INSTANTANEOUS AND RESIDUAL-STRESSES DEVELOPED IN HOT ISOSTATIC PRESSING OF METALS AND CERAMICS

Under many conditions, hot isostatic pressing (HIP) of metallic or ceramic porous preforms occurs by the densification of a shell at the surface of the preform, which then thickens until the whole sample is fully densified.[2,4] The development of such a dense shell reduces the effective pressure acting to densify the remaining porosity. Furthermore, this pressure difference can lead to anisotropic creep of the shell, and this may be a contributary cause of shape change of samples during HIP. The stresses occurring during cooling of the sample and the residual stresses are calculated as a function of all of the various material and pressing parameters. It is found that, in many cases, the cooling stresses which are tensile at the surface may well be large enough to cause cracking in ceramic samples.