Mechanical properties and microstructure of centrifugally compacted alumina and hot-isostatically-pressed alumina

High purity alumina powder was compacted under a high centrifugal force. Mechanical properties of the sintered body were studied by the three-point bending test at room temperature and by the compressive test at elevated temperatures. Comparison was made with hot-isostatically-pressed (HIP) alumina. The room-temperature flexural strength of the centrifugally compacted (CC) alumina was found to be 1330 MPa compared with 585 MPa of the HIP alumina. The difference in the room-temperature strength was attributed to the presence of the amorphous phase along the grain boundaries of the HIP alumina caused by the segregation of carbon and sulfur during HIP. A large ductility was observed above 1473 K in the CC alumina and above 1573 K in the HIP alumina. High-temperature ductility was lost in the HIP alumina at 1773 K where the amorphous grain-boundary phase was considered to be melted.