A new design strategy has been recently introduced in the field of alloys for high-temperature applications. Enabled by additive manufacturing (AM), it combines oxide-dispersion-strengthening (ODS) and multi-principal element alloy (MPEA) concepts further opening up a vast unexplored compositional space to develop new 3D printable structural materials. One of the new compositions, an AM produced CrCoNi-based ODS-MPEA called GRX-810, exhibits extraordinary tensile strength, oxidation resistance and over 1000-fold better creep performance at temperature of 1093 degrees C than the AM variants of traditional polycrystalline wrought Ni-based alloys. The present study investigates origins of the high-temperature capabilities of GRX-810 through identification and detailed characterization of all relevant microstructural features and their evolution during creep, in direct comparison to the ODS-CrCoNi-ReB alloy. For the first time, a state-of-the-art multi-scale, multi-modal approach is used based on various high-resolution characterization techniques including high-energy synchrotron X-ray diffraction and the stereo-scanning transmission electron microscopy diffraction contrast imaging crosscorrelated with energy dispersive X-ray spectroscopy. Detailed characteristics of oxide nanoparticle dispersoids were accurately quantified as well as the secondary phases both before and after creep testing. The evolution of the original hierarchical lattice defect substructures and the dislocation-dispersoid interactions was analyzed in detail for both alloys and correlated with the macroscopic creep response. The extensive datasets obtained via comparative analyses are discussed in context of conventional strengthening models to understand improved properties of GRX-810 alloy, and to provide guidelines for future design and optimization of 3D printable ODS alloys potentially enabling even higher temperature capabilities or specific service targeted performance abilities.

Achieving a uniform distribution of oxide particles is a critical aspect of additive manufacturing of oxide dispersion-strengthened (ODS) alloys. In this study, we systematically varied the laser power, scanning velocity, and hatch spacing to study their impact on the oxide distribution in a Ni-20Cr + 0.8% mass fraction Y2O3 ODS alloy fabricated by powder bed fusion - laser beam (PBF-LB). The results show that melt pool overlap (defined as 1 − H/W, where H is hatch spacing and W is melt pool width) strongly influences the entrapment of micrometer-scale oxide inclusions but has an insignificant effect on the size and number density of nanometer-scale dispersoids. The area fraction of micrometer-scale inclusions decreases by an order of magnitude as overlap increases from 33% to 56%. At overlaps near 70%, we observed heat accumulation-related defects such as cracking and geometric distortion. These results suggest that an optimal hatch spacing exists (corresponding to 48% to 58% overlap) that minimizes micrometer-scale inclusions while avoiding excessive heat accumulation. In contrast, nanometer-scale dispersoids are largely unaffected by the melt pool overlap, exhibiting mean diameters of 24 nm to 29 nm and number densities of 1 × 1020 m−3 to 2 × 1020 m−3 across the range of processing conditions studied in this work. These findings establish the critical role of melt pool overlap in controlling inclusion entrapment in ODS alloys processed by PBF-LB, supporting the development of processing strategies.

Additively manufactured (AM) alloys exhibit pronounced direction-dependent mechanical behavior arising from process-induced microstructures; however, the extent of their influence on multiaxial yielding remains insufficiently quantified. In this work, the anisotropic yield surface of L-PBF GRX-810, a NiCoCr-based medium-entropy alloy, is experimentally constructed using proportional axial-torsional loading of tubular specimens fabricated in vertical and diagonal orientations, under both as-built (AB) and hot isostatically pressed (HIP) conditions. Yield stresses are determined using a 0.2% offset criterion, with stress corrections based on surface roughness and X-ray computed tomography to account for the effective load-bearing area. The measured yield loci reveal pronounced anisotropy and tension-compression asymmetry. Vertical specimens exhibit enhanced shear strength relative to isotropic predictions, whereas diagonal specimens, characterized by a similar to 45 degrees-tilted texture, show increased axial strength and reduced shear strength. These trends are consistent with Schmid factor analysis, which links the behavior to texture-driven variations in slip-system activation under different loading modes. Comparison with established yield criteria shows that the von Mises model underperforms in capturing anisotropy and strength asymmetry, while the Hill criterion is only adequate when the yield surface approaches a quadratic form. In contrast, the adopted CPB06 formulation accurately captures the non-quadratic distortions and orientation-dependent asymmetry across all conditions. Although such advanced models typically require extensive calibration, the present framework extracts all required parameters from a single axial-torsional testing configuration, significantly reducing experimental complexity. This study establishes a transferable methodology for characterizing multiaxial anisotropic behavior in AM alloys and provides a direct link between AM processing, microstructure, and yield-surface evolution, with implications for the design and certification of AM components under complex loading conditions.

