Elemental Distribution and Site Occupancy of Multi-Component Cobalt-Based Superalloys

Abstract

γ′-phase strengthened cobalt-based superalloys show promise for higher temperature-capability over nickel-based superalloys due to higher melting temperatures. This study investigates a multicomponent cobalt-based superalloy with composition 30Ni-7Al-1Ta-4Ti-2W-Bal.Co (at.%) in terms of elemental partitioning and site occupancy. The alloy exhibits a γ/γ′ coherent microstructure with misfit of 0.44%. APT reveals preferential partitioning of Ni, Al, Ti, Ta, W to the γ′-phase and Co to the γ-matrix. HADDF-STEM and EDS along the [001] zone axis of L12 γ′-phase indicates that Co, Ni substitute on α sublattice sites, while Al, Ti, Ta, W prefer the β sublattice sites. DFT calculations confirm the results of partitioning behaviors and site preferences. Clarifying elemental partitioning and site occupancy provides insights into alloy design principles for advanced cobalt-based superalloys.

Keywords: Cobalt-based superalloy, Solute partitioning, Site occupancy, Atom probe tomography (APT), Scanning transmission electron microscopy (STEM)