Solid-state cold spraying of Ti and its alloys: A literature review

Compared to conventional high temperature processes, e.g. arc additive manufacturing, thermal spraying and laser/electron-beam cladding/additive manufacturing, coatings of Ti and its alloys with cold spraying (CS) are increasingly attracting attention from researchers and industries, because of the low temperature and high velocity characteristics of sprayed particles, which strictly restrict the oxidation of the sprayed powder and bring about prominent metallurgical benefits. However, coatings of Ti and its alloys by CS have been found limited industrial applications compared to other materials (e.g. Cu and Al), partly due to the special particle deposition behavior of Ti and its alloys and the lack of comprehensive knowledge of its control. This review therefore focuses on the deposition characteristics of Ti and its alloys during CS in an effort to shed light on them and expand their applications. The first part presents a brief introduction of CS and the basic characteristics of Ti and its alloys coatings by CS. The second part describes the effects of CS process parameters on the deposition characteristics of Ti and its alloys. The third part discusses the bonding mechanisms of Ti and its alloy particles during CS. The fourth part discusses the strengthening methods such as in-situ shot peening and laser-assisted CS. The coating properties can also be improved with post-spray treatment, such as heat treatment, laser treatment, hot rolling, hot isostatic pressing and friction stir processing. In addition, further applications are suggested, such as protective coatings, biocompatible coatings, and additive manufacturing. Finally, the summary and prospects for the deposition of Ti and its alloys are presented.