Ultrasonic surface rolling processing was conducted on the pure titanium TA2, and the microstructure and residual stress distribution on cross section were studied. The load-indentation depth curves at different distances from surface were measured by nanoindentaion tests, and then the stress-strain curves were obtained by inversion. With the stress-strain relationship as the material property, the load-indentation depth curves were simulated by the finite element method, and were compared with the test curves to verify the inversion method. The influence of the initial yield stress and strain hardening exponent on the load-indentation depth curves was investigated. The results show that a gradient structure with gradually increasing grain size was formed in the sample surface layer, and the residual compressive stress increased and then decreased with increasing distance from surface. The load-indentation depth simulation curves were basically consistent with the test curves, and the relative errors of the maximum indentation depth were within 8%, indicating the inversion method was reliable. With increasing initial yield stress and strain hardening exponent, the loading curvature of the load-indentaion depth curves increased, the plastic work to total work ratio decreased, and the variation of the initial stiffness was not obvious.

The high temperature endurance test of G115 steel was carried out under different stresses at 625—700 ℃ to study its high temperature endurance performance, and the 1×10⁵ h long-term endurance strength of the steel was extrapolated by the Larson-Miller(LM) parameter method. The oxidation test of G115 steel was carried out at 650 ℃/27 MPa steam parameter for 2 000 h, and the surface and cross-section morphology, phase composition and microarea composition of the oxide film were studied and compared with those of T92 steel. The results show that under the action of reinforcement of copper-rich phase, the long-term endurance strength of G115 steel at 650 ℃ was 82 MPa, which was significantly higher than 53 MPa of T92 steel. The steam oxidation resistance of G115 steel was better than that of T92 steel, and the thickness of oxide film on the surface of G115 steel was about 102 μm, which was smaller than about 110 μm of T92 steel. The oxide film structure of the two was similar. The outer oxide layer consisted of coarse columnar Fe₃O₄, and the inner oxide layer consisted of fine Fe-Cr spinel and a small amount of Fe₃O₄; the outer oxide layer had many holes, and the tendency of spalling was relatively large.

The surface of recrystallized tungsten was irradiated by helium ions with different energy and ion fluence. The microstructure of tungsten with irradiation damage of 0.2,0.5,1.0 dpa was observed. The nanoindentation test was conducted with spherical indenter of different radius (1,5,10 μm) to obtain the indentation stress-strain curve, and the change of mechanical properties and reason for the change were explored. The results show that the thickness of damage layer on tungsten surface was 554-558 nm after irradiation with different damage degree. With increasing damage degree, the density of dislocation loop in tungsten increased obviously. The indentation stress-strain curves of tungsten after irradiation did not exhibit pop-in phenomenon, and the yield strength increased with damage degree, and the indentation elastic modulus basically unchanged. The dislocation loop defect caused by irradiation was the direct cause of the change of mechanical properties of tungsten. The mechanical properties of tungsten had the effect of indentation size. The smaller the indenter radius, the higher the yield strength of tungsten, and the greater the indentation stress when the stress-strain curve of unirradiated tungsten showed pop-in.

Transient liquid phase diffusion bonding of 5A06 aluminum alloy was carried out by using Al-Cu-Si-Ni amorphous foil as the interlayer in argon protection atmosphere with banding time of 10 min and bonding pressure of 2.5 MPa. The influences of bonding temperature (550-590℃) on the microstructure and performance of joints were studied. The results show that the increase of bonding temperature could promote the diffusion of interlayer melting point depressant elements(Cu,Si and Ni), and reduce the formation of brittle phase in weld microstructure, and thus improve the tensile strength of the joint; but the tensile strength of the joint decreased when the bonding temperature was 590℃. The optimum bonding temperature was 580℃ under test conditions; at this point, the diffusion of melting point depressant elements between the interlayer and the base metal was sufficient, and the joint interface was fuzzy, indicating the joint quality was good; the weld center had the smallest hardness of 76.5 HV and the largest tensile strength of 239 MPa, and the fracture mode was ductile fracture.

