The assisting and stabilizing role played by ω phase during the[formula omitted] twinning in Ti-Mo alloys: A first-principles insight

Abstract

The ω phase is commonly observed in β-Ti alloys and plays a significant role on various properties of β-Ti alloys. Although many results about the role of ω phase on mechanical properties of β-Ti alloys have been derived from theoretical and experimental studies, the role of ω phase on deformation mechanism hitherto remains elusive and deserves to be further studied. In this work, the role played by ω phase during the 112111β twinning in Ti-Mo alloys were investigated by first-principles calculations at atomic scale. In the energy favorable interface of (112)β/(101¯0)ω, we found that partial dislocations slipping on the successive 101¯0ω planes of ω phase can lead to the formation of 112111β twin nucleus. And the twin nucleus grows inwards ω grain interior through atomic shuffle. Thus, a new twinning mechanism of 112111β assisted by ω phase was proposed. Furthermore, our calculations indicated that the appearance of ITB (interfacial twin boundary) ω phase can improve the stability of the symmetrical 112111β twin boundary (TB), which can well explain the experimental phenomenon that the ITB ω phase always accompanies the formation of 112111β twin. Finally, a probable microstructure evolution sequence was suggested, namely β matrix → β matrix + athermal ω phase → 112111¯β twin → 112111¯β twin + ITB ω phase. Our calculations provide new insights on the role played by ω phase during the twinning process of 112111β, which can deepen the understanding on the deformation behaviors of β-Ti alloys.