N dependent tribochemistry: Achieving superhard wear-resistant low-friction TaCxNy films

Wear-resistant low-friction films have been widely applied to various engineered components to prolong their service lifetime, in which the mechanical properties of films need to be optimized for their intended applications and contact situations. The design and fabrication of superhard wear-resistant low-friction films can broaden the work situations of machine parts to some harsh conditions, i.e. subjecting to the attack of hard particles. Here, superhard wear-resistant low-friction TaCxNy films were deposited by sputtering a TaC composite target in the mixed discharge gases of N-2 and Ar. The N content in solid solution TaCxNy films can tailor the valence electron concentration (VEC) and surface chemistry forming graphitic clusters, achieving the maximum hardness of 41.5 GPa and lowest wear rate of 0.6 x 10(-6) mm(3)/Nm, coupled with low friction coefficient (mu) of 0.18 in TaC0.60N0.33 film, simultaneously. The results show that the wear rate of solid solution TaCxNy films is mainly governed by hardness and the ratio of hardness (H) and elastic modulus (E). The tribochemistry could be identified as TaCxNy + O-2 -> TaOx + C + N-2 / NOx by the combined results of Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscope. The reduction of the mu is shown to depend on the amount of the graphitic clusters generated in tribochemical reaction caused by shear stress, which can be tailored by N content. (C) 2017 Elsevier By. All rights reserved.