TEM studies of ETA carbide precipitate particles in a DS cast Ni3Al base superalloy

Relatively large needle-shaped precipitate particles with a rectangular cross section have been observed in a DS cast Ni3Al base superalloy aged at 1100 °C for 200 h. Thin film transmission electron microscopy studies, using energy dispersive spectroscopy, selected area diffraction, and convergent beam diffraction techniques were successful in identifying these particles as eta carbides. They have a definite orientation relationship with the γ′ matrix; this has been unambiguously determined to be: (11̄1̄)η − c//(1̄11)γ′;[211]η − c//[211]γ′