The influence of stacking fault energy on the creep behaviour of Ni-Cu-solid-solution alloys at intermediate temperatures

Abstract

The creep characteristics of Ni-Cu alloys at intermediate temperatures (T<0.55Tm, where T m is the absolute melting temperature), including the stress exponent (≥ 7) and the activation energy for creep (which is less than the activation energy for lattice diffusion), suggest that the creep mechanism is dislocation climb controlled by pipe diffusion. The present analysis shows that the creep rates of these alloys are consistent with a rate equation of the form $$\dot \varepsilon = 50A \frac{{D_p Gb}}{{kT}} (\Gamma /Gb)^3 (\sigma /G)^7$$ where A is a dimensionless constant with a value of ∼1013, D p is the pipe diffusion coefficient, G is the shear modulus, b is the magnitude of the Burgers vector, kT is the Boltzmann's constant times the absolute temperature, Γ is the stacking fault energy and σ is the applied stress. The Γ-values used in the present investigation were determined using high-temperature, latticediffusion, dislocation-climb-controlled creep rates. In addition, this equation can satisfactorily predict the pipe-diffusion-controlled creep behaviour in pure metals at intermediate temperatures.