Abstract Polycrystalline Ni-based superalloys rely on compositional modifications for high-temperature, structural aerospace applications. However, these changes must be carefully managed to avoid deleterious phases. While the individual effects of Ti and Ta are well documented, their synergistic co-addition has received limited attention in high Co-containing alloys. This study investigates the influence of Ti and Ta on the load partitioning behavior between the γ and γ ′ phases using in situ synchrotron diffraction under tensile loads in the temperature range from 600 °C to 800 °C. Our findings show that the ratio of Ti:Ta directly impacts how load is distributed, with a higher ratio leading to a greater load-carrying capacity in the γ ′ phase, thereby improving strength at intermediate temperatures (700 °C). However, this benefit seems thermally limited, coinciding with a significant reduction in stiffness in the high-Ti alloy at 800 °C. Conversely, a balanced Ti:Ta ratio maintains consistent load partitioning and strength stability across the entire temperature range. By linking lattice misfit and stiffness evolution to bulk behavior, this work identifies load transfer efficiency as a critical metric for the design of future high-performance superalloys. By understanding this relationship, the compositional limits for optimizing alloy performance in service can be better defined. This work highlights a critical design pathway for future high-performance superalloys by demonstrating the link between controlled alloying, lattice misfit, and load partitioning.
Synnott et al. (2026) studied this question.