This study examines the influence of post-processing operations, i.e., surface machining and hot isostatic pressing (HIP), on the fatigue behavior of newly developed, oxide dispersion strengthened GRX-810 alloy at room temperature. The GRX-810 specimens are manufactured via laser powder bed fusion additive manufacturing technology. The effects of individual and combined post-processing operations are investigated by comparing the micro-mechanisms affecting the fatigue behavior of un-machined specimens with machined ones in non-HIP and HIP conditions. Crystallographic facets are found at the crack initiation sites of both machined and unmachined specimens, which are due to operation of persistent slip bands (PSBs). Surface defects (i.e., surface micronotches) and volumetric defects promote the formation of PSBs, accelerate fatigue crack initiation, and reduce fatigue life. By removing and minimizing these defects, both machining and HIP improve fatigue resistance. In addition to its reducing effect on volumetric defects, HIP also improves fatigue lives by forming large populations of intragranular carbide particles which could impede PSBs and delay crack initiation. Finally, the combined operation of both machining and HIP results in the best fatigue resistance.

The demand for metal alloys that can perform at extreme temperatures above 1100 °C while remaining manufacturable has sparked renewed interest in printable oxide dispersion strengthened (ODS) alloys. Recently, NASA developed an ODS alloy designed for additive manufacturing, known as GRX-810, which has demonstrated exceptional tensile and creep performance at temperatures of 1093 °C and higher. In the present study, tensile tests of GRX-810 are conducted up to 1316 °C and creep tests are performed in both the horizontal and vertical orientations, relative to the build direction. Thermal cycling is executed at 1100 °C, 1200 °C, and 1300 °C in air. The oxidation behavior of GRX-810 is compared to that of alumina forming single crystal Ni-base superalloys and chromia-forming wrought alloys such as superalloys 718 and 625. High resolution atomic-scale characterization and atomistic modeling are employed to explain the exceptional high temperature properties observed in GRX-810, particularly in relation to the unique, finer trigonal yttrium oxides produced during the additive manufacturing process. GRX-810, an oxide dispersion strengthened alloy, shows excellent structural performance above 1100°C and stability up to 1300 °C. Grain-size effects, additive manufacturing–induced anisotropy, and fine trigonal Y₂O₃ particles enhance creep resistance.

Recent developments in oxide dispersion strengthened (ODS) alloys have revealed significant improvements in creep and oxidation properties compared to their non-ODS counterparts. The mechanistic origin of such property improvements is not well understood, particularly with regards to creep performance where ODS alloys can exhibit significantly different responses compared to their non-ODS counterparts. Investigation of such effects through simulation has recently been enabled through the development of new computationally efficient charge transfer ionic potential for the Ni-O system. Using this newly developed capability, we performed molecular dynamics simulation to investigate the mechanism of creep strengthening in ODS alloys by simulating oxide-dislocation interactions. These simulations demonstrated that the bypass of the oxide is controlled by the direct dislocation-particle interaction at the oxide-metal interface, rather than repulsion of the dislocation as required for Orowan looping. Therefore, the dislocation interactions must be governed by effects acting on the dissociated dislocation core over the Ni-NiO interface. The ODS strengthening effect is likewise observed to be relatively insensitive to temperature variation, which is in line with experimental measurements demonstrating ODS strengthening at a wide range of temperatures. Finally, this improved understanding of the fundamental oxide strengthening mechanisms indicates that local structure at the metal-oxide interface is critical for strengthening of the ODS alloys.

