Healing behavior of microcracks on the surface of yttria-stabilized polycrystals using an ultrafast high-temperature sintering method

A technique to heal microcracks on ceramic surfaces in a relatively short time is an attractive proposition for extending the lifetime of ceramics. To this end, we used the ultrafast high-temperature sintering (UHS) method, which permits a rapid temperature increase, to heal Vickers indentation microcracks generated in a 4 mol% Y2O3-doped ZrO2 polycrystal. We examined the microstructure following microcrack healing using transmission electron microscopy and scanning electron microscopy with continuous focused ion beam slicing along the microcrack plane. This revealed that the microcrack healing process involves crack pinching and neck formation, followed by the growth of the neck. The microcracks were fully healed at the surface by UHS treatment at 2000 degrees C for 20 s. However, residual pores corresponding to the unhealed state were observed inside the material. We hypothesized that these pore residues were caused by significant grain coarsening during UHS. It is essential to optimize the UHS temperature and time to account for grain coarsening and facilitate the application of this method to microcrack healing.