Hot Isostatic Pressing of Alumina

Abstract

Effects of hot isostatic pressing (HIP) conditions on the densification were studied for alumina powder compacts having various particle characteristics. HIP conditions examined are temperature, pressure and time. Powder characteristics were represented by particle size. The results were analyzed with the Ashby's model, and the mechanism of densification as well as the validity of the model was discussed. Alumina densified by the grain boundary diffusion mechanism in HIPing. The densification rate increased markedly with increasing temperature and pressure, and with decreasing particle size. The rates found were much lower than those predicted by the model for all conditions. The difference between the model and the experiment became increasingly significant with decreasing particle size of the powders and with increasing apparent density. The difference is approximately constant for each powder for the apparent density below 90%, but increased markedly with increasing apparent density over 90%. The disagreement between the model and the experiment was attributed to the uncertainty of grain boundary diffusion coefficients applied to the analysis, the agglomeration of powder particles and the grain growth occurring in the final stage of densification.