Micromechanical analysis and theoretical predictions towards thermal shock resistance of HfO2-Si environmental barrier coatings

Abstract

As HfO2-doped Si bond coat acts a pivotal part in application of progressive environmental barrier coating (EBC) system owing to improving the high-temperature capability and creep properties of bond coat, it is essential to control the doping content and to balance the mechanical and thermal properties of doped coatings challenge in terms of upgrading service life and operating temperature of EBC system. In this study, the physical properties and thermal shock performance at 1723 K of HfO2-Si composite coatings with three different compositions were investigated via first-principle calculations and micromechanical model. Evidently, the composite coatings deposited by magnetron sputtering exhibit a better resistance towards crack initiation and propagation than pure Si bond coat up to 100 h thermal cycling time. Such improvement is attributed to the dispersion toughening effect caused by the characteristic structure of dispersed HfSiO4 particle within cristobalite “mortar”. With thermal cycling, the continuous Ostwald ripening of HfSiO4 particles decreased the elastic modulus and effective thermal expansion coefficient gap at room and high temperature of composite coatings, which was advantageous to thermal shock resistance. Unfortunately, as a consequence of excessive volume expansion during particle ripening, the composite coatings encountered varying degrees of interface separation after 100 cycles and hence not protective anymore. The results suggested that the further modification for low-frequency vibration patterns of HfSiO4 and realizing the interfacial metallurgical bonding can reduce the thermal expansion coefficient of HfO2-doped Si composite coatings and strengthen interface adhesion.