Nickel-based self-lubricating rare earth composite coating was prepared on the surface of 35CrMo steel by high-frequency induction cladding technology, and it was subjected to solution treatment at different temperatures. The effects of solution treatment at different temperatures on the microstructure, microhardness and wear resistance of the coating were studied by means of optical microscope(OM), scanning electron microscopy(SEM), X-ray diffraction(XRD), Vickers microhardness tester and friction and wear testing machine. The results show that after solution treatment, the elements diffuse fully, the dendritic form gradually becomes single, and the microstructure at the interface mostly changes from columnar dendritic to cellular dendritic. After solution treatment at 850℃, the main phases of the composite coating are γ-(Ni, Fe), Cr(Fe-Ni-Cr), Ni₃Fe, TiC, Cr₂₃C₆ and CrB phases, the average microhardness is the highest, reaching 867.7 HV0.2, the friction coefficient and wear amount are relatively small, which are reduced by 17.21% and 21.66% respectively compared to the coating before solution treatment, and the relative wear resistance is relatively high, which is 2.46.

The properties of traditional particle reinforced aluminum matrix composites are mainly improved by adding single micron or nano particles as reinforcement phase. Micron particles can significantly improve the strength, hardness and wear resistance of aluminum matrix composites, but the plasticity and toughness decrease significantly. While the addition of nano reinforced particles can improved the strength and maintain good plastic toughness of the aluminum matrix composites, but due to the large specific surface energy and easy agglomeration of nanoparticles, it is difficult to prepare high volume fraction particle reinforced aluminum matrix composites. Therefore, the application of traditional aluminum matrix composites in high-tech fields is limited. In order to solve the bottleneck of the development of composite materials, the micro and nano hybrid particles reinforced aluminum matrix composite materials with high performance were prepared by using the design idea of micro and nano hybrid particles reinforcement and giving full play to the advantages and coupling effect of each reinforcing phase. In this paper, the design idea, strengthening mechanism and preparation technology of micro and nano hybrid particles reinforced aluminum matrix composites are reviewed. The existing problems of micro and nano hybrid particles reinforced aluminum matrix composites are pointed out, and the future development direction and problems to be solved are prospected.

Mg-10Gd-3Sm-0.5Zr alloy with addition of 0%-2% Zn (mass fraction) was prepared by smelting casting method, and the hot compression tests of the Mg-10Gd-3Sm-xZn-0.5Zr alloys were carried out after solution treatment. The hot deformation behavior of the alloys under the condition of hot compression temperature of 350-500℃, strain rate of 0.002-1 s^-1 and maximum deformation of 70% was studied, the deformation activation energy was calculated, and the constitutive equation of hot compression deformation and the hot processing map of the alloys were established and analyzed. The results show that the peak stress of the alloy increases first and then decreases after adding Zn, and the peak stress of the alloy with 1% Zn is the highest. The thermal activation energy of the alloy without Zn addition is 256.87 kJ/mol, and that of the alloy with 1% Zn addition is 290.45 kJ/mol. After adding Zn element, the instability zone of hot processing map decreases, the machinable area increases, and the microstructure becomes finer and more uniform at high temperature.

Thermal simulation compression experiment of a new type of β titanium alloy Ti-34521 was carried out by using a Gleeble-3500 thermal simulation compression tester under the deformation condition of strain rates of 0.1-30 s^-1, deformation temperature of 750-1000℃ and height reduction of 50%, and microstructure of the alloy after deformation was characterized by optical microscope and electron backscatter diffraction (EBSD) technique in order to study the microstructure evolution mechanism of the alloy during the high temperature deformation. The results show that the β grains of the alloy after deformation are elongated along the direction perpendicular to compression, and the deformed <001> and <111> fiber texture is formed. The increase of deformation temperature and the decrease of strain rate promote the dynamic recovery (DRV) and dynamic recrystallization (DRX) of the β grains, and the grain boundary bulging and the generation of DRX grains make the β grain boundaries show the serrated and necklace-like morphology. Finally, the relationship between microstructure evolution and mechanical behavior of the alloy is discussed, and it is found that when the strain increases to 0.4, the apparent deformation activation energy of the alloy is 221.533-201.207 kJ/mol, which is similar to the self-diffusion activation energy of β-Ti, becasue the dynamic recovery is the main dynamic softening mechanism in the deformation process of the alloy.

Ultra-high strength structural steel is a kind of steel with yield strength of more than 1200 MPa and excellent fracture toughness and ductility, and it is widely used in manufacturing fields such as aviation, aerospace, naval vessels, offshore engineering and engineering machinery. It is a key problem in the research field of ultra-high strength structural steel to maintain ultra-high strength, high ductility and high toughness at the same time. In this paper, the development and research progress of typical low alloy ultra-high strength steel, secondary hardening ultra-high strength steel and maraging steel are summarized, and the strengthening, toughening and ductility mechanism of ultra-high strength structural steel are introduced. The ultra-high strength of the ultra-high strength structural steel is obtained by precipitating a large number of nanoscale carbides, intermetallic compounds, or Cu-rich phases in the high-density dislocation martensite matrix; the excellent fracture toughness is achieved by the design of multi-phase and multi-scale layered microstructure of martensite laths, blocks and metastable austenite; and the key to high ductility is the introduction of metastable austenite in the high-density removable dislocation matrix. The research progress of the martensite with high dislocation density, the multi-phase multi-scale microstructure and the metastable austenite TRIP effect is expected to break through the trade-off between strength and toughness or ductility for ultra-high strength structural steel.

AlCrFeNiTi high entropy alloy was prepared by non-consumable vacuum arc melting and then annealed at high temperature. Microstructure and properties of the as-cast and annealed AlCrFeNiTi high entropy alloy were studied by means of X-ray diffraction, scanning election microscopy and reciprocating electrochemical corrosion friction and wear tester. The results show that there is no significant change in phase composition of the alloy after high temperature annealing. The intergranular region of the alloy decreases after annealing, and the existence of "uphill diffusion" leads to the segregation of alloy composition. Meanwhile, after high temperature annealing, the hardness of the alloy decreases from 434.16 HV to 408.00 HV, the friction coefficient decreases from 0.7420 to 0.3635, wear volume loss increases from 9.7231 mm³ to 16.9675 mm³, and the changes in the above properties are closely related to the composition segregation and microstructure transformation of the alloy.

In order to improve the performance of the pure electroplated Ni coating, Ni-GO composite coating was prepared on the surface of Q235 steel by adding different contents of graphene oxide (GO) to the plating solution. Morphology, phase structure and composition of the composite coating were characterized by laser confocal scanning microscopy(LCSM),X-ray diffractometer(XRD), scanning electron microscopy/energy dispersive spectrometer(SEM/EDS), and the hardness, wear resistance and corrosion resistance of the composite coating were analyzed by means of Vickers microhardness tester, multifunctional material surface performance tester and electrochemical workstation. The results show that when the GO content in the plating solution is 200 mg/L, the surface of the Ni-GO composite coating is smooth and compact, and the dispersion effect of GO in the coating is good. Compared with the substrate and the pure Ni coating, the microhardness of the composite coating prepared with the optimal GO content is 420.1 HV0.1, the friction coefficient (0.52) is lower, which has good wear resistance. The Ni-GO composite coating exhibits a lower self-corrosion current density (9.339×10^-6 A/cm²) in 3.5% NaCl solution, which shows good corrosion resistance.