Study of Thermal Shock Resistance of Plasma Sprayed VW75 Alloy

Abstract

The thermal shock resistance of T5-state VW75 Mg alloy after the plasma spraying was tested, the service process of material under the real environment was simulated, the reasons and mechanism for the coating shedding were revealed, and the comprehensive thermal shock resistance of alloy was acquired. The results showed that before the thermal shock test, the sample surface was flat with the gray color, and after the test was started, the coating surface was turned into white ZrO2 again. As the number of thermal cycles was increased, the black brown color started appearing on the sample surface, and the coating presented the overall shedding after the 158 cycles. The microcracks and pores in the ceramic layer and bonding layer were not developed into macrocracks yet, it could be deemed that the internal bonding at each layer was rather compact, and the coating quality was very high. The failure of thermal barrier coating occurred between the Mg alloy matrix and bonding layer, the thermal expansion coefficient varied from layer to layer of the coating, thus aggravating the interlayer thermal stress and leading to the overall shedding of coating, and in addition, the thickening of thermally grown oxidation layer was also an important cause for the shedding.