In modern industry, plasma spraying technology has become an important method to improve the wear resistance and corrosion resistance of the surface of mechanical parts. As a spraying material, the nano-powder can effectively improve the wear resistance, corrosion resistance, oxidation resistance and other aspects of plasma spraying coating, which has research value in the application of surface protection of parts and components. It is of great significance for the energy conservation and environmental protection, and has become a research hot spot in the field of surface modification at home and abroad. Based on this, on the basis of a large number of literature, the preparation method of nano powder from three aspects as solid phase method, liquid phase method and gas phase method is introduced, research on the regranulation technology of nano-powder at home and abroad is summarized, the preparation methods of nano-powder feed, including spray drying, mechanical grinding and liquid phase precursor synthesis are described, and the preparation method of liquid phase precursor synthesis method is focused on. From the selection of nano-powder for plasma spraying to the preparation of coating, the application results of nano-coating in wear resistance, corrosion resistance, thermal barrier and self-lubrication are reviewed in detail, furthermore, the influence of plasma spraying parameters (spraying power, spraying distance, moving speed of spray gun, spraying gas parameters) on quality of the nano-coating is inductively analyzed. Finally, the problems and shortcomings in the preparation of plasma sprayed nano-powder feed are discussed, and the future research direction of plasma sprayed nano-coating is prospected.

Electron backscatter diffraction (EBSD) was used to characterize the grain size, recrystallization and texture of cold-rolled and annealed TA5 titanium alloy plates, the effects of deformation non-uniformity on recrystallization behavior and texture evolution were discussed. The results show that <0002>//TD-oriented grains are more prone to deforming than <0002>//ND-oriented grains, combined with the limited-slip system of hcp structure, which jointly determine the non-uniformity of cold-rolled deformation of TA5 alloy plates. In the early stage of annealing, the recrystallization rapidly nucleates in the high-stored-energy regions, and the greater the deformation, the more nucleation number, and the smaller the grain size of the sample after recrystallization. The recrystallized grains rapidly complete nucleation through the "oriented nucleation" mechanism in high-stored-energy regions during the early stage of annealing and then grow, including a small amount of residual severely deformed <0002>//TD-oriented grains. At the same time, the recrystallized grains nucleate slowly through the "strain-induced boundary migration" mechanism in the regions with low-stored-energy during the entire recrystallization process. These two mechanisms work together to weaken the texture of the annealed plate, but the cold-rolled state basal texture is still dominated. The hardness curve can well reflect the degree of recrystallization, however, the hardness values of different test surfaces affected by the texture are significantly different. The larger the angle between the loading axis and the crystal c axis, the smaller the hardness value.

The microstructure and high temperature mechanical properties of a low carbon steel at different temperatures were studied and discussed in detail by means of field emission scanning electron microscopy(FE-SEM), electron backscatter diffraction(EBSD) and electronic universal testing machine. The results show that regardless of room temperature tensile test or high temperature tensile test, carbide(Fe₃C) particles located on grain boundaries are the main factor for inducing cracks for the tested low carbon steel. Compared with the tensile properties at room temperature, increasing the heating temperature, the tensile strength is significantly reduced and the elongation is significantly increased. At high temperatures, with the increase of temperature, the tensile strength decreases linearly, while the elongation decreases first and then stabilizes. A large number of slip bands are observed during the stretching at 520℃, which induces dynamic recovery. When the temperature is increased to 720℃, the pearlite structure becomes spheroidized, and the equiaxed small grains appear in the deformed ferrite grains, which means that dynamic recrystallization has occurred. According to the EBSD analysis, the misorientation between the deformed ferrite grains is large, and the misorientation between the equiaxed small grains where recrystallization occurs is small.

Laser cladding improves the performance of metal surfaces and achieves surface strengthening. However, it is often found that due to the reduced toughness of the coating, cracks and defects appear on the surface of the coating. The reasons for cracks in laser clad coatings due to reduced toughness are summarized, including internal stress caused by temperature gradient difference, stress concentration in laser clad layers, and small pores in clad layers. At the same time, factors affecting the toughness of laser clad layers are summarized, including the selection of clad materials, the setting of laser cladding process parameters, and the heat treatment methods of cladding materials. On this basis, the progress in improving the crack defects of laser clad coatings in recent years is emphasized, and methods to enhance the toughness of laser clad coatings are studied and searched for, including adding composite ceramic reinforcement phase and rare earth element powder to the cladding powder to change its composition, adding a transition layer between the substrate and the cladding layer, changing laser cladding process parameters such as the laser power, scanning rate, and spot diameter, preheating the substrate before cladding and heat treating the coating after cladding, external ultrasonic vibration and electromagnetic field, as well as coupling of ultrasonic vibration and electromagnetic field and other energy field assistance. Aiming at the shortcomings of various methods for enhancing the toughness of laser clad coatings, the research prospects of future methods for toughening and modifying laser clad coatings are explored.

