Tailoring the microstructure homogeneity to improve the mechanical property of Ti-6Al-4V alloy through heavily warm rolling acicular martensitic microstructure
摘要
Micro-textured regions (MTRs), which are formed by thermomechanical processing of titanium alloys with α + β lamellar structure, induce incompatible deformation and result in early crack initiation during plastic deformation. In this study, we developed an innovative thermomechanical processing routine that eliminates the formation of band-like MTRs in Ti-6Al-4V alloy. The first step of this routine is solution treatment at 1050 °C for 20 min followed by ice water quenching, to obtain an initial microstructure of full acicular α’ martensite. As a comparison, a sample with typical α + β lamellar structure was fabricated by solution treatment at 1050 °C for 20 min followed furnace cooling. Thereafter, both the two samples were processed with a heavy warm rolling procedure at 700 °C and an annealing treatment at 700 °C for one hours. Microstructure characterization showed that after heavy warm rolling and subsequent annealing at 700 °C, acicular α’ martensitic transform into homogeneous and random fine equiaxed grains. This is in contrast with the annealed α + β lamellar structure that a large number of band-like MTRs are formed. Mechanical properties of the sample with annealed martensite are thus significantly improved due to the elimination of MTRs. The strength reaches 1100 MPa, and the total elongation is approximately 14.3%, nearly twice that of the annealed α + β lamellar structure.