ABSTRACT Thermodynamic prediction‐driven phase‐field kinetic simulation, with experimental verification, is utilized to explore the high‐performance cobalt–nickel based (CoNi‐based) superalloys. The roles of aluminum (Al) in microstructural evolution and precipitation kinetics of ordered L1 2 ‐ γ ′ strengthened Co–Ni– x Al superalloys are revealed. The alloy containing 11 at% Al exhibits a low density of 8.124 g cm −3 and a superior Vickers hardness of 360 HV. The Al content influences the stability of the γ ′ phase, elemental partitioning, and lattice mismatch between γ / γ ′ phases. Thermodynamic calculations and experimental characterizations demonstrate that Al can elevate the γ ′ solvus temperature (Per 2 at% Al raises ∼100 K), enhance the partitioning of Ni and Al into the γ ′ phase, and enlarge the lattice mismatch between γ / γ ′ phases. Three distinct kinetic stages of γ ′ phase are revealed in this CoNi‐based superalloy by phase‐field simulation: initial nucleation and growth stage, growth stage, and steady‐state coarsening stage as Al content increases from 11 at% to 15 at%, the γ ′ average radius is refined from 21.5 to 15.1 nm, keeping a high γ ′ volume fraction of 70.6%, while enlarging the interfacial energy. Transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and X‐ray diffraction (XRD) confirm the coherence of the γ / γ ′ interface and the element distribution between γ / γ ′ phases. Furthermore, the phase‐field simulation and experiments are consistent for the γ / γ ′ interface structure, element segregation, and coarsening kinetics. This study reveals that Al is a crucial factor in regulating the kinetics and microstructural stability of γ ′ phase, also demonstrating the effectiveness of phase‐field‐guided design in high‐performance and low‐density CoNi‐based superalloys.
Niu et al. (Thu,) studied this question.