Effects of Ta Addition on the Solidification and Homogenization of Ni-Based Superalloy GH4065A

TL;DR

Adding tantalum to a nickel-based superalloy helps stabilize harmful phases during manufacturing without affecting overall performance.

Contribution

This study shows how Ta addition affects solidification and homogenization in GH4065A superalloy, enabling better manufacturing.

Findings

Ta stabilizes the η phase and increases its solidification temperature and fraction.

Ta preferentially partitions into MC carbides and the η phase during homogenization.

Optimum homogenization parameters dissolve the η phase and eliminate microsegregation.

Abstract

Increased alloying content in advanced Ni-based superalloys for large disc forgings intensifies microsegregation and promotes the formation of detrimental secondary phases, challenging the cast-and-wrought processing route. This study investigates the effects of Ta addition on the solidification and homogenization behaviors of a high-alloyed GH4065A superalloy by comparing the base alloy with a variant containing 5 wt.% Ta (5Ta alloy). As-cast and homogenized microstructures were characterized using SEM and EPMA, solidification behavior was analyzed via DSC, and homogenization kinetics were modeled. Results demonstrate that Ta addition stabilizes the η phase, increasing its solidification temperature and fraction in the as-cast microstructure, but does not alter the solidification sequence. During homogenization, Nb remained the most segregated element and governed the homogenization kinetics, whereas Ta preferentially partitioned into MC carbides and the η phase. The diffusion activation energy for Nb in the 5Ta alloy was determined, and a diffusion model was established to describe the elimination of microsegregation. Optimum homogenization parameters were determined to completely dissolve the η phase and eliminate microsegregation. The results indicate that strategic Ta addition for enhanced performance does not compromise ingot manufacturability, providing valuable guidance for the processing and composition design of advanced disc superalloys.

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