Phase Precipitation Behavior of TB17 Titanium Alloy During Isothermal Aging Process

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 beta ->beta+omega phase transformation mainly happens at 350 degrees C, and the precipitated phase omega is the shape of fine granular. After aging treatment at 450 degrees C, the alpha phase is nucleated through the assistance nucleation of omega phase. The phase transformation of beta ->beta+alpha occurs at 550 and 650 degrees C and the alpha phase exhibits lamellar structure. However, there are two types of alpha phase precipitated after aging at 550 and 650 degrees C for long time: the Burgers alpha (Type 1 alpha) phase which satisfies the Burgers orientation relationship and the Type 2 alpha phase which does not satisfy the Burgers orientation relationship. The Type 2 alpha phase is a twin crystal phase nucleated on the {10 (1) over bar2} twin plane inside the Burgers alpha phase. The aging characteristic of TB17 titanium alloy is similar to that of most beta 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 degrees C, and then decreased with increasing the aging temperatures.