THE INFLUENCE OF STACKING-FAULT ENERGY ON THE CREEP-BEHAVIOR OF NI-CU-SOLID-SOLUTION ALLOYS AT INTERMEDIATE TEMPERATURES

The creep characteristics of Ni-Cu alloys at intermediate temperatures (T <0.55 T-m, where T-m is the absolute melting temperature), including the stress exponent (greater than or equal to 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 epsilon = 50AD(p)Gb/kT(Gamma/Gb)(3)(sigma/G)(7) where A is a dimensionless constant with a value of similar to 10(13), 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, Gamma is the stacking fault energy and sigma is the applied stress. The Gamma-values used in the present investigation were determined using high-temperature, lattice-diffusion, dislocation-climb-controlled creep rates. In addition, this equation can satisfactorily predict the pipe-diffusion-controlled creep behaviour in pure metals at intermediate temperatures.