Evolution of Structure and Strain Hardening in Ni–Crx (x < 12.5 at %) Alloys upon High-Pressure Torsion

High-pressure torsion (HPT) represents one of the most effective methods for producing nanostructured materials exhibiting enhanced strength and functional properties. The structural evolution upon HPT is governed by strain hardening mechanisms, and identifying transitions between these mechanisms enables the determination of deformation stages and prediction of the thermal stability of nanostructured materials. This work investigates the stages of strain hardening and structural evolution in single-phase Ni‒Cr alloys (2–12.5 at % Cr) upon HPT. Analysis of experimental hardness data as a function of true strain and Cr content was performed using a piecewise model that accounts for the dominant deformation mechanism at each stage. Modeling results are correlated with structural characterization using electron microscopy techniques. The piecewise model accurately describes the structural changes upon deformation. Alloying-induced restriction of the dislocation glide promotes strain localization and reduces the hardening exponent (a parameter describing the degree of system nonlinearity) at the stage when the dislocation mechanism of deformation is acted. Conversely, under conditions dominated by the rotational mechanism of deformation, alloying increases the strain hardening exponent.