Creep response of Ti-6Al-4V alloy produced by additive manufacturing: Effect of annealing at 1050 °C

The present study mainly aims at investigating the creep response of a Ti-6Al-4V alloy produced by additive manufacturing and annealed above the 8-transus, and at rationalizing the differences observed when comparing its behaviour to that of the same alloy annealed at lower temperatures. Herein, the creep response of this alloy produced by additive manufacturing and subsequently annealed at 1050 degrees C is investigated at temperatures ranging from 500 to 650 degrees C. The heat treatment produces the typical Widmansta center dot tten microstructure with thin 8 -lamellae interposed between coarse a-lamellae. The minimum creep rate dependence on the applied stress and temperature is compared with literature data of tests of alloys with Widmansta center dot tten microstructures produced by traditional technologies. A modified form of an equation, successfully used to describe the creep responses of the Ti-6Al-4V alloy with different initial microstructures, was here proposed. The suggested modification introduces a threshold stress, which is related to the presence of finely spaced a-8 interfaces and a2-Ti3Al particles. This threshold stress is considered to be negligible when the distance between the a-8 interfaces is long and the a2-Ti3Al particles are absent or excessively spaced. In contrast, in the materials with Widmansta center dot tten microstruc- tures, even minor differences in the heat treatment conditions and/or the processing history cause considerable variations in the distance between the a-8 interfaces. This coupled with the occasional precipitation of a2-Ti3Al particles results in different threshold stress values.