Phase transformation generating coherent twin boundaries in titanium alloys

Abstract

• (10 1 ¯ 1) α and (10 1 ¯ 3) α CTBs can be generated during α precipitation. • (10 1 ¯ 1) α CTB forms when the angle between (0001) α planes in two α variants is 120°. • (10 1 ¯ 3) α CTB is generated when the angle between (0001) α planes in two α variants is 60°. • Generation of the CTBs results in lattic distortion or interfacial dislocations. In this work, α-α precipitates boundaries were characterized using aberration-corrected scanning transmission electron microscope. We reported an interesting view that (10 1 ¯ 1) α and (10 1 ¯ 3) α coherent twin boundaries (CTBs) could be generated by the impingement of (0 0 0 1) α planes in two α variants during α precipitation in a metastable Ti-5Al-5Mo-1Fe-1Cr (wt.%) alloy. When the (0001) α plane in one of the variants is at 120° to that in another variant, the (10 1 ¯ 1) α CTB could form, and when the angle of (0001) α planes in two variants is 60°, the (10 1 ¯ 3) α CTB could be generated. The generation of the CTBs causes (0001) α planes of two variants to rotate 1.4° around their common [2 1 ¯ 1 ¯ 0] α axis, resulting in slight lattic distortion or introducing interfacial dislocations to accommodate the strain. These findings provide a new insight to the formation of CTBs and are applicable in other metastable β titanium alloys.