THE DENSIFICATION OF POWDERS BY POWER-LAW CREEP DURING HOT ISOSTATIC PRESSING

Hot isostatic pressing (HIP) is potentially a cost-effective and efficient process for the manufacture of high quality metal components from powders. The densification of the powder during HIP proceeds in stages marked by changes in the geometry of the pores and by the dominance of different densification mechanisms. When the density is high and the pores are isolated and roughly spherical, the densification rate under a compressive load due to creep can be approximated by the densification rate of a sphere of creeping material containing a single, centered void. The densification rates predicted by such a model are significantly increased by small deviations of the load from purely hydrostatic compression. Thus, a careful account of the coupling between the hydrostatic and deviatoric stresses is important in the accurate modelling of the process and the design of an efficient HIP cycle; this can be achieved through the introduction of an approximate strain rate potential for the porous body.