In-situ modulating laminated microstructure of α+β+TiC in titanium composites by laser powder bed fusion of Mo2C/Ti powder mixture towards biomedical applications

Abstract

Additive manufacturing offers a revolutionary pathway for customising patient-specific metal implants. However, clinical practice calls for balanced material properties besides a patient-matched geometry, including good biocompatibility, low elastic modulus, good material strength and enhanced wear resistance. This study demonstrates an in-situ microscale composition modulation method by laser powder bed fusion (LPBF) using a Mo2C/Ti powder mixture, achieving adaptive microstructure and successfully combining balanced mechanical and wear properties in the Ti-7.5Mo-2.4TiC composites. The modulation is made through partial homogenisation of raw materials, leaving entangled Mo-rich and Mo-poor streaks around the molten pool boundary and a Ti–Mo matrix at the molten pool centre. By optimising volumetric energy density to 82.3 J/mm3, the modulated composition inhomogeneity produces an alternately laminated microstructure with entangled α and β streaks around the molten pool boundary and mixed α+β phases at the molten pool centre. Such that the molten pool boundary reveals a lower elastic modulus relative to the molten pool centre. The uneven allocation of elastic moduli throughout layers of molten pools enables a step-by-step deformation mode under compressive loading, lowering the component-related elastic modulus to 90.4 ± 2.1 GPa; on the other hand, it suppresses crack propagation, extending the material's elongation to 16.4 ± 1.4%. The synergistic effect of grain refinement and dispersion strengthening provided by in-situ precipitated TiC improves yield strength (936.9 ± 19.8 MPa) and ultimate compressive strength (1415.5 ± 23.1 MPa). The hard TiC also enhances the wear property, obtaining lower wear rates (down to 8.6 × 10−4 mm3N−1m−1) than the pure Ti. The balanced mechanical and wear properties could expand the potential of this composite in clinical use. More importantly, this LPBF-based approach creates a pathway for microscale composition modulation in material design and performance customisation towards biomedical applications.