Effect of Thermal Cycling and Thermal Aging on the Mechanical Properties of, and Residual Stresses in, Ni-YSZ/YSZ Bi-Layers

Abstract

In this paper we report the effect of thermal cycling, between 20 °C and 800 °C in a gas mixture of 4% H 2 and 96%Ar, on the physical and mechanical properties of Ni-YSZ/YSZ bi-layers. It was found that the porosity and Young's modulus of the bi-layers did not change significantly after thermal cycling. However, the characteristic biaxial strength, as determined by the ring-on-ring test method, was found to decrease by as much as 15% after 1250 thermal cycles. Similar trends were observed from the evaluation of test specimens that had been thermally aged in a similar environment at 800 °C for 625 hours. It was also found that the magnitude of the compressive residual stress in the YSZ layer changes significantly during thermal cycling and aging. Potential mechanisms responsible for this behavior are discussed.