J. Cirne, R. Dormeval, et al.
J. Phys. IV France 134 (2006) 1137-1144
DOI: 10.1051/jp4:2006134174
Microstructural evolution and grain refinement in HCP-Zr shear bands
B.K. Kad1, M. Gebert2, M.E. Kassner3 and M.A. Meyers11 University of California, San Diego, La Jolla 92093-0085 CA, USA
2 Institute of Materials Science I, University of Karlsruhe, Germany
3 University of Southern California, Los Angeles 90089-1453 CA, USA
Published online: 26 July 2006
Abstract
The mechanics of shear band formation has been studied in
HCP-Zr to examine the microstructural evolution of the finite volume of
material that comprises the shear band at several levels of deformation.
Commercial grade HCP-Zr alloy is employed in the study for its relative ease
in forming shear bands owing to its significant work hardening rate and
significant plastic anisotropy. Hat shaped specimens are subjected to large
plastic shear strains (of the order of 25-100) at strain rates of 
104s-1 in a split-Hopkinson bar experimental setup. The extent
of deformation is controlled using different hat heights (0.75mm, 1.0mm and
2.0mm) that produce discrete levels of shear strain implicit in the shear
band formed. Results suggest that despite the extreme constraint of the
hat-shape specimen multiple shear bands occur in the confined region, which
coalesce upon large deformations. Electron Microscopy examinations of the
narrow shear band regions reveal a microstructure dominated by ultra-fine
grains of the order of 200 nm. Such observations of fine grain size are
consistent across the range of deformation studied here despite the vast
differences in diffraction signature. Thus while the occurrence of a shear
band ensures fine-grain size, subsequent reorganizations most likely occur
as deformation is incremented. The microstructural evolution exhibits a
characteristic path including a radical alteration of the grain orientation
spectrum in the shear band. Experimental evidence suggests that this process
is sub-divided in two parts i) formation of fine grains, with spatial
textural relationships, which upon continuing deformation create ii)
completely randomized structures. The criteria and bounds of such
reorganizations are evaluated.
© EDP Sciences 2006