Coarsening of Ni 3Ge precipitates in Ni–Ge alloys aged under uniaxial compression

Abstract

The kinetics of coarsening of Ni 3Ge precipitates under applied compressive stress was investigated in [1 0 0]-oriented monocrystalline Ni–Ge alloy specimens (nominal composition 12.92 ± 0.5 at.% Ge) aged at 625 °C. The maximum stress used was ∼100 MPa, and the strains were predominantly elastic (plastic deformation was less than 1% except for the largest stress, where it was 3%). The microstructures were examined by transmission electron microscopy of the (1 0 0) sections cut perpendicular to the applied stress. The effects of applied stress are small, but conclusive. Compressive stress retards the kinetics of coarsening, tends to make the precipitates more spherical in shape and reduces their aspect ratio. These results are discussed in light of recent data from comparable measurements on Ni 3Al precipitates. The elastic anisotropy of Ni 3Al is greater than that of Ni 3Ge, and it is suggested that this parameter might be important, even though it is not included in treatments of elastic interactions among precipitates.