Temperature sensitivity of mechanical properties and microstructure during moderate temperature deformation of selective laser melted Ti-6Al-4V alloy

Abstract In this paper, the temperature sensitivity of mechanical properties and microstructure of the additive manufactured Ti-6Al-4V alloy via selective laser melting was investigated in the deformation temperature range between room temperature (RT) and 550 °C. Mechanical properties and microstructure were characterized by the means of tensile testing, optical microscope, scanning electron microscope and transmission electron microscope. The results show that the ultimate tensile strength (UTS) of the experimental Ti-6Al-4V alloy exhibits two-stage temperature sensitivity, which is reflected in the fact that the temperature sensitivity of UTS below 500 °C is conventional, whereas, the UTS decreases drastically from 834 MPa to 562 MPa as the temperature increases from 500 °C to 550 °C. Compared with the Ti-6Al-4V alloys prepared by conventional processing methods and other additive manufacturing methods, this experimental Ti-6Al-4V alloy exhibits a competitive strength below 500 °C and possesses excellent comprehensive mechanical properties at RT. The analysis shows that the microstructure is composed of α′ martensite with plenty of twinning structures when the as-built samples are deformed below 500 °C. However, above 500 °C, martensite gradually transformed into equilibrium α phase, the microstructure changed from acicular to lamellar, and β and α2 (Ti3Al) appear due to the elemental distribution homogenization and martensite decomposition, which account for the dramatic decrease of the tensile strength of the experimental Ti-6Al-4V alloy above 500 °C.