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Damage resistance in gum metal through cold work-induced microstructural heterogeneity

Zhang, J.-L., Tasan, C. C., Lai, M. L., Zhang, J., Raabe, D.
Journal of materials science 2015 v.50 no.17 pp. 5694-5708
X-ray diffraction, alloys, cold, deformation, image analysis, microstructure, rolling, scanning electron microscopy, texture, transmission electron microscopy
Cold-worked alloys exhibit high strength, but suffer from limited ductility. In contrast, Ti-based gum metal was reported to exhibit high strength combined with good ductility upon severe pre-straining. Motivated by this anomaly, we systematically studied the evolution of gum metal microstructure during severe cold working (swaging and rolling) and the resulting deformation and damage micro-mechanical mechanisms during follow-up tensile deformation. To this end, various experimental in situ and post-mortem methodologies are employed, including scanning electron microscopy imaging, high-resolution electron backscatter diffraction mapping and transmission electron microscopy. These observations reveal that intense grain refinement takes place through dislocation plasticity-dominated deformation banding upon cold working. The observed enhancement in crack blunting and failure resistance which prolongs the post-necking ductility of gum metal during follow-up tensile straining can be attributed to the deformation-induced development of local heterogeneities in texture and grain size.