Phase transformation mechanism of the APS yttria partially stabilized hafnia coating undergoing thermal exposure

Abstract

8 mol.% Y2O3 partially stabilized HfO2 (YSH8) free-standing coating was prepared by air plasma spraying (APS) method, and the crystal structure and phase transformation under 1300 °C were studied using Rietveld method of XRD, SEM and TEM. Results show that the as-sprayed YSH8 coating is mainly composed of tetragonal structure (T phase). The phase transformation of YSH8 coating is controlled by the diffusion of Y element. As the thermal exposure time prolongs, the weight fraction of monoclinic phase (M phase) quickly increases and reaches 68.1 % after 24 h. The Y content at the interface between the M phase and the original microstructure increases to 9 %–17 % after 24 h, and is in cubic phase. After exposure for 24, the T phase completely transforms to C + M phase.