Microscale fracture mechanisms of HfO2-Si environmental barrier coatings

Abstract Environmental barrier coatings (EBCs) play a vital role in protecting advanced turbine components subjected to extreme service environments, where mechanical, thermal and chemical behaviors typically dominate the design criteria. This study focuses on investigating the mechanical properties of individual phases within a HfO 2 -Si ceramic matrix composite (CMC) structure through implementation of notched microcantilevers and micropillar splitting experiments. The microcantilever experiments resulted in fracture toughnesses ranging between 1.38–1.52 MPa-m 1/2 for the Si-rich phase and 2.26–2.38 MPa-m 1/2 for the HfO 2 -rich phase depending on the method of analysis. From our micropillar splitting experiments, we found fracture toughnesses of 1.13 ± 0.39 MPa-m 1/2 for the Si-rich phase and 1.18 ± 0.26 MPa-m 1/2 for the HfO 2 -rich phase. Comparisons with bulk single edge V-notched beams (SEVNBs) suggest the micropillar results are accurate whereas the microcantilever experiments may overestimate K IC of the Si-rich and HfO 2 -rich phases by ˜0.2–1.2 MPa-m 1/2 , most likely, due to dimensional errors that affect specimen and model compliances.