Abstract
ZrCo2 and HfCo2 Laves phases were found and characterized in γ-γ′ Co-base superalloys using high-energy X-ray diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy. They formed during casting and are stable during long-term annealing at 900 °C. The ZrCo2 phase with a cubic MgCu2-type structure exhibits numerous nano-twins and stacking faults, while HfCo2 has a hexagonal MgNi2-type structure instead of MgCu2-type in contrast to literature. Their chemical compositions strongly deviated from stoichiometry and significant amounts of Al and W are contained in these phases. These could affect the atomic radius ratio and valence electron concentration and thus change the structure of the Laves phases.
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