Papers by Keyword: Intergranular Stress

Abstract: This paper reports results of an in-situ compression experiment carried out on a hot rolled Zircaloy-4 plate at ENGIN-X, ISIS. The experiment was aimed at characterizing the plastic anisotropy of the alloy, which can give rise to high intergranular stresses in the polycrystal. As expected from the crystal anisotropy, the various lattice reflections had very different behaviours. In the compression directions, the basal <0002> reflections appeared to bear much more load than the other planes. The resulting intergranular elastic strains could therefore reach up to 5000 microstrain after 10% total deformation, and were responsible for high type II residual stresses after unloading. Considering the macroscopic behaviour, the normal direction had higher mechanical properties than the other two processing directions. The strong texture measured from EBSD measurements suggest that the crystal anisotropy has been brought to a macroscopic level. The experiment also evidenced a significant change in texture for compression along the rolling direction which indicates twinning activation.

Abstract: Neutron diffraction has been used to study the progress of deformation twinning and intergranular strain evolution in extruded magnesium during cyclic and monotonic loading at two temperatures. Differences in the intergranular strains generated during tensile and compressive tests are attributed to the operation of twinning in compression. Twinning activity is reduced relative to slip at higher temperature, leading to greater similarities between tension and compression. During cyclic loading, a distinct Bauschinger effect is observed after each compressive loading stage. The origin of this effect is identified as the reversal of twinning during unloading and subsequent tensile loading.