New insight into deformation induced α variant selection in a metastable β titanium alloy during isothermal compression at 600 °C

Variant selection during phase transformation creates a specific transformation texture and finally affects the mechanical properties of the alloys. The transformation lattice deformation associated selection mechanism has not been well addressed. In the present work, the alpha variant selection in a Ti-7Mo-3Nb-3Cr-3Al alloy under isothermal compression at low temperature was investigated. The results show that the selection of the alpha variants is strongly affected by the imposed strain and the load with the dependence on the effective strain distribution induced by macroscopic shape deformation. In the center region of the compressed sample, 4 Burgers orientation relationship (BOR) variants orienting in four different directions and forming two sets of 'cross-shaped' clusters were selected. Such variants consumed the maximum strain contribution to the macroscopic compression. In the edge region of the compressed sample, only 2 BOR variants with 90 degrees/ <1 1.38 <(2.38)over bar> 0> or 10 degrees/<001> disorientation relationship were selected. The selection criterion was still obeyed by the variants but with restriction from the local effective strain distribution induced by macroscopic shape deformation. The present work provides the clear information on the interweaving of the imposed compression with the internal lattice deformation and its impact on the beta to alpha transformation variant selection.