A 3D printable alloy designed for extreme environments

The study addresses the need for alloys that maintain strength, creep resistance, and oxidation resistance in extreme environments, particularly at elevated temperatures relevant to aerospace and energy applications. Building on advances in high-/medium-entropy alloys (notably the Cantor alloy family and the NiCoCr derivative), the authors investigate whether combining model-driven alloy design with additive manufacturing and oxide dispersion strengthening can overcome the strength–ductility trade-off and deliver superior elevated-temperature performance. The research focuses on optimizing NiCoCr-based compositions and processing routes to create a printable, oxidation-resistant, high-strength alloy suitable for complex components, hypothesizing that nanoscale oxide dispersoids and targeted segregation/carbide stability can markedly enhance high-temperature tensile and creep properties.

The paper reviews the progression of high-/medium-entropy alloys (HEAs/MPEAs), emphasizing the Cantor alloy (CoCrFeMnNi) and derivatives (e.g., NiCoCr) with excellent strain hardening, ductility, and cryogenic strength due to mechanisms like FCC–HCP transformations and stacking-fault energy variations. Prior work shows property enhancements via minor alloying additions: ppm-level B improving grain boundary/interstitial strengthening; C additions increasing strength; and W additions refining grains and elevating yield strength while retaining ductility. Oxide-dispersion-strengthened (ODS) MPEAs have exhibited improved high-temperature strength/creep and irradiation resistance. Earlier additive approaches (L-PBF) introduced oxides via mechanical/in situ alloying or reactions but raised complexity and repeatability concerns. A prior study demonstrated coating NiCoCr powders with nanoscale Y₂O₃ via high-energy mixing (binderless, no fluids), yielding ODS NiCoCr with higher tensile strength and ductility at 1,093 °C. This body of work motivates a model-driven optimization of NiCoCr with integrated oxide dispersion to achieve robust high-temperature performance in additively manufactured components.

• Model-driven alloy design: Computational thermodynamics and first-principles (DFT) calculations examined phase stability across Ni–Co–Cr compositions, identifying conditions where HCP is most stable at 0 K and leveraging entropy to favor FCC at service temperatures. Compositional optimization incorporated elements (e.g., Al, Ti, Nb, W, Re) to balance processability, carbide stability (MC-type), grain boundary chemistry, and high-temperature performance.
• Oxide dispersion introduction: Nanoscale Y₂O₃ particles were incorporated by coating NiCoCr-based powders via a high-energy dry mixing process (no binders/fluids) prior to laser powder bed fusion (L-PBF), avoiding mechanical or in situ alloying.
• Additive manufacturing and post-processing: Specimens were fabricated by L-PBF. Some builds underwent hot isostatic pressing (HIP). Both as-built and HIP conditions were studied to assess microstructure and anisotropy effects.
• Microstructural characterization: High-resolution STEM (LAADF/DCI, HAADF) probed dislocations, stacking faults, stacking-fault tetrahedra, and oxide–matrix interfaces; EDS mapped solute segregation (Cr, W, Re enrichment; Ni, Co depletion) and identified Nb/Ti-rich MC carbides; SEM corroborated carbide presence and grain structure; assessment of short-range order found no local chemical ordering despite L1₂-forming elements.
• Mechanical testing: Tensile tests at 1,093 °C for multiple alloys and conditions (NiCoCr, NiCoCr-ODS, ODS-ReB, GRX-810, non-ODS GRX-810; as-built and HIP). Room-temperature and cryogenic tensile tests also performed (Extended Data). Creep tests at 1,093 °C under 20 MPa (primary comparison) and 31 MPa (additional) included AM 718, AM 625, and wrought Haynes 230 references. Time-to-1% strain and rupture life were recorded.
• Oxidation testing: Cyclic oxidation in air at 1,093 °C and 1,200 °C up to 35 h; post-exposure mass change, spallation behavior, and visual assessment documented.
• Comparative analysis: Benchmarked GRX-810 against state-of-the-art AM superalloys (718, 625) and wrought Haynes 230, as well as prior ODS variants (NiCoCr-ODS, ODS-ReB) and non-ODS counterparts.

