Low temperature deposition of Cr(N)/TiO2 coatings using a duplex process of unbalanced magnetron sputtering and micro-arc oxidation

The surface modification of light-weight metals (such as Mg-, Al- and Ti-al loys) using plasma technology is being increasingly investigated. We have r ecently shown that thick oxide coatings on Ti-alloys can be successfully de posited using a micro-are discharge oxidation (MDO) technique. The hardness of the TiO2 coatings is in the range of only 600-900 HV0.05 and their wear resistance is thus limited. Nevertheless, from the viewpoint of improving load support, a thick TiO2, coating with a hardness of approximately 900 HV 0.05 should provide a more adequate underlying load support layer for a har d top coat. Therefore, a duplex process of micro-are oxidation and unbalanc ed magnetron sputtering has been investigated, in which a TiO2 layer was de posited on a Ti6Al4V alloy substrate (using MDO) for load support, and Cr(N ) hard coatings were deposited on top of the TiO2 layer for wear resistance (using magnetron sputtering). The morphology and phase composition of the Cr(N) coatings were observed and analysed by scanning electron microscopy a nd X-ray diffractometry (XRD). The coating residual stress was also assesse d using XRD. Mechanical and corrosion properties of the bilayered Cr(N)/TiO 2 coatings were tested. The results indicate that duplex Cr(N)/TiO2 coating s can provide a combination of good wear resistance and load-bearing capaci ty as well as corrosion resistance. (C) 2000 Elsevier Science B.V. All righ ts reserved.