Thermal sprayed metal coating is an early 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 technology are used. .
When the aluminum alloy plasma spraying technology is used to spray the piston ring, synchronizing ring and cylinder and other parts, the coating has good wear resistance, high bonding strength and excellent adhesion wear resistance, and has good wear resistance under the condition of lubricating oil. Anti-seize and tensile properties. High carbon steel wire and stainless steel (Crl3 type, 18-8 type, etc.) alloy wire are commonly used wear and corrosion resistant spraying materials. It has the characteristics of high strength, good wear resistance, wide source and low price. NiCr coating has good properties of 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 by flame and plasma spraying methods with different structures. 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. It is a crystalline or amorphous compound composed of metal elements and non-metal elements. The ceramic coating has the characteristics of high melting point, high hardness and good wear resistance, corrosion resistance and high temperature stability. However, the spraying ceramic coating process is complicated, the cost is high, and the surface of the coating is prone to cracks, and the thermal fatigue resistance is not as good as that of 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 coating was higher than that of A12O3-40%TiO2 coating, and the wear mechanism of Cr2O3 coating was mainly Because of abrasive wear, the wear of Cr2O3 coating exhibits brittle fracture characteristics under larger load. The wear mechanism of A12O3-40%TiO2 coating is mainly manifested as plastic deformation and lamellar peeling. The A12O3 plus TiO2 plus NiCrAlY composite ceramic coating studied by Chen Chuanzhong et al. can reduce the porosity of the coating and further improve the strength, toughness and wear resistance of the coating because the molten TiO2 and A12O3 form a certain degree of mutual solubility.
Lin et al. studied the sliding friction and wear characteristics of plasma sprayed multi-layer metal and ceramic coatings. The spraying sequence is as follows: First, spray NiCr on the substrate to make a bottom layer, then a NiCr-Cr2O3 transition layer with different proportions, and the surface is 100% Cr2O3. A transition layer with an appropriate ratio of metal to ceramic was found to improve the wear resistance of the coating. The main wear mechanisms of coatings are brittle fracture, abrasive wear, adhesion and oxidative wear.
3. Research status of cermet coatings
Metal and ceramic materials have their own unique excellent properties and obvious performance weaknesses. How to combine the respective advantages and properties of metal and ceramic materials has always been the research direction of materials science and engineering. Metal-ceramic composite coating technology, that is, the ceramic phase with appropriate particle shape and size is evenly distributed on the plastic matrix, and the advantages of metal and ceramic are successfully combined. , wear resistance, corrosion resistance and other advantages of composite materials, greatly broaden the application scope of metal materials and ceramic materials, and have been successfully used in aviation, aerospace, chemical, machinery, electric power and other industrial fields. The most widely used cermet coatings in industry are: 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 parts that work under high temperature (530～9000℃) abrasive wear, corrosive 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 coatings have high melting point, high hardness, good electrical and magnetic properties, and high corrosion resistance, and are a potential alternative to Cr3C2 for high-temperature, wear-resistant cermets. It has higher wear resistance than A12O3, Cr3C2-NiCr, 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 coatings. The results show that the initial stage of fretting wear of the coating is mainly adhesive wear, the coating has high hardness, strong anti-adhesion ability, and slight wear; the stable stage is dominated by fatigue delamination and brittle cracking and spalling, the coating is brittle, and the spray particles The bonding strength is low and easy to wear. Oxide inclusions inside the spray coating are the main reasons for the insufficient fretting wear resistance of the coating.
4. Research status of amorphous coatings
Amorphous is a material with long-range disorder and short-range order. The physical and chemical properties of amorphous materials are often better than the corresponding crystalline materials, with high strength, high toughness, high hardness, high corrosion resistance, soft magnetic properties, etc., is a promising new type of metal materials. . Thermal spraying of amorphous alloy coatings is a new field that has been extensively studied in materials science in recent years. As one of the preparation methods of large-area amorphous coatings, thermal spraying technology has begun to attract widespread attention. The commonly used methods include plasma spraying, HVOF and Explosive spray.
Xiang Xinghua et al. used a plasma spraying process to prepare Fe-based amorphous alloy coatings (including Si, B, Cr, Ni, etc.), and the structure of each area of the coating was uniform, the coating had high density, low porosity, and oxide content. Less, and has high hardness, the microhardness is in the range of 530 ~ 790HV0.1, and the coating is well combined with the substrate.
Jin et al. studied 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. 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.
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 matrix material. In-depth research on the wear mechanism of thermal spray coating and the influence of coating structure on wear characteristics can provide theoretical basis for improving coating structure, optimizing spraying process and developing new wear-resistant coatings.
