Regulation of Mechanical and Tribological Properties of Laser Powder Bed Fusion Ti-6Al-4V by Heat Treatments

The effects of different heat treatments, including direct aging (DA), solid solution (T4) and solid solution + aging (T6), on the microstructure, mechanical and tribological properties of Ti-6Al-4V alloy prepared by laser powder bed fusion were studied. The As-built and DA-treated samples had refined acicular alpha(') martensite phase and beta phase. The T4-treated sample had lamellar alpha phase and globular alpha phase, whereas the T6-treated sample had lamellar alpha phase and basketweave microstructure. The dislocation density was decreased after heat treatments. The samples exhibited lower strength but higher plasticity after heat treatments, which was a comprehensive reflection of the decomposition of alpha(') phase, the increase in beta phase content, the coarsening of grains and the reduction of dislocation density. The wear resistance of the samples increased in the order of DA-treated sample < As-built sample < T6-treated sample < T4-treated sample, which was mainly related to the morphology and content of the alpha/alpha(') phases on their surfaces. A favorable comprehensive performance was found for the T4-treated sample: It possessed the highest microhardness (447.51 +/- 18.6 HV), the moderate yield strength (791.68 +/- 15.8 MPa) and ultimate tensile strength (887.25 +/- 13.25 MPa), the largest elongation (15.24 +/- 0.57%), the lowest wear rate (0.76 +/- 0.03 x 10(-3) mm(3)/(N m)).