Precipitation of secondary Laves phases and its effect on notch sensitivity

The precipitation of secondary Laves phases and its effect on notch sensitivity are systematically studied in Thermo-Span alloy. The results show that the precipitation peak temperature of secondary Laves phases is 925 °C. Below 925 °C, the volume fraction of secondary Laves phases increases with the rise of the temperature, and its morphology changes from granular to thin-film; above 925 °C, the volume fraction of secondary Laves phases shows an opposite trend to temperature, and its morphology changes from thin-film to granular. A detailed explanation through linear density (ρ) is provided that the influence of secondary Laves phases at the grain boundaries (GBs) on notch sensitivity depends on the coupling competition effect of their size, quantity, and morphology. Notably, the granular Laves phases are more beneficial to improving the notch sensitivity of the alloy compared with thin-film Laves phases. Granular secondary Laves phases can promote the formation of γ′ phases depletion zone to improve the ability of GBs to accommodate high strain localization, and effectively inhibit the crack initiation and propagation.