As-extruded 6061 aluminum alloy was subjected to solution treatment and aging treatment,respectively.The mechanical properties of the alloy were tested by universal testing machine,and the microstructure was characterized by means of SEM and TEM to investigate the microstructure evolution law of the alloy in different heat treatment states.The results show that the extruded 6061 aluminum alloy after solution treatment and aging treatment show obvious anisotropic mechanical properties,and aging treatment can effectively improve the strength of the alloy.At the same time,the extruded alloy after aging treatment shows strain rate sensitivity,however,the alloy after solution treatment has no obvious strain rate sensitivity.The extruded 6061 aluminum alloy after solution treatment and aging treatment are composed of equiaxed grains with two kinds of grain sizes,which the larger one being up to 200 μm and the smaller one being less than10 μm.The types and strength of texture components of the extruded 6061 aluminum alloy solution-treated or as-aged are the same,both are composed of strong { 001} < 100 > cubic texture and weak { 011 } < 100 > Goss texture.After tensile deformation,a large number of dislocations pile up,and the short rod like precipitates will be evenly distributed in the alloy after aging treatment,which can effectively block the movement of dislocations and improve the deformation resistance of materials.

Heat treatment is an important part in the manufacturing industry. In view of the multi variety and variable batch production mode of heat treatment enterprises,it is an urgent problem for heat treatment enterprises to reasonably coordinate workshop production resources,ensure product quality,improve production efficiency,reduce production energy consumption,and improve enterprise intelligent management level. Based on the actual production process of heat treatment,a set of intelligent control system platform of heat treatment was constructed by using the technology of internet of things information collection,heterogeneous information data fusion,production process information management and control,combined with production scheduling genetic algorithm. Through the system platform,the real-time production scheduling of heat treatment process is realized,the production efficiency is improved,and the control ability of quality consistency of heat treatment products is improved.

Properties of high-entropy alloys can be tuned by changing the types and ratios of alloying elements, which affect the stacking fault energy and phase stability of the alloy system, then the plastic deformation mechanism of the alloy can be changed, thus the optimal comprehensive mechanical properties can be obtained. The factors that affect the stacking fault energy of face centered cubic high-entropy alloys, and the influence of stacking fault energy on deformation mechanism, are reviewed. And the methods that can affect the mechanical properties by changing the activation order of deformation mechanisms by adjusting the stacking fault energy are prospected.

Heat treatment process of 42CrMoVNb steel was optimized by single factor and orthogonal tests. The mechanical properties of the 42CrMoVNb steel were tested by Rockwell hardness tester, universal tensile testing machine and metal pendulum impact testing machine. The effect of heat treatment process on microstructure and mechanical properties of the 42CrMoVNb steel was studied. The results show that the optimal heat treatment process of the 42CrMoVNb steel is quenching at 860 ℃ for 20 min, oil cooling and tempering at 440 ℃ for 150 min, air cooling. The microstructure under the optimal heat treatment process is tempered troostite matrix dispersed with fine carbide particles, the hardness, tensile strength, yield strength, yield ratio, elongation after fracture, percentage reduction of area and impact absorbed energy at -20 ℃ are 44.5 HRC, 1467 MPa, 1357 MPa, 0.93, 10.5%, 46% and 27.1 J, respectively, which all meet the mechanical properties requirements of 14.9 grade high strength bolts.

Based on the continuous annealing process and system analyses for cold-rolled stainless steel, the heating system of continuous annealing furnace was designed, and the furnace length configuration and the combustion power configuration were respectively calculated by the surface energy balance equation and the energy conservation equation. By comparison and analysis of the actual calculation example and the actual operation, it verifies that the design method is effective and has the ability to complete the design process from the product outline and process analysis basis to the unit heating system integration, arrangement and overall arrangement of equipment. Thus, it provides a theoretical basis for the secondary model of the heating system of the cold-rolled stainless steel continuous annealing furnace.

Al Si10 Mg aluminum alloy lattice materials were prepared by selecting different laser 3 D printing parameters,and the optimized printing parameters were explored.The microstructure and properties of aluminum alloy lattice materials and the influence of subsequent heat treatment on it were studied.The results show that the optimal printing parameters include printing temperature( 80 ℃),microns powder layer thickness( 30 μm),lasing beam diameter( 80 μm),laser energy( 370 W),and laser scanning speed( 1300 mm/s).The prepared aluminum alloy lattice material has few cavity defects,high compactness,and the microstructure is a layer upon layer crisscrossing laser molten pool,which is composed of small α-Al equiaxial cellular crystal and spherical Si particle phase,and has good performance.After heat treatment,the features of the original laser molten pool defects and equiaxial cellular crystals disappear,the Si particle phase continuously precipitates and grows up,meantime,the hardness and platform stress decrease under the compression performance,so does the static compression properties.

