2026 Bezold Ti Ta CoNi Superalloys

Polycrystalline CoNi-based superalloys exhibit an attractive property profile for intermediate-temperature applications, particularly with Ti- and Ta-rich variants showing exceptional creep resistance. This study aimed to clarify the mechanisms underlying these improvements by systematically examining the deformation and segregation behavior of three CoNi-based alloys with varying Ti and Ta contents. Interrupted compression creep tests at 750 °C were conducted alongside advanced scanning transmission electron microscopy and atomic-scale energy dispersive spectroscopy to analyze the controlling mechanisms at play. The results indicate that the addition of Ti and Ta increases the anti-phase boundary energy (APB) of the c¢ phase, which facilitates a transition from APB-based shearing to a more creep-resistant, stacking fault-dominated deformation regime. A quantitative correlation was established between APB energy and the diffusional length of c-forming elements, providing insight into this transition. Localized phase transformations along planar faults were found to strengthen the alloys, though these were kinetically limited by solute diffusion, particularly of W. Notably, the presence of Ta proved beneficial due to its higher diffusivity, enabling rapid formation of ordered phases and suppressing detrimental microtwin thickening. Conversely, Ta-free alloys exhibited delayed transformation and initial softening. These findings offer valuable guidelines for the design of next-generation creep-resistant superalloys.