Martensitic structures and deformation twinning in the U-Nb shape-memory alloys

An investigation of the microstructures of four U-Nb alloys has been conducted. The nominal Nb contents are 5, 9, 13 and 18at.% (approximately 2, 4, 5.5 and 8wt%). The self-accommodating twin structures have been characterized and considered in terms of the lattice parameters of the martensite phases as well as the tetragonal distortion associated with the previously proposed intermediate γ⁰ phase. In addition, active deformation twinning systems during deformation of the U-13at.% Nb shape-memory alloy have been identified and are discussed with respect to the α″ monoclinic distortion and ease of propagation in the microstructure.