3D-imaging of selective laser melting defects in a Co–Cr–Mo alloy by synchrotron radiation micro-CT

Abstract

Microstructure defects set the mechanical property limits for solid Co–Cr–Mo alloy prepared by selective laser melting (SLM). Previous studies were mainly based on 2D SEM images and thus not able to provide information of the 3D morphologies of the complex defects. In this paper, the remaining porosities in Co–Cr–Mo alloy parts prepared by selective laser melting were presented in relation to the laser processing parameters. In order to understand the defect forming mechanism, accurate 3D images of defects inside SLM fabricated Co–Cr–Mo samples were provided by synchrotron radiation micro-CT imaging of 300μm thick slices cut from a 10mm cube. With 3D reconstructed images distinctive morphologies of SLM defects spanning across the consolidated powder layers were generated. The faults can be classified as single layer or multi-layers defects. The accidental single layer defects form as gaps between adjacent laser melt tracks or melt track discontinuousness caused by inherent fluid instability under various disturbances. The first formed single layer defect generates often a multi-layer defect spanning for 2–3 subsequent powder layers. By stabilizing the melt pool flow and by reducing the surface roughness through adjusting processing parameters it appears possible to reduce the defect concentrations.