Phase stability in additively manufactured N-doped CoCrMo alloys via in-situ synchrotron X-ray diffraction during tensile testing

Nitrogen is a critical yet challenging alloying element to incorporate into metals and alloys due to its inherently low solubility and poor capture efficiency. In this research, we demonstrate that CoCrMo (CCM) alloys manufactured via laser powder bed fusion (LPBF) using N2 gas-atomized precursor powders achieved a remarkably high supersaturated nitrogen content (∼0.19 wt.%). Compared with alloys produced using Ar gas-atomized powders (LPBF CCM-Ar), the as-built LPBF CCM-N alloy exhibits a reduced density of stacking faults (SFs), attributed to the increased SF energy resulting from nitrogen incorporation. Meanwhile, both alloys demonstrate high yield strengths (YS >900 MPa) due to the presence of dense sub-micro Mo/Cr-decorated dislocation cells and SFs. Notably, nitrogen incorporation further enhances the YS (by >60 MPa) and elastic modulus in LPBF CCM-N alloys. In contrast, the LPBF CCM-Ar alloys demonstrated an elevated deformation-induced martensite proliferation rate during tensile deformation, contributing to greater work hardening capacity.