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 para llel manner within any given colony or packet. Packets of alternately twin related laths and clusters of three mutually twin related lath martensite v ariants have been observed and the twinning plane is of {1 (1) over bar 01} (H) type. With increasing niobium content a continuous transition from larg e colonies of lath martensites, through smaller lath colonies, to individua l plates of the acicular martensites occurs. The lath-lath interface consis ts 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) ove r bar 101}(H) < 2 (1) over bar (1) over bar(H), shear system. This result i s consistent with results predicted by the phenomenological theory. The pre ferred two and three habit plane variant grouping clustering is explained o n the basis of self-accommodation effects. (C) 2000 Elsevier Science S.A. A ll rights reserved.