Negative mixing enthalpy and mixing enthalpy alloying leads to interface and size effects towards superb creep resistance of nickel-based single crystalline superalloys

Nickel (Ni)-based single crystalline superalloys are the most important high-temperature service metallic materials for aircraft engine blades. These alloys' microstructures and mechanical properties must remain stable under high temperature and stress conditions for long periods of time. Rhenium (Re) has been the most effective alloying element, which serves as a guide to distinguish the third-generation Ni-based single crystalline superalloys. However, the Re-alloying effect seems to have been exhausted in terms of further improving superalloy creep lives, although the continuous demand for longer creep lives at high temperatures persists. This study uses the mixing enthalpy alloying route by combining negative enthalpy (N-enthalpy) alloying and positive enthalpy (P-enthalpy) alloying strategies to explore a new alloying paradigm in which the Os element is uniquely selected. The P-enthalpy effect of osmium (Os) with Ni leads to the segregation of Os elements along the γ/γ' interface, which, in turn, yields a small-size γ' phase and narrower γ channels by the P-enthalpy-produced interface effect and size effect. The N-enthalpy effect of Os with chromium (Cr) and other alloying elements further synchronizes the formation of local chemical ordering in the γ phase channel. These synergistic interface and size effects, together with local chemical ordering, increase the stability of the microstructure and the resistance of the dislocation movement. With these, the creep life of the Os N-enthalpy alloying superalloys approaches 1273 h under 760°C/800 MPa conditions, which is almost six times more than that of the base alloy, setting a high record among all existing metals and alloys. These findings highlight the mixing enthalpy alloying paradigm of designing new materials with excellent high-temperature performance.