The influence of the yttrium content on the structure and properties of Ti1−x−y−zAlxCryYzN PVD hard coatings

Abstract Ti 1− x − y − z Al x Cr y Y z N and Ti 1− x − y Al x Cr y N coatings have been grown in a multiple target PVD coating unit using the combined steered arc evaporation/unbalanced magnetron deposition technique. Ti 1− x − y − z Al x Cr y Y z N film properties and yttrium distributions have been found to change significantly when three targets with equal yttrium content (Ti 0.495 Al 0.495 Y 0.01 ) or one yttrium-containing target (Ti 0.48 Al 0.48 Y 0.04 ) with two neighbouring pure Ti 0.5 Al 0.5 targets to produce a non-homogeneous distribution were used. The structural characteristics and residual stresses present in the coatings were determined by X-ray diffraction using both Bragg–Brentano and glancing angle parallel beam (sin 2 ψ method) geometries. In all cases the state of stress was found to be compressive, with values at 1° incidence angles of −6.5 GPa using a single 4 at.% yttrium containing target and −3.2 GPa using three TiAlY targets each containing 1 at.% Y. The residual stress value at 1° angle of incidence for the Ti 1− x − y Al x Cr y N film was similar to that of the homogeneously grown yttrium containing film, i.e. −3.8 GPa. The surface chemistry of the as-deposited and thermally treated films has been further analysed using high-resolution monochromatic X-ray photoelectron spectroscopy (XPS). Large area (700 μm×300 μm) and small spot (55 μm) XPS analysis was used to examine the role of low concentrations of the elements Y and Cr during the oxidation process. XPS imaging using O 1s, Ti 2p, Cr 2p and Fe 2p photoelectron peaks has been used to study the distribution of oxides formed on the surface after heat treatment. High resolution analysis of the Y 3d core level identified two chemical species for the as-deposited TiAlCrYN films at positions Y 3d 156.0 and 158.1 eV respectively, whilst only single species were identified in the oxidised film at Y 3d 158 eV.