Morphology and substructure of lath martensites in dilute Zr-Nb alloys

The morphology and substructure of lath martensites formed in beta quenched dilute Zr-Nb alloys are described. The laths are arranged in a nearly parallel manner within any given colony or packet. Packets of alternately twin related laths and clusters of three mutually twin related lath martensite variants have been observed and the twinning plane is of {1 (1) over bar 01}(H) type. With increasing niobium content a continuous transition from large colonies of lath martensites, through smaller lath colonies, to individual plates of the acicular martensites occurs. The lath-lath interface consists of regularly spaced parallel arrays of dislocations of 2 (1) over bar (1) over bar 3> type. The habit plane traces of lath martensite lie close to {334} type poles and the operating lattice invariant shear mode is {(1) over bar 101}(H) < 2 (1) over bar (1) over bar(H), shear system. This result is consistent with results predicted by the phenomenological theory. The preferred two and three habit plane variant grouping clustering is explained on the basis of self-accommodation effects. (C) 2000 Elsevier Science S.A. All rights reserved.