Carbon ceramic composite for aircraft brake block with density of 2.0-2.2 g·cm^-3 was prepared on the basis of carbon carbon body by liquid phase siliconizing method. The phase composition, microstructure and mechanical properties of the material were studied. By simulating different braking conditions of aircraft, the dry and wet friction and wear performance of the material friction pair under 1.4 MJ load was studied by a large sample test bench. The results show that the material was composed of carbon phase, β-SiC phase and silicon phase, and SiC phase mainly distributed between carben fiber bundles and the mesh layer composed of chopped carbon fibers. The material had vertical and parallel bending strength of 132.7, 135.5 MPa, respectively and interlaminar shear strength of 12.2 MPa. Under the braking pressure of 0.2-0.5 MPa and the braking speed of 5-27 m·s^-1, with increasing the braking speed, the dry dynamic friction coefficient of the material increased first and then decreased in the range of 0.30-0.65, and was negatively correlated with the braking pressure. Under the braking pressure of 0.5 MPa, when the braking speed increased from 25 m·s^-1 to 27 m·s^-1, the attenuation rate of wet dynamic friction coefficient was less than 10%. Under the braking pressure of 0.55 MPa and the braking speed of 25 m·s^-1, the average linear wear rate of each surface per time was 0.001 2-0.001 3 mm, and the overall wear rate was small and relatively stable.

CaO-Al₂O₃-SiO₂ (CAS) series glass with TiO₂ doping amount (mole fraction) of 0-5.0% was prepared by traditional melt cooling method, and the effect of TiO₂ doping amount on the micro structure, thermal stability and bending strength of the glass was studied. The results show that TiO₂ mainly existed in the form of[TiO₅] unit in CAS series glass network. With increasing TiO₂ doping amount, the number of[TiO₅] unit and Ti-O-Si bond in the glass, the number of bridge oxygen in the glass network, and optical band gap of the glass all first increased and then decreased, and all reached the largest value when the TiO₂ doping amount was 4.0%. With increasing TiO₂ doping amount, the thermal stability and flexural strength of CAS series glass first increased and then decreased. When the doping amount of TiO₂ was 4%, the comprehensive performance was the best, and the glass transition temperature, bending strength and optical band gap were 798.24℃, 95.58 MPa and 3.75 eV, respectively.

As a main raw material for metal additive manufacturing, spherical metal powder characteristics play an important role in the performance of additive manufacturing parts. The efficient preparation of high-quality spherical metal powder has become an important development direction to promote the upgrading of additive manufacturing technologies and industrial applications. The main preparation methods of spherical metal powder including gas atomization, plasma rotating electrode atomization and plasma atomization are introduced. The technical principle and the influence of important process parameters on powder characteristics are discussed, and the future development direction of these three types of technologies is prospected.

Using Y₂O₃ as sintering aid, α-Sialon ceramics with MoSi₂ as a second phase were prepared by spark plasma sintering. The effect of the MoSi₂ adding amount (0-10wt%) on the microstructure and properties of the ceramics was studied. The results show that after adding MoSi₂, the α-Sialon grains in the ceramics changed from equiaxed to long rod-like. With increasing MoSi₂ adding amount, the long rod-like α-Sialon grains increased significantly, and the aspect ratio increased; when the addition of MoSi₂ was 10wt%, the grain size exhibited a significant bimodal distribution. When the addition of MoSi₂ increased from 0 to 10wt%, the relative density of the ceramics increased from 99.0% to 99.7%, the hardness decreased from 21.12 GPa to 20.44 GPa, and the fracture toughness increased from 4.80 MPa·m^1/2 to 6.13 MPa·m^1/2. In dry cutting of nickel-based superalloy, the cutting length of the ceramic tool with 10wt% MoSi₂ was 1.5 times that of the ceramic tool without MoSi₂ when it reached the wear standard, indicating the tool had excellent cutting performance; the main wear forms of the tool were flank wear and groove wear, and the main wear mechanisms were adhesive wear and abrasive wear.

HR3C steels with three grain morphologies (fine, coarse and elongated) were prepared by hot forging and solution treatment. The microstructure, precipitation morphology, hardness and impact toughness were investigated after aging at 700℃ for 500-2 000 h, and the effect of grain morphology on aging brittleness was discussed. The results show that HR3C steel with coarse grains had uniform grain size distribution, and M₂₃C₆ carbides continuously precipitated along grain boundaries. The steel had low hardness and impact toughness, and exhibited brittle fracture after aging. HR3C steel with fine grains had uniform grain size distribution, M₂₃C₆ carbides were distributed in chains at grain boundaries. The steel had higher hardness and impact toughness, and exhibited a mixed fracture of brittleness and ductility after aging. HR3C steel with elongated grains had an uneven grain size distribution, and M₂₃C₆ carbides had a discontinuous distribution grain boundaries. The steel had high hardness and impact toughness, and exhibited ductile fracture after aging.

