Bonding of alumina ceramics with nanoscaled alumina powders

Nanoscaled Al2O3-powders can be employed for diffusion bonding of alumina ceramics. In order to accomplish bonding of the ceramics, Al2O3-nanopowder with a median particle size of 14 nm in diameter is sandwiched between two commercial microcrystalline corund discs,followed by uniaxially hot compressing of the assembly in vacuum at 80 MPa and 1100 degrees C for 2 h. Scanning electron microscopic investigations reveal a nanocrystalline structure of the joint with a mean grain size of about 50 nm in diameter and extensive consolidation of the powder without substantial shrinkage void formation. Microhardness measurements across the interface yield a value of 200 HV. In order to achieve complete densification and strength enhancement of the joint material, the sample 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 depends strongly on the porosity content and/or grain size and that a hardness 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 diffusion bonding of alumina ceramics. Possible mechanisms are discussed. Copyright (C) 1996 Acta Metallurgica Inc.