Heterogeneity of Microstructure and Mechanical Response in Steel–Titanium Multilayer Wires Subjected to Severe Plastic Deformation

This study addresses the fundamental problem of representing the rheological properties of heterostructured materials composed of metals that differ significantly in their crystal structure, stacking fault energy, and related characteristics. The necessity of accounting for essential strengthening mechanisms is highlighted. The study is based on experimental results related to the fabrication of a multilayer, heterogeneous system via multistage wire drawing, supported by microstructural analysis, microhardness measurements, and numerical simulations employing various flow-stress models. A discussion is presented regarding the effectiveness of these models in representing the deformation behavior of the investigated materials. The primary materials examined were a multilayer system composed of microalloyed steel and titanium. The obtained results indicate that, in addition to incorporating strengthening mechanisms, it is necessary to consider significant microstructural changes affecting microstructure evolution—particularly grain refinement induced by continuous recrystallization and the effects of strain hardening. Moreover, the findings point to the potential intensification of strengthening associated with pile-up mechanisms, linked to the development of dislocation substructures and the possible fragmentation of the hard phase in the vicinity of the more ductile microalloyed steel phase. In conclusion, the discussion integrates measurements of rheological properties obtained through tensile tests, supported by microstructural analysis, digital image correlation (DIC), and microhardness measurements, which collectively demonstrate the effectiveness of the adopted analytical approach.