The research question centers on developing a high-performance alloy suitable for extreme environments, specifically addressing the limitations of existing materials in terms of strength, creep resistance, and oxidation resistance at high temperatures. The context is the growing need for advanced materials in aerospace and energy applications where components operate under severe conditions. Multiprincipal-element alloys (MPEAs), also known as high-entropy alloys, are a promising class of materials due to their exceptional properties. However, traditional methods of alloy development are resource-intensive and often rely on trial-and-error. This study aims to overcome these limitations by employing a model-driven alloy design approach combined with additive manufacturing (AM) techniques, specifically L-PBF, to create a superior alloy with significantly improved high-temperature properties. The importance of this research lies in its potential to accelerate the development of advanced materials for demanding applications, reducing development costs and time while enhancing performance.

The literature review examines the properties and applications of MPEAs, focusing on the Cantor alloy (CoCrFeMnNi) and its derivatives, particularly NiCoCr. Studies have shown that NiCoCr exhibits high room-temperature strength, and further improvements can be achieved through alloying with refractory elements or the addition of interstitials like boron or carbon. The concept of oxide-dispersion strengthening (ODS) in MPEAs has also been investigated, showing improved high-temperature strength and creep resistance. Existing methods for producing ODS alloys using AM often involve complex and less repeatable processes like mechanical alloying or in situ alloying. Previous work by Smith et al. demonstrated the potential of a high-energy mixing process to coat NiCoCr powder with Y₂O₃ nanoparticles for L-PBF, resulting in improved tensile strength and ductility at high temperatures. This study builds upon this previous work, using a model-driven approach to optimize the NiCoCr alloy system for high-temperature performance.

The research employed a model-driven alloy design approach to optimize the NiCoCr alloy system for high-temperature applications. This involved computational modeling to predict phase stability and optimize composition. The selected composition was then processed using L-PBF, incorporating nanoscale Y₂O₃ dispersoids without the use of resource-intensive steps. High-resolution characterization techniques, including high-resolution scanning transmission electron microscopy (HR-STEM), energy-dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD) were used to analyze the microstructure of the resulting alloy, GRX-810. The microstructure was characterized in terms of phase stability, oxide dispersion, dislocation density, solute segregation, and presence of carbides. Mechanical testing was performed at 1,093 °C to evaluate the tensile and creep properties of GRX-810. The results were compared with those of several other alloys, including NiCoCr, NiCoCr-ODS, ODS-ReB, and commercially available high-temperature alloys (AM 718, AM 625, and wrought Haynes 230). Cyclic oxidation tests were also conducted to assess the oxidation resistance of GRX-810. The high-resolution characterization involved techniques such as low-angle annular dark-field (LAADF)-STEM, high-angle annular dark-field (HAADF)-STEM, and EDS mapping to reveal details about the microstructure. The modelling approach is described in the methods section, providing details on the computational methods used to predict phase stability and guide alloy composition. The AM process used L-PBF with a previously developed method for coating the NiCoCr powder with Y2O3 nanoparticles. The experimental conditions for tensile, creep and cyclic oxidation tests are provided in the supplementary materials.

The microstructure analysis of GRX-810 revealed a successful incorporation and dispersion of nanoscale Y₂O₃ particles throughout the build volume. Carbon segregation was observed along some oxide-matrix interfaces. The alloy exhibits a network of dissociated dislocations and a high density of stacking-fault tetrahedra, which contribute to its enhanced mechanical properties. Solute segregation of Cr, W, and Re at grain boundaries, with depletion of Ni and Co, was observed. EDS mapping showed the presence of Nb/Ti-rich metal carbides. High-resolution HAADF-STEM analysis showed no short-range elemental ordering. Mechanical testing at 1,093 °C demonstrated that GRX-810 exhibits a twofold improvement in tensile strength compared to conventional alloys like AM 718, AM 625, and wrought Haynes 230. More importantly, GRX-810 showed over 1,000-fold better creep performance, with a time to 1% creep strain exceeding 2,800 h at 20 MPa, while other alloys failed within 40 h. GRX-810 also exhibited twofold better oxidation resistance at 1,093 °C compared to AM 718. The superior creep performance is linked to the suppression of grain boundary failure mechanisms observed in other ODS alloys. The stable MC carbides and solute segregation of W, Cr, and Re along grain boundaries contribute significantly to the prevention of grain boundary failure, leading to remarkably improved creep resistance. As-built GRX-810 consistently showed better high-temperature properties compared to HIP-treated GRX-810. Unexpectedly, GRX-810 demonstrated high cryogenic tensile strength (1.3 GPa). Even at high stress (31 MPa), as-built GRX-810 exhibited a remarkable 2,000-fold improvement in lifespan compared to NiCoCr.

The findings demonstrate that the combination of model-driven alloy design and additive manufacturing can lead to the creation of superior high-temperature materials. The enhanced properties of GRX-810 are attributed to the synergistic effects of the optimized composition and the nanoscale oxide dispersion strengthening. The computational modeling allowed for the identification of a composition that balances desirable properties with processability. The superior creep resistance is particularly noteworthy, suggesting that GRX-810 could be a game-changer for high-temperature applications requiring exceptional durability. The suppression of grain boundary failure mechanisms through carbide stabilization and solute segregation highlights the importance of microstructural control in achieving superior performance. The results showcase the potential of this design approach and manufacturing process to rapidly develop new materials with exceptional properties. Further research should explore the scalability of the production method and investigate the long-term performance of GRX-810 under different operating conditions.

This study successfully demonstrates the development of GRX-810, a NiCoCr-based ODS alloy with dramatically enhanced high-temperature mechanical properties and oxidation resistance compared to conventional alloys. This success highlights the efficacy of the combined model-driven alloy design and additive manufacturing approach. The superior creep resistance of GRX-810 is particularly significant for high-temperature applications, opening avenues for innovative component designs in extreme environments. Future research could focus on exploring variations in the oxide dispersion, further compositional optimization, and long-term stability under diverse conditions.

The study focused on the high-temperature behavior of GRX-810, and further investigation is needed to fully characterize its properties across a wider range of temperatures and conditions. The current research is limited to laboratory-scale testing, and additional studies are required to assess the scalability and reproducibility of the fabrication process for industrial-scale production. The long-term performance and reliability of GRX-810 need further evaluation under real-world operating conditions.