BONDING OF ALUMINA CERAMICS WITH NANOSCALED ALUMINA POWDERS

Nanoscaled Al2O3-powders can be employed for diffusion bonding of alum ina ceramics. In order to accomplish bonding of the ceramics, Al2O3-na nopowder with a median particle size of 14 nm in diameter is sandwiche d between two commercial microcrystalline corund discs,followed by uni axially hot compressing of the assembly in vacuum at 80 MPa and 1100 d egrees C for 2 h. Scanning electron microscopic investigations reveal a nanocrystalline structure of the joint with a mean grain size of abo ut 50 nm in diameter and extensive consolidation of the powder without substantial shrinkage void formation. Microhardness measurements acro ss the interface yield a value of 200 HV. In order to achieve complete densification and strength enhancement of the joint material, the sam ple is subsequently sintered at 1500 degrees C and 1600 degrees C for several hours in air. It was found that the hardness of the joint depe nds strongly on the porosity content and/or grain size and that a hard ness of 1700 HV is obtained when both a mean particle size of about 1 mu m and complete densification of the joint is achieved. The results show for the first time that Al2O3-nanopowders are suitable for diffus ion bonding of alumina ceramics. Possible mechanisms are discussed. Co pyright (C) 1996 Acta Metallurgica Inc.