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

Abstract

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 α^′ martensite phase and β phase. The T4-treated sample had lamellar α phase and globular α phase, whereas the T6-treated sample had lamellar α 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 α^′ phase, the increase in β 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 α/α^′ 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 × 10⁻³ mm³/(N m)).

Graphical Abstract