Behaviour of Ir-24 at.-%Ta films on Ni based single crystal superalloys

The properties of Ir-24Ta (at.-%) films prepared by dc magnetron cosputtering from a composite target on a 〈100〉 oriented Ni based single crystal superalloy TMS-75 were investigated. Ir-Ta was proposed as a novel oxidation resistant bond coat material for thermal barrier coatings. XRD showed the formation of a Ir₃Ta fcc phase with a fibre texture with 〈111〉 orientation tilted by ∼ 10° with respect to the plane normal to the substrate surface. The Ir-Ta film subjected to post-heat treatment was found to be very stable, with no secondary phase formation up to 1073 K, and there seems to be interdiffusion at 1273 K. Nanoindentation measurements indicated that the addition of tantalum decreased Young's modulus and increased the hardness obtained in the as deposited films compared with the hardness of iridium films. The Ir-Ta films heat treated up to 1273 K also exhibited nanomechanical properties comparable with those of as deposited films at 573 K.