Cathodic arc deposited (Cr,Six)N coatings: From solid solution to nanocomposite structure

Abstract

This paper aims to investigate the effect of silicon addition on the microstructure and mechanical properties of CrN coatings with an emphasis on their stability at high temperature. Thin films were deposited onto M2 tool steels using a cathodic arc deposition process. Silicon was introduced using duplex Cr–Cr3Si targets, allowing Si enrichment within the 0.6–10.8at.% range.The microstructure of the films was characterized by SEM and TEM, while their crystalline structure at room temperature and after high temperature annealing treatments (up to 1000°C) was determined by XRD analyses. Mechanical properties were deduced from nanoindentation measurements and from residual stress experiments.A minimum content of 2at.% was evidenced as the solubility limit of Si in CrN. Below this value, Si substituted Cr in the CrN lattice to form a solid solution. Above 2at.% Si, a nanocomposite bi-phased structure appeared, composed of Si-poor CrN nanograins surrounded by an amorphous Si-rich CrN matrix. Si addition induced significant grain shrinkage, without a significant effect on hardness at room temperature. For (Cr,Six)N films annealed at high temperatures, the nanocomposite structure allowed a delay in structural transformations linked to nitrogen losses, preserving better and more stable mechanical properties.