Effect of Heat Treatment and Hot Isostatic Pressing on the Morphology and Size of Pores in Additive Manufactured Ti-6Al-4V Parts

Abstract

Additive manufactured parts suffer from porosity, among other defects. The slit-shaped pores due to lack of fusion are the most detrimental to fatigue and mechanical properties. Their sharp edges generate severe stress concentration and serve as preferred sites for crack initiation. The sharp edges also have low formation energy of surface adatoms, increasing their tendency to spheroidize under elevated temperatures, such as during heat treatment (HT). In hot isostatic pressing (HIP), the combined action of high temperature/pressure also reduces the size of the pores. In this work, HT and HIP were performed on Ti-6Al-4V parts manufactured from laser-based powder bed fusion to investigate the effect of HT and HIP on morphology/size of pores. Using scanning electron microscopy combined with X-ray computed tomography, special attention is paid to the evolution of the shape of the pore1s under controlled exposures to elevated temperature during HT. The results will be used, in our subsequent work, to validate a phase field porosity evolution model based on density functional theory.