Heterogeneous microstructural evolution and reactions during repeated intense deformation

With the recent improvements in severe plastic deformation and cold rolling, deformation processing has become an alternative to rapid-solidification processing for the synthesis of bulk metastable structures. The systematic study of the deformation patterns that develop during repeated rolling of multilayer based on a stacked elemental crystalline array including the analysis of interface areas and the evolution of interface roughening, offers an effective approach to the examination of the mechanism involved in deformation alloying, nanostructure synthesis and amorphization. A key-factor for deformation-induced phase transformations is the occurrence of atomic scale mixing effects at interfaces. The results from cold rolling experiments on Al-Pt and Al-Hf alloys demonstrate that the overall multilayer refinement represents an essential component for the prediction of amorphization by cold rolling in addition to the heat of mixing and a deformation enhanced mixing kinetics at individual interfaces. The effect of cold rolling on the devitrification behavior of Al-based glasses has also been addressed in a systematic study. For marginal glass formers, such as melt-spun Al88Y7Fe5, cold rolling induced a complete crystallization without annealing while for melt-spun Al85Ni10Ce5, a crystalline phase has not been observed under the same deformation conditions. The structural changes are observed to develop heterogeneously throughout the sample over several deformation cycles due to the distribution of microstructural size scales. These developments highlight the importance of the localized micro structural response to the overall sample deformation.