Influence of sintering process on microstructure and mechanical properties of alumina ceramics: Spark plasma and microwave hybrid sintering

Improvement in hardness of alumina has advantages in ballistic performance and wear resistance of the material. Spark plasma sintering (SPS) and microwave hybrid sintering (MHS) were examined for improving the hardness of alumina and results are compared with conventional sintering (CS). Results show that the highest hardness is produced by SPS (20.4 GPa) followed by conventional sintering (18.6 GPa) and microwave hybrid sintering (18.5 GPa) process. Two separate Hall-Petch relations satisfy hardness variation in both SPS, and MHS/CS. The rate of densification is found to be higher for microwave hybrid sintering than the conventional sintering. Sintering of alumina at 1500 degrees C, the microwave hybrid sintering produced a higher density and grain size (90.6 % & 0.8 mu m at 0 h; 98.8 % & 2.3 mu m at 1 h) in comparison with conventional sintering (87.4 % & 0.8 mu m at 0 h; 98.3 % & 2.1 mu m at 1 h) for same sintering (dwell) duration.