Microstructures of Rene 142 nickel-based superalloy fabricated by electron beam melting

Rene 142, a commercial, columnar grained, gas turbine airfoil Ni-based superalloy, has been fabricated from a pre-alloyed, atomized powder by additive manufacturing using electron beam melting. Monolithic components having [0 0 1] oriented, columnar grain structures exhibited a creep-optimized 59% volume fraction of cuboidal, coherent, γ′-phase precipitates averaging 275 nm on the side, and with γ/γ′ channel widths ranging from 25 to 75 nm. Transmission electron microscopy, utilizing bright and dark field imaging of optimally oriented γ/γ′ interfaces showed prominent misfit coherency strains as δ-fringe patterns. Corresponding hardness measurements also indicated the possibility of creep strength comparable with the commercial alloy. The notable feature of this study was the monolithic development of desirable superalloy properties without conventional, multi-step heat treatments.