Cause and Effect of Non-Uniform Densification During Hot Isostatic Pressing

Abstract

Hot isostatic pressing (hipping) is an extremely efficient way of densifying ceramic and high alloy metallic powders, or for healing porosity in castings. However, depending on the parameters of pressure, temperature, rate of heating, and sample size, hipping can result in a non-uniform mode of densification. This mainly occurs when a rapidly heated sample, or a sample of large dimensions, densifies quickly at the surface to produce, in effect, a fully dense, hard shell. It is shown in this paper that there can be a number of negative factors resulting from this, including reduced rates of densification, sample shape change, non-uniform shrinkage, and the development of residual stresses in the sample. Criteria for predicting whether or not non-uniform densification will occur are presented and evaluated. PM/0554