Microstructures and Key Properties of Cold Sprayed and Low-pressure Plasma Sprayed Ni-Ti Coatings

Ni-Ti composite coatings were prepared by cold spray (CS) and low-pressure plasma spray (LPPS) using a mechanically mixed powder of Ni/Ti at the atomic ratio of 1:1. Upon utilization CS and LPPS techniques, spray processes played a significant role in the microstructures, phase compositions, mechanical property, and wear and corrosion performances of the two coatings. The results show that no oxidation is characterized in these two coatings. Nevertheless, two very different coating structures are found. CS coating shows a much lower porosity and a mechanical bonding of plastically deformed particles, and XRD denotes no NiTi intermetallic is formed during CS deposition. However, high temperature can lead to the significant differences in the LPPS coating, which exhibits a lamellar structure with the formation of Ni-rich and Ti-rich intermetallics around the interface. The LPPS coating presents the excellent performances due to the element diffusion during LPPS process, such as a higher hardness value, which is nearly three times higher than that of CS coating, and a lower wear rate. In addition, the coating also exhibits a much higher corrosion potential and a much lower corrosion current, indicating its better corrosion resistance.