Stress relaxation in nickel at 15 to 300 k

Abstract

Logarithmic stress relaxation was studied in 99.999% polycrystalline nickel at natural strains of up to 8% at 15. 25, 40, 50, 77, 150 and 295 K. The structural and activation characteristics of the stress relaxation were investigated theoretically by a tentative model. The temperature dependence of the yield stress was interpreted by a theoretical model which provided an agreement with the expérimental results. The activation energies, i.e.1.15 ± 0.2 eV, deduced from a single barrier model of logarithmic stress relaxation, i.e. u 0 ~ k × (T 0+AT 2)[m+2.3 (dσ 0 ds] (where T 0 and A are constants), allows for “quantum” effects below T ⩽ 70 K, favours cross-slip and also the dynamic “recovery” as the rate determining process. For temperatures 77 and 150K, the activation energies obtained from equation, s = 2.3 kT σ 0 (u 0 - mkT ) , suggest that vacancy formation by jogged dislocations is a rate determining process except at 295 K, where the thermal “recovery” process occurs due to dislocation/dislocation intersection.