Formation of a shock deformation induced ω phase in Zr 20 Nb alloy

Abstract The formation of a plate shaped ω phase in Zr–Nb alloy after shock deformation has been studied with a view to ascertaining the nature of this transformation. The orientation relationship between the β and the ω lattices was {1 1 1}β//(0 0 0 1)ω and 〈 1 1 ¯ 0 〉 β / / 〈 1 1 2 ¯ 0 〉 ω which is identical to that seen in case of ω phase forming in this alloy on thermal treatment. The experimentally determined habit plane of the plate shaped ω phase has been compared with that predicted from the phenomenological theory of martensite formation. A mechanism of transformation involving shear on the 〈1 1 2〉 planes has been considered. The importance of mechanical instability of the β phase in bringing about this transformation has been investigated. The mechanism of initiation of ω transformation has been ascertained by high resolution electron microscopy (HREM) of the β lattice and compared with that happening during ω formation in the same alloy by thermal treatment.