1. Research status of metal coating

Thermal sprayed metal coating is an earlier research and application of wear-resistant coatings, commonly used metal (Mo, Ni), carbon steel and low alloy steel, stainless steel and Ni-Cr alloy series coatings. Generally, flame spraying, arc spraying, plasma spraying, HVOF and explosive spraying processes are used. The coating has the advantages of high bonding strength with the substrate, good wear resistance and corrosion resistance, and is used to repair wear parts and machinery. Processing out of tolerance parts.

When aluminum alloy plasma spraying technology is used to spray piston rings, synchronizer rings, cylinders and other parts, the coating has good wear resistance, high bonding strength and excellent adhesion and wear resistance, and has good performance in the presence of lubricating oil. The anti-seize and anti-strain performance. High carbon steel wire and stainless steel (Crl3 type, 18-8 type, etc.) alloy wire are commonly used wear-resistant and corrosion-resistant spray materials. It has the characteristics of high strength, good wear resistance, wide sources, and low price. NiCr coating has good heat resistance, corrosion resistance and erosion resistance. It can be used as a protective coating for superheater tubes and reheater tubes of power station boilers. It can be prepared with different structures by flame and plasma spraying methods. The NiCr metal wear-resistant coating has high porosity and oxide content in the coating.

2. Research status of ceramic coatings

Thermal spraying ceramic powder includes oxides, carbides, borides, nitrides and silicides, etc., which are crystalline or amorphous compounds composed of metallic and non-metallic elements. Ceramic coating has the characteristics of high melting point, high hardness, good wear resistance, corrosion resistance and high temperature stability. However, the spraying ceramic coating process is complicated and the cost is high, and the surface of the coating is prone to cracks, and the thermal fatigue resistance is not as good as the metal coating; and the coating has poor toughness and cannot be used to withstand large impact loads. At present, the commonly used ceramic coatings are A12O3, TiO2, Cr2O3, ZrO2, WC, TiC, Cr3C2, TiB2, etc., which are generally prepared by plasma spraying, flame spraying, HVOF and explosive spraying techniques.

Ren Jingri et al. studied the sliding friction and wear characteristics of plasma sprayed A12O3-40%TiO2 and Cr2O3 ceramic powder coatings, and pointed out that the wear resistance of Cr2O3 coatings is higher than that of A12O3-40%TiO2 coatings. The main wear mechanism of Cr2O3 coatings is For abrasive wear, the wear of Cr2O3 coating exhibits brittle fracture characteristics under larger loads. The wear mechanism of A12O3-40%TiO2 coating is mainly manifested by plastic deformation and delamination. The A12O3 plus TiO2 plus NiCrAlY composite ceramic coating studied by Chen Chuanzhong et al., because the molten TiO2 and A12O3 form a certain degree of mutual solubility, it can reduce the porosity of the coating and further improve the strength, toughness and wear resistance of the coating.

Et al. studied the sliding friction and wear characteristics of plasma sprayed multilayer metal and ceramic coatings. The spraying sequence is as follows: first spray NiCr on the substrate as a primer layer, then a different proportion of NiCr-Cr2O3 transition layer, the surface is 100% Cr2O3. It was found that a transition layer with an appropriate metal and ceramic ratio can improve the wear resistance of the coating. The main wear mechanisms of the coating are brittle fracture, abrasive wear, adhesion and oxidative wear.

3. Research status of cermet coating

Metal and ceramic materials each have their own unique excellent properties and obvious performance weaknesses. How to combine the respective advantages of metal and ceramic materials has always been the research direction of materials science and engineering. Metal-ceramic composite coating technology, that is, uniformly distributing ceramic phases with appropriate particle shapes and sizes on a plastic matrix, successfully realizing the combination of advantages of metal and ceramics, preparing both metal strength and toughness, and ceramics with high temperature resistance The composite materials with the advantages of, wear resistance, corrosion resistance, etc., have greatly expanded the respective application ranges of metal materials and ceramic materials, and have been successfully applied in aviation, aerospace, chemical, machinery, electric power and other industrial fields. The most widely used cermet coatings in industry mainly include: Cr3C2-NiCr, WC-Co. Most of them use HVOF, plasma and explosive spraying processes.

The Cr3C2-NiCr cermet coating is composed of a refractory chromium carbide hard phase and a nickel-chromium alloy phase with good toughness. It has high high temperature hardness, excellent high temperature wear resistance, corrosion resistance, oxidation resistance and high Bonding strength, widely used in high temperature (530～9000℃) abrasive wear, corrosion wear and erosion wear conditions, such as furnace rolls in continuous annealing lines, core rolls in continuous production lines in rolling mills, cylinder piston rings , Cylinder lining, etc. TiB2-based cermet coating has high melting point, high hardness, good electrical and magnetic properties and high corrosion resistance. It is a potential substitute for Cr3C2 for high temperature and wear-resistant cermet. It has higher wear resistance than A12O3, Cr3C2-NiCr and WC-Co.

WC-based cermet coatings are often used in abrasive wear and erosion wear conditions below 450°C. Xu Xiangyang et al. studied the fretting wear mechanism of plasma sprayed WC/18Co coating. The results show that the initial stage of the fretting wear of the coating is dominated by adhesive wear. The coating has high hardness, strong anti-adhesive ability and slight wear; the stable phase is mainly due to fatigue delamination and brittle cracking. The coating is brittle and sprayed particles The bonding strength is low and easy to wear. The oxide inclusions in the spray coating are the main reason for the insufficient fretting resistance of the coating.

4. Research status of amorphous coatings

Amorphous state is a material with long-range disorder and short-range order. The physical and chemical properties of amorphous materials are often better than those of corresponding crystalline materials. They have high strength, high toughness, high hardness, high corrosion resistance, soft magnetic properties, etc., and they are a new type of metal material with great development prospects. . Thermal spraying of amorphous alloy coatings is a new field of extensive research in materials science in recent years. Thermal spraying technology has begun to attract widespread attention as one of the preparation methods of large-area amorphous coatings. Common methods include plasma spraying, HVOF and Explosive spraying.

Xiang Xinghua et al. used plasma spraying process to prepare Fe-based amorphous alloy coating (including Si, B, Cr, Ni, etc.), the structure of each area of ​​the coating is uniform, the coating is dense, the porosity is low, and the oxide content Less, and has high hardness, the microhardness is in the range of 530-790HV0.1, the coating and the substrate are well bonded.

Researched the microstructure and wear resistance of explosive sprayed Fe-Cr-B alloy coatings. The results show that the coating has good anti-wear and anti-corrosion properties, and the coating dynamically generates an amorphous surface film during the sliding wear process, which significantly improves the wear resistance of the coating and reduces the friction coefficient significantly.

In summary, the use of HVOF, plasma spraying, arc spraying, explosive spraying and other methods to spray metal, ceramic, cermet and amorphous wear-resistant coatings can effectively improve the wear resistance of the base material. In-depth study of the wear mechanism of the thermal spray coating and the influence of the coating structure on the wear characteristics provide a theoretical basis for improving the coating structure, optimizing the spraying process and developing new wear-resistant coatings.