A three-dimensional finite element model for continuous ball indentation tests was established, and the relationship between residual indentation strains and different material tensile property parameters (elastic modulus of 90-210 GPa, yield strength of 180-300 MPa, strain hardening exponent of 0.1-0.3) was simulated by a single variable method. Finite element simulation of continuous ball indentation tests was performed under 125 sets of material tensile property parameter combinations, and formulas for calculating material tensile property parameters based on residual indentation strains were obtained and verified experimentally. The results show that there was a log-linear relationship between the residual indentation strain and the modulus of elasticity and yield strength, respectively, and a power-law relationship between the residual indentation strain logarithm and the strain hardening exponent. The residual indentation strains of 316L stainless steel measured by the continuous ball indentation test were substituted into the material tensile property parameter calculation formula, and the relative errors between the elastic modulus, yield strength, and strain hardening exponent obtained by inversion and the tensile test results were 1.50%, 1.57%, and 0.22%, respectively, indicating that the stainless steel material tensile property parameter calculation method based on the residual indentation strain could meet the engineering needs.

TC4 titanium alloy and 15-5PH stainless steel was vacuum diffusion welded with Ta+Cu as composite interlayer under conventional process (raise temperature to 1 000℃ at rate of 20℃·s^-1, holding for 1 200 s with pressure of 6.7 MPa, air cooling) and step process (raise temperature to 1 050℃ at rate of 20℃·s^-1, holding for 2 s, then lower temperature to 950℃ at rate of 10℃·s^-1 with pressure of 2.8 MPa, and holding at a pressure of 6.7 MPa for 1 200 s, air cooling). The microstructure and properties of the joint were studied. The results show that the composite interlayer could prevent the element diffusion between titanium alloy and stainless steel. The tensile strength of the joint under step process was 550 MPa, and was higher than 390 MPa under conventional process, which was related to the small and shallow Kirkendal diffusion cavity, small thickness of the composite interlayer and good banding quality of Cu/Ta interface.

Poly(L-lactic acid) (PLLA)/poly(butylene adipate-co-terephthalate) (PBAT) (80/20, parts by mass)blend was prepared by melting blending. The effect of adding 1 part by mass of chain extender ADR and 1 part by mass of nucleating agent LAK on the crystallization behavior, mechanical properties, rheological behavior and thermal stability of PLLA/PBAT blend were investigated. The results show that after adding chain extender ADR, the crystallinity of PLLA/PBAT blend decreased, while the toughness and impact strength increased, and the compatibility between PLLA and PBAT was improved. After further adding nucleating agent LAK, the crystallinity of the blend increased significantly, the elongation at break and impact strength decreased, but the blend still had good toughness. Chain extender ADR improved the molding processability and heat resistance of the blend, while the improvement effect decreased slightly after further adding nucleating agent LAK. After adding chain extender ADR and nucleating agent LAK simultaneously, PLLA/PBAT blend had both high crystallinity and good properties at the same time.

The macroscopic finite element numerical model and the mesoscopic parametric evolution numerical model of laser shock peening were established. A three-dimensional multi-scale simulation method for laser shock peening was proposed. The distribution law of residual stress, dislocation density and grain size of Inconel 718 superalloy after laser shock peening was analyzed. The Sines fatigue life criterion was modified considering the influence of residual stress and grain refinement caused by laser shock peening on fatigue life, and was verified by tests. The results show that residual compressive stresses no less than 550 MPa within the impact range of the light spot on the sample surface were obtained by simulation; significant dislocation proliferation existed in the surface area, and the local grain size could be refined by about 25%; the simulation was basically consistent with the test results. The fatigue lives predicted by the modified Sines criterion were within 3 times the dispersion band, indicating that the model could predict the fatigue life of Inconel 718 superalloy after laser shock peening.

Referring to the chemical composition of 4Cr5Mo2V hot-work die steel, test steels with V mass fraction of 0, 0.55% and 0.9% were prepared, and surface ion nitriding treatment was carried out. The effect of V content on the microstructure and properties of hot-work die steel after nitriding was studied. The results show that the matrix structures of three test steels were all martensite, and the nitriding layer was mainly composed of white bright layer and diffusion layer. With increasing V content, the matrix structure of test steel was obviously refined, the distribution of white bright layer became continuous, and the thickness of diffusion layer first increased and then decreased. When the V content was 0.55wt%, the matrix structure was the finest and the diffusion layer was the thickest. Fine granular precipitates rich in C, N, Cr and V appeared in diffusion layer after added V. As the V content increased to 0.9wt%, the number of precipitates decreased and the size increased. The surface hardness and wear resistance of test steels increased first and then decreased with increasing V content. When the V content was 0.55wt%, the surface hardness was the highest, 1 287.3 HV, the friction coefficient was the lowest, 0.15, and the wear mechanism was abrasive wear.

