Structure—properties relationship of metastable Al-Cr and Al-Ti alloys deposited by r.f. magnetron sputtering: role of nitrogen

Abstract

Aluminium-based alloy films are potential candidates for anodic corrosion protection of construction steels. However, the mechanical properties of such coatings must be reinforced, for example by addition of transition elements. In this paper, we will first present some results concerning Al-Cr and Al-Ti coatings synthesized by r.f. sputtering of composite targets. We will further discuss the influence of nitrogen incorporation into the coatings reactively sputter-deposited in different Ar-N 2 mixtures. After a description of the structural and microstructural features of Al-Cr-(N) and Al-Ti-(N) coatings, we will link the effect of their composition upon their mechanical characteristics such as intrinsic stress, microhardness or wear resistance as well as upon their corrosion resistance. The as-sputtered Al-Cr and Al-Ti coatings always remain microcrystalline or amorphous solid solutions, and their microhardness can reach about 10 000 MPa. Nitrogen incorporation favours the amorphization of the coatings. An extensive-to-compressive stress transition, which is clearly related to a densification of the coatings, is also observed as the Cr or Ti content increases and when nitrogen is incorporated into the reactor. Owing to the mechanical properties obtained for coatings remaining anodic compared with the construction steel substrate, future applications in mechanics are expected.