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 beta high strength titanium alloy Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe were investigated. Microstructure observation indicates that the primary alpha phase, which formed during solution treatment, can effectively limit the growth of beta grains. Aging treatments were performed at temperatures ranging from 440 degrees C to 560 degrees C for 8 h to study the effect of aging temperature on microstructure and tensile properties. Finer acicular alpha precipitates in beta 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 alpha phase with a width of 50 nm in aging at 440 degrees C for 8 h, with an acceptable elongation of 5.6% due to small beta grain size. The ductility is up to 18% at 560 degrees C with a high strength of 1400 MPa. Further aging treatments were performed at 560 degrees C ranging from 2 h to 24 h to investigate the effect of aging time on microstructures and tensile properties. The grain boundary alpha growth and coarsen with increasing of aging time. EBSD analysis shows that grain boundary alpha phase followed by Burgers orientation relationship randomly with one adjacent beta grain. The coarsening of grain boundary alpha layer is deleterious to mechanical properties of alloys both of strength and ductility. (C) 2013 Elsevier B. V. All rights reserved.