Ferrite/austenite duplex stainless steel has a combination of good ductility and toughness, excellent corrosion resistance and high strength due to its unique microstructure characteristics, and has a wide application prospect in many fields such as marine engineering, petrochemical engineering. High-energy-density welding technique has attracted attention from scholars in recent years because of its narrow heat affected zone, low deformation level, low residual stress, high welding speed and high productivity. The research progress of high-energy-density welding is introduced from two aspects of welding method and process, and then the microstructure and properties of duplex stainless steel with high-energy-density welding and post-weld heat treatment are reviewed. Finally, the problems existing in the current research of high-energy-density welding of duplex stainless steel are pointed out and the future research direction is given.

The quasi-static mechanical properties at room temperature and dynamic mechanical properties at 20-400 ℃ of the aircraft engine casing material GH907 superalloy were investigated on the universal test machine, Hopkinson tension bar and Hopkinson pressure bar equipments. Based on the test results, the parameters in the Johnson-Cook (J-C) constitutive model and failure model were obtained by fitting, and the dynamic compression process of the test alloy was simulated. The effectiveness of the constitutive model parameters were evaluated. The results show that during tension at room temperature and the strain rates of 0-3 000 s^-1, the test alloy was sensitive to strain rates, but during compression was not. At temperatures of 20-400 ℃, the softening behaviour of the test alloy was obvious. The established J-C models could accurately predict the mechanical behavior of the alloy at different temperatures and strain rates; the relative errors between the simulation and the test results of the sample geometrical size and maximum stress were within 2%.

The F45MnVS non-quenched and tempered steel was subjected to single-pass compression tests with different deformation amounts (5%-56%) at deformation temperatures of 950-1 050 ℃ and strain rates of 0.01-5 s^-1. The effects of deformation temperature, strain rate and deformation amount on the deformation behavior and grain size of the steel were studied. According to the experimental data, the dynamic recrystallization critical strain model and the average grain size model were established, and the average size of dynamic recrystallization grains was simulated with Deform software embedded with the two models. The results show that with increasing deformation amount or strain rate, or decreasing deformation temperature, the average grain size of the test steel decreased. At relatively high strain rates, the decrease in stress by work softening was not obvious, and the dynamic recrystallization degree was relatively low; the opposite was true at relatively low strain rates. The average recrystallization grain size obtained by the simulation was in good agreement with the experimental results, and the variation of the average grain size with the deformation temperature, strain rate and deformation amount was consistent with the experimental results.

45 steel rods in forged and normalized state with a diameter of 8 mm for sealing plug were quenched at 750-880℃ for 15 min and high temperature tempered at 550℃ for 30 min. The microstructure, fracture morphology and hardness of the specimens at different quenching temperatures were studied. The effect of quenching temperature on quenching cracking was analyzed and the heat treatment process was optimized. The results show that the specimens did not crack after quenching at 750℃ and 780℃, and cracked after quenching at 800-880℃. With increasing quenching temperature, the ferrite content in microstructure decreased, the grain size increased, and the hardness first increased and then decreased. When the quenching temperature ranged from 800℃ to 830℃, the cause of quenching cracking was that the cooling rate of undercooled austenite in the martensite transformation phase region was too large, and the structural stress was concentrated in the outer layer of the specimen, which led to the propagation of crack in a mixed mode of intergranular and transgranular. When the quenching temperature ranged from 850℃ to 880℃, the grain boundary was weakened due to the higher quenching temperature, and cracks propagated along grain boundaries under the combined action of the structural stress and the thermal stress. The best tempered sorbite structure and relatively high hardness of 45 steel could be obtained and the quenching cracking could be avoided by setting a slow cooling process of 3-5 s at room temperature before quenching at 830℃ and then tempering.

