2 Results and Discussion 2.1 The microstructure and properties of the coating 2.1 The Al2O3-TiO2 and WC Co cermet coatings are formed by overlapping particles. The coating structure is compact, without obvious cracks and coarse pores. It is composed of Al2O3, TiO2 and other phases, and also contains a small amount of Fe3O4, which is due to the high temperature of the arc zone and the oxidation of the material during the arc spraying process.
2.2 Friction and wear properties and surface microhardness The microhardness of the cermet coating is significantly higher than that of the matrix. The microhardness (Vickers hardness) of the Al2O3-TiO2 coating is the highest, reaching 1463, while the microhardness (Vickers hardness) of the matrix is only 524. Due to the formation of hard intermetallic compounds such as Al2O3, TiO2, WC and Co2O3 by surface deposition, the surface hardness of the plasma coating is significantly higher than that of the substrate. The wear resistance of the friction pairs of Al2O3-TiO2 and WC Co cermet coatings prepared by plasma spraying is significantly improved compared with that of untreated friction pairs, and the wear resistance of WC Co cermet coatings is slightly better than that of Al2O3-TiO2 cermet coatings, The reason why the plasma sprayed coating has high wear resistance is that it has high microhardness and nanocrystalline particles are dispersed in the coating. The high hardness coating is difficult to plastic deformation, and can not produce obvious brittle peeling under contact. The dispersed nanocrystalline particles have a good dispersion strengthening effect on the coating, Both of them improve the wear resistance of the friction pair.

Maintenance of packing
1. The packing is directly related to whether the key sealing element leaks when the valve is opened and closed. If the packing fails, causing leakage, the valve is also invalid. Strengthening maintenance can extend the service life of the packing
2. When the valve leaves the factory, in order to ensure the elasticity of the packing, it is generally subject to the static pressure test without leakage. After the valve is installed into the pipeline, due to temperature and other factors, leakage may occur. At this time, the nuts on both sides of the packing gland should be tightened in time as long as there is no leakage. In the future, leakage should occur again, and tightening should not be done once, so as to avoid the loss of elasticity and sealing performance of the packing.
3. Some valve packing contains molybdenum disulfide lubricating paste. After several months of use, corresponding lubricating grease should be added in time. When it is found that the packing needs to be supplemented, corresponding packing should be added in time to ensure its sealing performance.