Pore tracing in additive manufactured and hot isostatic pressed components

Abstract

Despite past scientific efforts and the increased use of hot isostatic pressing (HIP) in additive manufacturing applications, a complete understanding of the exact pore-closing behaviour has yet to be achieved. The present research focuses on laser powder bed fused (LPBF), hot isostatic pressed components made of AlSi10Mg, and process-related defects. The study shows the effect of HIPing in relation to various pore characteristics, such as pore shape, size, and type. A pore tracing method using X-ray data was developed to characterise the pores before and after HIP. The method is based on the k-nearest neighbours approach and allows to match leftover pores with the initial ones. Hence, the efficiency of the pore-closing behaviour for different HIP settings can be analysed. Moreover, the exact number of pore transformations can be tracked, providing a comprehensive insight into the change of pore characteristics during HIP. In this framework, eight different HIP settings and a total number of 274,886 pores were examined and discussed. The findings demonstrate that longer treatment times and higher pressure and temperature settings accelerated the pore transformation. Irregularly shaped and large pores close faster than spherically shaped and smaller ones. Furthermore, regardless of the initial pore type, all pores started transforming their shape towards irregular shapes and small pore diameters. Some pores remained after the HIP treatments, probably due to the inefficiency of HIP in closing pores connected with the component surface or the presence of oxide particles interfering with the diffusion bonding process.