Improving the Tribological Behavior of NiTi Alloy via Self-Catalytically Flame Growing Amorphous Carbon Coating

In this work, for surface protection of NiTi alloy, an amorphous carbon layer was directly deposited onto it via a self-catalytic flame coating method. The effect of the flame coating time on the physicochemical structure and mechanical hardness of the products was investigated, as well as its friction and wear resistance performance. The Vickers microhardness of the carbon-coated NiTi alloy decreased with the flame coating time, which was identified to be caused by the inherent thermal treatment during the flame coating process. The tribological test results indicated that both the friction coefficient (COF) and specific wear-rate of NiTi alloy were significantly reduced after the flame coating of the alloy. After direct flame treatment of the alloy for 20 min, 82.8% and 91.4% reduction in the COF and specific wear-rate could be achieved, respectively. The wear mechanisms of the coated NiTi alloy were found to be involved with the oxidation wear, adhesive wear, and the carbon transfer film, all of which had an important influence on the friction process. The carbon layer prepared by the flame coating method as a protective layer of NiTi alloy will greatly promote its versatile applications.