Thermal fatigue performance of hot work die steel is the main factor that affects the service life of dies.The research status and evaluation methods of thermal fatigue performance of hot work die steel were overviewed,the effects of structural evolution,crack initiation and propagation on thermal fatigue performance were analyzed.At the same time,the factors influencing the thermal fatigue performance and the methods to improve the thermal fatigue performance were discussed and summarized,and the trend of the thermal fatigue research of hot work die steel was prospected.

Rolled Q345/40Cr bimetal rings were quenched at 860-950 ℃ and tempered at 520-610 ℃, the microstructure and properties after heat treatment was observed, analyzed and tested. The results show that the grains are refined after quenching, and coarsened with the increase of quenching temperature. The hardness of the 40Cr steel and hardness of its adjacent bonding layer decreases first and then increases, while the hardness of the Q345 steel decreases slightly, and the hardness of its adjacent bonding layer decreases. The alloying elements in the 40Cr steel side dissolves incompletely when quenched at 860 ℃, and the optimal quenching temperature is 890 ℃. The results of mechanical properties tests show that after 890 ℃ quenching and with the increase of tempering temperature, the tensile strength and hardness of the bimetal ring decrease, the elongation of the Q345 steel and its adjacent bonding layer increases first and then decreases, and the impact property of the bimetal ring is improved. The fracture position of bonding layer is on the side of Q345 steel. The comprehensive performance of the bimetal ring is the best after quenching at 890 ℃ and tempering at 550 ℃, which meets the practical application requirements.

T2 pure copper wire was obtained by cold drawing, then low-temperature long-term annealing(400℃×60 min) and hightemperature short-term annealing(at 850℃ for 20, 40, 60 s, respectively) tests were carried out. The microstructure, mechanical and electrical properties of the wires in different states were studied by means of OM, SEM, universal testing machine and DC wheat stone bridge.The results show that the fibrous structure of the cold drawn T2 pure copper wire forms recrystallized grains after annealing accompanied by annealing twins. With the increase of annealing time at 850℃, the recrystallized grains of the wire grow continuously, and the grains morphologies tend to equiaxed, and the uniformity of wire structure is improved. The average tensile strength of annealed wire is about 57.1%of that of drawn wire, the percentage elongation after breaking was about 10 times of that of drawn wire, after annealing at 400℃ for 60 min, the conductivity of the wire is only 0.3% higher than that of the drawn wire; after annealing at 850℃ for 20, 40 and 60 s, the average conductivity of the wire is 5.2% higher than that of the drawn wire. The mechanical and electrical conductivity properties of the wire after hightemperature short-time annealing are not only better than low-temperature long-time annealing, but have a higher annealing efficiency. In conclusion, the wire annealed at 850℃ for 40 s has high mechanical properties and electrical conductivity.

Microstructure and properties of hot dip aluminized coatings on the surface of TA15 titanium alloy under the action of alternating electromagnetic field were studied, and the thermal diffusion treatment was carried out at 800℃. The morphology, microstructure and element distribution of the coatings were analyzed by means of energy dispersive spectroscopy, scanning electron microscope and X-ray diffractometer. The microhardness of the coatings was tested by microhardness tester. The results show that after applying alternating electromagnetic field with current intensity of 15 A and 20 A during the process of hot dip aluminizing and thermal diffusion, the coatings bind well with the alloy substrate, no obvious crack is found, the formation of pores and cavities is significantly reduced, the dipping time is shortened, and thus the production cycle is accelerated. When the current intensity is 15 A and 20 A, the maximum hardness of the bonding zones can reach 518.7 HV0.2. When the current intensity increases to 25 A, the electromagnetic stirring effect sharply increases, and no high-quality coating can be obtained.

Four heat treatment processes on a Si-Mn brass with the Mn/Si ratio of 2 were carried out at 500 ℃and 800 ℃respectively for 1 h and 6 h. Then the microstructure,wear scar morphology and mechanical properties of the tested brass samples were analyzed and characterized by scanning electron microscope,white light interference,optical microscope and hardness tester. The results show that the wear resistance of the brass is improved after four kinds of heat treatment,and is the best when the heat treatment temperature is 800 ℃and the holding time is 6 h. The fine Si-Mn phase in the brass is dissolved at 500 ℃,and more Si-Mn phase is dissolved into the matrix at 800 ℃.The friction and wear properties and hardness of the Si-Mn brass are improved by the precipitated slender and sharp Si-Mn phase.

