Search NASA⌕ Search

SEARCH · Search NASA

Results for “superalloy”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Effects of Cr and Nb alloying additions on high temperature creep deformation of Ni-based superalloys

Micro-twinning is the major creep deformation mechanism in Ni-based superalloys at temperatures above 700 °C. Recent experiments suggest that superlattice stacking faults y ' in phase may serve as the precursors to twin formation. Segregation of alloying elements to these precursors may have a significant effect on formation and extension of micro-twins. Using atomistic modeling we investigate and explain the effects of Cr and Nb alloying additions on these processes. We consider the experimentally obtained creep curves for several Ni-based superalloys with different elemental compositions and relate the observed trends to the simulation results presented in this study. Our results help to rationalize the experimentally observed puzzling effects of elemental composition of the alloy on creep resistance.

Valery V. Borovikov↗
DOE OSTI2022

Creep resistant Ni-based superalloy casting and method of manufacture for advanced high-temperature applications

One or more embodiments relates to a method of casting a creep-resistant Ni-based superalloy and a homogenization heat treatment for the alloy. The method includes forming a feed stock having Nickel (Ni) and at least one of Chromium (Cr), Cobalt (Co), Aluminum (Al), Titanium (Ti), Niobium (Nb), Iron (Fe), Carbon (C), Manganese (Mn), Molybdenum (Mo), Silicon (Si), Copper (Cu), Phosphorus (P), Sulfur (S) and Boron (B). The method further includes fabricating the creep-resistant Ni-based superalloy in a predetermined shape using the feed stock and at least one process such as vacuum induction melting (VIM), electroslag remelting (ESR) and/or vacuum arc remelting (VAR).

Jablonski, Paul D.↗
DOE OSTI2024

Microstructure and Mechanical Properties of Ni-Based Superalloy Nimonic 105 with Varying Carbon Content

High carbon levels have been found to improve the fabricability of high-strength cast and wrought Ni-based superalloys, enabling the development of superior cast/wrought materials. However, carbon also strongly influences the microstructure and mechanical properties of the alloys. Nimonic 105 variants with three different carbon concentrations were manufactured. A bimodal grain size was found in the intermediate carbon content variant, while the high (low) carbon resulted in fine (coarse) grains thereby significantly affecting creep performance. The variations in grain structure were attributed to the primary carbides. An intermediate carbon level showed the best combination of strength and ductility in tension at high-temperature but little improvement in, or even inferior, creep performance. Discussion of the results will establish an understanding of the influence of carbon on the microstructure and mechanical properties of high strength cast and wrought superalloys, providing insights into obtaining high-quality alloys for future high-temperature applications.

Fang, Xiaotian↗
DOE OSTI2022

Improved Creep and Tensile Properties of a Corrosion Resistant Ni-Based Superalloy Using High Temperature Aging and Nb/Ta Additions

Resistance to creep deformation is essential for cast and wrought Ni-based superalloys in next generation energy systems due to the considerable exposure times required at the operating temperature. Here the amount of precipitate strengthening was increased in variants to Inconel alloy 725 (IN725), a corrosion resistant alloy, to improve its elevated temperature mechanical strength. Additions of Nb or Ta coupled with a high temperature aging (HTA) heat treatment promoted the formation of γ" precipitates and grain boundary phases which led to significant increases in time to failure. The HTA increased the creep life of various alloy formulations as compared to the standard aging heat treatment with a maximum improvement of 371%. The Nb and Ta additions lowered the minimum creep rate (MCR) and had a similar effect on increasing creep life. The positive effect of the additions was more pronounced when coupled with the HTA which employed a higher temperature in the first step of the heat treatment to promote precipitate phase formation. The Ti/Al ratio was used to design alloys with preferential formation of ' or γ" precipitates. Compact morphology precipitates were formed in the alloys with a low Ti/Al ratio. While a low Ti/Al ratio was primarily associated with lower MCRs, the effect on the creep life was less evident than that of the HTA. By using additions of Nb or Ta and a HTA heat treatment, the creep life of IN725 for testing at 973 K (700 °C) and 483 MPa was improved by up to 256%.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Development of a heterogeneous nanostructure through abnormal recrystallization of a nanotwinned Ni superalloy

