Effects of Co addition on microstructure and cavitation erosion resistance of plasma sprayed TiNi based coating

TiNi shape memory alloy exhibits an excellent cavitation erosion resistance. Therefore, it's an effective method for preventing cavitation erosion by applying this material as a coating. In this paper, the effect of Co element addition on cavitation erosion resistance of TiNi based coating deposited by atmospheric plasma spraying (APS) was investigated. The microstructure and microhardness were characterized. The results show that the lamellar microstructures with defects, such as porosities, microcracks and unmelted particles are presented in all TiNi based coatings. The appropriate addition of Co element is beneficial to reduce the porosity of the TiNi based coating and obtain a denser microstructure. The matrix phase of the TiNi based coatings is TiNi phase. After adding Co element, TiNiCo phase is formed in the coating. Microhardness of TiNi based coatings is slightly increased after adding Co element due to the formed TiNiCo phase and the decreased porosity. All TiNi based coatings do not show the incubation period in the initial stage of cavitation. The cavitation erosion resistance of TiNi based coating can be improved by the appropriate addition of Co element due to the formed dense microstructure with low porosity.