Microstructural investigation and castability anticipation in modern Ti/Al/Nb-containing nickel-based superalloys
(Department of Materials Engineering, Faculty of Engineering,
Tarbiat Modares University, P. O. Box 14115-143, Tehran, Iran)
Tarbiat Modares University, P. O. Box 14115-143, Tehran, Iran)
Abstract: A quantitative relation between the γ/γ′ and γ/Laves intermetallics was investigated with the change of chemical composition, i.e., Ti, Al and Nb in the third generation of nickel-based superalloys. The results demonstrated that the maximum amount of intermetallic eutectics (i.e., 41.5%, mass fraction) has been formed in 9.8% (Ti+Al). It is predicted that high level of intermetallics formed in the 3GSA-HNM-1 (γ-9.8%(Ti+Al)) deteriorates its castability. The type and morphology of eutectic intermetallics change and the amount considerably diminishes by decreasing Ti+Al in 3GSA-HNM-2 (γ-7.6%(Ti+Al), 1.5% Nb). Thus, it is predicted that the castability for the 3GSA-HNM-2 improves. The amount of Laves intermetallics shows an ascending behavior again, however, with less intensity by increasing the Nb content in the 3GSA-HNM-3 (γ-5.7%(Ti+Al), 2.9% Nb). It can be concluded that for 3GSA-HNM-3 with composition of γ-5.7%(Ti+Al) and 2.9% Nb, the optimized castability can be anticipated, because the minimum amount of eutectic intermetallics (i.e., 4.7%) is formed.
Key words: nickel-based super alloys; secondary phases; castability; segregation; microstructure