MECHANICAL-PROPERTIES AND MICROSTRUCTURE OF CENTRIFUGALLY COMPACTED ALUMINA AND HOT-ISOSTATICALLY-PRESSED ALUMINA

High purity alumina powder was compacted under a high centrifugal forc e. Mechanical properties of the sintered body were studied by the thre e-point bending test at room temperature and by the compressive test a t elevated temperatures. Comparison was made with hot-isostatically-pr essed (HIP) alumina. The room-temperature flexural strength of the cen trifugally compacted (CC) alumina was found to be 1330 MPa compared wi th 585 MPa of the HIP alumina. The difference in the room-temperature strength was attributed to the presence of the amorphous phase along t he grain boundaries of the HIP alumina caused by the segregation of ca rbon 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-temperat ure ductility was lost in the HIP alumina at 1773 K where the amorphou s grain-boundary phase was considered to be melted.