Phase transformation generating coherent twin boundaries in titanium alloys

In this work, alpha-alpha precipitates boundaries were characterized using aberration-corrected scanning transmission electron microscope. We reported an interesting view that (10 (1) over bar1)(alpha) and (10 (1) over bar3)(alpha) coherent twin boundaries (CTBs) could be generated by the impingement of (0 0 0 1)(alpha) planes in two alpha variants during alpha precipitation in a metastable Ti-5Al-5Mo-1Fe-1Cr (wt.%) alloy. When the (0001)(alpha) plane in one of the variants is at 120 degrees to that in another variant, the (10 (1) over bar1)(alpha) CTB could form, and when the angle of (0001)(alpha) planes in two variants is 60 degrees, the (1013)(alpha) CTB could be generated. The generation of the CTBs causes (0001)(alpha) planes of two variants to rotate 1.4 degrees around their common [2 (1) over bar(1) over bar0](alpha) 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 beta titanium alloys.

Automated summary

In this study, aberration-corrected scanning transmission electron microscope was used to characterize alpha-alpha precipitates boundaries. The formation mechanism of (10 (1) over bar1)(α) and (10 (1) over bar3)(α) coherent twin boundaries (CTBs) was reported, along with the resulting lattice distortion and introduced dislocations.