Research Status of Ceramic Coatings
Thermal spray ceramic powder, including oxides, carbides, borides, nitrides and silicides, are metal and non-metallic elements of the crystal or amorphous compounds. Ceramic coating with high melting point, high hardness and good wear resistance, corrosion resistance and high temperature stability and so on. However, the coating ceramic coating process is complex, high cost, and the coating surface prone to crack, thermal fatigue performance as metal coating; and coating toughness is poor, can not be used to withstand greater impact load. At present, the commonly used ceramic coatings are A12O3, TiO2, Cr2O3, ZrO2, WC, TiC, Cr3C2, TiB2, etc., generally prepared by plasma spraying, flame spraying, HVOF and explosive spraying technology.
Jing Ri et al.  studied the sliding friction and wear properties of plasma sprayed A12O3-40% TiO2 and Cr2O3 ceramic powder coatings. It was pointed out that the wear resistance of Cr2O3 coating was higher than that of A12O3-40% TiO2 coating and the wear of Cr2O3 coating The mechanism is mainly abrasive wear, under a large load, Cr2O3 coating wear brittle fracture characteristics. The wear mechanism of A12O3-40% TiO2 coating is mainly plastic deformation and layered peeling. Chen et al  studied A12O3 plus TiO2 plus NiCrAlY composite ceramic coating, due to the melting of TiO2 and A12O3 formed a certain degree of miscibility, can reduce the coating porosity, and further improve the coating strength, toughness and wear performance.
Lin et al.  studied the sliding friction and wear characteristics of plasma sprayed multilayer metal and ceramic coatings. The coating sequence is first sprayed on the substrate NiCr primer layer, and then a different proportion of NiCr-Cr2O3 transition layer, the surface of 100% Cr2O3. It is found that the transition layer of the appropriate metal and ceramic ratio can improve the wear resistance of the coating. The main wear mechanism of the coating is brittle fracture, abrasive wear, adhesion and oxidation wear.
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