The formation mechanism of void in thin-walled capsule welding joint induced by HIP

Abstract

Thin-walled capsule significantly impacts the overall quality of hot isostatic pressing (HIP）products, with capsule reliability being a crucial factor in determining the success or failure of the HIP process. High-temperature creep is essential for the densification of HIP powder. However, the capsule, made of dense metal, undergoes its own creep process. High temperature and high pressure may induce void formation in the capsule due to diffusion and creep. The integrity of the capsule typically relies on the welding process, and void formation at welded joints poses a significant challenge to the capsule’s reliability, increasing the likelihood of failure. This study investigates the mechanisms of void formation in welded joints during the HIP process. Results indicate that high temperature and high pressure during HIP promote the formation of two types of voids in mild steel: Kirkendall voids and creep voids. Kirkendall voids are driven by diffusion and influenced by the HIP insulation temperature, which affects their state but not their formation. Creep voids, however, originate from stress concentration at grain boundaries during creep deformation. Their distribution density is positively correlated with the degree of creep deformation, which is primarily controlled by HIP pressure and temperature.