This work explores the development of a heterogeneous nanostructured material through leveraging abnormal recrystallization, which is a prominent phenomenon in coarse-grained Ni-based superalloys. Additionally, through synthesis of a sputtered Inconel 725 film with a heterogeneous distribution of stored energy and subsequent aging treatments at 730°C, a unique combination of grain sizes and morphologies was observed throughout the thickness of the material. Three distinct domains are formed in the aged microstructure, where abnormally large grains are observed in-between a nanocrystalline and a nanotwinned region. In order to investigate the transitions towards a heterogeneous structure, crystallographic orientation and elemental mapping at interval aging times up to 8 h revealed the microstructural evolution and precipitation behavior. From the experimental observations and the detailed analysis of this study, the current methodology can be utilized to further expand the design space of current heterogeneous nanostructured materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Co-Based superalloy morphology evolution: A phase field study based on experimental thermodynamic and kinetic data

Cobalt-based superalloys with two phase $\gamma$/$\gamma '$ microstructures offer great promise as candidates for next-generation high-temperature alloys for applications, such as turbine blades. It is essential to understand the thermodynamic and kinetic factors that influence the microstructural evolution of these alloys in order to optimize the alloy compositions and processing steps with a goal to improve their coarsening, creep and rafting behavior. We are using a continuum phase field approach to study the diffusion process and to predict the equilibrium shapes of Co-Al-W $\gamma '$ precipitates. In order to obtain quantitatively predictive capabilities, we extract chemical free energies for the $\gamma$/$\gamma '$ phases based on CALculation of PHAse Diagrams (CALPHAD) thermodynamic data and diffusion mobilities for Co alloys based on CALPHAD kinetic data. We also use experimental or first-principles data for other quantities, such as misfit strain and interface information, for the parameterization of our model. A particular focus of our study is to understand how different energy balances, misfit strain and kinetics affect the coarsening and rafting behavior of $\gamma '$ precipitates, and the sensitivity of the final precipitate shape to materials parameters. Here, we find that the equilibrium shape of the precipitate results from a delicate competition between chemical, interfacial, and elastic energies, and it is very sensitive to changes in model parameters. Here, we examine how modeling input parameters affect the equilibrium shape of precipitates and relate these parameters to experimentally available values.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Slip localization behavior at triple junctions in nickel-base superalloys

Incipient slip localization in the vicinity of hundreds of grain boundary triple junctions (TJs) in a lightly deformed nickel-base superalloy IN718 is studied using a combination of three-dimensional (3D) crystal plasticity finite element (CPFE) modeling, high resolution digital image correlation (HR-DIC) and 3D electron back-scatter diffraction tomography (3D EBSD). A 3D reconstruction method enables identification of thousands of TJs and correspondence of any observed slip bands with their originating TJ lines below the specimen surface. Here, we present a large-scale CPFE model of the experimental 3D microstructure composed of high-fidelity representation of the TJ lines and the boundaries and interiors of the parent grains and use it to calculate the local micromechanical response and slip activity of all TJs at the onset of macroscopic yielding. Statistical analysis of the calculated quantities reveal TJs develop larger stress concentration and grain-average re-orientation than grain interiors and grain boundaries, however no substantial differences in cumulative slip were found among these microstructural regions. We find that TJs with observed slip bands generate lower grain-average re-orientation, fewer active slip systems, and more localized slip on a single system than those without. The distinctions in the reorientation and slip activity are stronger in TJs that experience more intense slip.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Mechanical properties of an Al 10 Nb 20 Ta 15 Ti 30 V 5 Zr 20 A2/B2 refractory superalloy and its constituent phases

