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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.

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At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Microstructure evolution and mechanical performance of nickel based superalloy C1023 at elevated temperatures

Highlights: • Growth and strengthening mechanisms of carbide in superalloy C1023 were investigated. • Carbide dendrite primary arm grows selectively based on the vertex of blocky carbonitride. • Monolayer or multilayer carbide dendrite arm has certain crystal relationship with γ′ and γ. • Plastic deformation of γ hinders interior crack propagating from MC to matrix at 650 °C. • Oxidation of GBs significantly weakens the tensile strength of the superalloy at 850 °C. - Abstract: Microstructure evolution of polycrystalline nickel based superalloy C1023 casting was investigated by comparing as cast superalloy and heat treated superalloy in the paper. Influences of strengtheners and carbides on the tensile behaviors of heat treated superalloy at different temperatures (20 °C, 650 °C, and 850 °C) were studied. Resulting data from deep corrosion suggested that growth mode of scripted carbide included nucleation on the vertex of blocky carbonitride, expansion of dendrite arm in C-rich area, and enlargement of dendrite cap. Decomposition of MC carbide generated numerous octahedral M{sub 23}C{sub 6} carbide as well as nanoscale Cr-Mo-rich nuclei. Diffusion of Mo from γ to precipitates such as γ', MC, and M{sub 23}C{sub 6}, occurred during the heat treatment while irregular γ' (4 nm–500 nm) transformed into cuboidal particles. At 650 °C, no significant deterioration of tensile strength was found while plastic deformation ability of γ base was improved. Oxidation of grain boundaries (GBs) dominated the crack behavior of the superalloy at 850 °C.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Strengthening effects and thermal stability of the ultrafine grained microstructure of a nickel base superalloy at room and elevated temperatures

Highlights: • UFG Alloy 718-5 vol.%Y{sub 2}O{sub 3} alloy is fabricated from alloy machining chips. • The kind of oxide nanoparticles is identified in Nb-rich superalloys. • High thermal stable nanoparticles and UFG microstructure is achieved. • The GB strengthening effects at 25 °C and 650 °C of UFG alloy are calculated. - Abstract: An ultrafine grained (UFG) nickel base superalloy doped with 5 vol.%Y{sub 2}O{sub 3} nanoparticles, Alloy 718-5 vol.%Y{sub 2}O{sub 3}, was fabricated by a powder metallurgy route which combines high energy mechanical milling of Alloy 718 machining chips, spark plasma sintering, hot extrusion and heat treatment, and its microstructure and mechanical properties at room temperature and 650 °C were studied. The study showed that the Y{sub 2}O{sub 3} nanoparticles reacted with Al from the base alloy and transformed to Y{sub 4}Al{sub 2}O{sub 9} nanoparticles (average diameter: 12.5 nm) which were stable during heat treatment at 970 °C (0.78T{sub m}, where T{sub m} is the solidus temperature of the alloy in K). As a result of the high thermal stability of Y{sub 4}Al{sub 2}O{sub 9} nanoparticles and their effective pinning of the grain boundaries, the UFG microstructure (average grain size: 179 nm) of the alloy was stable during heat treatment. Grain boundary and nanoparticle strengthening rendered the heat treated Alloy 718-5 vol.%Y{sub 2}O{sub 3} alloy with a notable room temperature tensile yield strength of 1870 MPa. It was demonstrated that the grain boundary strengthening effect associated with the UFG microstructure was still significant at 650 °C, but clearly decreased from its level at room temperature. The grain boundary strengthening and nanoparticle strengthening effects which are likely to be independent of test temperature sustain a reasonably high tensile yield strength of 800 MPa at 650 °C, despite the absence of γ′ and γ″ precipitates in the UFG microstructure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Study on the creep deformation behavior and characterization of 9Cr-1Mo-V-Nb steel at elevated temperatures

