Study on the formation mechanism of α lamellae in a near β titanium alloy

In order to obtain more insight in the two existing mechanisms on the nucleation, i.e., sympathetic nucleation and interface instability nucleation, of α lamellae in the near β Ti alloys, the micro-texture of α lamellae in Ti-7Mo-3Nb-3Cr-3Al has been investigated by using electron backscatter diffraction (EBSD). The results show that the α_WGB lamellae can not only grow up from α_GB grains by inheriting the orientations but also sympathetically nucleate at the α_GB/β interface during the slow cooling process. These observations provide the first direct experimental evidence that the formation mode of α lamellae in Ti-7333 alloy consists of sympathetic nucleation and interface instability nucleation. Based on the present results together with some previous studies on α phase transformation in Ti-based alloys the influence of β-stabilizers parameter on the change of formation mechanism of α lamellae was discussed.