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.

Based on the fourth generation nickel-based single crystal superalloy DD15, single crystal superalloys were prepared by adjusting its Re content (mass fraction) to 5%, 6% and 7%, respectively. The effects of Re content on the solidification microstructure characteristic and element distribution of the alloy were studied. The results show that with increasing Re content, the precipitation temperature and dissolution temperature of γ' phase of the alloy increased, while the solidus temperature decreased slightly and the liquidus temperature had no obvious change. With increasing Re content, both the primary and secondary dendrite spacings increased, the content of (γSymbolk@@γ') eutectic microstructure increased, while the size and volume fraction of γ' phase decreased. Increase in Re content could decrease the segregation degree of negative segregation elements such as Re, W, Mo, Cr and Co in the alloy structure, but increase the segregation degree of the positive segregation element Ta.

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.

A Ni60CuMo alloy coating was prepared by plasma spraying on the surface of ZL109 aluminum alloy for engine piston. The microstructure, phase composition, microhardness and wear resistance under different conditions of the coating were studied. The results show that the coating was composed of alternately overlapping Cr-rich zone and Ni-rich zone, and the bonding mode between coating and substrate was mechanical bonding. The porosity of the coating was 2.48%. The average microhardness was 792.91 HV and was about more than 6 times that of the substrate. The friction coefficient and wear mass loss decreased with increasing test temperature from 25 ℃ to 450 ℃. Under 450 ℃ oil lubrication condition, the average friction coefficient of the coating was 0.037, and the wear mass loss was 7.35 mg, which was only about 1/4 of the substrate. With increasing test temperature, the wear mechanism of the coating changed from peeling failure to oxidation wear and adhesive wear under dry friction condition, and from abrasive wear to abrasive wear and adhesive wear under oil lubrication condition, and finally to adhesive wear.

Micro super-fine-polishing treatment (MST) was conducted on cemented carbide milling cutters before and after surface ion-plating TiAlN coatings. The effect of MST on the wear behavior and wear mechanism of the cutters was analyzed by methods such as scratch tests, wear loss measurement, roughness testing, morphology observation and composition analysis. The results show that applying MST after plating did not affect the bond strength of the coating and could reduce the surface roughness of the cutter, thereby reducing the cutting resistance; so the wear resistance of the MST cutter was significantly better than that of the cutter without MST. Although applying MST first and then preparing the coating could reduce the surface roughness of the cutter, it deteriorated the bonding performance of the coating, thereby affecting the effective protection of the coating on the cutter; so the wear resistance of the MST cutter was poorer than that of the cutter without MST. The wear mechanisms of the cemented carbide cutters were adhesive wear and oxidative wear, and applying MST after plating could inhibit adhesive wear and oxidative wear.

Diamond-like carbon (DLC) is a kind of metastable amorphous material containing diamond structure (sp ³ hybrid bond) and graphite structure (sp ² hybrid bond), and has excellent characteristics such as high hardness, corrosion resistance, low friction coefficient, wear resistance. However, DLC also has problems such as large internal stress, poor thermal stability and sensitive tribological behavior caused by different preparation process and deposition parameters, which greatly limits its industrial application. The affecting factors of DLC film tribology properties are summarized from two aspects of the intrinsic factors and external factors. The improvements of DLC film tribology properties are discussed from heterogeneous elements doping and surface texture. The research trend of tribological properties of DLC film is prospected.

Al-Cu alloy films with copper atomic fractions of 0-11.8% were prepared on stainless steel by magnetron sputtering method. The effects of copper content on the microstructure, nanoindentation mechanical properties and strengthening mechanism of the films were investigated. The results show that the pure aluminum film had a face-centered cubic structure. When the copper atomic fraction was between 2.2% and 6.5%, supersaturated solid solution phases were formed in Al-Cu alloy films. When the copper atomic fraction exceeded 6.5%, AlCu compounds were formed in films. With the increase of copper content, the grain size of the film decreased, and the hardness and elastic modulus increased. When the copper atomic fraction increased to 11.8%, the grain size was 34.7 nm, and the hardness and elastic modulus increased by 212.5% and 2.2% those of the pure aluminum film, respectively. When the copper atomic fraction was between 0 and 6.5%, the strengthening of films mainly depended on grain refinement strengthening and solid solution strengthening. When the copper atomic fraction exceeded 6.5%, the strengthening of films was determined by the combination of grain refinement strengthening, solid solution strengthening and second phase strengthening.

The tensile and fracture properties at 20℃ room temperature and -158℃ low temperature of 9Ni steel welded joint, base metal and weld were obtained by experiments, and the effects of temperature on the properties were compared and analyzed. Approximate R6 option 2 failure assessment curves (FAC) for the base metal and weld, as well as FAC for the 9Ni steel welded joint were established and compared. The results show that the tensile and fracture properties of the base metal and the tensile properties of the joint and weld at low temperature were higher than those at room temperature, but the fracture toughness of the weld hardly changed with temperature. The yield strength and fracture toughness of the weld at different temperatures were lower than those of the base metal, and the weld was a weak area of the 9Ni steel welded joint. The envelope area of the approximate option 2 FAC constructed with room temperature tensile properties was slightly smaller than that with low temperature tensile properties, so the approximate option 2 FAC constructed with room temperature tensile properties can be used for safety evaluation of 9Ni steel welded joints. The FAC of 9Ni steel welded joint constructed by segment selection of the approximate option 2 FACs of the base metal and weld at room temperature can be used for safety evaluation of 9Ni steel defect-containing structures at low temperatures in the most conservative way.

NbTiN ₂ coating was prepared on TC4 alloy surface by dual cathode plasma sputtering deposition. The phase composition, microstructure, hardness, adhesion to matrix and friction and wear properties of the coating were studied. The results show that the NbTiN ₂ coating had strong (220) preferred orientation. The coating had good surface quality, no obvious defects and a thickness of about 10 μm. The average hardness of the coating was 2 478.46 HV, about 6 times that of the matrix, and the critical load of coating in scratch test was 68.5 N, indicating that the coating was well combined with the matrix. The friction coefficient of the coating was lower than that of the matrix under the load of 2-5 N at room temperature; the wear scar was narrower than that of the matrix, and the wear rate of the coating was one order of magnitude lower than that of the matrix; the main wear mechanism of the coating was fatigue wear. At 500 ℃, the friction coefficient was higher than that at room temperature, and the wear scar of the coating was narrower and shallower; the wear rate was lower, and the wear mechanism was adhesive wear and oxidation wear, indicating the coating had better wear resistance.

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%.