Tailoring the microstructure and mechanical property of laser powder bed fusion fabricated Ti–6Al–2Sn–4Zr–2Mo via heat treatment

Abstract The heat treatment effect on the microstructure evolution and mechanical properties of the laser powder bed fusion fabricated Ti–6Al–2Sn–4Zr–2Mo (Ti6242) alloy was investigated in this study. The highly dense Ti6242 samples comprising acicular α΄ martensite and deformation twinning could be fabricated. The as-built alloy exhibited a high yield strength (σy, 1296 ± 44 MPa) yet a limited tensile elongation (ɛf, 5.7 ± 1.1%). Four different heat treatment profiles were conducted to tailor the microstructure and tensile properties. The direct annealing at 630 °C and 850 °C caused martensite decomposition. The annealing at 630 °C/8 h/air cooling led to the formation of β nano-particles and layers, leading to a slight increase of σy and a reduction of ɛf. Annealing at 850 °C/3 h/air cooling led to coarsening of α lamellae and growth of β phase, resulting in a decreased σy and enhanced ɛf compared with those at 630 °C. The two-stage heat treatment and thermal cycling triggered the formation of partially globularized primary α and Widmanstatten structure (secondary αs + β). These two heat treatments gave rise to a balanced combination of strength and ductility that could be comparable to those of wrought counterparts. This work demonstrates that a combination of laser powder bed fusion and post heat treatment could allow for the fabrication of complex-shaped Ti6242 components with little compromise of mechanical property for industrial applications.