Room temperature nitriding of pure titanium induced by cyclic compressive loading

Nitriding treatment of titanium enhances wear resistance by forming nitrogen compounds, such as TiN and Ti₂N, on the surface layer. Typically, high temperatures and an extended operating time are required for nitriding treatment to diffuse nitrogen into the titanium microstructure. Recently, we developed a new surface modification technique called scanning cyclic press (SCP), which scans the metal surface with a vibrating indenter to refine the microstructure by applying cyclically compressive loads. In this study, we aimed to establish a new nitriding technique using SCP to create titanium nitride at room temperature. SCP was applied to pure titanium in a nitrogen environment, and observations, along with elemental and crystal structure analyses of the modified surface areas, were conducted using a transmission electron microscope. As a result, we detected nitrogen at the surface of the specimen and confirmed the formation of a polycrystalline TiN layer with grain sizes ranging from several to a few dozen nanometers. Furthermore, no nitrogen diffusion layer was observed beneath the TiN layer. This finding indicates that SCP's nitriding mechanism at room temperature fundamentally differs from the conventional nitriding process using thermal diffusion of nitrogen.