Search for: All records

Abstract Multiprincipal-element alloys are an enabling class of materials owing to their impressive mechanical and oxidation-resistant properties, especially in extreme environments^1,2. Here we develop a new oxide-dispersion-strengthened NiCoCr-based alloy using a model-driven alloy design approach and laser-based additive manufacturing. This oxide-dispersion-strengthened alloy, called GRX-810, uses laser powder bed fusion to disperse nanoscale Y₂O₃particles throughout the microstructure without the use of resource-intensive processing steps such as mechanical or in situ alloying^3,4. We show the successful incorporation and dispersion of nanoscale oxides throughout the GRX-810 build volume via high-resolution characterization of its microstructure. The mechanical results of GRX-810 show a twofold improvement in strength, over 1,000-fold better creep performance and twofold improvement in oxidation resistance compared with the traditional polycrystalline wrought Ni-based alloys used extensively in additive manufacturing at 1,093 °C^5,6. The success of this alloy highlights how model-driven alloy designs can provide superior compositions using far fewer resources compared with the ‘trial-and-error’ methods of the past. These results showcase how future alloy development that leverages dispersion strengthening combined with additive manufacturing processing can accelerate the discovery of revolutionary materials. 

CoNi-based superalloys offer excellent high-temperature properties; yet, Co is also a strategic alloying element, and its content should only be as high as necessary. This study investigates Fe as a partial substitute for Co to reduce costs while evaluating its impact on mechanical properties. To evaluate this, we systematically investigate the effect of Fe substitutions on thermophysical properties, microstructure, partitioning behavior, lattice misfit, yield strength, and creep performance of three polycrystalline CoNi-based superalloys derived from CoWAlloy1 (Co–32Ni–12Cr–6Al–3W–2.5Ti–1.5Ta–0.4Si–0.1Hf–0.08B all in at. %). In these alloys, 4, 8, and 12 at. % Co is replaced with Fe. Increasing Fe content results in a gradual reduction in the solvus, solidus, and liquidus temperatures by 3.0, 1.9, and 1.4 °C per at. % Fe, respectively. The γ′ volume fraction and the lattice misfit decrease by about 0.7% and 0.01%, respectively, per at. % Fe substitution for Co. Fe predominantly partitions to the γ matrix, enhancing the partitioning of Co and Ni while reducing that of Al, Cr, and Ta, with no significant effect on Ti and W. Substituting Co with Fe moderately reduces yield and creep strength, primarily due to the decreasing γ′ volume fraction and a transition in the dominant deformation mechanisms from stacking fault shearing and microtwinning to matrix-based deformation as Fe content increases. Beneficial elemental segregation behaviors and localized phase transformations along creep-induced stacking faults remain active in alloys with high Fe content. These findings highlight the potential of Fe alloying to reduce costs while maintaining high-temperature strength in CoNi-based superalloys. 

Creep strength in polycrystalline Ni-based superalloys is influenced by the formation of a rich variety of planar faults forming within the strengthening γ' phase. The lengthening and thickening rate of these faults – and therefore the creep rate – depends on an intriguing combination of dislocation interactions at the γ/γ' interface and diffusional processes of the alloying elements at the core of the fault tip. The effect of alloy composition on this process is not fully understood. In this work we use correlative high resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy to study the deformation faults in two different Ni-based superalloys with carefully designed ratios of disordering-to-ordering-promoting elements (Co-Cr against Nb-Ta-Ti). The results show that the additions of ordering-promoting elements reduce the diffusional processes required for the faults to lengthen and thicken thus reducing the creep rates found for the higher Nb-Ta-Ti alloy. These insights provide a path to follow in the design of improved grades of creep-resistant polycrystalline alloys beyond 700 °C.