Microstructure and mechanical properties of Co–Cr–Mo alloy fabricated by selective laser melting: Effect of hot isostatic pressing

Abstract Selective laser melting (SLM) is an additive manufacturing process that builds metal components according to computer-aided design (CAD), selectively fusing and consolidating metal powders one layer at a time. This incremental building approach can yield components with complex geometries, without the economic constraints of traditional large-scale manufacturing. This study systematically investigates the influence of various laser conditions (i.e., scanning speed and scanning strategy) on the microstructure and mechanical properties of Co–Cr–Mo alloys fabricated by SLM. Hot isostatic pressing (HIP) was applied after SLM to further densify the fabricated components, and their microstructures and mechanical properties were compared with those of untreated components. Parts with relative density of ∼97.26% were obtained with a high-energy laser and double laser scanning, and subsequent HIP effectively eliminated the majority of pores. X-ray diffraction revealed that γ and e phases co-existed owing to the high solidification rate during SLM. Directional columnar grains and fine cellular dendrites that were parallel and normal, respectively, to the build direction were observed. Although variations in microstructure resulting from different SLM conditions were small, the deformation behavior remarkably changed. The improved mechanical properties was attributed mainly to increased densification and grain-boundary strengthening. However, the HIP treatment increased the tensile ductility and reduced the yield strength, despite the increased densification. The tension-fractured surface suggests that mostly quasi-cleavage brittle fracture took place in the SLM-processed parts.