Densification of hydroxyapatite ceramics by field-assisted sintering followed by controlled current ramp sintering

Field-assisted sintering technique (FAST) and flash sintering experiments were conducted on hydroxyapatite (HAp) ceramics to attaining highly densified HAp body with uniform microstructure. FAST region, in which the densification was gradually accelerated, was observed from 800 °C under all fields examined. Under the field strength beyond 1000 V·cm−1, the FAST followed by flash sintering took place. The phase decomposition can be effectively suppressed by the FAST/flash sintering. During the FAST region, microstructure remained uniform and the relative density of 94 % was achieved. By the flash sintering at 1000 V·cm−1, the relative density of 97 % was achieved, but inhomogeneous microstructure appeared. By conducting controlled current rate sintering, the densification of the HAp with homogeneous microstructure was attained. The avoidance of current surge and localized current path through the specimen was crucial to attain the uniform, densified microstructure in the HAp ceramics.