**Deposition of Titanium Dioxide Coating by the Cold-Spray Process on Annealed Stainless Steel Substrate**

#### **Noor irinah Omar 1,2,\*, Santirraprahkash Selvami 1, Makoto Kaisho 1, Motohiro Yamada 1, Toshiaki Yasui 1 and Masahiro Fukumoto 1**

1 Department of Mechanical Engineering, Toyohashi University of Technology,1-1, Tempaku-Cho, Toyohashi, Aichi 441-8580, Japan; santirraprahkash@gmail.com (S.S.); Kaisho.makoto.ik@tut.jp (M.K.); yamada@me.tut.ac.jp(M.Y.);yasui@tut.jp(T.Y.);fukumoto@tut.jp(M.F.)


Received: 18 September 2020; Accepted: 15 October 2020; Published: 17 October 2020

**Abstract:** The surface of most metals is covered with thin native oxide films. It has generally been believed that to achieve bonding, the oxide covering the surface of metallic particles or metal substrates must be broken and removed by adiabatic shear instability (ASI), whether induced at the particle–substrate interface or at the particle–particle interface. The aim of the present research is to investigate the correlation between the remaining oxide amorphous layer and substrate-deformation with the adhesion strength of cold-sprayed TiO2 coatings towards the bonding mechanism involved. Relevant experiments were executed using stainless steel (SUS 304), subjected to various annealing temperatures and cold-sprayed with TiO2 powder. The results indicate an increasing trend of coating adhesion strength with increasing annealed substrate temperature. The influence of substrate plastic deformation and atomic intermixing at the remaining amorphous oxide layer is discussed as the factors contributing to the increasing adhesion strength of cold-sprayed TiO2 coatings.

**Keywords:** adiabatic shear instability (ASI); cold spray; titanium dioxide; bonding mechanism; adhesion strength; substrate deformation; amorphous interface layer