Cu-1.9Be-0.25Co alloy was treated by solid solution treatment at 780℃ for 4 h and aging treatment at different temperatures(300, 320, 340, 360℃) for different holding times(1, 2, 4, 8, 16 h). The effect of aging on the precipitation behavior of the alloy was studied. The results show that the peak aging process was 320℃×8 h, and the hardness of the alloy under this process was 422 HV. The evolution of precipitates in Cu-1.9Be-0.25Co alloy during aging at 320℃ was metastable γ' phase → semi-coherent γ' phase → non-coherent equilibrium γ phase. A large number of precipitates in the early stage of aging (1-2 h) in a short time was the main factor for the rapid increase of alloy hardness. The semi-coherent relationship between precipitates and copper matrix in the middle of aging (2-8 h) was the main reason for peak aging. At the later stage of aging (8-16 h), the precipitates separated from the semi-coherent relationship with the matrix, the alloy was over aged and the hardness decreased.

The processing of GH4169 alloy forgings was simulated by 950℃ high temperature compression test. The high temperature compression deformation and dynamic recrystallization behavior of the alloy under the conditions of pulse current with different densities (0-4.5 kA·mm^-2), and the influence mechanism of pulse current was discussed. The results show that the alloy was more prone to yield during compression under the action of pulse current, and the compressive deformation resistance decreased; the decrease degree of compressive deformation resistance become more obvious with increasing pulse current density, which was directly related to the fact that the electronic wind force generated by pulse current promoted the dislocation motion. With increasing pulse current density, secondary recrystallization occurred after primary recrystallization, this was because that the pulse current could promote atom diffusion, reduce the difficulty of grain boundary migration and promote dynamic recrystallization.

Surface quenching treatment of 35CrMo steel was carried out by high power laser. The microstructure, hardness and wear resistance of surface layer under different laser power(1.6,2.4,3.2,4.0 kW) were studied. The results show that when the laser power was 1.6 and 2.4 kW, the undissolved ferrite existed on the surface layer of 35CrMo steel, and the surface layer hardness was lower than that of the substrate; the wear mass rate of the steel was almost the same as that of the substrate after grinding with GCr15 steel, indicating the steel had bad wear resistance. When the laser power was 3.2, 4.0 kW, the surface layer microstructure was all tempered martensite, and the average surface layer hardness reached 640 HV, which was about 20% higher than that after conventional water quenching. The wear mass rate under laser power of 3.2 kW was the lowest, no obvious wear trace could be found on the surface, and the wear resistance was significantly improved compared with the substrate. When the laser power was up to 4.0 kW, the higher self-tempering degree of martensite resulted in a slight decrease in hardness and wear resistance compared with the laser power of 3.2 kW.

NiCrMo alloy coating was prepared on 15CrMo steel tube surface of waste incinerator by laser cladding technique. In the simulated high-temperature corrosion environment of waste incineration plant, the high-temperature corrosion resistance of coating was studied. The results show that the laser cladding NiCrMo alloy coating was uniform and dense, and metallurgical bonded with the substrate. The weight loss rate of the coating after corrosion for 72 h in the simulated high-temperature corrosion environment of waste incineration plant was 119.02 g·m^-2, which was only 40% of that of the substrate, indicating that the coating had excellent high-temperature corrosion resistance which was mainly related to Cr₂O₃, Fe₂ (MoO₄) ₃ and NiO oxides generated in the corrosion process.

Creep-fatigue tests under stress control and strain control were conducted on P92 steel at 600 ℃. The effects of load level and load holding time on the creep-fatigue damage were analyzed. By combination of stress controlled creep-fatigue test data, introducing the modified Chaboche nonlinear follow-up hardening rate and creep strain under the framework of viscoplastic unified constitutive theory, and considering the damage evolution law, the coupled creep-fatigue damage constitutive model based on Chaboche theory was established. The creep-fatigue cyclic curves of P92 steel were simulated. The results show that P92 steel exhibited cyclic softening characteristics at 600 ℃. Under stress control, the damage of P92 steel at high load holding was positively correlated with the average stress, while the damage at low load holding was negatively correlated with the average stress. Under strain control, P92 steel showed stress relaxation behavior, and the longer the load holding time, the more obvious the stress relaxation. The established creep-fatigue damage constitutive model could simulate the cyclic characteristics of P92 steel well, and the maximum relative error of the stress simulation in creep-fatigue process was 7.30%.

