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

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 degrees 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 degrees C is conventional, whereas, the UTS decreases drastically from 834 MPa to 562 MPa as the temperature increases from 500 degrees C to 550 degrees 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 degrees C and possesses excellent comprehensive mechanical properties at RT. The analysis shows that the microstructure is composed of alpha' martensite with plenty of twinning structures when the as-built samples are deformed below 500 degrees C. However, above 500 degrees C, martensite gradually transformed into equilibrium alpha phase, the microstructure changed from acicular to lamellar, and beta and alpha(2) (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 degrees C.