Undulating and porous structure tuned surface cracking behavior of Yb₂Si₂O₇ environmental barrier coatings under steam cycling

Ytterbium disilicate (Yb₂Si₂O₇, YbDS) is an excellent top-layer material for environmental barrier coatings (EBCs) to protect ceramic matrix composites (CMCs) from harsh corrosion. However, the EBC surface cracking due to the corrosion transformation from YbDS to ytterbium monosilicate (Yb₂SiO₅, YbMS) during steam cycling is a bottleneck problem for its application. In this paper, four distinct geometric models of EBC with pre-cracks were developed to determine how the undulating and porous structure tuned EBC surface cracking. It was found that the pre-cracks in the valleys of the EBC surface were more likely to propagate than those at the peaks. Wavelength variation on the EBC surface had a more pronounced effect on crack propagation than amplitude variation. The porous structure not only alleviated EBC surface cracking, but also reduced the promotion of crack propagation caused by increasing wavelength. This indicates that optimizing the microstructure of EBCs will contribute to improving their performance.