Stiffness of Plasma Sprayed Zirconia Top Coats in Thermal Barrier Coatings

Authors: J.A. Thompson, T.W. Clyne, University of Cambridge, Cambridge, UK

Abstract

Yttria-stabilised zirconia coatings have been deposited onto nickel superalloy substrates by air plasma spraying (APS). Free standing layers were then obtained by chemical dissolution techniques. The in-plane Young’s modulus values exhibited by these layers were measured using the techniques of cantilever ending and ultrasonic resonant frequency testing during flexural vibration. Young’s modulus data were also obtained by nanoindentation of regions remote from microcracks. The values obtained by bending and frequency measurement were found to be considerably lower than that expected for bulk zirconia, whereas those obtained by the nanoindentation experiments were much closer to that of the bulk ceramic. Tests were also performed on samples which had been heat treated at 1100°C and 1300°C. It was found that the stiffness rose significantly after such treatments. This is attributed to sintering processes which generated extensive healing of microcracks.