Highlights: • The true creep deformation mechanism has been found by an evaluation of threshold stresses. • The analysed creep data suggest that the rate-controlling mechanism of creep is dislocation climb. • Coarsening of the M{sub 23}C{sub 6} carbides has been observed at 650 °C and 700 °C during creep. In this study, creep tests were conducted on a set of specimens made from the same tube of T91 steel at different temperatures (600 °C, 650 °C and 700 °C) with the applied stresses ranging from 30 MPa to 180 MPa and rupture times from 28.7 to 7957 h for understanding the creep mechanism. The stress dependence of minimum creep rates exhibits a power law with different exponents were found to be 14.3, 11 and 4.6 at 600 °C, 650 °C and 700 °C, respectively. Activation energy of creep was determined to be ~573 kJ/mol, which is ~53% higher than that of the lattice self-diffusion in α-iron. Based on the stress exponents, the modified Bird-Murkherjee-Dorn (BMD) equation was used to find the threshold stresses which has shown the strongly dependent on the test temperature. After incorporating the threshold stress, true activation energy of creep was found to be decreased ~271 kJ/mol, which is equivalent to that of lattice-self diffusion in α-iron. This subsequently led to evaluation of true stress exponent ~4. The results of creep data suggest that the rate-controlling mechanism of creep is dislocation climb for T91 steel. Microstructural observation of T91 steel is mainly consisting of lath martensite structure with fine MX carbonitrides and M{sub 23}C{sub 6} carbides were characterized using the scanning and transmission electron microscopes. The stress dependence of creep rupture life has shown that the operating mechanism of creep is similar. Furthermore, creep data was analysed for validity of the Monkman-Grant relationship and creep damage tolerance parameter. The qualitative microstructure of the crept samples show that less number of MX carbonitrides within grains is responsible for creep cavity formation and decreasing the rupture life. Thus, microstructural degradation is attributed to M{sub 23}C{sub 6} carbides coarsened and dislocation sub-structure boundaries are mainly responsible for creep damage. The fracture morphology of the samples has revealed with dimples is a typical transgranular ductile failure.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mechanisms of stored energy release in silicon carbide materials neutron-irradiated at elevated temperatures

Understanding the stored energy release behavior of SiC is crucial for the design of SiC-based fuel cladding for light water reactors because stored energy release affects response during accident conditions. Differential scanning calorimetry was used to evaluate the stored energy of monolithic SiC and SiC fiber–reinforced SiC matrix composite variants following neutron irradiation under light water reactor–relevant dose and temperature conditions. The tests were performed at heating rates of 0.5, 3, and 20 K/min up to 1,273 K. The onset temperature of the energy release roughly corresponded to the irradiation temperature, and energy release was delayed as the heating rate increased. The monolithic and composite specimens exhibited similar stored energy release behavior up to ~1,000 K, and above that temperature, the energy release depended more on material type. The energy release measured in this study is below the material-specific heat capacity at temperatures below ~1,000 K but exceeds it under certain material and annealing conditions at temperatures above ~1,000 K. The amount of irradiation-induced volumetric swelling of the specimens was an indication of the total stored energy. Based on this observation, the energy release behavior was described by a swelling recovery model.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Influences of elevated thermal decomposition of ammonia gas on indium nitride grown by sol–gel spin coating method

Highlights: • A study on indium nitride growth via sol-gel spin coating and nitridation. • Thermal decomposition effects of ammonia gas on films properties are investigated. • Chemical processes describing InN crystal growth are revealed. • Thermal etching effect and metallic indium are observed at increasing temperature. • New insights in synthesizing InN thin films with a simple and low cost method. - Abstract: Indium nitride (InN) thin films grown on aluminum nitride on p-type silicon (111) [AlN/p-Si(111)] substrates are prepared via sol–gel spin coating method followed by nitridation. The thermal decomposition effects of ammonia (NH{sub 3}) gas on the structural properties and surface morphologies of the deposited films are investigated. X-ray diffraction results reveal that the crystalline quality of InN degrades markedly as thermal decomposition of NH{sub 3} gas increases from 700 to 850 °C, at which indium oxide (In{sub 2}O{sub 3}) forms in the deposited films. The thermal etching effect and formation of indium droplet on the film are observed at 850 °C. These findings are consistent with those of elementary and cross-sectional analysis obtained through energy dispersive spectroscopy and field-emission scanning electron microscopy. The findings deduced that InN thin films with densely packed grains can be grown at NH{sub 3} decomposition temperature of 700 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Elevated temperature contact creep and friction of nickel-based superalloys using machine learning assisted finite element analysis

