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.

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.

Development of high speed and high performance of mechanical equipments requires higher strength and better wear resistance of wear-resistant copper alloys. Although performance of traditional aluminum bronze series, manganese brass series and lead brass series alloys has been improved, their application scope is limited by various factors, such as material characteristics, processing technology and environmental protection, respectively. The application status and research progress of five typical wear-resistant copper alloys with high application values including Cu-Ni-Sn series, Cu-Al₂O₃ series, Cu-Nb series, Cu-C series (including copper/graphite, copper/graphene and copper/carbon nanotubes) and complex brass are described from preparation process, properties and application field. The problems in their development and application are analyzed, and their development prospect is also discussed.

The hardness of the 1Cr5Mo steel fastening nut of a supercritical unit steam turbine in a thermal power plant was reduced significantly after service. Aiming at this phenomenon, the aging tests (equivalent to service) of the 1Cr5Mo steel nut were carried out at 566 ℃. The effect of aging time on the microstructure and mechanical properties was studied, and the microstructure and performance were compared with those of the nut served at 566 ℃ for 10⁵ h. The results show that at temperatures not higher than 566 ℃, the microstructure of the 1Cr5Mo steel nut changed slowly; the microstructure was still martensite and carbide after aging for 2 880 h. But the microstructure changed to tempered sorbite after service for 10⁵ h. With the extension of the aging/service time, the carbides migrated and concentrated from the inside grain to the grain boundary, and became obviously coarsened. The deterioration of the structure led to the reduction of the hardness, strength, and impact energy of the nut.

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.

Two types of unclosed staircase chart were cited, and reasonable assumptions were made on the test results that may appear during the staircase fatigue test. The effect of test data closed or not on the fatigue strength was analyzed when the fatigue strength was statistically estimated by the staircase method. The results show that when the last-level stress in the staircase chart of unclosed test data was lower than the first effective stress, the statistically estimated fatigue strength after subsequent supplementary of hypothetical staircase chart was also lower than the statistically estimated fatigue strength from the original unclosed fatigue test staircase chart. When the last-level stress of the staircase chart of unclosed test data was higher than the first effective stress, the statistically estimated fatigue strength after subsequent supplementary of hypothetical staircase chart was also higher than the statistically estimated fatigue strength from the original unclosed fatigue test staircase chart. Even if test data was not closed, the fatigue strength statistically estimated from failure events and non-failure events may be equal.

Microstructure, mechanical properties and corrosion resistance of 25Cr2Ni4MoV steel welded joint were compared and studied under conditions of pre-welding and post-welding quenching and tempering treatments. The quenching and tempering process was oil quenching at 920 ℃ for 1 h and tempering at 580 ℃ for 2 h. The welding process was manual electrode arc welding. The results show that by pre-welding quenching and tempering, the microstructure of the joint weld zone consisted of lath martensite, network δ-ferrite and M₂₃C₆ carbide. After the post-welding quenching and tempering, the δ-ferrite in the weld was dissolved, and the lath martensite, tempered sorbite and M₂₃C₆ carbide were formed. Under the post-welding quenching and tempering condition, the lath martensite in the weld was small and uniform, and the M₂₃C₆ carbide distributed in granular shapes on original austenite grain boundaries and martensite lath grain boundaries; the strength, impact toughness and corrosion resistance were better than those by the pre-welding quenching and tempering treatment.

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 Zn²⁺.

40Cr13 plastic die steel was quenched at different temperatures (960,1 020,1 080,1 140 ℃), and the effect of quenching temperature on microstructure and hardness was studied. The steel was tempered at 200 ℃,and the corrosion resistance of the steel was studied by immersion test and electrochemical test. The results show that the microstructure of the test steel after quenching at different temperatures was composed of quenched martensite, carbides and a small amount of retained austenite. The microstructure became coarse with increasing quenching temperature, and the number of carbides decreased. When the quenching temperature was 1 140 ℃, network carbides precipitated on austenite grain boundaries in the microstructure. The hardness of the test steel increased first and then decreased with increasing quenching temperature. When the quenching temperature increased from 960 ℃to 1 080 ℃, the corrosion rate of the test steel after tempering in FeCl₃ solution decreased; the diameter and depth of pitting holes on the surface of the test steel decreased, and the number increased. The free-corrosion potential of the test steel in NaCl solution increased, and the free-corrosion current density decreased; the corrosion rate decreased and the corrosion tendency decreased. The optimum the quenching temperature was 1 020 ℃; at this point, the quenched martensite was relatively small, and the hardness was the largest; the corrosion resistance was relatively good.

