Study of plasma nitriding followed by sol-gel process to prepare composite coating on the titanium alloy

摘要

The oxidation is an important factor to limit the titanium and titanium alloy application at elevated temperature. This paper presents the ideological that by controlling the surface chemical composition in the titanium alloy substrate to form a dense thermal barrier layer and anti-oxidation layer to improve the oxidation resistance of titanium alloy. First, a dense layer of the gradient distribution of nitrogen was prepared by plasma nitriding of titanium alloy surface, and then followed by preparing the composite coating by the sol-gel. The zirconia powder with low thermal conductivity was added in the alumina sol in the process. The effects of factors such as the sol composition, proportion, and heat treatment process on the coatings properties were studied. Heat-treatment by thermal pressure filtration sintering in the process applied much lower temperature than ordinary sintering, thereby reducing the trend of crack initiation and obtaining the good composite coating. After the plasma nitriding treatment, the microhardness of the surface increased more than twice. XRD analysis showed that the main phases of the plasma nitrided surface were TiN and Ti2N and on the top Al2O3 and ZrO2 The surface and cross section morphology were observed and analyzed by the scanning electron microscopy. The results showed that a dense composite coating without obvious crack on surface of TC4 can be prepared by plasma nitriding and sol-gel composite process. The thermal cycling oxidation experiment at 700℃ showed that the composite coating improved the oxidation resistance.