High entropy alloys(HEAs) are a new kind of alloys,which break through the traditional alloy design with one or two elements as principal constituent and a few elements as auxiliary constituent.As an important branch of high entropy alloy system,FCC structure HEAs show excellent properties,such as high damage tolerance,good irradiation resistance,high wear resistance and corrosion resistance.However,the strength-ductility tradeoff dilemma of FCC structure HEAs severely limits their engineering applications.Previous researches indicate that precipitation strengthening can effectively improve the strength of FCC structure HEAs and produce excellent strength-ductility synergy properties.The research progress on precipitation strengthening of FCC structure HEAs was mainly introduced,including incoherent and coherent precipitates.The current research status and underlying influence mechanisms of precipitation-strengthening were briefly reviewed.The future prospective of precipitation-strengthening in FCC structure HEAs was also discussed.

Isothermal dilatation tests of the 20CrMnTi steel at different temperatures and holding time were carried out through Gleeble-3500 thermal simulator, and the phase transformation thermal dilatation curves were obtained. Isothermal phase transformation behavior of the 20CrMnTi steel was analyzed by metallographic microscope, and the isothermal phase transformation curve (TTT curve) of the steel was drawn. Johnson-Mehl-Avrami (JMA) equation and Koistinen-Marburger (KM) equation were introduced to establish the diffusion-type and non-diffusion-type phase transformation kinetic models respectively. The results show that the TTT curve of the 20CrMnTi steel is of"double C"shaped and the nose temperatures are 630℃ and 530℃, respectively. At 730-580℃, the austenite transforms into pearlite + ferrite and the isothermal transformation rate first accelerates and then slows down with the decrease of temperature. The austenite transforms into bainite when the steel is held at 580-430℃ and the isothermal transformation rate also first accelerates and then slows down with the decrease of temperature. The austenite transforms into martensite below 430℃ and the volume fraction of the martensite increases rapidly at first and then slows down with the decrease of temperature. The calculated results of established kinetic model of the 20CrMnTi steel are in good agreement with the experimental results.

Effect of aging time on microstructure, hardness and high temperature tensile properties of GH4169 alloy under the tested conditions of over-temperature service at 900 ℃ were studied.The results show that with the extension of aging time, the δ phase is precipitated from the grain boundary with a short rod shape, and then precipitated the whole grain with long needles; the grain is grown at the initial stage of aging, and with the δ phase gradual precipitating along the grain boundary, the phenomenon of grain growth is disappeared.The strengthening phase of the alloy is dissolved and transformed when the GH4169 alloy aged at 900 ℃, which results in the microhardness of the alloy dropping sharply from 44.0 HRC to 13.6 HRC, but the microhardness is changed a little with the increase of holding time.The precipitation of δ phase has a significant effect on the high temperature mechanical properties of the alloy.The proper amount of precipitation can increase the tensile strength and high temperature plasticity of the alloy.A large amount of precipitation results in a decrease of tensile strength and a deterioration on the high-temperature plasticity.The high temperature tensile of the alloy after different aging treatments is a typical elastic-uniform plastic deformation, and the deformation fracture mechanism is a microporous aggregate fracture.

Al and Ti elements were added to re-alloy the 42 CrMo steel with basic composition. The effect of Al on the hardenability of 42 CrMo steel was analyzed by means of end quenching test and section hardness test. The mechanical properties of the new 42 CrMo steel were compared by conventional mechanical properties. The results show that the addition of Al and Ti can further improve the hardenability, and the strength of the steel reaches 1200 MPa, and KV₂ ≥ 27 J at-40℃, which meets the technical requirements at low temperature environment for the wind turbine bolt steel. Through chemical phase analysis test and TTT curves measurement, it is shown that Ti added to steel exerts obvious nitrogen fixation effect. Al is mostly dissolved in steel, making C curves shift to the right, which lowers the critical transformation temperature of austenite and significantly improves the hardenability of steel.

Taking foreign similar products as references, many kinds of duplex-phase and induction quenching treatments were applied to 42CrMo steel picks. Hardness, impact absorbed energy, microstructure and fracture morphology of the 42CrMo steel picks after different heat treatments were investigated. The effects of heat treatments on microstructure and mechanical properties were analyzed. The results show that after duplex-phase heat treatment process, the microstructure includes lower bainite/martensite (LB/M) and a small amount of retained austenite (RA), grain size is smaller and LB has better comprehensive mechanical properties, and impact absorbed energy is higher than that after quenching and low temperature tempering (Q-T) process. Local induction quenching process not only has the highest impact absorbed energy and the hardness of pick head, but also realizes the axial hardness distribution of hard head and soft handle of the pick, which is beneficial to extending the service life. The fracture morphology of the specimen treated by Q-T process shows cleavage brittle fracture morphology, the specimen treated by multiphase shows quasi cleavage fracture morphology, and the impact specimen treated by local induction quenching shows ductile fracture morphology, which is resulted from the excellent mechanical properties of the quenched and tempered (Q&T) microstructure. The tested data show that the Q&T plus local induction quenching is more suitable for picks used in hard substrate.

