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 th e degeneration of the [0001](alpha), [10 (1) over bar 0](alpha) and [1 0 (1) over bar 1](alpha) directions into [110](beta) directions. The c rystallographic mechanisms implied in the accommodation of the microsc opic 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 'paral lel plate' and 'basketweave' morphologies observed by microscopy and t he texture of the beta transformed tube. The macroscopic Bain strain w as calculated and agrees with the dimensional measurements. The deform ation mechanisms of beta transformed Zircaloy-4 are identified from th e new texture and from deformation experiments as twinning and interpl atelet glide. The interplatelet glide induces a fragile character of f racture in the 'parallel plate' morphology.