Self-accommodation in Ti–Nb shape memory alloys

Self-accommodation morphology of the α″α″ martensites in Ti–Nb shape memory alloys with Nb content ranging from 20 to 24 at.% was investigated. Hollow and solid triangular morphologies consisting of three α″α″ variants were found to be the α″α″ self-accommodation morphologies. The α″α″ variants are related to each other by twinning on {11¯1}α″. A V-shaped morphology consisting of two α″α″ variants coupled with a solid triangular morphology consisting of three α″α″ variants was found to be another type of self-accommodation morphology. The α″α″ variants from the V-shaped morphology are related by twinning on {111}α″, whereas the α″α″ variants from the solid triangular morphology are related to each other by twinning on {11¯1}α″. Pairs of crystallographically equivalent {11¯1}α″ twinning dislocations with steps of opposite signs were found to cause the overall orientation of the twinning terraces and steps to be parallel to the {11¯1}α″ twinning interface.