Creep behavior of a polycrystalline nickel aluminide: Ni-23.5 at.% A1-0.5 at.% Hf-0.2 at.% B

Abstract

The creep behavior of a poly crystalline nickel aluminide with the composition Ni-23.5 at.% Al-0.5 at. % Hf-0.2 at. % B has been measured as a function of stress, temperature, and grain size. At high stresses, of the order of 100 MPa, the strain rate is nonlinear in the stress, with a stress exponent greater than two. Below approximately 10 MPa, at 1033 K, the steady-state strain rate is almost proportional to the stress, indicating that diffusional creep is rate controlling. Calculations of expected Nabarro—Herring and Coble creep rates did not answer whether diffusive mass transport through the grains, or along the grain boundaries, is rate controlling. The grain-size dependence of the strain rate, however, indicates predominance of volume diffusion control, i.e., Nabarro—Herring creep, for our experimental conditions.