Plasma spraying technology has been widely used in traditional fields, such as wear-resistant coatings and corrosion-resistant coatings. Since the 1950s, its application fields have expanded from aviation and aerospace to steel industry, automobile manufacturing, petrochemical industry, textile machinery, shipbuilding and other fields. In recent years, the application and research of plasma spraying technology in high-tech fields such as nano-coating, functionally gradient materials, superconducting coatings, and biological functional coatings have gradually attracted people's attention. 1 Nano coating Compared with the conventional coating, the hardness, toughness and wear resistance of the coating have been greatly improved by plasma spraying. Under the load of 40-60 N, the wear rate of nano WC/Co coating is only 1/6 of that of traditional coating. The University of Connecticut et al. conducted systematic research on the plasma sprayed nanostructured Al2O3-TiO2 coating, including the drying and agglomeration reconstruction of nano powder spraying, optimization of plasma spraying process parameters, process diagnosis, simulation, and analysis of coating structure and performance, indicating that the coating has two states of microstructure, and shows unique and excellent performance. Compared with the corresponding conventional coating, its adhesive strength is increased by 100%, its wear resistance is increased by 300%, and its resistance to indentation cracking, bending and cupping test is higher. Zhu Yingchun of the Shanghai Institute of Ceramics, China, and others studied the structural changes and particle injection characteristics of nano-TiO2 during plasma spraying. It was found that TiO2 nanoparticles changed from amorphous to anatase and rutile structures. The coating shows good Li+injection current and electrochemical stability. Chen Huang and others used atmospheric plasma spraying technology to prepare zirconia nano-coating on stainless steel substrate. The obtained coating has a dense structure, its porosity is about 7%, and the bonding strength between the coating and the substrate is 45MPa, which is significantly better than the bonding strength between the traditional zirconia coating and the substrate 2 Gradient functional materials (FGMs) At present, the preparation of functionally gradient materials by plasma spraying is one of the most important research fields in materials science. Its research scope mainly includes the design, preparation and performance evaluation of functionally gradient materials. Due to the high temperature of plasma flame, it is especially suitable for spraying refractory metal, ceramic and composite coatings, which provides a broader space for the development of functionally gradient materials. At present, using NiCrAlY as the intermediate layer to coat ZrO2 coating on metal has become the focus of most plasma sprayed FGMs structure research, and a good preparation process has been established. In addition, other systems that have been studied also include: Cu/W and Cu/B4C, Ni-based alloys combined with Al2O3-Cr2O3, ZrO2 with CoCrAlY or NiCoCrAlY, TiC with Mo, Ni-20% Cr with YSZ coating, Ni/Al2O3, WC/Co, etc. The study of YSZ/NiCoCrAlY system by K. A. Khor et al. shows that the functionally gradient coating has better performance than the traditional double-layer material. The bonding strength of the obtained FGM coating is 18 MPa, and that of the double-layer coating is only 9 MPa, while the thermal cycle resistance life of the FGM coating is 6 times that of the double-layer coating. Sudarshan Rangaraj et al. designed five kinds of YSZ gradient coatings with different compositions and studied the effect of coating design on the properties of YSZ coatings. The results showed that the addition of mullite composition would reduce the driving force of crack growth on the coating surface. 3 Superconducting coating The plasma spraying arc temperature is very high, which is especially suitable for spraying composite oxide ceramics. It does not need protective atmosphere, and can spray superconducting parts with complex shapes. It has high deposition efficiency and is easy to prepare thick film coating and large area coating. The superconducting ceramic coating materials suitable for plasma spraying mainly include YBa2Cu3O7 - x (YBCO) and Bi2Sr2Cu2CaO. YBCO is a typical superconducting material with a critical temperature of 94 K. The plasma sprayed YBCO coating does not have superconductivity because of the oxygen loss of the material during the spraying process, the pores, cracks and uneven contact between particles in the coating structure. Superconductivity can be obtained only when the coating is properly heat treated in oxygen or air atmosphere to form a dense, uniform and stable crystal structure. The heat treatment condition of YBCO coating is 920 ℃ × 1 h, reduce to 400 ℃ and keep it warm for 1 h. When Bi2Sr2Cu2CaOy ceramic is quenched or quenched from high temperature, it will produce superconducting state. This characteristic is of special significance to plasma spraying, because plasma spraying can make the coating material obtain a rapid cooling rate of up to 106 ℃/s. As long as the plasma spraying conditions and process parameters are adjusted, it is easy to make the sprayed coating of Bi2Sr2Cu2CaOy have superconducting properties. 4 Biological function coating Plasma spraying technology is an effective method to prepare medical biological coating materials. The powder materials of specific components are melted at high temperature and deposited on the surface of metal artificial bone implant to form artificial bone and artificial joint with ductile metal as skeleton and ceramic coating on the surface. This method fully takes advantage of metal and ceramic materials. There are many reports on plasma sprayed hydroxyapatite (HA) coating and titanium coating at home and abroad, and they have been successfully applied in clinical trials. Hydroxyapatite coating is non-toxic to organisms, resistant to body fluid corrosion, and has good adaptability and affinity to biological tissues, resistant to wear during long-term exercise, and has sufficient mechanical properties. Titanium implants have good chemical stability, good combination with tissues and compatibility with body fluids. Titanium coating on stainless steel root and bone plate by vacuum plasma spraying has been successfully applied in clinic. These coatings not only utilize the strength of stainless steel, but also utilize the biocompatibility of titanium coating to prevent the release of toxic elements in stainless steel. China's Shanghai Silicate Research Institute has also made good progress in the research of biological coating materials.