On the Temperature Limits of Ni-Based Superalloys

The peculiar atomic structure of γ′ precipitates [Ni3(Al/Ti)-L12] in Ni-based superalloys produces high-energy faults when dislocations glide them, giving their significant strength at high temperatures. The mechanisms behind the strength failure of these alloys above 800 °C are still controversial. Recent advances in atomic resolution microscopy have allowed to study these mechanisms with unprecedented detail. In our study, we have characterised a SX superalloy from RT to 1000 °C. Multiscale microscopy (TEM and SEM) are combined with physical modelling to fully understand the correlation between the strength drop and the changes in the γ′ shearing mechanism. Our results show that, far from previous beliefs, the initial failing of alloy strength is not a consequence of dislocation climbing. Instead, local chemical changes around the γ′ shearing dislocations boost their gliding, thus producing the sudden drop of strength. This new understanding can be used to beat the current temperature limits of these alloys.