Thermally Induced Porosity within HIPed Ti64 Parts: Effect of Entrapped Argon versus Helium in L-PBF

Paper in proceeding, 2019

For Laser-Powder Bed Fusion (L-PBF), gas porosity is likely to be introduced by gas entrapment within the rapidly solidifying melt pool. Under standard argon processing conditions, argon is likely to be within these pores. It is believed that porosity can be efficiently removed by Hot Isostatic Pressing (HIP). However, when Ti-6Al-4V parts are HIPed and further subjected to high temperatures, there is a risk for thermally induced porosity (TIP) to occur. The latter is formed by the previously pressurized argon gas, not eliminated during the HIP because of the limited diffusion of atomic argon within the metal matrix. Helium, because of its smaller atomic radius, is suspected to diffuse faster. In this study, effect of helium on process induced porosity and its elimination during HIP in comparison to Ar is investigated. This is done through the X-ray computed tomography study of the porosity evolution through the AM process chain.