Elastoplastic-viscoplastic modelling of metal powder compaction: application to hot isostatic pressing

A constitutive model is proposed for the densification of metal powder during hot isostatic pressing. The model considers an inelastic deformation resulting from time dependent (viscoplastic) and time independent (plastic) mechanisms during loading. With employing the Abouaf's formalism for viscoplastic part, the paper is focused mainly on the plasticity contribution including the hardening effects of both relative density and the equivalent plastic strain. The proposed plastic-viscoplastic model is summarised to an equation expressing the densification rate under hydrostatic loading. The gas atomised 316LN stainless steel powder was used in this study. Model parameters necessary for simulation of HIP process during a given pressure ramp at constant temperature are identified using previously published data. The identified model is then verified using experimental data obtained from HIP trials performed at another fixed temperature but with varied pressure ramp rates. A good agreement was found between the model prediction and the experimental results.