Effect of molybdenum content on the microstructure and tribological properties of Ti-Nb-Cu alloys produced by LPBF additive manufacturing

Obtaining excellent wear resistance is critical for titanium alloys used as orthopedic implants. In this study, the β-type Ti-35Nb-5Cu- x Mo alloys (Ti355 x , x = 0, 1, 2, and 4 wt%) were fabricated by the laser powder bed fusion (LPBF) method. In the meantime, the influence mechanism of Mo content on the microstructure and tribological properties was systematically investigated. The results show that all the LPBF-produced Ti355 x alloys exhibit a bimodal columnar-equiaxed grain structure, with Mo refining columnar grains and suppressing the α″ phase formation. Moreover, increasing the Mo content reduced the relative density, while enhancing the microhardness. However, tribological responses exhibited an initial decrease followed by an increase with increasing Mo content. When the Mo content reached 2 wt% (in Ti3552 alloy), the friction coefficient and the wear rate decreased to ∼0.76 and ∼3.8 × 10 −4 mm 3 N −1 m −1 , respectively, whereas both parameters (∼0.80 and ∼4.3 × 10 −4 mm 3 N −1 m −1 ) significantly increased when the Mo content rose to 4 wt%. This phenomenon stems from the exceptional hardness homogeneity of the Ti3552 alloy (with the Weibull shape parameter of ∼18.2), which facilitated continuous TiO 2 film formation and suppressed the stress-concentration-induced fracture, enhancing the wear resistance. ● LPBF-fabricated Ti-35Nb-5Cu- x Mo (Ti355 x ) utilized the powder blends with the x = 0, 1, 2, and 4 wt%. ● Adding Mo particles improved the tribological properties of LPBF-fabricated Ti355 x . ● The optimal addition amount of Mo is 2 wt% in this work. ● Optimal hardness homogeneity (Weibull shape parameter: 18.2) in Ti3522 facilitated intact protective TiO 2 film formation.