Work hardening and recovery in creep

Abstract

An extensive experimental test on nickel and aluminium has been made of the Bailey-Orowan equation ⋵ = r/h, where έ is the steady state creep rate, r is the rate of recovery, and h is the strain hardening coefficient; ⋵ and r were measured, and the value of h calculated from this equation was compared with that measured in a room temperature tensile test; the agreement is within a factor of 2, provided that h is measured on creep tested specimens and not on annealed ones. This proviso arises because, as the experiments showed, h increases several times during primary creep. The experiments also showed that if the stress dependencies are expressed as (stress)ⁿ then for creep rate n is 4 1/2, for recovery rate 3 to 3 1/2 and for 1/h 1 to 1 1/2. Most of the stress-sensitivity of creep rate is therefore due to the stress-sensitivity of recovery rate and is understandable, since dislocation network theory predicts r ∝ (stress)³.