Nickel-based superalloys with superior thermochemical, mechanical, and tribological properties are highly utilized for critical components in several high temperature applications such as gas turbines and nuclear reactors. Inconel 617, in particular, is considered as one of the main candidate superalloys for tribo-components in very-high-temperature gas-cooled nuclear reactors. Recent findings indicate that this alloy grows unique surface oxide especially in a high-temperature helium environment with distinctive wear, friction, and contact properties. Here, this study investigates the high temperature contact area evolution and frictional behavior of Inconel 617 using finite element simulation and provides predictive models for the contact and friction performance at different normal loads, dwell times, and temperatures. High temperature helium-aged Inconel 617 top surface properties (up to 600 °C) are utilized along with a single asperity-based deformable elastic-plastic contact model under combined normal and tangential loading. Machine learning is used to assist the finite element results and to predict friction coefficient as well as contact area evolution. While a small difference is observed in the instantaneous friction coefficient (no dwell time) for all temperatures, friction coefficient increases considerably with dwell time. This shows that the effect of contact creep for longer dwell times significantly dominants the effect of high temperature variation in basic mechanical parameters such as modulus and yield strength. It is found that increasing temperature and dwell times lead to the friction coefficient increase, yet the dominance of dwell time effects decreases at higher temperatures and loads. While the analysis is presented for Inconel 617, the methodology is easy to be generalized and can be applied to other HT alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

In situ high-energy X-ray diffraction investigation of the micromechanical behavior of Fe-0.1C-10Mn-0/2Al steel at room and elevated temperatures

The micromechanical behavior of medium-Mn transformation-induced-plasticity (TRIP) steels with nominal chemical compositions of Fe-0.1C-10Mn (mass%) (0Al steel) and Fe-0.1C-10Mn-2Al (mass%) (2Al steel) fabricated by intercritical annealing 600 degrees C for 1 h and 650 degrees C for 1 h, respectively, was investigated using in situ high-energy X-ray diffraction (HE-XRD) with uniaxial tensile tests at 25 degrees C and 100 degrees C. We found that Liiders band propagation promoted lower volume fraction of austenite transformation to martensite in 0Al steel than 2Al steel at 25 degrees C while higher volume fraction of austenite transformation to martensite in 0Al steel than 2Al steel at 100 degrees C. Portevin-Le Chatelier (PLC) band propagation promoted higher volume fraction of austenite transformation to martensite in 0Al steel than 2Al steel during deformation at 25 degrees C and 100 degrees C. Moreover, the addition of Al obviously suppresses the formation of intermediate epsilon martensite during tensile deformation, thus the zigzag change in lattice strain of austenite was completely depressed in 2Al steel. Due to the controlled stability of metastable austenite, the 2Al steel demonstrated the best combination of ultimate tensile strength and total elongation at 25 degrees C.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Analytical models of the strength and ductility of CNT reinforced metal matrix nano composites under elevated temperatures

Carbon nanotubes (CNTs) can greatly enhance the strength of metal matrix composites while resulting in ductility loss. This strength-ductility tradeoff dilemma always confines the development of material design and real-life applications. Here in this work, a temperature dependent strengthening analytical model is proposed for CNT reinforced metal matrix composites which considers three common strengthening mechanisms: Orowan looping effect, thermal expansion mismatch effect, and load bearing effect. The proposed model can predict composite material strength with different volume fractions of CNTs and under different temperatures. Combining the strengthening model with the stress based modified Mohr-Coulomb (sMMC) ductile fracture model, a ductility analytical model is then derived. This ductility analytical model includes the influences of temperature, multi-axial stress loading conditions, as well as the aforementioned three strengthening mechanisms. A good agreement has been achieved between literature published experimental data and analytical predictions for both composite material strength and ductility loss. The proposed two analytical models can provide a straightforward way to study the strength-ductility relationship for CNT reinforced metal matrix composites over a wide range of temperatures and different stress states, and then provide guidance on new material design and processing.

