Phase Precipitation Behavior of TB17 Titanium Alloy During Isothermal Aging Process

Abstract:

The precipitation phase evolution and the aging response of TB17 titanium alloy, a new titanium alloy with ultra-high strength and toughness, were studied by X-ray diffraction, scanning electron microscope, transmission electron microscope, and Vickers hardness tests during isothermal aging process. The results show that β→β+ω phase transformation mainly happens at 350 °C, and the precipitated phase ω is the shape of fine granular. After aging treatment at 450 °C, the α phase is nucleated through the assistance nucleation of ω phase. The phase transformation of β→β+α occurs at 550 and 650 °C and the α phase exhibits lamellar structure. However, there are two types of α phase precipitated after aging at 550 and 650 °C for long time: the Burgers α (Type 1α) phase which satisfies the Burgers orientation relationship and the Type 2α phase which does not satisfy the Burgers orientation relationship. The Type 2α phase is a twin crystal phase nucleated on the {102} twin plane inside the Burgers α phase. The aging characteristic of TB17 titanium alloy is similar to that of most β type titanium alloys. The aging response of TB17 titanium alloy is fast. The Vickers hardness of TB17 titanium alloy is increased firstly, reaching the maximum value at 450 °C, and then decreased with increasing the aging temperatures.

Key words:TB17 titanium alloy;isothermal aging;phase transformation;two types of α phase;aging response