Creep in face-centred metals and solid solutions with special reference to ?-brasses

Abstract

The creep of a-brasses containing 10–35%Zn was studied in the range 350–650°c. The equilibrium creep rate satisfied the relation i=A ₀(T) exp (-H/kT) sinh (qσ/kT), but two sets of the parameters A _e, H and of the activation volume q associated with the tensile stress σ were required, one above and one below a critical stress σ_e ¹(T) above which Cottrell-Lomer locking appeared t o become a less effective impediment to slip than at lower stresses. A peak in the activation energy H' (below σ_c') close to the composition represented by Cu₃Zn is interpreted in terms of local order near dislocation cores. This affects the migration of jogs and hence recovery by climb. Below σ_c', H is equal to 1–6 times the activation energy for grain boundary self-diffusion. Two models are proposed in which the climb of dislocations over intragranular obstacles or within grain boundaries are rate determining, depending on whether σ<σ_c' or σ>_c'. The temperature dependence of A _o', A _o, q' and q is explained on the basis of the assumption that the dimensions of the intragranular substructure developing during creep attain lower limiting values which, at any given temperature, depend only on σ_c'.