36 MATERIALS SCIENCE↗
DOE OSTI2022

In situ study on heavy ion irradiation induced microstructure evolution in single crystal Cu with nanovoids at elevated temperature

Understanding the response of nanovoids to irradiation damage advances our capability to design radiation tolerant materials. Recent in situ studies reveal the shrinkage of hexagon-shaped nanovoids in (110) textured Cu. However, the evolution of voids with irregular geometries under irradiation is less well understood. Here, in situ Kr ion irradiation was performed at 100 °C on single-crystal Cu (112) that possesses nanovoids with high aspect ratio. In situ studies show these elongated voids fragment into smaller voids and shrink gradually with increasing dose. Phase field simulations confirm that fragmentation of the void is governed by the competing kinetics between atoms diffusing toward and away from the elongated nanovoid. In conclusion, cost irradiation analysis reveals the formation of high-density defect clusters.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

Corrosion analysis of Al-Ce-Ni and Al-Cu-Ce cast alloys in dilute boric acid at room and elevated temperatures

Two Al-Ce-Ni cast alloys, and an Al-Cu-Ce cast alloy, as candidate wet storage materials for spent nuclear fuels, were tested in 0.23 wt% H 3 BO 3 solution to assess the alloy corrosion resistance. Electrochemical and gravimetric corrosion data suggest that the three Al alloys are unlikely to undergo any severe corrosion in dilute H 3 BO 3 at or below 50 °C. Post-exposure characterization of the three Al alloys, including scanning and transmission electron microscopy and electron dispersive spectroscopy, revealed a corrosion product layer, mostly Al 2 O 3 , on the exposed surface and local penetration of oxygen into the alloy matrix. The degree of oxide layer growth and oxygen penetration is greater at 80 °C than the temperature at/below 50 °C. The Al-Cu-Ce alloy is considered less corrosion resistant than the other two alloys studied.

Al-Ce alloy↗
DOE OSTI2023

Behavior and properties of helium cavities in ductile-phase-toughened tungsten irradiated with He + ions at an elevated temperature

Ductile-phase toughened tungsten (DPT W) composites have demonstrated a great potential for plasma-facing components in fusion power systems. These materials can retain the outstanding thermomechanical properties of W while significantly enhancing the fracture toughness. The DPT W composite in this study consists of W particles (88 wt.%) embedded in a ductile NiFeW (12 wt.%) solution matrix. Irradiation of the composite was performed with 90 keV He + ions to 1.0 × 10 17 He + /cm 2 at 973 K. The He cavities formed in both W and NiFeW phases are examined using convergent-beam scanning transmission electron microscopy (CB-STEM) at an atomic-level resolution. Full-range depth profiles of the He cavity diameters and number densities are analyzed. The results show that the average cavity diameter in NiFeW is ~2.7 times that in W, while the number density is an order of magnitude lower. A quantitative analysis of the He density and pressure in the cavities is also achieved using STEM electron energy loss spectroscopy (STEM-EELS) mapping. The He atoms in the cavities in NiFeW are found to be under-pressurized, while those in similar-sized cavities in W are not detectable. Further, the He energy-loss shift exhibits a linear relationship with the He density in cavities in NiFeW, with the slope comparable to that for martensitic steel.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Interfacial engineering for stabilizing polymer electrolytes with 4V cathodes in lithium metal batteries at elevated temperature

Poly (ethylene oxide) (PEO) polymer electrolytes are promising candidates for next-generation rechargeable lithium batteries. However, the poor interfacial stability between 4 V cathodes and PEO electrolytes impedes their applications in 4 V lithium batteries with high energy density. Here, we demonstrate a facile and effective strategy to enhance the interfacial stability by the synergy of Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) coating on the cathode surface, and salt combination in the electrolyte, even with a cut-off voltage of 4.25–4.4 V vs. Li + /Li. Nano-LAGP coated Li|PEO|LiCoO 2 cell delivers stable cycling with a capacity retention of 81.9%/400 cycles and 84.7%/200 cycles at 60 °C when charged to 4.25 and 4.3 V in pure polyether electrolyte, respectively. Steady cycling is also demonstrated at room temperature and with LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) cathode. This work offers a viable and scalable approach to improve the stability between PEO electrolytes and 4 V cathodes and open up new possibilities for practical application of 4 V lithium metal batteries.

25 ENERGY STORAGE↗