Texture, morphology and deformation mechanisms in beta-transformed Zircaloy-4

The morphology of the beta(bcc) transformed Zircaloy-4 may be treated as a lenticular-twinned martensite. The texture is a consequence of the degeneration of the [0001](alpha), [10 (1) over bar 0](alpha) and [10 (1) over bar 1](alpha) directions into [110](beta) directions. The crystallographic mechanisms implied in the accommodation of the microscopic Bain strain are (10 (1) over bar 0)[11 (2) over bar 0] prism slip, (10 (1) over bar 2)[10 (1) over bar 1] twinning and (10 (1) over bar 1)[10 (1) over bar 2] twinning. This degeneration explains the 'parallel plate' and 'basketweave' morphologies observed by microscopy and the texture of the beta transformed tube. The macroscopic Bain strain was calculated and agrees with the dimensional measurements. The deformation mechanisms of beta transformed Zircaloy-4 are identified from the new texture and from deformation experiments as twinning and interplatelet glide. The interplatelet glide induces a fragile character of fracture in the 'parallel plate' morphology.