The deformation mechanism and mechanical properties of nanocrystalline copper with a bimodal structure (grain size obeying bimodal distribution in statistics) were systematically investigated by combination of molecular dynamics simulation, visco-plastic constitutive model and nanoindentation test verification. The results show that during the plastic deformation, dislocations were first nucleated and expanded in the fine grain zone of the nanocrystalline copper, and the directions were parallel to each other; while the dislocation slip directions in the coarse grain zone crossed each other, and the larger the size of coarse grains, the more likely dislocation entanglement and cross-slip occurred. The flow stresses of the nanocrystalline copper with a bimodal structure increased with increasing coarse grain size, and the hardness decreased with increasing volume fraction of coarse grains. The stress variation law calculated by the visco-plastic constitutive equation was consistent with that by the empirical formula and molecular dynamics simulation, and the relative error between the flow stresses calculated by the constitutive equation and the empirical formula was less than 5%.

TiC particle-reinforced titanium matrix composites (TMC1) were fabricated by cryomilling combined with plasma activated sintering. The phase composition, microstructure, mechanical properties and strengthening mechanism of TMC1 sample were studied and compared with the composites (TMC2) prepared by ordinary high energy ball milling combined with plasma activated sintering. The results show that the matrix of TMC1 sample was composed of uniform and fine equiaxial α grains and β transformed phase with TiC particles dispersed evenly. The grain size of TMC1 sample was much smaller than that of TMC2 sample. TMC1 samples sintered at 900-1 200 ℃ were compact, and the compressive strength and hardness decreased with increasing sintering temperature. The relative density, hardness, and strength of TMC1 sample were higher than those of TMC2 sample. The strengthening mechanism of TMC1 sample was particle strengthening mechanism and fine grain strengthening mechanism.

The microstructure evolution, formation and propagation of type Ⅳ cracks, and creep rupture mechanism of ferritic/austenitic steel welded joints in thermal power plant during service are reviewed. The creep rupture behavior of weak position of the welded joints is emphatically analyzed. The influencing factors of creep rupture in the heat-affected zone of ferritic steel are summarized, and relevant suggestions for improving the creep performance of welded joints are given. Finally, the future research direction is prospected.

Friction tests were conducted on the pin-disk friction pair that was composed of cast Q235B steel for magnetic rail brake pole shoes and oil quenched hardened 45 steel. Effects of sliding speed (10-100 km·h^-1), normal load (10-80 N) and lubrication condition (dry friction, water lubrication) on the friction coefficient and wear mechanism were studied. The results show that with increasing sliding speed, the friction coefficient of the friction pair became stable within 3 s. The stable friction coefficients increased first and then decreased with increasing sliding speed. But the variation range of the friction coefficients was small, which was in 0.40-0.55. The normal load had little effect on the friction coefficient. With increasing sliding speed, the wear mechanism of the Q235B steel pin sample changed from abrasive wear to adhesive wear, and increasing normal load led to more serious adhesive wear. Water lubrication during friction could reduce the friction coefficient and the wear degree.

H13 steel formed part was prepared by cold metal transfer wire-arc additive manufacturing in different deposition paths. Based on the thermo-elastic-plastic finite element method, the thermal history of the formed part was studied. The microstructure and hardness evolution of formed part was studied by tests. The results show that the thermal history of the 5-layer single-pass and single-layer 5-pass formed part deposited in the codirection and bidirection path was basically the same. The peak temperature of the middle point of the third layer of bidirection deposited 5-layer single-pass formed part was much higher than that of the middle point of the third pass of bidirection deposited single-layer 5-pass formed part, and the heat accumulation effect of the 5-layer single-pass formed part was more obvious. The lath martensite structure of 5-layer single-pass formed part was coarsened than that of single-layer 5-pass formed part. The hardness of the codirection deposited 5-layer single-pass formed part at the same height was slightly higher than that of bidirection deposited formed part, and the hardness of the codirection deposited and bidirection deposited 5-layer single-pass formed part was basically the same. The average hardness of the 5-layer single-pass formed part was slightly smaller than that of single-layer 5-pass formed part.

TA15 titanium alloy bars were fored in (α+β) phase region, and the effect of three forging temperatures, namely t_β-15℃, t_β-30℃ and t_β-50℃ (t_β was β phase transition temperature), on the microstructure and tensile strength aeolotropy of the alloy was investigated. The results show that with the decrease of forging temperature, the content of primary α_p phase in the TA15 titanium alloy increased while that of lamellar α phase decreased, and the thickness and aspect ratio of lamellar α phase decreased; therefore the tensile strength increased. After forging at T_β-50℃, the tensile strength along the streamline direction of the TA15 titanium alloy reached 973 MPa. The tensile strength difference in three directions decreased with decreasing forging temperature. The tensile fracture of the forged TA15 titanium alloy was ductile fracture. The lower the forging temperature, the higher the content of primary α_p phase, the deeper the dimples on fractures; when more slender lamellar α phases existed, the fracture dimples were shallower.

