Ion beam assisted deposition of TiN–Ni nanocomposite coatings

Hard and tough nanocomposite coatings consisting of hard TiN nanograins embedded in a soft metallic intergranular phase of Ni have been produced using ion beam assisted deposition. The chemical composition has been obtained by Rutherford Backscattering and the microstructural properties: phases, grain size, and texture of the coatings have been investigated by X-Ray Diffraction. In the composition range 0–22.5at.% Ni, δ-TiN is the only crystalline phase and Ni appears as an X Ray amorphous phase. The hardness increases up to a maximum of 41GPa at ~7at.% Ni which corresponds to a TiN crystallite size of ~8nm and a Ni intergranular phase thickness of roughly 1 monolayer. It is shown that the hardness enhancement in TiN–Ni nanocomposite coatings is not correlated with residual stresses, but rather with the intrinsic properties of the nanostructure. An important improvement in wear resistance is obtained for the coatings exhibiting the highest toughness and not the highest hardness. These results show that ion assisted processing is an effective tool for producing dense TiN–Ni nanocomposite coatings and tailoring their structure and mechanical properties.