In view of the characteristics of heat treatment enterprises, the requirements of the standard for heat treatment enterprises in basic requirements, heat treatment plant, heat treatment equipment, heat treatment process materials, heat treatment process, management system, environmental emissions and other aspects specified in the GB/T 38819-2020 were interpreted carefully, and the evaluation method of green heat treatment was explained.

High strength 6061 aluminum alloy was printed by the laser powder bed fusion laser additive manufacturing technology. Firstly, the crack free 6061 aluminum alloy was obtained with the substrate preheating. And then, the printed alloys were heat treated, and the corresponding effect of heat treatments on the microstructure and mechanical properties was compared and analyzed. The results show that under the as printed (AP) condition, the alloy elements exist in the matrix in the form of supersaturated solution, and the tensile strength of the alloy is only 249 MPa. In the solution treatment (ST)+aging treatment (AT) and direct manual AT process, the mechanical properties of the aluminum alloy are significantly improved. After direct AT treatment, the alloy has high tensile strength and fraction elongation, 359 MPa and 12.5%, respectively. While after ST+AT, the alloy has a higher strength of 377 MPa and a lower elongation of 10.1%. The AT treatment is conducive to promoting the diffusion and precipitation of fine-needle Mg₂Si phase in the Al matrix, and the tensile strength of the alloy is significantly improved by the precipitate strengthening effect.

Microstructure and properties in transversal and longitudinal directions of 316 L stainless steel additive manufacturing specimens produced by selective laser melting( SLM) were analyzed.The results show that the substructure of the SLM additive manufacturing specimens is composed of cellular microstructure with the size of 0.4 μm,and with no obvious composition segregation.Their transversal and longitudinal tensile strengths are 808 MPa and 713 MPa,respectively.After heat treatment at 1050 ℃,some of the cellular microstructures disappear,and the transversal and longitudinal strengths are reduced to 673 MPa and 579 MPa,respectively,which still have obvious strength advantages compared with the conventional hot rolled 316 L steel( 550 MPa).There are unfused defects in the SLM specimens,and the directivity and geometry of the defects have significant effect on the ability of the defects joining into a crack under the action of tensile stress.The elongation of the longitudinal specimen with defect length direction parallel to the tensile direction is 47.5%,and that of the transversal specimen is 20%after heat treatment.The elongation of the SLM specimen is significantly lower than that of the hot rolled 316 L steel specimen.The unfused defect is one of the main factors leading to the decrease of plastic properties of the 316 L stainless steel specimens processed by SLM.

High entropy alloy is a new type of atom-ordered and chemically disordered alloy with multi-principal elements,which can obtain outstanding comprehensive mechanical properties,because that by changing the type and concentration of alloying elements,the stacking fault energy and phase stability of alloys can be controlled,then inducing deformation twins,martensitic transformation and other plastic deformation mechanisms. The design concept of such high entropy alloys is called“metastable engineering”,and the microstructure,phase structures and deformation mechanisms of high entropy alloys are closely related to stacking fault energy of the alloy system. For the Fe MnCoCr system,the phase stability of face-centered cubic structure decreases with the decreasing of stacking fault energy,and so the interface hardening and the transformation induced hardening( γ → ε) are introduced,improving the strength and plasticity of the alloy simultaneously. The composition design,preparation and processing method,microstructures and mechanical properties of the Fe MnCoCr metastable high entropy alloys are reviewed here,and its future research direction is prospected.

38CrMoAl steel was austenitized by heating to 1000-1200 ℃ for 0-300 s by different process configurations.The effect of austenitizing temperature and holding time on the austenite grain growth behavior was studied.The results show that the average grain size of austenite in the tested steel increases with the increase of austenitizing temperature, and the grain growth rate increases with the increase of temperature.At the same austenitizing temperature, the average grain size of austenite increases with the increase of holding time, and the grain growth rate decreases with the increase of holding time.According to the test data of austenite grain size of the tested steel, the Sellars model of the austenite grain size and austenitizing temperature and holding time of the 38CrMoAl steel was established, and the accuracy of the model was verified.

