Cold Swaging, Recovery and Recrystallization of Oligocrystalline INCOLOY MA 956-Part II: Annealed State

Abstract

The combination of a coarse-grained structure (oligocrystalline material), a strong initial texture, and the presence of fine particles make ODS superalloys like INCOLOY MA 956 very interesting materials for recrystallization studies. In the present paper, we have investigated the annealing behavior of the MA 956 alloy deformed by cold swaging to reductions of 20, 47, 61, and 72% followed by annealing at temperatures ranging from 600 to 1450°C. Light optical, scanning, and transmission electron microscopy were used to follow the microstructural changes upon annealing. Orientations of individual grains as well as microtexture were determined by electron backscatter diffraction (EBSD). Recrystallization texture was determined by X-ray diffraction (XRD). The isothermal softening kinetics curves were determined for all samples. Discontinuous recrystallization and extended recovery are responsible for the softening of this alloy. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) model was used to test our experimental data. The Avrami exponents (0.26≤n≤0.48) showed substantially smaller values than those predicted theoretically. This can be attributed to concurrent recovery and to a non-random distribution of recrystallization nuclei.