Kinetics of FCC to HCP Transformation During Aging Heat Treatment of Co-28Cr-6Mo Alloy Fabricated by Laser-Powder Bed Fusion

Co-based alloys have been used as biomedical materials in the cast or wrought form for more than fifty years. Since then, studies have been performed to better understand the high mechanical strength and wear resistance of these alloys. Recently, additive manufacturing techniques, such as laser-powder bed fusion (L-PBF), are being employed to produce metallic implants directly from metal precursor powder. To achieve a balance between strength and ductility of L-PBF Co-based alloys, a manipulation of phase constituents through heat treatments is essential. In the present work, an in situ analysis of the gamma-FCC -> epsilon-HCP phase transformation occurring during aging heat treatment of the Co-28Cr-6Mo alloy produced by L-PBF was performed. For this, time-resolved synchrotron X-ray diffraction was employed. Our results revealed that a solution heat treatment before aging changes the kinetics of the gamma-FCC -> epsilon-HCP phase transformation as well as the epsilon-HCP phase morphology.