Anisotropic shrinkage during hip of encapsulated powder

In P/M HIP, the capsule volume is reduced to 25–30% depending on the initial relative density of the powder after pre-consolidation. Under isostatic pressing conditions the capsule should have a uniform shrinkage, but in practice this is often not the case. This phenomenon is driven through many factors including, but not limited to, the temperature gradient, inhomogeneity of powder inside the capsule and capsule thickness of which the influence will be further examined in this study. Experimental Image Analysis is used to investigate the initial powder distribution which is subsequently implemented in a FEM model as initial condition to simulate the shape changes of hot isostatically pressed products. To analyze the effect of a temperature gradient in the capsule, the temperature is assumed to be inhomogeneously distributed on the surfaces of the capsules. Different temperature fields are then applied to a FEM model. Additionally, capsule thickness will be varied to study its influence on the final shape. Finally the simulation results are compared with experimental findings. Based on that the conclusion about the influence of inhomogeneous powder distributions, temperature gradients and capsule thickness on the final shape of powder HIP-ed products can be given.