GRX-810 is a novel Multi-Principal Element Alloy (MPEA) belonging to the NiCoCr family, primarily strengthened through the Oxide Dispersion Strengthening (ODS) mechanism. This alloy demonstrates high tensile strength and exceptional creep resistance, coupled with significant oxidation resistance, while maintaining remarkable ductility for applications in extreme-temperature environments. Additive manufacturing enabled the development of this alloy by the dispersion of the nano-scale Y2O3 throughout the microstructure. However, meeting industrial and production demands requires comprehensive characterization of the microstructure, mechanical and thermophysical properties, as well as variations in geometry and machine parameters. This study investigates the size and temperature-dependent mechanical properties and deformation mechanisms of GRX-810, focusing on the relation between its pristine (pre-deformed) microstructural features and mechanical behavior for elevated temperatures up to 1148 degrees C. Asa medium entropy alloy, GRX-810 benefits from an atomic scale strengthening mechanism and precipitates in the form of carbides and nano-scale yttria oxides, resulting in desirable properties for extreme environment applications. A size-dependent variation in porosity volume, with higher porosity in thinner GRX-810 samples is observed. However, no evidence of size-dependent variation in mechanical properties was identified. Fracture surface analysis revealed deformation twinning through different temperatures, particularly during the later stages of plastic deformation, serving as a strengthening mechanism by delaying necking and fracture. At 537 degrees C, the Portevin-Le Chatelier (PLC) effect was observed and attributed to lattice distortion impeding dislocation movement. Overall, quasi-static tensile testing demonstrated a progressive linear decrease in yield strength (YS) and ultimate tensile strength (UTS) with increasing temperature, while elongation remained consistently above 30% up to 871 degrees C for all thicknesses.

Controlling microstructure in fusion-based metal additive manufacturing (AM) remains a significant challenge due to the many parameters that directly impact solidification condition. Multiprincipal element alloys (MPEAs), also known as high entropy alloys, offer a vast compositional space to design for microstructural engineering due to their chemical complexity and exceptional properties. Here, we use the FeMnCoCr system as a model platform for exploring alloy design in MPEAs for AM. By exploiting the decreasing stability of the face-centered cubic phase with increasing Mn content, we achieve notable grain refinement and breakdown of epitaxial columnar grain growth. We employ a multifaceted approach encompassing thermodynamic modeling, operando synchrotron X-ray diffraction, multiscale microstructural characterization, and mechanical testing to gain insight into the solidification physics and its ramifications on the resulting microstructure of FeMnCoCr MPEAs. This work aims toward tailoring desirable grain sizes and morphology through targeted manipulation of phase stability, thereby advancing microstructure control in AM applications.

High energy stacking faults generated by lattice dislocations entering the strengthening precipitates of Ni-based superalloys are responsible for the unique mechanical properties of these structural materials. However, the question about stability of these faults has not received the attention it deserves. Using atomistic simulations, we show that the anti-phase boundary (APB) can spontaneously transform into super intrinsic stacking fault (SISF) and the complex stacking fault (CSF) can spontaneously transform into L12 lattice structure. The former transformation explains the experimentally observed presence of isolated SISFs and super extrinsic stacking faults (SESFs) in the precipitates. Finally, multiple studies were focused on finding alloying additions which increase the APB and CSF energies. We demonstrate therefore that alloying additions which increase stacking fault energies may conversely decrease their stabilities.

The recently identified multiprincipal-element alloy (MEA), known as GRX-810, exhibits a dramatic improvement in the creep resistance at elevated temperatures. Initial studies have identified segregation atmospheres around the oxide-dispersion particles, which likely contribute to this phenomenon. However, the many details remain elusive, especially the co-segregation effects. Such effects include both substitutional and interstitial type segregation, leading to a complex alloying environment. To investigate these segregation effects, Monte Carlo/ab initio based molecular dynamics (MC/AIMD) hybrid simulations were performed. Coupled with an algorithm to identify potential interstitial sites, evaluation of the joint interstitial and substitutional segregation events was made possible. The simulations have revealed critical elements of carbon segregation near the oxide-dispersoid particles, where carbon atoms are repelled from the oxygen-terminated metal-yttria interface but attracted to the yttrium-terminated interface. This discovery identifies critical distinctions between yttrium-based oxide dispersoids, which control critical solute atmospheres.

