Elastic properties of monoclinic hafnium oxide

The elastic properties of monoclinic hafnium oxide were studied as functions of porosity, temperature and grain size. An important finding of this study was that hafnium oxide is subject to microcracking when the grain size exceeds a critical value between 2 and 3 mu m. The behavior of the elastic moduli with porosity and temperature for crack-free hafnium oxide was typical for polycrystalline ceramics. The nature of the thermal expansion and the internal friction supported this finding. The elastic properties for the microcracked material exhibited trends similar to those observed for other microcracked materials. However, some new characteristics of the microcracking effects were observed in this study. An increase in internal friction was associated with the microcrack healing process. It was also found that there is an atmospheric effect that enhances microcrack growth. Additionally, thermal treatments of microcracked hafnium oxide were found to result in significant changes in the microcrack system