As a commonly used metal material, copper is limited in its application due to its low strength. Because of its excellent comprehensive properties, graphene has attracted wide attention as a potential reinforcement. Graphene reinforced copper matrix composites combine the great properties of both copper and graphene, and have become an research hotspot. The preparation processes and comprehensive properties of graphene reinforced copper matrix composites are introduced. The characteristics of various preparation processes, strengthening mechanism and configuration design are emphatically discussed, and the improvement approaches to solve the two main technical difficulties of weak bonding of composite interface and difficult dispersion of graphene are summarized. Finally, the preparation process of graphene reinforced copper matrix composites is prospected.

6061-T6 aluminum alloy plate and AISI 1045 galvanized steel plate were welded by laser fusion brazing with ER4043 welding wires; the bevel angle of the aluminum alloy plate was 30°, and that of the steel was 30° and 60°, respectively.The microstructure and micro-zone composition of the brazing interface on the steel side were studied, and the tensile properties of the joint were tested.The results show that zinc-rich areas and microvoids were formed at weld toe and weld root on the brazing interface of the joint when the bevel angle of steel plate was 60°, and a continuous intermetallic compound layer was formed at other areas on the interface.For the joint wth the steel plate bevel angle of 30°, zinc-rich areas were only formed at the weld toe, and a continuous intermetallic compound layer was formed at the entire brazing interface.In the two joints, the thickness of the intermetallic compound layer on the lower area of the steel plate groove surface was higher.The thickness of the intermetallic compound layer in the joint with the steel plate bevel angle of 30° was greater than that with the steel plate bevel angle of 60°.The average tensile strength of joints with the steel bevel angles of 30° and 60° was 120.3, 151.7 MPa, respectively.The two joints fractured at the steel/weld interface during tension, and both fractured in cleavage fracture form.

Al-3.0Mg-xRE (mass fraction/%, x=0, 0.12, 0.31, RE=La+Ce) alloys containing different-content rare earth were smelted. The evolution of the microstructure, hardness and tensile properties of the alloys were investigated in cold drawing. The results show that during the cold drawing, the grains of the test alloys were elongated; the second phase particles were also elongated and fragmented to small particles, and then gradually aligned on grain boundaries and dendrite boundaries in linearity; the intensity of Copper {112}〈111〉 deforming texture increased. With increasing deformation amount, the strength of the alloys increased linearly, the plasticity decreased and the hardness increased. Proper rare earth addition (0.12%) could improve the microstructure and the mechanical properties of the alloy. However, excessive rare earth addition (0.31%) increased the number and size of the second phases in the alloy, thereby reducing the mechanical properties of the alloy. After cold drawing, the Al-3.0Mg-0.12RE alloy had the smallest and the least second phases, the highest deforming texture intensity and the best mechanical properties.

Al-8.8Zn-1.4Mg-0.5Cu-0.1Sc-0.1Er-0.1Zr alloy was subjected to isothermal compression tests on Gleeble 3800 thermal simulation testing machine under conditions of deformation temperature of 380-440℃, strain rate of 0.01-10 s^-1 and deformation amount of 45%, 60%. The hot deformation behavior of the alloy was studied, and the deformation constitutive equation and hot processing map based on dynamic material model were established. The best range of hot processing parameters was confirmed, and the microstructure of characteristic zone was observed. The results show that test alloy showed characteristics of isothermal rheological, sensitivity of positive strain rate and negative temperature. The best range of hot processing parameters within test range was deformation temperature of 425-440℃ and strain rate of 0.01-0.02 s^-1. The instability zone of the alloy mainly appeared in the condition of large strain, low deformation temperature and large deformation amount. The dislocation pile-up and adiabatic shear band in the microstructure were main reasons for the instability of test alloy.

Based on Eulerian-Eulerian gas-solid two-phase flow model, instantaneous velocity and velocity distribution of shot during shot peening process were simulated and analyzed by of Fluent-EDEM coupling calculation. Space position of shot was recorded by high-speed camera, and the real-time data of shot peening equipment and the image of high-speed camera were uploaded to cloud platform by 5G communication technology. Shot velocity was obtained by image processing, so as to realize the test verification of shot peening simulation. The results show that the relative error between simulation results and measured values of shot velocity under different process parameters was not more than 12.1%, indicating the simulation prediction accuracy of the model was high. The velocity of shot after ejection increased first and then decreased with increasing distance from the nozzle, and the spatial distribution of shot velocity presented a parabolic trend. The developed shot peening intensity analysis software had prediction accuracy of 95%.

