Ductility enhancement of additively manufactured CoCrMo alloy via residual stress tailored high stacking fault probability

CoCrMo (CCM) alloys fabricated by laser powder bed fusion (LPBF) normally exhibit low ductility. In the present study, a new plastic deformation mode of residual stress tailored high stacking fault (SF) is proposed for LPBF fabricated CCM alloy, delivering an excellent ductility (-14.5%) in the as-fabricated state. Elaborate microstructural characterization elucidated that low level of initial residual stress contributes to a high stacking fault probability, generating extensive amounts of SFs to sustain the plastic deformation. Such massive deformation faulting activities mitigated the strain localization between FCC/HCP phase of CCM alloy with high residual stress level. Further low temperature annealing treatment validated the above theory, and increased the ductility to -21.4% with a high tensile strength of -1181 MPa. The present study demonstrated that the ductility of LPBF fabricated CCM alloy can be significantly enhanced by tuning the internal residual stress and the associated stacking fault probability.