• GRX-810 integrates uniformly dispersed nanoscale Y₂O₃ particles via L-PBF without mechanical or in situ alloying, confirmed by high-resolution microscopy across the build volume.
• Mechanical performance at 1,093 °C:
  • Tensile behavior: ODS additions increase strength and ductility versus non-ODS NiCoCr. GRX-810 exhibits roughly twofold higher tensile strength than conventional wrought Ni-based alloys used in AM at 1,093 °C, with as-built GRX-810 generally stronger than HIP due to retained finer grain structure and AM-induced anisotropy.
  • Creep (20 MPa, 1,093 °C): As-built GRX-810 reached 1% strain at 2,804 h; HIP GRX-810 at 2,122 h. In contrast, NiCoCr, AM 718, AM 625 (tested at 14 MPa), and wrought Haynes 230 ruptured in under 40 h. Compared with wrought Haynes 230, as-built GRX-810 required >500× longer to reach 1% strain; >1,000× longer compared with AM 718. At 31 MPa, as-built GRX-810 lasted nearly 2,500 h versus ~1 h for NiCoCr (~2,000× improvement).
• Oxidation resistance: GRX-810 outperforms AM 718 under cyclic oxidation at 1,093 °C and maintains substantially better performance at 1,200 °C, where AM 718 suffers catastrophic oxidation within hours.
• Microstructural mechanisms: Dense networks of dissociated 1/2⟨110⟩ dislocations, stacking faults, and stacking-fault tetrahedra impede dislocation motion. Grain boundaries exhibit Cr, W, and Re segregation and stable Nb/Ti-rich MC carbides. No short-range order detected despite presence of L1₂-forming elements.
• Anisotropy and temperature range: As-built GRX-810 shows higher strength in transverse (x–y) vs vertical (z) directions, typical for L-PBF. Cryogenic tests show high strength (~1.3 GPa tensile strength as-built) with retained ductility, indicating nanoscale oxides are not detrimental at low temperatures.
• Overall: Relative to current AM superalloys (718, 625) and wrought Haynes 230, GRX-810 provides orders-of-magnitude better creep life at 1,093 °C while also improving tensile and oxidation performance.

The results validate the hypothesis that combining model-driven compositional optimization with nanoscale oxide dispersion via L-PBF can produce an alloy with exceptional high-temperature capabilities. The Y₂O₃ dispersoids strengthen the matrix by hindering dislocation motion, contributing to both tensile and creep resistance. Microstructural observations—networks of dissociated dislocations and stacking-fault tetrahedra—support reduced dislocation mobility at elevated temperatures. Superior creep performance of GRX-810 relative to earlier ODS variants is not explained by oxide size/distribution alone; instead, the synergy of stable MC carbides and grain-boundary segregation of slow-diffusing species (W, Re) and Cr appears to suppress grain-boundary voiding and shear failure, mitigating common creep damage mechanisms. Enhanced oxidation resistance further protects the microstructure at temperature. As-built specimens often outperform HIP counterparts, consistent with finer retained grains and limited recrystallization, though anisotropy typical of L-PBF persists, with lower strength in the build (z) direction. Collectively, these mechanisms explain the pronounced gains in creep life and elevated-temperature strength, establishing GRX-810 as a superior material for extreme environments and complex additively manufactured components.

This work presents GRX-810, a NiCoCr-based oxide-dispersion-strengthened alloy designed via computational modeling and realized through L-PBF with nanoscale Y₂O₃ dispersoids. GRX-810 delivers substantial improvements in tensile strength, oxidation resistance, and especially creep life at 1,093 °C compared with benchmark AM superalloys (718, 625) and wrought Haynes 230, achieving up to >1,000× increases in time to 1% creep strain. Microstructural analyses reveal mechanisms underpinning performance, including dispersoid strengthening, stable carbides, and beneficial grain-boundary segregation that suppresses creep damage modes. The study demonstrates how model-driven alloy design combined with AM-enabled dispersion strengthening can accelerate the development of materials for extreme environments. Future work could expand long-term oxidation and creep assessments across broader stress/temperature regimes, elucidate kinetics of nitride formation, optimize post-processing to balance anisotropy and grain size, and explore compositional variants and processing windows to further enhance printable high-temperature alloys.

• AM-induced anisotropy remains: strength is lower in the build (z) direction, and HIP did not fully eliminate anisotropy.
• Some comparison tests use different stresses (e.g., AM 625 at 14 MPa vs 20 MPa), complicating direct equivalence.
• Oxidation assessments were limited to cyclic tests up to 35 h (main text), with longer-term behavior requiring further study.
• Internal nitridation was observed (Al- and Cr-rich nitrides in GRX-810), which may be detrimental; impacts need deeper quantification.
• While oxide distributions were characterized, differences in creep among ODS variants were not attributable to oxide size/spacing alone; more detailed mechanistic studies of grain-boundary chemistry/diffusivity would strengthen causality.
• Most mechanical emphasis is at 1,093 °C; broader temperature–stress–environment matrices (including fatigue) were not detailed in the main text.