Investigations on printability and sintering of additively manufactured binder jet Co-Cr-Mo alloy parts for biomedical applications

Binder jet additively manufactured (BJAM) parts offering enhanced structural integrity and time- material efficiency, are being actively used for biomedical applications. Co-Cr-Mo alloys because of their unique combination of superior mechanical strength, biocompatibility, wear, and corrosion resistance have gained significant attention for biomedical applications. This study evaluates the processability of BJAM Co-Cr-Mo alloy (ASTM F75) parts by examining the effect of particle size distribution (PSD) and sintering conditions (atmosphere, temperature) on part densification, strength, and microstructure. A systematic experimental study comprising of coarser PSD-Laser Powder Bed Fusion (LPBF)-cut and finer PSD-Metal Injection Molding (MIM)-cut powder shows green density and green flexural strength increasing with higher binder saturation and decreasing with faster recoating speed. Final densification depends strongly on sintering atmosphere, with vacuum and N 2 –5%H 2 maximizing density to ≈97%, whereas for Ar-5%H 2 it was limited to ≈93%. Coarser particle size in LPBF-cut powder showed better packing and densification than finer MIM-cut. Sintering atmosphere also influenced microstructure by controlling precipitation of Cr₂₃C₆ and σ-phase in vacuum/ Ar-5%H 2 , and Cr₂N, Cr Mo rich carbonitride in N 2 –5%H 2 . Grain growth in finer PSD was restricted by Zener pinning from porosity and prior particle boundary (PPB) precipitates. γ-ε transformation followed Shoji-Nishiyama (S N) orientation relationship for both the PSD. However, ε morphology was influenced by grain size with more lamellar in coarser PSD and more globular for finer PSD. The findings in this study establish key process–microstructure correlations for binder jetting (BJ) Co–Cr–Mo alloys allowing for microstructural optimization by careful selection of PSD, printing parameters and sintering conditions. • Vacuum yields highest final density followed by N 2 –5%H 2 and Ar-5%H 2 • Sintering impacts precipitation: Vac/Ar-5%H 2 (Cr₂₃C₆,σ), N 2 –5%H 2 (Cr 2 N,Cr-Mo(C,N)) • Finer PSD and higher porosity reduce grain size by Zener pinning mechanism • ε has more lamellar morphology in coarser PSD and more globular in finer PSD • γ -ε transformation by S N OR, no variant selection and random texture