Refractory superalloys (RSAs) are a new class of high-temperature structural materials consisting of a nanometer-sized mixture of two coherent A2 (disordered BCC) and B2 (ordered) phases. While these RSAs typically exhibit superior mechanical properties at elevated temperatures, they suffer from limited plasticity at lower temperatures, often attributed to the continuous ordered B2 matrix in these two-phase alloys. To knowledgably control the microstructure and mechanical properties of these alloys, the properties of the constitutive phases in RSAs should be known. Currently this information is absent. Here, in the present work, the microstructure and mechanical properties (at 20–1200 °C) of a candidate Al 0.5 NbTa 0.8 Ti 1.5 V 0.2 Zr RSA and two single-phase alloys, which compositions correspond to the compositions of the A2 and B2 phases in the selected RSA, are reported. Interestingly, and quite unexpectedly, the intrinsic mechanical behavior of the constituent A2 and B2 phases, deciphered for the first time in the present study, revealed that they are softer and substantially more ductile than the parent two-phase RSA. Furthermore, the ordered B2 phase exhibits a deformation twinning mechanism leading to twinning induced plasticity (TWIP) coupled with a low APB energy and activity of 1/2<111> dislocations. These mechanisms are thought to be responsible for the high plasticity of the ordered B2 phase. The results presented here question the current assumption that the ordered B2 phase in these RSAs has limited plasticity and strongly indicate that the nature of the B2/A2 interface boundaries and coherency strengthening play an important role in controlling the mechanical properties of the two-phase RSA.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Multi-scale microstructural investigation of a laser 3D printed Ni-based superalloy

The heterogeneous microstructure of a laser 3D printed Ni-based superalloy was examined at multiple length scales. The sub-millimeter-sized columnar crystal grains are composed of micron-sized cellular colonies. The crystal grains grow in epitaxy with the substrate under the large temperature gradient and high cooling rate. The cell boundaries, decorated with γ/γ' eutectics, μ-phase precipitates and high density of dislocations, show enrichment of γ' forming elements and low-angle misorientations. Dislocations trapped in the intra-cellular regions are characterized as statistically stored dislocations with no detectable contribution to lattice curvature, and are the results of the interaction between dislocations and γ' precipitates.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Deep learning approaches to semantic segmentation of fatigue cracking within cyclically loaded nickel superalloy

Improvements to synchrotron-based micro-computed tomography scanning capabilities have gifted researchers the ability to characterize 4D material thermomechanical responses more thoroughly than ever before. These advancements, however, have brought about new challenges in analyzing the resulting deluge of data. We report on a nickel-based superalloy specimen imaged 26 times in-situ during cyclic loading at Argonne National Laboratory Advanced Photon Source beamline 1ID, in order to monitor crack growth within the microstructure. Therefore, several deep learning approaches which utilize convolutional neural networks are implemented to segment crack features from reconstructed tomography scans. U-Net architecture implementations are found to be especially effective, achieving IoU = 0.995 +/- 0.004 and Matthews correlation coefficient scores of Φ = 0.826 +/- 0.085. These advancements broaden possibilities for scientists seeking to automate segmentation analyses of similar large datasets.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High Temperature Oxidation Behavior of Ni-based High Entropy Superalloys

A new class of polycrystalline gamma-prime strengthened superalloys with alloy compositions of (wt%) Ni-20Co-13Cr-6Fe-4Al-3W-2Mo-(4-x)Nb-(x)Ti (x = 0,1,2) were subjected to cyclic oxidation exposures in dry air at 800 °C for 3600 h. The alloys were borderline chromia/alumina formers, showing good oxidation resistance relative to commercially available materials of similar composition. While all alloys formed alumina scales initially, only the alloy with the lowest Ti/Nb ratio retained an alumina scale for the duration of the exposure. Formation of a continuous layer of rutile TiO 2 at the alumina/alloy interface is proposed to cause eventual alumina failure for the alloys containing Ti.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Creep anisotropy modeling and uncertainty quantification of an additively manufactured Ni-based superalloy

