Evolution of lattice strains in three dimensions during in situ compression of textured Zircaloy-2

Abstract

The evolution of lattice strains in Zircaloy-2 was investigated in situ by time-of-flight neutron diffraction during uni-axial compression in three principal directions, normal, transverse and rolling. The material is a warm-worked Zircaloy-2 slab with basal plane normals mostly concentrated in ND. Lattice strains relative to the undeformed sample were measured by neutron diffraction during cyclic compression and unloading for three test directions and three scattering vector directions. Intensity variations of the reflections were monitored to assess the grain rotations. Substantial tensile twinning was inferred from the evolution of {0002} lattice strains and the intensity of prismatic and basal poles. The spread of lattice strains in the test direction (amongst different crystal orientations) is much greater in compression than in tension. The sources leading to this asymmetry were ascribed, through preliminary simulations using an elasto-plastic self-consistent model, to the compressive load, the occurrence of tensile twinning and thermal residual strains.