Design route for single-crystal superalloys against 1200 °C: extending classical multiple creep strengthening mechanisms to ultrahigh-temperature service

For turbine-manufacturing single-crystal superalloys, widely accepted multiple creep strengthening mechanism has been established, but arousing an undesired theoretical operating temperature limit of approximately 1140 °C. Although exploratory studies have demonstrated the potential for achieving 1200 °C capability, the underlying strengthening mechanisms for ultrahigh-temperature service remain insufficiently understood. We reveal that the creep at 1200 °C originates from the well-recognized mechanism of dislocations interacting with precipitates. By quantitatively mapping rupture life at 1200 °C against γ′ volume fraction and γ/γ′ lattice misfit, however, we show that effective strengthening occurs only when γ′ precipitates are sufficiently sustained. The dominant role of precipitation strengthening at 1200 °C explains why classical theory fails here, as it does not account for the activated thermal instability of γ′ precipitates.