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.

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 Mg₂Si phase gradually disappeard and redissolved in the matrix; but the solution time had no effect on the content and morphology of α-Al₈Fe₂Si phase and β-Al₅FeSi phase. After solution treatment, with increasing aging temperature or aging time, the number of second phase Mg₂Si increased, but a higher temperature or a longer aging time resulted in the coarse of the Mg₂Si 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 Mg₂Si 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.

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.

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.

The pulsed ultra-narrow-gap welding (UNGW) was applied to 1Cr18Ni9Ti austenitic stainless steel plate with 20 mm thickness. The microstructure, mechanical properties and corrosion resistance of the pulsed UNGW joint were analyzed. The results show that the microstructures of backing weld zone in pulsed UNGW joint were austenitic equiaxed grain+lath δ-ferrite; the microstructures of filling bead and cover pass weld zone were columnar austenite+lath and cellular δ-ferrite. The microstructures of partially melted zone were austenite + vermicular δ-ferrite; the microstructures of imperfect mixing zone were austenite+δ-ferrite, and their shape was disorderly. The microstructures of heat affected zone were austenite+striped δ-ferrite. The ductility and toughness of the pulsed UNGW joint were better than those of the direct-current UNGW joint, but the strength was lower than that of the direct-current UNGW joint. The corrosion resistance of fusion zone+heat affected zone, weld zone, whole joint and base metal of the pulsed UNGW joint increased in turn in NaCl solution. The intergranular corrosion resistance of the pulsed UNGW joint in nitric acid solution was worse than that of the base metal without sensitizing and the direct-current UNGW joint, but was better than that of the sensitized base metal.

The grain growth during the annealing process of pure copper with homogeneous and heterogeneous structure (gradient structure and bimodal structure) were simulated by the phase field model and the ideal grain growth model. The results show that the change of grain boundary energy barrier had little effect on the growth rate of grain with homogeneous structure. When the annealing time was longer than 600 s, the growth rate of homogeneous structural grains had a larger step change. For heterostructural grains, the greater the grain boundary energy barrier, the slower the grain growth. In the gradient structure, the growth rate of small grains was the fastest, followed by that of medium grains, and that of large grains was the slowest. The larger the grain size, the smaller the influence of the grain boundary energy barrier on the growth rate. In the bimodal structure, the grain boundary energy barrier had greater influence on the growth rate of coarse grains than the fine grains. The growth rate of fine grains significantly decreased and of coarse grains increased after increasing number of coarse grains.

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.

Applying an external electromagnetic field is one of the ways to improve the tribological performance of the friction pair. From three aspects of the promotion of dislocation movement, the enhancement of the oxidation of the contact surface and the refinement and oxidation of the wear debris by the external electromagnetic field, the mechanism of the electromagnetic field improving the tribological performance of the metal material friction pair is reviewed. The influence of the external electromagnetic field type, the magnetic field strength, the magnetic field application direction, the magnetic field frequency, the magnitude and difference of magnetic permeability of the friction pair material and the size of the external magnetic particle on the friction and wear of the friction pair is discribed. The future research direction on the anti-friction of the electromagnetic field is pointed out.

The microstructure and mechanical properties at different positions of the two cast iron dryers in a paper mill after service for 62 a and 43 a were studied. The results show that there was no obvious surface defects and crack defects on the cylinder and end cover of the two dryers. The microstructure of substrate was pearlite without obvious spheroidization, and the size and distribution of the graphite sheets were mainly A type. The length of the graphite sheet of the front end cover of the dryer after service for 62 a and the rear end cover of the dryer after service for 43 a was relatively long. The hardness of the cylinder and the end cover of the two dryers all met the standards. The tensile strength of the front end cover of the dryer after service for 62 a was lower than the standard requirements, while those of the other positions of the two dryers all met the standard requirements. The tensile strength of the front end cover of the dryer after service for 62 a and the rear end cover of the dryer after service for 43 a was obviously lower than that of other positions. Both the two dryers still had sufficient strength under the maximum working internal pressure load of 0.22 MPa.

