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

Abstract

The morphology evolution of γ′ precipitates during isothermal aging at 1173 K is investigated for wrought Ni-based superalloys with various combinations of lattice misfit (δ) and γ′ volume fraction (f_v) (i.e., Inconel X-750, Alloy 80A, Udimet 520, and Udimet 720Li). The resulting morphology evolution strongly depends on |δ|, which was classified into three types. The spherical morphology for |δ| < 0.10% remains unchanged with the increasing diameter of the γ′ precipitates (d) (Type A). In the case of 0.10 ≦ |δ| < 0.30%, the γ′ morphology evolves from spherical to cuboidal with a maintained coherency at the γ/γ′ interface with an increasing d, accompanied by the alignment of the cuboidal γ′ precipitates (Type B). The morphology evolution of the γ′ precipitates when |δ| ≧ 0.30% is from spherical to cuboidal and finally to globular. The coherent γ/γ′ interface turns to a semi-coherent one with the coalescence of the γ′ precipitates (Type C). The alignment of the cuboidal γ′ precipitates is promoted for superalloys with a larger f_v value, whereas the effect of f_v on the morphology evolution of the γ′ precipitates during aging treatment is quite limited.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 84 (2020) 151–160.

Fig. 13 Map of the morphology evolution of the γ′ precipitates during the aging treatment at 1173 K for the wrought Ni-based superalloys. The γ′ morphology evolved from spherical (○) to cuboidal (■) and finally to globular (×) with the increasing diameter of the γ′ precipitates (d). The critical value of d between spherical and cuboidal decreased with the increase of the lattice misfit (|δ|).