Effect of normalizing temperature on the microstructure and hardness of USS122G ultra-high strength stainless steel was studied by means of optical microscope,electron scanning microscope,physicochemical phase analysis,etc.The results indicate that with the increase of normalizing temperature,the hardness and the secondary phase content decrease,while the retained austenite content and the prior austenite grain size increase.By comprehensive analysis of the relationship between the normalizing temperature with the type,mass fraction,hardness and grain size of the secondary phase in the steel,it is concluded that the optimum normalizing temperature of the tested steel is 1020℃.

Fatigue life of the high fatigue life Q345 FCA steel for engineering machinery was determined by using QBWP-6000 J rotary bending fatigue testing machine for simply supported beams.The fatigue fracture morphology was observed by scanning electron microscope(SEM)and the inclusions on fracture surface were searched by energy dispersive spectrometer(EDS).The inclusions were analyzed by inclusion automatic analysis system, and the critical size of inclusions was calculated through experimental data analysis.The results show that the fatigue strength of Q345 FCA steel and Q345 steels is 273 MPa and 266 MPa, respectively.The size of the inclusions in the Q345 FCA steel and Q345 steel is all small, which is smaller than the critical size of the inclusions, and the fracture morphologies show that all the fatigue fractures are not caused by inclusions, which are not the source of fatigue.

Silver/steel composite plate with typical explosive wavy bonding interface was fabricated by explosive welding. Under the same holding time, the effect of different annealing temperatures on structure and microhardness of the silver layer and the interface shear strength of the composite plate interface was studied. The results show that there is a mixture of Ag and Fe in the wavy vortex zone generated by explosive welding, and a temperature gradient is generated in the vortex zone during the heat treatment cooling process, which makes the silver layer present a columnar grain growth mode during recrystallization. As the annealing temperature increases, the diffusion of Ag and Fe atoms intensifies within the vortex zone, leading to the disappearance of temperature gradients and the uniform growth of silver layer grains towards the surrounding areas. The hardness of the silver layer reaches its maximum around 90 HV0.1 in the explosive state. When the annealing temperature exceeds 200℃, the hardness of the silver layer decreases by 36% and its sensitivity to the annealing temperature decreases, with the average hardness remaining around 60 HV0.1. The interface shear strength of the composite plate reaches the maximum 238 MPa under the explosive state. With the increase of annealing temperature, the shear strength decreases. When the temperature reaches 500℃, the shear strength remains stable at about 150 MPa, which is 37% lower than that of the explosive state.

In the preparation process of 7X50 aluminum alloy wire, intermediate annealing-cold drawing-cold heading and other intermediate processes are required. After single-stage annealing, the wire often occurs natural aging and strength increases, which seriously affects the re-drawing forming. The microstructure and properties of the single-stage and double-stage intermediate annealed 7X50 aluminum alloy wires were analyzed by means of optical microscope, transmission electron microscope and electronic tensile testing machine. The results show that partial recrystallization occurs after single-stage annealing at 404℃ for 2 h, and the strength decreases from 235 MPa(before annealing) to 188 MPa, and increases to 244 MPa after placing for 270 d because of obvious natural aging effect. After double-stage annealing at 404℃ for 2 h and 233℃ for 4 h, partial recrystallization occurs and the strength decreases to 173 MPa, and no obvious natural aging hardening effect occurs during the 270 d placing. The second stage 233℃×4 h annealing holding process promotes the precipitation and growth of AlZnMgCu phases and Mg, Zn phases, which consumes a large amount of Zn, Mg elements, effectively eliminates the natural aging hardening effect during the process of placing.

Microstructure and mechanical properties of TC4 titanium alloy prepared by 3 D printing after solution at different temperature and then aging at 490℃ were studied through microstructure observation and mechanical property test.The results indicate that the microstructure of the original 3 D printed deposition sate is non-uniform basket-weave structure.After solution and aging treatment,with the increase of solution temperature,the α phase first grows in the form of flakes near the complete original grain boundary,and then gradually transforms into a coarse lath shape,and the strength gradually increases while the plasticity decreases,reaching the maximum value of 1100 MPa when solution temperature is 920℃. As the solution temperature further increases and exceeds 960℃,the α phase is gradually dissolved,which leads to the decrease of the strength and the plasticity.The macro morphologies of the tensile fracture under different solution temperature are all dark gray.According to a large number of dimples observed in the micro morphologies of those fracture,the tensile fracture mechanism of the TC4 titanium alloy can be judged as ductile fracture when solution treated at 890-960℃ and aged at 490℃.Combining the changes in the microstructure and mechanical properties of the TC4 titanium alloy after different solution and aging treatments,it can be concluded that the TC4 titanium alloy prepared by 3 D printing has better comprehensive mechanical properties when solution treated at 920℃ and then aged at 490℃.