Selective laser melting (SLM) is one of the most widely used metal additive manufacturing techniques. Many defects are inevitably produced in the SLM formed parts, including pores, surface layer powder spheroidization, cracks and so on. The formation of defects not only affect the smoothness of the forming process, but also damage the internal integrity of the part and reduce its serviceability. The main characteristics of three defects including pores, surface layer powder spheroidization and cracks in SLM formed 316L stainless steel parts are reviewed. The formation mechanisms and influencing factors of these three defects are summarised, and the main measures to control the defects are proposed. Finally, future research directions are put forword.

The quantitative relationship between system energy consumption, specific energy consumption (indicating energy efficiency) and process parameters was established by analyzing the energy consumption composition and characteristics of selective laser melting (SLM) system. A process parameter optimization strategy for optimizing the energy efficiency was proposed. The results show that the contradiction between the cladding efficiency and the energy consumption should be considered in selecting the laser power. The reasonable increase of laser scanning speed could improve the cladding efficiency and shorten working time of laser cladding under the disadvantage of reducing the cladding channel size, and then reduce energy consumption. Larger powder-bed thickness and scanning speed, as well as smaller transverse overlap rate matching the appropriate laser power, could effectively reduce the specific energy consumption of the SLM system. Choosing a direction with a smaller height for stacking could shorten the interlayer time and reduce the energy consumption of the system.

The flow of the molten pool during tungsten inert gas (TIG) welding has an important impact on the final geometry, microstructure, residual stress of the weld, and understanding the flow characteristics of the molten pool had a great significance to control the quality and properties of the weld. At present, the research methods of molten pool flow characteristics are mainly divided into experimental test, numerical simulation and dimensional analysis. The status of research methods of the molten pool flow characteristics during TIG welding are summarized, and the characteristics of different research methods are compared and analyzed. The future research direction is prospected.

Taking cubic boron nitride (cBN), TiN, and aluminum as raw materials, polycrystalline cubic boron nitride (PcBN) composites by sintering at 1 500℃ and 5.5 GPa. The effect of the mass ratio (21:4,17:8,13:12,9:16) of TiN to Al in the TiN-Al system binder on the phase composition, microstructure, hardness and wear resistance of PcBN composites was studied. The results show that PcBN composite was mainly composed of BN, TiB₂, TiN, AlN and Al₂O₃ phases. With increasing the aluminum content in the binder, the structure of PcBN composite became denser, and the porosity decreased; the hardness and wear ratio first increased and then decreased. When the mass ratio of TiN to Al was 17:8, the comprehensive property was the best with the largest hardness and wear ratio of 35.8 GPa and 7 500, respectively, and the relatively small porosity of 0.83%.

With multilayer (10-layer) and few-layer (3-layer) carbon fiber composite winding aluminum alloy tube (Al-CFRP mixed tube) as the research object, the single-layer shell model, multi-layer conventional shell model and multi-layer continuous shell model were established with ABAQUS/Explicit finite element software. The axial compression deformation process of the hybrid tube was simulated with Hashin failure criterion. The simulation accuracy of each model was compared. The simulation relative errors of the initial peak load, specific energy absorption and average compression load and the simulation time were made dimensionless and weighted to evaluate each model comprehensively. The results show that the multi-layer shell model could better predict the damage deformation and energy absorption characteristics of the hybrid tubes under axial compression. For the multilayer winding hybrid tube, the best model was the multi-layer continuous shell model, while for the few-layer winding hybrid tube, the multilayer conventional shell model had the smallest error.

TA32 titanium alloy samples were prepared by laser selective melting (SLM), and the effects of laser power (200—400 W), scanning speed (800—1 200 mm·s^-1) and scanning distance (90—130 μm) on the forming quality and hardness were studied. The results show that as the scanning speed increased, the surface roughness of SLM formed TA32 titanium alloy decreased first and then increased, and the relative density and Vickers hardness gradually decreased. As the scanning distance increased, the surface roughness of the titanium alloy decreased first and then increased, and the relative density and Vickers hardness decreased and then increased. As the laser power increased, the surface roughness of the titanium alloy decreased first and then increased, and the relative density and Vickers hardness increased first and then decreased. The laser energy density range suitable for SLM forming of TA32 titanium alloy was 45—75 J·mm^-3.