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 $\left\{ 112 \right\}{{111}_{\beta }}$ twinning in Ti-Mo alloys were investigated by first-principles calculations at atomic scale. In the energy favorable interface of${{(112)}_{\beta }}/{{(10\bar{1}0)}_{\omega }}$, we found that partial dislocations slipping on the successive ${{\left( 10\bar{1}0 \right)}_{\omega }}$ planes of ω phase can lead to the formation of $\left\{ 112 \right\}{{111}_{\beta }}$ twin nucleus. And the twin nucleus grows inwards ω grain interior through atomic shuffle. Thus, a new twinning mechanism of $\left\{ 112 \right\}{{111}_{\beta }}$ 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 $\left\{ 112 \right\}{{111}_{\beta }}$twin boundary (TB), which can well explain the experimental phenomenon that the ITB ω phase always accompanies the formation of $\left\{ 112 \right\}{{111}_{\beta }}$ twin. Finally, a probable microstructure evolution sequence was suggested, namely β matrix → β matrix + athermal ω phase →$\left( 112 \right){{\left[ 11\bar{1} \right]}_{\beta }}$ twin →$\left( 112 \right){{\left[ 11\bar{1} \right]}_{\beta }}$ twin + ITB ω phase. Our calculations provide new insights on the role played by ω phase during the twinning process of $\left\{ 112 \right\}{{111}_{\beta }}$, which can deepen the understanding on the deformation behaviors of β-Ti alloys.

Key words: Titanium alloys, Twin, Interfacial twin boundary phase, Generalized planar fault energy, First-principles