Novel high damage-tolerant, wear resistant MoSi2-based nanocomposite coatings

Abstract

In this study, novel MoSi 2 -based nanocomposite coatings were deposited on Ti-6Al-4V substrates by a two-step process involving firstly, deposition of MoSi 2 -based coatings, using a double cathode glow discharge process and, secondly, plasma nitridation of the as-deposited coatings. The aim of this latter step is to introduce nitrogen into the coating and promote the formation of amorphous silicon nitride. The resulting coatings were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that the nanocomposite coatings were composed of nanocrystallite Mo 5 Si 3 and MoSi 2 grains embedded in an amorphous Si 3 N 4 matrix. The mechanical properties and damage resistance of the coatings were evaluated by both Vickers indentation and nanoindentation techniques. Dry sliding wear tests were performed using a ball-on-disc type tribometer, in which the coated samples were tested against a ZrO 2 ceramic ball at normal loads of 2.8 and 4.3 N under ambient conditions. Compared with the monolithic MoSi 2 nanocrystalline coating, the specific wear rates of the nanocomposite coatings decreased by an order of magnitude. The specific wear rate was further improved by about 20% through the addition of Al, which was attributed to an optimum combination of mechanical properties. © 2013 Elsevier B.V.