Understanding the composition-dependent stability of ? phase for future Ni-Co-based superalloys

Knowledge associated with the alloying effects of Al, Ti, Ta and Nb on phase stability of Ni-Co-based superalloys plays a significant role in efficiently exploring the multi-component space for future alloy designs, and thus were systematically investigated using a high-throughput dual-anneal multi-component diffusion multiple (MCDM) approach. In this work, eta phase presenting considerably different morphology and spatial distribution was confirmed in the Ta-rich and Nb-rich alloys, and its zero-phase-fraction (ZPF) line at 800 degrees C was determined that suggests a maximum Nb + Ta content of about 2.5 at.% while avoiding the eta formation. The composition criterion regarding the stability of eta was updated by taking into account the destabilizing effect of Co such that the eta formation can be significantly suppressed with increasing Co from a critical level of about 12 at.%, providing essential guidance to design alloy chemistry for superior microstructural stability at high-temperature service conditions.