A Novel Strategy to Strengthen Directionally Solidified Superalloy Through Grain Boundary Simplified Design

TL;DR

This paper introduces a subtractive alloy design strategy for nickel-based superalloys that enhances creep resistance by eliminating traditional grain boundary strengthening elements, leading to microstructural improvements and a 60% performance increase.

Contribution

It presents a novel approach to improve creep performance by removing conventional grain boundary strengthening elements, shifting failure modes, and stabilizing microstructures in directionally solidified superalloys.

Findings

Creep performance improved by 60%

Failure mode shifted from transgranular to intergranular

Suppression of deleterious grain boundary phases

Abstract

Conventional strategies for enhancing creep resistance often rely on grain boundary strengthening, yet this approach can inadvertently promote premature grain boundary fracture. This study presents a subtractive alloy design strategy for nickel-based directionally solidified superalloys (DS superalloy) through elimination of conventional grain boundary strengthening elements (C, B, Zr) and the strategy improves the creep performance by 60% rivaling 2nd generation single crystal superalloys. Through characterization of heat-treated and heat-exposed microstructures, we confirm the suppression of deleterious grain boundary phases. Creep tests and fracture analysis reveal a critical transition in failure mechanism: the removal of these elements shifts the fracture mode from transgranular to intergranular. Our discussion comprehensively links this microstructural engineering to the underlying creep deformation mechanisms, showing that the enhanced performance stems from stabilization of {\gamma} channel and phase interfaces within grains, as well as strengthening of grain boundaries through serration. This work establishes a novel materials design principle that decouples grain boundary strengthening from elemental additions, offering transformative potential for next-generation high-efficiency turbine blade applications.