CHARACTERIZATION OF MECHANICALLY ALLOYED OXIDE DISPERSION-STRENGTHENED NICKEL-BASE SUPERALLOY MA760

The directional recrystallization behavior, the nature and stability o f particles, and the gamma' precipitation behavior of a mechanically a lloyed oxide dispersion-strengthened (ODS) nickel-base superalloy MA76 0 have been studied using a combination of microscopy, microanalysis, microhardness, and calorimetric techniques. The extruded material is i n a primary recrystallized condition with a submicron grain size. Seco ndary recrystallization into a coarse, directional microstructure occu rs by heating above 1215-degrees-C. The stored energy driving the seco ndary recrystallization is estimated to be about 1 J g-1. Y2O3, Al2O3- Y2O3 garnets, and chromium carbides have been identified in the extrud ed alloy. More Al2O3-Y2O3 garnets are formed during subsequent heat tr eatment; with continuous variation of composition, the garnets are ric her in Al2O3 with increasing particle size. The chromium carbides pres ent in the as-extruded material dissolve completely during heating to temperatures well below the recrystallization temperature. They can re precipitate during cooling if the alloy is not recrystallized. The all oy contains a variety of inhomogeneities, including stringers of oxide particles and carbide depleted zones. The gamma' precipitation and di ssolution characteristics are also reported.