The microstructure, tensile properties and corrosion resistance of a new BGNDMA low-alloy steel were studied and compared with the properties of 09CrCuSb steel and 2205 duplex stainless steel. The results show that the microstructure of the BGNDMA steel was ferrite and pearlite, and the tensile properties were better than those of 09CrCuSb steel. When immersed in 70 ℃, 50wt% H₂SO₄ solution for 24 h, the corrosion rates of most samples were not higher than 80 g·m^-2·h^-1, and the statistical average value was about 36.367 g·m^-2·h^-1, indicating the excellent resistance to sulfuric acid corrosion. In the dead green liquor and the industrial flue gas dew point (not higher than 80 ℃) corrosion environment, the BGNDMA steel underwent uniform corrosion, and 2205 duplex stainless steel underwent local corrosion such as pitting corrosion and crevice corrosion; BGNDMA steel was expected to replace 2205 duplex stainless steel in H₂SO₄-HCl mixed acid dew point corrosion environment. In an industrial flue gas dew point corrosion environment, the corrosion resistance of the hot rolled BGNDMA steel was better than that of the normalized steel.

The bainite transformation point at different quenching temperatures (950-1 100 ℃) and the continuous cooling phase transformation point at the optimal quenching temperature of 20Cr1Mo1VTiB steel were measured on a thermal dilatometer. Then the continuous cooling transformation curves were drawn by combination of the phase transformation points, microstructure observation and hardness test. The relationship between the phase transformation point or transformation amount and the cooling rate was established with empirical equations, and the phase transition activation energy was calculated. The results show that the bainite transformation temperature of the test steel decreased with increasing quenching temperature; the preferred quenching temperature was 1 050 ℃. The supercooled austenite transformation products were proeutectoid ferrite, pearlite and bainite with cooling rates not higher than 0.5 ℃·s^-1, and were single bainite with cooling rates higher than 0.5 ℃·s^-1. The fitting curves of phase transformation point- and phase transformation amount-cooling rate were in good agreement with the test results. The activation energy of proeutectoid ferrite and bainite transition was 744.8, 274.9 kJ·mol^-1, respectively.

The plastic parameters of materials were extracted from the loading part of load-depth curves obtained by coupling single indentation test and finite element simulation, and combining inverse method and simulated annealing particle swarm optimization. The strength of different metal materials was estimated on the basis of Ludwig hardening model and compared with the results obtained by uniaxial tensile test. The results show that the load-depth curves obtained by simulation almost coincided with those obtained by tests, and the relative error was less than 0.5%, indicating that plastic parameters could be extracted from indentation load-depth curves by simulated annealing particle swarm optimization. The true stress-true plastic strain curves extracted from indentation load-depth curves by inverse method based on Ludwig hardening model were not unique, but obvious convergence tendency of the strength estimated from the extracted true stress-true plastic strain could be observed. The strength of different metal materials obtained by the indentation tests was close to that obtained by tensile tests; the biggest relative errors of the yield strength and tensile strength were 5.9% and 4.3%, respectively, indicating that the strength of the metal materials could be evaluated accurately by indentation test method.

Slow tensile stress corrosion tests and stress corrosion crack growth tests were used to study the stress corrosion behavior of AISI4340 steel in water at 100 ℃ containing saturated oxygen and/or 0.1 mol·L^-1 Cl^-. The results show that the presence of oxygen or Cl^- in water at 100 ℃ could increase the stress corrosion tendency of AISI4340 steel. The stress corrosion tendency in deoxygenated 100 ℃ water containing Cl^- was not significant, and the slow tensile fracture retained some ductile fracture characteristics; complete brittle fracture of AISI4340 steel occurred in the high temperature water containing saturated oxygen, and the stress corrosion tendency was significant. Oxygen or Cl^- could increase the stress corrosion crack growth rate of AISI4340 steel in water at 100 ℃. There was an interaction between oxygen and Cl^-, so their co-existence significantly increased the stress corrosion tendency and caused rapid crack growth after cracking.

LZ92 magnesium lithium alloy plate with thickness of 2 mm was welded by CO₂ laser, and the microstructure, phase composition, micro-hardness and tensile properties of the welded joint were studied. The results show that LZ92 magnesium lithium alloy welded joint had good formability, and no obvious pores and cracks were found in the weld. The phase composition of the base metal and the weld was the same, consisting of α phase, β phase and intermediate phase Mg₇Zn₃. The base metal was composed of equiaxed β phase and dendritic and granular α phase; the heat-affected zone was composed of coarse β phase and a few fine granular α phase; a large amount of fine needle and granular α phases evenly distributed in the β phase in the weld and the grain boundaries of β phase disappeared. The hardness of the weld was the highest, followed by the base metal, and the hardness of the heat affected zone was the lowest. The tensile strength of welded joint was 158 MPa, which was 86.8% that of the base metal, and the elongation was 27%. The tensile fracture of the welded joint was located at the fusion line between the heat-affected zone and the weld; the fracture was composed of dimples and cleavage surfaces, indicating the fracture form was a mixed fracture.