Micro-twinningMicro-twinning is the major creepCreep deformation mechanismDeformation mechanisms in Ni-based superalloysNi-based superalloy at temperatures above 700 °C. Recent experiments suggest that superlattice stacking faultsStacking faults in γ′ phase may serve as the precursors to twin formation. SegregationSegregation of alloying elements to these precursors may have a significant effect on formation and extension of micro-twinsMicro-twins. Using atomistic modelingAtomistic modeling we investigate and explain the effects of Nb and Cr alloying additions on these processes. The simulation shows that Nb increases the creep resistanceCreep resistance which is mostly associated with impeding the reordering of the high energy double complex stacking faultStacking faults. Cr, on the other hand, promotes twin growth, degrading the high temperatureHigh temperature creep propertiesCreep properties. These results can help to understand the effects of elemental composition of the alloy on creep resistanceCreep resistance.

Chemical and microstructural alterations at near-atomic scale can influence the high temperature mechanical performance of superalloys. These alterations are strongly associated with solute segregation at crystal defects, such as dislocations and stacking faults. This review provides an overview of the phenomena that occurs during deformation at elevated temperatures due to the interactions of solutes with crystal defects. These interactions are discussed based on investigations conducted by exploiting the recent technological advancements of advanced characterization methods, such as transmission electron microscopy and atom probe tomography. Insights on local phase transformation mechanisms along stacking faults are discussed providing perspectives on new alloy design concepts. Besides, various microstructural alterations controlled by the interactions of solutes with dislocations are discussed. Bringing together observations at near-atomic scale that control superalloys in the macroscopic level, we aim to bridge an atomic scale microanalysis gap. Thus, providing insights that future alloy designers, modelers, and engineers can incorporate these effects into their analyses, alloy design models and life prediction calculations.

Previous work on additively-manufactured oxide dispersion strengthened alloys focused on experimental approaches, resulting in larger dispersoid sizes and lower number densities than can be achieved with conventional powder metallurgy. To improve the as-fabricated microstructure, this work integrates experiments with a thermodynamic and kinetic modeling framework to probe the limits of the dispersoid sizes and number densities that can be achieved with powder bed fusion-laser beam. Bulk samples of a Ni–20Cr ＋ 1 wt% Y2O3 alloy are fabricated using a range of laser power and scanning velocity combinations. Scanning transmission electron microscopy characterization is performed to quantify the dispersoid size distributions across the processing space. The smallest mean dispersoid diameter (29 nm) is observed at 300 W and 1200 mm/s, with a number density of 1.0 × 1020 m−3. The largest mean diameter (72 nm) is observed at 200 W and 200 mm/s, with a number density of 1.5 × 1019 m−3. Scanning electron microscopy suggests that a considerable fraction of the oxide added to the feedstock is lost during processing, due to oxide agglomeration and the ejection of oxide-rich spatter from the melt pool. After accounting for these losses, the model predictions for the dispersoid diameter and number density align with the experimental trends. The results suggest that the mechanism that limits the final number density is collision coarsening of dispersoids in the melt pool. The modeling framework is leveraged to propose processing strategies to limit dispersoid size and increase number density.

The structural evolution of oxides in dispersion-strengthened superalloys during laser-powder bed fusion is considered in detail. Alloy chemistry and process parameter effects on oxide structure are assessed through a parameter study on the model alloy Ni-20Cr, doped with varying concentrations of Y2O3 and Al. Small angle neutron scattering measurements of the dispersoid size distribution show the dispersoid size increases with higher laser power, slower scan speed, and increasing Y2O3 and Al content. Complementary electron microscopy measurements reveal reactions between Y2O3 and Al, even in nanoscale dispersoids, and the presence of micron- scale oxide slag inclusions in select specimens. A scaling analysis of mass and momentum transport within the melt pool, presented here, establishes that diffusional structural evolution mechanisms dominate for nanoscale dispersoids, while fluid forces and advection become significant for larger slag inclusions. These findings are developed into a theory of dispersoid structural evolution, integrating quantitative models of diffusional processes - dispersoid dissolution, nucleation, growth, coarsening - with a reduced order model of time-temperature trajectories of fluid parcels within the melt pool. Calculations of the dispersoid size in single-pass melting reveal a zone in the center of the melt track in which the oxide feedstock fully dissolves. Within this zone the final Y2O3 size is independent of feedstock size and determined by nucleation and growth kinetics. If the dissolution zones of adjacent melt tracks overlap sufficiently with each other to dissolve large oxides, formed during printing or present in the powder feedstock, then the dispersoid structure throughout the build volume is homogeneous and matches that from a single pass within the dissolution zone. Gaps between adjacent dissolution zones result in oxide accumulation into larger slag inclusions. Predictions of final dispersoid size and slag formation using this dissolution zone model match the present experimental data and explain process-structure linkages speculated in the open literature.

