Morphology Evolution of γ′ Precipitates for Wrought Ni-Based Superalloys

The morphology evolution of gamma' precipitates during isothermal aging at 1173 K was investigated for wrought Ni-based superalloys with various combinations of lattice misfit (delta) and gamma ' volume fraction (f(v)): Inconal X-750, Alloy 80A, Udimet 520, and Udimet 720Li. The resulting morphology as a function of vertical bar delta vertical bar value is presented. For vertical bar delta vertical bar < 0.10%, the spherical morphology remains unchanged with increasing diameter of gamma' precipitates (4) (Type A). In the case of 0.10 <= vertical bar delta vertical bar < 0.30%, the gamma' morphology evolves from spherical to cuboidal with remaining coherency at the gamma/gamma' interface with increasing d, accompanied by the alignment of cuboidal gamma' precipitates (Type B). And, when vertical bar delta vertical bar >= 0.30%, the morphology evolution of gamma' is from spherical to cuboidal and finally to globular. The coherent gamma/gamma' interface changes to semi-coherent with the coalescence of gamma' precipitates (Type C). The alignment of cuboidal gamma' precipitates is activated for superalloys with a higher value of f(v), while the f(v) value scarcely depends on the morphology evolution of gamma' precipitates during aging treatment.