Strain hardening behavior of pure Ni at cryogenic temperatures: Experiments and modeling

Research on the mechanical properties of metals under cryogenic conditions has attracted considerable attention, driven by the increasing demand for applications in extreme environments. The current study examines the tensile properties, and strain-hardening behavior of pure nickel across a temperature range from 77 K to 298 K. Findings indicate a marked increase in yield strength, tensile strength, and uniform elongation of pure nickel as temperature decreases, with pronounced effects observed at 77 K. Tensile strength increases by roughly 200 MPa at 77 K compared to 298 K. The cryogenic temperature significantly enhances strain-hardening, primarily by inhibiting dynamic recovery. Enhanced strain hardening and the formation of diffuse shear bands, which support uniform deformation, contribute to the improvement in uniform elongation at lower temperatures. Utilizing experimental data and the Kocks-Mecking model, a modified constitutive model for cryogenic temperatures has been developed to describe the effect of temperature reduction on dynamic recovery and quantitatively linking temperature reduction to strain-hardening enhancement, with its accuracy verified. This research elucidates the mechanisms underlying the simultaneous enhancement of strength and ductility in pure nickel under cryogenic conditions, providing essential theoretical guidance for optimizing the properties of metallic materials in cryogenic conditions and their potential for cryo-forming applications.