Additive manufacturing ( AM) has revolutionized component design for liquid rocket engines by offering rapid manufacturing capabilities. This has led to significant opportunities for development and flight programs in the propulsion industry, resulting in cost and schedule savings, as well as performance improvements through new designs and alloy development. A noteworthy example is the GRX-810 oxide dispersion strengthened (ODS) alloy, which was specifically developed for extreme temperatures. This Ni-Co-Cr based alloy was created using integrated computational materials engineering (ICME) techniques to focus on a new class of materials with exceptional temperature and oxidation-resistant properties. The GRX-810 alloy utilizes AM processes to incorporate nano-scale yttria particles throughout its microstructure, resulting in remarkable enhancements. Compared to traditional Nickel-based superalloys, the GRX-810 alloy offers a twofold increase in tensile strength, 1,000-fold better creep properties, and two-fold improvement in oxidation resistance. NASA successfully demonstrated the development and manufacturing of components using the GRX-810 alloy through laser powder bed fusion (L-PBF) and laser powder directed energy deposition (LP-DED) processes. Extensive efforts were made to model, evaluate metallurgical properties, develop heat treatment processes, characterize the microstructure, and determine mechanical properties. The GRX-810 alloy was specifically designed for aerospace applications, including liquid rocket engine injectors, preburners, turbines, and hot-section components, capable of withstanding temperatures up to 1,100 degrees C. The objective of this alloy development is to bridge the temperature gap between traditional Nickel-based superalloys and refractory alloys. This paper provides a comprehensive comparison of the GRX-810 alloy with other aerospace alloys, discussing its microstructure, mechanical properties, processing advancements, component development, and hot-fire testing results. The ultimate goal of this development was to elevate the Technology Readiness Level (TRL) of the GRX-810 alloy, enabling its integration into NASA and commercial aerospace applications.

As the operating temperature of jet turbine engines increase, creep becomes the life-limiting property for turbine disks and blades. At intermediate temperatures, between 600-800°C, microtwinning contributes significantly to creep strain in these alloys. Therefore, understanding how microtwins form and grow is critical to improving the creep life of future Ni-base superalloy components. In addition, exploring the effect of different alloying elements, such as Nb and Ta, on the formation of microtwins is critical for future alloy development. Several mechanisms of microtwinning have been proposed among which the Kolbe mechanism, based on thermally activated reordering, is believed to be dominant. In this work we employ atomistic simulation to investigate the effects of Nb solutes on the Kolbe mechanism. The simulation demonstrates that Nb atoms significantly slow down the reordering processes, explaining the experimentally observed improvement in the creep resistance.

Micro-twinning is the major creep deformation mechanism in Ni-based superalloys at temperatures above 700 °C. Recent experiments suggest that superlattice stacking faults in γ′ phase may serve as precursors for twin formation. Segregation of alloy elements to these precursors may have a significant effect on the formation and extension of micro-twins. Using atomistic modeling, we investigated and explained the effects of Cr on these processes. Our results indicate that depending on the site preference of Cr in Ni3Al γ′ phase, two drastically different deformation behaviors can be expected. Occupying Al sites, Cr significantly accelerates deformation twinning. Cr on Ni sites, on the other hand, suppresses twin growth and slows down the high temperature deformation creep. These results help to rationalize the experimentally observed puzzling effects of alloy composition on creep resistance.