Laser additive manufacturing of Co-Cr alloy and the induced defects thereof

In laser additive manufacturing (LAM), porosity is a common defect due to the high-temperature gradients involved in the material’s recurrent quick liquefaction and solidification. In this study, multi-physics involved in the porosity formation has been explained. For this purpose, a multi-physics-based model is presented to estimate the lack of fusion (LOF)- and melt flow (MFP)-based porosity in the laser powder bed fusion (LPBF) process. The present model relies on the operating conditions and material thermo-physical properties. Melt pool dimensions were computed using a transient thermal model. LOF- and MFP-based porosities were calculated using the melt pool dimensions attained via the thermal distribution model. A total of 15 Cobalt-Chromium (Co-Cr) samples with 10 × 10 × 10 (mm 3 ) dimensions were prepared via the LPBF process. All samples were subjected to X-ray computed tomography (XCT) to analyse pore formation and distribution. A close association was identified between modelling and experimental results with a mean absolute deviation of 7–15%. It was found that all Co-Cr samples yielded a combination of micro- and macro-pores. Experimentally, a linear link was determined between laser power and porosity (%) and hatch distance and porosity (%), while the laser scanning speed did not significantly influence the porosity (%). Initially, the porosity (%) remained unchanged with increased volume, energy, and density parameters, and afterward, it decayed linearly. The majority of pores had a volume of 0.010–0.069 mm 3 with a sphericity of 0.30–0.75, which confirms they are a mixture of regular, irregular and elongated shapes. This study provides an effective technique for efficiently estimating the LOF- and MFP-based porosities using input parameters.