Adherence of combined physically vapour-deposited and plasma-sprayed ceramic coatings

Abstract

Yttria-partially-stabilized zirconia (PSZ) has been shown to be a very effective material for use in high temperature applications, especially as a thermal barrier coating (TBC) in the aerospace industry and diesel engines. In this paper we present results on adherence and oxidation resistance of combined coating produced using a combination of physical vapour deposition (PVD) and plasma spraying (PS) deposition techniques. We substituted the metallic bond layer of the traditional TBC by a lighter dense ceramic coating (ZrO 2 coating stabilized by Y 2 O 3 ) produced by d.c. reactive magnetron sputtering (PVD coating). This coating system can be applied onto smooth substrates. The results show that it is possible to deposit an adherent PS coating onto a PVD layer without damaging it. Pull tests were used to determine the adhesive-cohesive strength of the combined coating. The adhesive strength of the PVD bond layer was 65 MPa. The cohesive strength of the PS top coat ranges from 20 to 40 MPa on decreasing the coating porosity. Prolonged heat treatment or thermal cycling up to 1000°C does not influence significantly the adherence of the coatings. Nevertheless, the cohesive strength of the growing Cr 2 O 3 interlayer which is about 30 MPa limits the pull strength of samples with combined coatings after the prolonged heat treatment at atmospheric pressure.