Phenomenological law and process of α phase evolution in a β-type bio-Titanium alloy TNTZ during aging

Abstract

The growth process of α phase in β-type bio-Titanium alloy TNTZ during aging at 723 K is investigated. The results show that acicular α phase has a Burgers orientation relationship with β matrix of {1−10}β//(0001)α, 〈111〉β//〈11−20〉α. The kinetics equation of acicular α phase length meets l = 333(t-3.95)^0.0764, while the kinetics equation of diameter meets d = 7.50(t-2.83)^0.353. The growth process of α phase can be divided into three stages. During stage I, α phase grows rapidly along both the long direction and the diameter. At beginning of stage I, fine acicular α phase grows with the long direction parallel to each other. Subsequently, α phase grows with another long direction beside the former one in a ‘V-shape’ or in a ‘near perpendicular shape’. During stage II, α phase grows slowly along the diameter, while, the growth along long direction will be gradually restricted with the other α around it. The phase distributes more homogeneously, and present 5 classic possible orientations between α variants. During stage III, α phase grows slowly along the diameter, and stops growing along long direction. The growth of α phase is affected by distortion energy, interface energy and diffusion anisotropy, and it is mainly controlled by Nb diffusion through the ledge riser of the interface between α and β phases.