Titanium nitride coating on nickel produced by a powder immersion reaction-assisted coating method

Coating of nickel substrates with a hard titanium nitride (TiN) layer was performed by employing a two-step titanization–nitriding powder immersion reaction-assisted coating (PIRAC) procedure. Titanization of nickel via annealing in Ti powder with admixed iodine at 750–900 °C yielded up to 20-μm-thick reaction zones with Ti2Ni on the surface followed by layers of TiNi, Ni3Ti, and Ni(Ti) solid solution. The growth of TiNi and Ti2Ni layers, as well as of the reaction zone as a whole, obeyed the parabolic law. The measured activation energy of TiNi layer growth (149 kJ/mol) was comparable with the earlier reported activation energy of chemical diffusion in NiTi. PIRAC nitriding of the titanized Ni specimens at 850–900 °C resulted in the formation of a thin (∼1 μm) TiN surface film, whereas the underlying three-layer Ti2Ni–TiNi–Ni3Ti zone was eventually transformed into a single Ni3Ti layer. The results obtained are discussed in terms of Ni–Ti and Ni–Ti–N phase diagrams.