CrAlN nano-multilayer films were prepared by magnetron sputtering technique under different bias voltages (-60,-70,-80,-90 V) of the substrate, and the effect of bias voltage of the substrate on the microstructure and mechanical properties of the film was studied. The results show that with increasing absolute value of the substrate bias voltage, the nitrogen content in the CrAlN nano-multilayer film increased, the phase composition unchanged, the preferred orientation changed from the CrN (111) crystal plane to the CrN (200) crystal plane, the pores on the film surface decreased, and the densification of microstructure was improved. When the bias voltage of the substrate was between -60 and -80 V, the bias voltage had little effect on the film deposition rate. When absolute value of the bias voltage was higher than 80 V, the deposition rate decreased significantly. With increasing absolute value of bias voltage of the substrate, the hardness and elastic modulus of the film increased, and the film base bonding force increased and then decreased, reaching the maximum at -80 V of bias voltage.

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.

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.

Resistance spot welding was performed on TC4 titanium alloy and 304 stainless steel sheet with copper foils of different types and thicknesses as transition layer materials. The influence of the type and thickness of the copper foils on the microstructure and properties of the joint was studied. The results show that the shear strength of the welding joint with pure copper foils as the transition layer was significantly higher than that of the copper alloy foils as the transition layer, and the welding joint with T4 copper foil as the transition layer had the highest shear strength. With increasing thickness of the T4 copper foil, the width of the reaction zone of the joint decreased, the width of the intermediate transition zone increased, and the Ti-Fe intermetallic compound in the fusion zone decreased, the shear strength of the joints increased first and then decreased, reaching the maximum when the thickness was 0.4 mm.

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%.

A mini mill rolling model was established with Deform software and then was used to simulate temperature rise and strains of the AISI1015 steel workpiece with different specifications (φ8 mm, φ10 mm, φ13 mm) and different initial temperatures (800, 850, 900, 950 ℃) during the rolling process. The reason for the difference in rolling temperature rise was analyzed. The results show that the relative errors were within 13% between the mini mill rolling model simulation and the test results of the surface temperature of the workpiece when exiting the rolling mill. During the rolling process, the temperature rise and accumulated equivalent strains in the core of the workpiece were the largest, and the smaller the rolling specification, the greater the temperature rise and strain in the core. The lower the initial temperature of the workpiece, the greater the temperature rise and the torque. The uneven temperature rise of the workpiece with different specifications was mainly caused by the uneven distribution of equivalent strains; the obvious difference of the temperature rise in the core at different initial temperatures was caused by different rolling loads.

Selective laser melting and electron beam selective melting additive manufacturing are ideal advanced high energy beam additive manufacturing techniques. The selective laser melted and energy beam selective melted Ti-Al alloy had a fine microstructure, and better mechanical properties than the cast alloy. The alloy can obtain good high-temperature creep resistance and ductility by reasonable heat treatments after the forming. The high energy beam additive manufacturing technique can solve the traditional forming problem of Ti-Al alloy component. The research progress on the preparation of Ti-Al prealloyed powder, the process and application of selective laser melting and electron beam selective melting, and the microstructure and properties of Ti-Al alloy are reviewed. The future research direction of Ti-Al alloy prepared by high-energy beam additive manufacturing is prospected.

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, Cr₂N and Mo₂N. 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.

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.

Cracks were produced prematurely in the transition area of the shoulder root of TC4 alloy fan rotor blade of an aero-engine. The cause of the cracks was studied through macromorphology observation, fracture analysis and contact discharge test. The results show that the cracks of the failed fan rotor blades were fatigue cracks, and initiated on the surface of the transition area from the root of the leaf pot side shoulder to the exhaust edge. The induction coil closed or contacted the blade substrate and contact discharge occurred, resulting in local melting and burning of the blade substrate and melting of the flow blocking agent during the brazing process of the wear-resistant layer of the blade shoulder, which was the cause of fatigue crack initiation of the blade. It was suggested that insulating the induction coil by insulating tape and using an appropriate induction current and welding distance to prevent contact discharge between the coil and the blade.

