The welding finite element model of DP780 dual phase steel was established. By the simulation and experiments, the optimal welding current and welding speed were determined with the minimum deformation of the joint as the index. The temperature field and the content of martensite in coarse-grained zone of heat affected zone (CGHAZ) of the joint were simulated by the welding finite element model, and verified by the thermal simulation experiment. The results show that the deformation of the welded joint was the smallest with the welding current of 100 A and the welding speed of 1.96 mm·s ^-1, and the relative error between the finite element simulation and the experimental result was 3.528%, indicating that the model was accurate. By the finite element simulation, the area with a distance of 2.44-6.97 mm from the weld center was the CGHAZ. The area fraction of martensite in CGHAZ was 43%, which was close to that (44%) in the CGHAZ sample prepared by the thermal simulation experiment, indicating that the established model could be used to simulate the CGHAZ structure.

Two titanium-sulfur containing free-cutting steels with titanium content (0.09wt% and 0.21wt%) were smelted and forged at 1 200 ℃. The morphology, size and quantity of sulfides in the structure and the mechanical properties of the as-cast and forged test steels were compared and studied. The results show that in the as-cast test steel, most of the manganese sulfides were short-rod-like and spherical, and distributed in chains or nets along the grain boundaries. After forging, the manganese sulfides extended along the forging direction, the statistically obtained length-width ratio increased, and the quantity per unit area decreased. The increase of titanicum content increased the quantity per unit area of manganese sulfides. The tensile fracture surface of the as-cast test steel showed cleavage terrace and river pattern, and the fracture mode was brittle fracture. The tensile fracture after forging showed cleavage and dimple mixed morphology, and the fracture mode was ductile fracture. The tensile properties and the impact toughness of the forged test steel were better than those of the as-cast steel, indicating forging was helpful to improve the mechanical properties of the titanium-sulfur containing free-cutting steel.

The effects of volume fraction of piezoelectric phase, and elastic modulus and Poisson's ratio of polymer on the piezoelectric properties of 1-3 type piezoelectric ceramic composite were simulated by finite element software, and the simulation was verified by experiments. The results show that the electromechanical coupling coefficient of the composite was relatively high and changed little when the volume fraction of the piezoelectric phase was 30%-85%. With increasing elastic modulus and Poisson's ratio of polymer, the series connection resonance frequency of the composite increased, and the electromechanical coupling coefficient decreased. The finite element model could accurately simulate the series connection resonance frequency and electromechanical coupling coefficient of the relatively hard polymer filled composites, and the relative error was less than 5%. The model was not suitable for the simulation of the electromechanical coupling coefficient of the relatively soft polymer filled composites.