Tailoring in-situ TiC-reinforced laser 3D printed β Ti-Nb alloy with graphite additions for biomedical implants

Abstract

beta-type titanium alloys, renowned for their low elastic moduli, combined with titanium carbide (TiC) reinforcements, have emerged as promising candidates for load-bearing and wear-resistant bioimplant components. However, the fabrication of beta-type titanium matrix composites (beta-TMCs) remains challenging, particularly in achieving a refined microstructure with a controlled reinforcement distribution. This investigation introduces an innovative approach using laser-based powder bed fusion (PBF-LB/M) for the in-situ fabrication of TiC-reinforced beta-TMCs. Powder mixtures composed of beta Ti-42Nb alloy and graphite (particle size similar to 3 mu m) were processed with graphite additions of 0.5, 1.0, 1.5, and 2.0 vol%, resulting in TiC fractions of approximately 2, 4, 6, and 8 vol%, respectively, in the PBF-LB/M as-built samples. The formation of TiC nanoparticles within the beta-Ti matrix was confirmed by microstructural characterization, including TEM/STEM with EDS and ASTAR analyses. While lower graphite levels led to the formation of rod-shaped TiC precipitates ranging from tens to hundreds of nanometers, higher graphite content produced nearly spherical TiC particles, consistent with a hypereutectic solidification path where TiC forms as a primary phase. The increasing TiC fraction enhanced hardness; specifically, the Ti-42Nb+2.0C composite (similar to 239 HV) demonstrated a 13 % increase compared to the unreinforced Ti-42Nb alloy (similar to 211 HV). The elastic modulus also increased with TiC content, reaching similar to 72 GPa compared to similar to 58 GPa for the alloy. Notably, all elastic modulus values were significantly lower than that of the Ti-6Al-4V alloy (similar to 110 GPa). These findings establish an alternative additive manufacturing route for the in-situ fabrication of beta-TMCs with a refined microstructure and enhanced mechanical properties, offering new possibilities for load-bearing implants.