Deposition of multicomponent chromium boride based coatings by pulsed magnetron sputtering of powder targets

It is well known that composite transition metal boride (and also nitride or carbide) based materials show great promise for a wide range of tribological applications. The wear and fiction properties of plasma assisted PVD hard films can, in certain cases, be enhanced significantly by introducing some amount of an additional material (such as a solid lubricant) into the coating. However such measures can, for example, introduce further issues with regard to reduced corrosion resistance (and even increased fiction in humid environments). An aim with complex multi-element composite materials is often, therefore, to combine the advantages of several constituent phases to enable the coating to survive under varying wear conditions by exhibiting "adaptive" properties, without harming other coating characteristics. Sputtering of multi-component coatings from blended powder targets offers a straightforward, rapid and cost-effective way of varying the elemental composition of the target and hence of the deposited film. It also solves potential cracking problems associated with overheating during the sputtering of brittle ceramic targets with relatively low thermal (and sometimes electrical) conductivity. Furthermore, pulsed magnetron sputtering can have a significant beneficial impact on PVD coating structure and properties. In this study, dense multicomponent chromium boride-based coatings with MoSx, Ti and C alloying additions were deposited by pulsed magnetron sputtering of blended powder targets. Auger Electron Spectroscopy revealed that the films had extremely uniform through-thickness compositions and that contamination by oxygen was below 3 at.%. Scratch testing of coatings with increasing amount of MoS, showed that improvements in adhesion are obtained only up to a certain point, beyond which properties deteriorate. Ti and C addition to the CrB-MoSx films dramatically improves their behaviour on stainless steel in corrosive environments, exceeding that of bare stainless steel. It also enhances the hardness and adhesion of the coatings. This paper presents the results of investigations of the structure, composition, corrosion resistance and mechanical and tribological properties of these coatings. (c) 2005 Elsevier B.V. All rights reserved.