Microstructure and hardness of two-step reverse-polarity flash sintered high-purity Al2O3 ceramics

In this work, high-purity alumina ceramics were prepared by using two-step reverse polarity flash sintering (PR-FS). The effects of the time distribution between the first flash and the second flash on microstructure and hardness were studied. The results show that compared to the conventional DC flash sintered alumina, the RP–FS–ed samples exhibited more uniform-microstructure, finer grains, higher relative density, and higher hardness. The underlying mechanism for such more homogeneous microstructure was related to uniform distribution of point defects under effect of reverse polarity. Two-step reverse polarity flash sintering method offers a great potential in obtaining highly densified alumina ceramics with homogeneous microstructure.