Characterization of Mechanically Alloyed, Oxide-Dispersion-Strengthened Nickel-Based Superalloy MA760

W. Sha and H. K. D. H. Bhadeshia


The directional recrystallization behavior, the nature and stability of particles, and the gamma' precipitation behavior of a mechanically alloyed oxide dispersion-strengthened (ODS) nickel-base superalloy MA760 have been studied using a combination of microscopy, microanalysis, microhardness, and calorimetric techniques. The extruded material is in a primary recrystallized condition with a submicron grain size. Secondary recrystallization into a coarse, directional microstructure occurs by heating above 1215°C. The stored energy driving the secondary recrystallization is estimated to be about 1 J g-1. Y2O3, Al2O3-Y2O3 garnets, and chromium carbides have been identified in the extruded alloy. More Al2O3-Y2O3 garnets are formed during subsequent heat treatment; with continuous variation of composition, the garnets are richer in Al2O3 with increasing particle size. The chromium carbides present in the as-extruded material dissolve completely during heating to temperatures well below the recrystallization temperature. They can reprecipitate during cooling if the alloy is not recrystallized. The alloy contains a variety of inhomogeneities, including stringers of oxide particles and carbide depleted zones. The gamma' precipitation and dissolution characteristics are also reported.


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