Effect of sulfur content on sulfide morphology and properties of Y12Cr18Ni9 free-cutting steel was studied by means of SEM, SEM-EDS, EPMA and EBSD, etc. The phase diagram and equilibrium solidification transformation path of the Y12Cr18Ni9 free-cutting steel were calculated by TCFE10 database of Thermo-Clac software, and the effect of sulfur content change on sulfide precipitation was analyzed. The result show that the main equilibrium phases in the Y12Cr18Ni9 free-cutting steel are Liquid, MnS, δ, γ, M₂₃C₆, σ and α. The sulfides are spherical, ellipsoidal, spindle shape or short-bar-like, which are distributed in chains at grain boundaries or clustered at the trident junction, belonging to a type of II sulfide. With the increase of sulfur content, the amount of sulfide precipitation per unit area in the tested steel increases, and the average area of sulfide increases. The increase of sulfur content can promote the precipitation of sulfide in the Y12Cr18Ni9 free-cutting steel. With the increase of the number of cluster sulfides in the tested steel, the quasi-cleavage surface area of the tensile fracture increases, gradually transforms into brittle fracture, and the mechanical properties of the material decrease.

In order to improve its mechanical properties, the effect of Si content and heat treatment on the microstructure and properties of the as-cast Al-Si alloy was studied systematically.The results show that the effect of Si content, cooling medium, solution treatment temperature, aging time and aging temperature on the hardness of the alloy decreases in turn.The optimal Si content and the optimal heat treatment process are 12% Si and solid solution treating at 480 ℃ for 120 min + salt bath cooling + aging at 175 ℃ for 90 min, respectively.With the increase of Si content, the hardness and tensile strength of the alloy increase; but when the Si content is too high, the precipitation of block-shaped primary silicon tends to form stress concentration then reduces the strength of the alloy, and the fracture mode changes from ductile fracture to cleavage fracture.The eutectic silicon in as-cast Al-Si alloy is long needle like.After using the optimal heat treatment, the long needle-like silicon transforms into short rod or granular shape, and the eutectic silicon is more dispersed, the stress concentration decreases during tension, and the dislocation movement resistance increases, all of which improve the mechanical properties of the Al-Si alloy.

Effect of cold rolling on the M/B duplex microstructure and mechanical properties of M50 steel was investigated by means of X-ray diffraction, scanning and transmission electron microscopy, uniaxial tensile and Charpy impact tests. The results show that an excellent combination of ultimate tensile strength (2535.7 MPa) and impact property (96.93 J) is achieved by combining 20% cold rolling with austempering, of which the ultimate tensile strength increases by about 5% whereas the impact absorbed energy increases by about 21% compared with the specimen which is not cold rolled. The microstructure observation indicates that with the increase of cold rolling deformation (< 20%), the microstructure becomes finer and the specimen with 20% cold rolling deformation shows the finest microstructure. However, when a higher cold rolling deformation (> 20%) is applied, the amount of bainite sheaves decreases, which weakens the refinement of martensite and leads to some coarsening of microstructure.

The M2052 alloy powder was prepared by the vacuum induction melting gas atomization(VIGA) method, and its physical properties and microstructure were analyzed. Then the Mn-Cu specimens were prepared by selective laser melting(SLM) technology and the microstructure and mechanical properties of the SLM printed specimens were analyzed. The results show that, the VIGA method can effectively control the shape of metal powders, and the VIGA Mn-Cu powders with a particle size range of 15-53 μm have high yield, high bulk density, and good degree of sphericity, thus effectively meet the requirements for that of SLM. The microstructure of SLM printed MnCu alloy is different in the horizontal and the vertical directions, and gradually changes into cellular crystals as the interior of the molten pool extends. Columnar crystals are formed along the welding interface, and the further away from the molten pool, the finer the columnar crystals.Compared with the as-cast, the SLM printed alloy has obvious difference in mechanical properties, with the tensile strength and the proof strength, plastic extension being 611 MPa and 504 MPa respectively, which are much higher than 454 MPa and 172 MPa of the as-cast master alloy. The reason is that the fine grain strengthening effect is obvious, but the existence of microcracks is not good for the plasticity.

Single-pass isothermal compression test with maximum deformation of 50% was conducted by using Gleeble-1500 thermo-mechanical simulator, and the true stress-strain curves for 34CrNi3MoV steel were obtained at deformation temperature of 800-1200 ℃ and strain rate of 0.01-10 s^-1. The results show that, at 800 ℃ and 900 ℃ (1, 10 s^-1), the 34CrNi3MoV steel undergoes dynamic recovery only, while at 1000-1200 ℃ and 900 ℃(0.01, 0.1 s^-1) undergoes dynamic recrystallization. By using Arrhenius equation to calculate the activation energy Q under different strains, the corresponding relationship between activation energy Q and strain is obtained by using the quintic polynomial Q=331.78+1401.47ε-10 233.34ε²+33 725.26ε³-52 745.07ε⁴+31 981.48ε⁵. The relationships between critical eigenvalues (ε_c, ε_p) and Z parameter are constructed by using work-hardening rate, and based on which a kinetic model for the 34CrNi3MoV steel to predict dynamic recrystallization volume fraction is established: X_DRX=1-exp[-0.564((ε-ε_c)/ε_p)^1.945].

