Effect of aging heat treatment on microstructure and tensile properties of a new β high strength titanium alloy

Microstructure and tensile properties of a new β high strength titanium alloy Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe were investigated. Microstructure observation indicates that the primary α phase, which formed during solution treatment, can effectively limit the growth of β grains. Aging treatments were performed at temperatures ranging from 440 C to 560 C for 8 h to study the effect of aging temperature on microstructure and tensile properties. Finer acicular α precipitates in β matrix during aging treatments and tends to coarser with increasing of temperature. This trend leads to the variation of tensile properties that the strength decreased and ductility changed in opposite way. A highest yield strength value of 1637 Mpa is obtained by strengthening of acicular α phase with a width of 50 nm in aging at 440 C for 8 h, with an acceptable elongation of 5.6% due to small β grain size. The ductility is up to 18% at 560 C with a high strength of 1400 MPa. Further aging treatments were performed at 560 C ranging from 2 h to 24 h to investigate the effect of aging time on microstructures and tensile properties. The grain boundary α growth and coarsen with increasing of aging time. EBSD analysis shows that grain boundary α phase followed by Burgers orientation relationship randomly with one adjacent β grain. The coarsening of grain boundary α layer is deleterious to mechanical properties of alloys both of strength and ductility.