The advantages offered by additive manufacturing over traditional processes has driven a great deal of industrial and academic interest in recent years. However, the process is relatively new and requires additional investigation to become sufficiently mature for wide scale industrial adoption. Electron beam melting powder bed fusion is one technology that has shown promise for fabricating high temperature resistant materials such as nickel based superalloys. The resulting microstructures typically exhibit a strong fiber texture in the build direction giving rise to anisotropic time-dependent deformation behavior. In order to accelerate the qualification of these materials for industrial adoption accurate numerical models are needed for simulating their behavior. In this work a crystal plasticity model including non-Schmid effects is presented for capturing creep anisotropy observed in additively manufactured IN738LC. The model is calibrated via a probabilistic framework where model parameters are treated as random variables. An iterative sequential design strategy is utilized to efficiently identify the probability density of the unknown model parameters. As a case study the model is utilized to investigate the behavior of randomly oriented equiaxed grain clusters sometimes observed embedded in the additively manufactured columnar structure. A synthetic realization is simulated and uncertainty is propagated through to the full-field response. Results indicate that these features are the source of significant creep relaxation and strain accumulation which partially explains observed grain boundary decohesion at these locations.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Characterization of γ′/γ″ compact and sandwich type precipitates during long-term high-temperature exposure in Ni-based superalloys

Here, the formation of γ′/γ″ co-precipitates is investigated in Ni-based superalloys with a varying Ti/Al ratio and Ta content and their stability is studied using long-term high-temperature exposure. Transmission electron microscopy and atom probe tomography analyses demonstrate that both higher Ti/Al ratios and increased Ta promote γ″ phase formation, leading to sandwich and compact structures. The compact co-precipitation significantly reduces γ′ precipitate coarsening during 10,000 h exposure at 700°C by restricting elemental diffusion, particularly of aluminum, from the γ matrix to the γ′ phase. For the alloy without a compact structure, and only γʹ precipitates, at the beginning of the exposure, the coarsening rate over 10,000 h was 3.5 times faster than for the alloy with compact γʹ/γʺ precipitates. Evidence of destabilization of the compact morphology was found to occur between 5,000 and 10,000 h exposure and originated from the extensive formation and growth of δ platelets that extended throughout the grains. Thus, the outer layer of the compact, which consists of γʺ, was subjected to the γ″ to δ phase transformation.

gamma double prime↗
DOE OSTI2025

Microstructural evolution and hardness changes in ion irradiated nickel-based Haynes 282 superalloy

This study investigated the crucial aspects of thermal and irradiation stability in precipitation hardened Haynes 282 Ni-based superalloy. The Haynes 282 Ni-based alloy was irradiated by 8 MeV Ni 3+ ions to assess its resistance to phase instabilities and mechanical property alterations. The mid-range doses (at a depth of ∼1 µm) were 1 and 10 displacements per atom (dpa) at temperatures of 600°C and 750°C. Nanoindentation tests provided insights into bulk equivalent hardness of the irradiated and pristine regions, while scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS) were used to examine the microstructural evolution of irradiation-induced defects and γ′ -Ni 3 (Al, Ti) precipitates and defect structure under irradiation. These precipitates, with an average diameter of 29 nm and a number density of 5 x 10 21 /m 3 , acted as robust dispersion strengthening agents with high radiation point defect sink strength. Remarkably, irradiation did not significantly alter the size or number density of the γ′ precipitates, indicating exceptional thermal stability and radiation resistance of these precipitates at the examined conditions. Radiation-induced dislocation loops were observed at 600°C, albeit without a substantial impact on mechanical properties due to the dominance of γ′ precipitates on the overall alloy strength. The superior stability of γ′ precipitates observed in this study contrasts with several previous research findings on Ni-based alloys that reported poor precipitate stability. Plausible reasons for this difference are discussed. Moreover, this work explicitly outlines a physically grounded approach to ensure accurate microstructure-hardness correlations and clarifies the hardening model by addressing common misapplications of superposition in prior studies.

