EFFECT OF PROCESSING PARAMETERS ON PHASE AND MICROSTRUCTURE EVOLUTION IN RBAO CERAMICS

Important parameters controlling the reaction-bonding of Al2O3 (RBAO) process are Al content, particle size, and green density. Successful fabrication of high-strength bodies requires fine and homogeneous powders. Low milling intensity does not lead to the required particle fineness, whereas overmilling causes extensive oxidation and hydrolyzation of Al. Oxidation of Al during milling is enhanced by ZrO2 additions. As much of the Al should be oxidized by solid/gas reaction as possible. Milled RBAO precursor power contains physically-adsorbed and chemically-bonded (aluminum hydroxide) water. Decomposition of chemically-bonded water promotes cracking in the temperature range 450-550-degrees-C. Bloating of RBAO occurs when the surface region becomes dense before complete decomposition of aluminum hydroxide in the interior of the body.