Deformation-induced martensitic transformation in Co-28Cr-6Mo alloy produced by laser powder bed fusion: Comparison surface vs. bulk

The wear resistance of the biomedical low-carbon Co-28Cr-6Mo (wt.-%) alloy is primarily determined by the onset and magnitude of the face-centered cubic to hexagonal close-packed deformation-induced martensitic phase transformation. In metal-on-metal joint bearings, local plastic deformation occurs on the surface and in the subsurface regions. This can cause deformation-assisted structural changes in the material, such as mechanical twinning and/or martensitic transformation. In the present work, we report the structural transition on the surface and bulk of a laser powder bed fusion additively manufactured Co-28Cr-6Mo alloy in response to an externally imposed load. This study was possible using in-situ synchrotron X-ray diffraction at two different energy levels. Our results revealed that from tensile deformation to fracture, the phase transformation kinetics and magnitude were marginally higher on the surface. During transformation, {200}FCC peak broadening was observed in the bulk and this was attributed to stacking fault accumulation.