Tensile test and high/ultrahigh cycle fatigue tests with 10⁵-10⁹ cycles were carried out on selective laser melting (SLM) formed GH4169 alloy; the alloy was heat treated standardly. The tensile properties, fatigue properties and fracture morphology were studied, and the fatigue fracture mechanism was analyzed. The results show that after heat treatment, the tensile strength and yield strength of SLM formed GH4169 alloy were higher than those of forgings, but the elongation was greatly reduced, and the elastic modulus was slightly reduced. The S-N curve of SLM formed GH4169 alloy presented a stepped shape, showing inflection points near the 4×10⁵ cycles and 5×10⁷ cycles. The cracks of specimens in the high-cycle fatigue interval of 10⁵-10⁷ cycles all originated on the surface, while those in the ultrahigh cycle fatigue life interval exceeding 10⁷ cycles were mostly generated inside. The internal crack source was the circular keyhole produced by the high laser energy density, and the residual carbide in the hole accelerated the crack initiation and reduced the fatigue life.

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.

AA5083 aluminum matrix composite reinforced by FeCoNiCrAl high-entropy alloy particles were prepared by friction stir processing. The effect of the traverse speeds (45,60,75 mm·min^-1) on the high-entropy alloy particle distribution, microhardness and wear resistance of the composite was studied. The results show that no new phases were formed in the prepared composite. The microhardness of the composite was higher than that of the aluminum alloy matrix. With the increase of the traverse speed, the distribution uniformity of the high-entropy alloy particles became worse and the microhardness of the composite decreased slightly. The average friction coefficient and wear rate of the composite were lower than those of the aluminum alloy matrix. With the increase of the traverse speed, the friction coefficient and wear rate of the composite increased, and the wear resistance decreased. The wear mechanisms of the composite and aluminum alloy were abrasive wear and adhesive wear, respectively.

TC8 titanium alloy was subjected to room temperature quasi-static tensile tests at different strain rates (0.000 1, 0.001, 0.01 s^-1) and dynamic compression tests at different strain rates and temperatures on the Hopkinson pressure bar device. The quasi-static and dynamic mechanical properties of the alloy were studied. The test data was fitted to obtain the parameters and then J-C constitutive model was established. The constitutive model was verified by tests. The results show that the yield strength, tensile strength and maximum equivalent failure plastic strain of TC8 titanium alloy all increased with increasing strain rate in the quasi-static tensile tests. The yield strength and ultimate strength of the alloy increased with increasing strain rate in the room temperature dynamic compression test, exhibiting an obvious strain rate strengthening effect; the yield strength and ultimate strength decreased with increasing temperature, exhibiting a significant temperature softening effect. The true stress-true strain curve calculated by the fitted J-C constitutive equation was consistent with the test results, and the average relative error was 4.82%, indicating that the constitutive model could predict the dynamic mechanical properties of TC8 titanium alloy at high temperature.

A rutile type SG90T-9C slag-gas bonded protection flux cored welding wire was developed. The effect of the amount of silicon and manganese on microstructure and properties of the welding wire deposited metal and weld metal by welding Q960E steel was studied. The effect of heat input on morphology of M/A island in the weld microstructure was studied. The comprehensive properties of SG90T-9C welding wire were compared with CHT91K2, ESAB91K2 welding wires and H08Mn2SiA welding wire coupling HJ431 flux. The results show that with increasing manganese and silicon addition, the tensile strength of the deposited metal increased, and the impact toughness increased and then decreased. With increasing heat input, the M/A island shape changed from point to block and the island gathered on boundaries. The heat input should be controlled within 10 kJ·cm^-1. Compared with other welding materials, the SG90T-9C welding wire deposited metal had excellent mechanical properties, the weld quality by welding Q960E steel was better, and the porosity and repair rate by welding Q960E steel frame reduced significantly.

Dense transverse cracks were found on the backfire surface of the water-wall tube in the soot blower cover after the supercritical boiler ran for 1.2×10⁴ h. By data investigation, material composition inspection, and analysis of microstructure, fracture morphology and tensile properties, the causes of surface cracks of the water-wall tube were investigated. The results show that the material of the water-wall tube was normal, and the cracks on the tube outer wall of the backfire surface were thermal fatigue cracks. The outer diameter of the soot blower cover was too large, making the cover being topped on the water-wall tube around the soot blowing hole. Meanwhile, the temperature was low, making the soot blowing steam carrying water. The water dropped along the gap between the water-wall tube and the soot blowing sleeve to the backfire surface of the water-wall tube, causing the bearing of long-term heat and cold alternating stresses, and finally thermal fatigue cracking occurred.

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.