Additive manufacturing process related mechanical performance of cobalt-chromium-molybdenum alloy: In-situ X-ray computed tomography study

Abstract

Laser powder bed fusion (PBF-LB) shows significant potential in additively manufacturing personalized CoCrMo alloy orthopedic implants. However, the characteristics of microstructures and defects, and especially their influence on the mechanical performance of PBF-LB processed CoCrMo alloy remain underexplored. Here, CoCrMo alloy is additively manufactured, and we first employ an in-situ X-ray computed tomography (XCT) tensile test to investigate the exclusive microstructures and defects and their influence mechanism on mechanical properties. Adequate laser energy density (E_v = 106.67–152.38 J/mm³) reduces defect number and increases sphericity, improving manufacturing quality, while insufficient or excessive energy input leads to LOF or keyhole defects, respectively. Besides, by first conducting the in-situ XCT tensile tests, we originally 3D visually reveal that the underlying failure mechanism is the defect growth and coalescence, which lead to the crack initiation and eventual brittle fracture. At E_v = 152.38 J/mm³, the alloy exhibits the best mechanical performance (tensile strength: 1193.41 MPa, elongation: 4.99 %), with fracture behavior governed by intrinsic microstructural characteristics. The PBF-LB processed CoCrMo alloy exhibits even higher ultimate strength and comparable elongation than the conventionally casted ones. Moreover, the heat treatment enables the recrystallization and precipitate formation, significantly improving the elongation of the PBF-LB processed CoCrMo alloy to 26.65 % at E_v = 266.67 J/mm³, achieving a marvelous balance between strength and ductility. This study fills the gap in understanding the relationship between additive manufacturing, defect formation, and mechanical performance of CoCrMo alloy, establishing a basis for efficient manufacturing and superb mechanical performance for its biomedical applications.