Computational investigation of particle segregation in capsule filling for hot isostatic pressing

Abstract

Particle segregation, which is defined as location-dependent congregation of particles of similar size in a powder batch, can happen during the capsule filling step of hot isostatic pressing (HIP). Segregation can lead to microstructural and macrostructural flaws of the post-HIP compact. Since a systematic study of segregation with respect to filling parameters is not reported in the literature, the current work computationally investigates the effects of the geometry of the HIP capsule, the particle size distribution of the powder batch, the vibration frequency, amplitude and duration on segregation using discrete element method simulations. The results prove that cone shaped capsules are more prone to segregation, particularly if the direction of the flow of the particles is towards the tip of the cone. Particle size distributions with larger particles are more susceptible to segregation too. Moreover, higher frequencies and amplitudes increase segregation to different extents. Vibration duration initially reduces the segregation by a small amount and then reaches to an asymptote at a characteristic duration.