The second phase, grain size, and micro-texture of N36 zirconium alloy strips processed through different rolling ways were investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). The results show that the textures of N36 alloy strip are mainly consist of { 0001} < 1210 > and { 0001} < 0110 > basal texture, and the second phase is mainly HCP type Zr(Nb, Fe)₂ particles. With the same total hot deformation, the deformation rate changes of each hot rolling pass have a little effect on the grain size and texture of the final strip but play an important role in the size of second phase particles(SPPs). With the larger deformation rate of the first hot rolling pass, the size of SPPs in final strip are smaller. During the hot rolling, the texture composition of final strips is affected by using cross rolling process, and also the[0001] axis of Zr lattice is more inclined to parallel to the normal direction (ND) of the strips. Meanwhile the grain is more scattering rotated on the RD-TD plane. In addition, during the final rolling of final strips, a larger deformation leads to a smaller grain size and a higher degree of recrystallization, which strengthens the { 0001} < 1210 > texture, and weakens the { 0001} < 0110 > texture.

TA15 titanium alloy were treated by laser shock peening (LSP) to study the effect of LSP on microstructure and fatigue property of the titanium alloy specimens with double holes. The results show that when the specimens are treated by LSP with laser energy of 25 J, circular spot diameter of φ4 mm and shock times of 2, a large number of high-density dislocations and dislocation walls are formed in the TA15 titanium alloy crystal, and introducing residual compressive stress of up to -500 MPa simultaneously on the material surface which can balance the tensile stress generated under fatigue load, effectively suppress fatigue crack initiation and slow down crack propagation rate. The LSP can obviously improve the fatigue life of the titanium alloy specimens with double holes, which is increased by 60%-89% compared to that of the untreated specimen. This is because the large residual compressive stress introduced by LSP greatly reduces the effective stress intensity factor at the crack tip. When the effective force intensity factor is less than the fracture toughness of the material, the fatigue crack growth will be suppressed or stopped, thus improving the fatigue life.

Compared with traditional alloys, high-entropy alloys(HEAs) have outstanding characteristics such as high strength and toughness, good soft magnetic properties, high temperature stability, and corrosion resistance. The application potential is huge in many fields. The research progress, advantages and disadvantages of preparing HEAs by means of vacuum melting, powder metallurgy, laser cladding and magnetron sputtering were mainly introduced. The influence of different heat treatment processes on the microstructure and properties was analyzed. And the prospects of high-entropy alloy preparation and simulation calculation were put forward.

In view of the high technical requirements of post-weld heat treatment for main steam thick-wall (especially for that with wall thickness greater than 100 mm) P92 steel pipe welded joint of 1000 MW unit in thermal power plant, post-weld heat treatment of the pipe specimen was carried out for the main steam P92 steel pipe welded joint with 118 mm wall thickness of a 1000 MW secondary reheat unit by medium frequency induction heating. The results show that after the post-weld heat treatment, the microstructures of the weld and the base material are normal, and the hardness of the weld meets the standard requirements, and after further optimization of the heat treatment by appropriately reducing the heating rate and constant temperature and increasing the width of heat preservation, 121 heat-treated welded joints of the same type are one-time all qualified in the pipeline construction process. The successful application of medium frequency induction heat treatment scheme for welded joints of thick-wall P92 steel pipe can provide reference for the subsequent post-weld heat treatment of the same type of parts.

In order to optimize the spheroidizing heat treatment process of high carbon martensitic stainless steel 8 Cr13 MoV and improve its cold working properties after annealing,the effects of austenitizing time and cooling rate on the spheroidization effect of 8 Cr13 MoV steel during the spheroidizing annealing process were investigated by microstructure analysis and tensile mechanical test. The obtained results indicate that with the increase of austenite holding time,the number of fine carbides decreases,while the number of sorbite increases. The hardness of the steel decreases first and then increases,and the elongation increases. The number of fine carbides and sorbite,the hardness and strength of the steel increase with the cooling rate increasing,while the elongation decreases. Comprehensive comparison shows that the comprehensive mechanical properties of the 8 Cr13 MoV steel are preferable when the austenitic holding time is 90 min,and the cooling rate should be controlled within 25℃ ·h^-1. Compared with holding time,the influence of cooling rate on the mechanical properties is more remarkable.