Precipitation behavior and strengthening-toughening mechanism of hot rolled sheet of Ti65 titanium alloy during aging process

Although the addition of various alloying elements to the near α alloy improves the high temperature service performance, the plasticity is always unsatisfactory while the strength is increased. In the present work, the strength and ductility of the Ti65 alloy sheet are successfully improved simultaneously by optimizing the aging heat treatment process. The effect of aging heat treatment on microstructure, precipitation behavior and tensile property of Ti65 alloy sheet has been investigated by contrast tests of the sheets before and after aging. The results reveal that the ratio of equiaxed α_p to lamellar α_s varies, two kinds of (TiZr)₆Si₃ silicide (globular and interfacial silicide) precipitate at different position and the interface transforms to be discontinuous during aging process. Besides, the strength and ductility of Ti65 alloy sheet are improved simultaneously during tensile tests after aging at 700 °C. The ultimate tensile strength and elongation strain gets 4.9% and 123.8% increase, respectively. The strengthening of the aged Ti65 alloy sheet is mainly attributed to the precipitation of the interfacial silicide (TiZr)₃Si and Ti₃Al. The significant improvement in ductility should benefit from the optimization of the ratios of the equiaxed α_p and lamellar α_s, and the formation of discontinuous lamellae interface.