36 MATERIALS SCIENCE↗
DOE OSTI2021

On the effect of elemental partitioning to secondary phases after solution and aging heat treatments in a Co-Ni-based superalloy

Here, this paper presents the phase stability and elemental partitioning in a Co-40Ni-10Al-7.5W-10Cr-3Nb-0.06B-0.6C (at.%) superalloy (referred to as 3Nb) after a two-step heat treatment. The resulting microstructure consisted of γ, γ', MC carbides and µ-Co 7 W 6 phase decorating the regions near and at the grain boundaries. Nb preferentially partitioned to the γ'-phase and other elements such as Ni, Cr and W were responsible for the μ-phase formation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Elevated temperature nanoscratch of Inconel 617 Superalloy

Inconel 617 superalloy is a main candidate to be used for mechanical and tribo-components in high temperature helium-cooled reactors. Recent findings show that it grows a unique surface oxide, especially under high temperature helium with distinct wear, friction, and contact properties. Here, this study reports the elevated temperature nanoscratch behavior of Inconel 617 and further utilizes it to understand the effect of temperature on contact friction constituent contributors, adhesion and plowing at small scales. Inconel 617 is aged in high temperature helium, and consequently, the total kinetic friction coefficient of the alloy surface oxide is obtained in temperatures ranging from 25 °C to 400 °C. A finite element model is developed and validated based on the experimental results. The model is then utilized along with previously established techniques to determine the adhesion and plowing components of the friction coefficient. At small scale, the experimental results show that with increasing temperature the friction coefficient increases. It was inferred that this increase is mainly due to the increased contribution of plowing friction at high levels of deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Implications of carbon content for the processing, stability, and mechanical properties of cast and wrought Ni-based superalloy Nimonic 105

As the temperature and pressure requirements in land-based turbines for power generation increase, the shift towards more advanced alloys, e.g., Ni-based superalloys, requires improved understanding of their long-term stability and mechanical properties. Additionally, the larger size of the components also presents fabrication and cost-reduction problems. In this study, we investigated Nimonic 105 as a potential rotor material at two carbon content levels – the commonly used maximum of the alloy specification and a lower carbon content variant. Reducing the carbon content presented fabrication challenges, resulting in surface crack formation during hot working. Additionally, a lower M 6 C carbide fraction was present after fabrication/solutioning, leading to a significantly larger grain size. After the standard aging treatment, similar γ' populations formed in the two variants, however the M 6 C carbides in the high-carbon variant already started transforming to intergranular M 23 C 6 . Although we did not observe a noticeable effect on the tensile properties of the two variants, the lower carbon content alloy possessed a superior creep property – mainly due to the larger grain size as the microstructural stability was inferior. Further, upon prolonged thermal exposure, the M 6 C carbides in the low-carbon variant further decomposed to intergranular and intragranular σ and μ precipitates, as opposed to mainly M 23 C 6 as in the high-carbon variant.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Directed energy deposition of Haynes 282 nickel superalloy

Laser powder directed energy deposition was employed to fabricate Haynes® 282 Ni-based superalloy for high temperature creep testing. Material was heat treated using a single-step aging heat treatment of 800 °C for 4 h. Microstructural analysis was conducted in the as-deposited, solution-annealed, and age-hardened conditions. γ′ precipitates were absent in the as-deposited and annealed condition but formed during aging with an average size of 48.5 ± 12 nm. γ’ denuded zones ranging in thickness from 73 to 469 nm were observed adjacent to an effectively continuous grain boundary carbide film that covered 72.5% of the measured boundary length. The heat-treated material contained a high-volume fraction of TiC carbides ranging in size from 38 to 457 nm. Electron backscatter diffraction showed partial recrystallization, with 77-83% recrystallized area and a heterogeneous grain-size distribution. Creep testing at 750 °C at 300, 320, and 350 MPa revealed significantly inferior performance compared to wrought material, with higher strain rates, earlier tertiary onset, and shorter rupture lives. Fractography shows that failure was dominated by intergranular rupture. Post rupture microstructural analysis results suggest that the creep behavior was primarily governed by the non-equilibrium interface network rather than the bulk γ/γ’ matrix. In conclusion, the findings indicate that achieving wrought-like creep performance necessitates substantial improvements in the additive process, specifically focusing on enhanced homogenization, full recrystallization, and precise control over the morphology and distribution of carbides.

36 - MATERIALS SCIENCE↗