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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

The Elevated-Temperature Cyclic Properties of Powder Metallurgy-Hot Isostatic Pressed 316H and 316L Stainless Steel

Section III, Division 5 of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code covers construction rules for elevated-temperature nuclear components. Microreactor developers have expressed a need for advanced manufacturing processes to fabricate microreactor components to reduce manufacturing costs. Components fabricated using manufacturing processes other than conventional techniques are not currently qualified in Section III, Division 5. An expeditious approach to qualifying an advanced manufacturing process for alloys whose wrought-product form is already qualified in Division 5 is to demonstrate the resultant properties from the advanced manufacturing process are equivalent or superior to the wrought-product form. Powder metallurgy-hot isostatic pressing (PM-HIP) is a mature technology that offers many advantages that are attractive to the microreactor industry. Preliminary data show that the elevated-temperature creep-fatigue properties of PM-HIP 316H stainless steel (SS) are reduced compared to the Wrought 316H SS, which is qualified in Section III, Division 5. Work is ongoing to identify the mechanisms responsible for the reduced creep-fatigue properties and to establish acceptance criteria to confirm the adequacy of the component for service.

316H stainless steel↗
DOE OSTI2020

In situ synchrotron X-ray tomography of 304 stainless steels undergoing chlorine-induced stress corrosion cracking

To understand the mechanisms behind chlorine-induced stress corrosion cracking (CISCC) in 304 stainless steel, synchrotron high energy x-rays were used to perform in-situ x-ray microtomography on a pre-cracked sample under load in a corrosive simulated marine environment. The tomography scans showed the crack morphology evolving into a branching crack around the surface of the sample. Finite element analysis and stress intensity analysis are conducted to explain the observed crack branching.

304 Stainless Steel↗
NASA NTRSDate not supplied

Effect of Heat Treatments on the Tensile Properties of Additively Manufactured 15-5 Ph Stainless Steel

This study investigated the effect of post-manufacture heat treatments on the microstructure and mechanical properties of 15-5 PH stainless steel (SS) fabricated by laser powder-directed energy deposition (LP-DED). Various heat treatment procedures (CA-H900 and CA-H1150) were conducted to evaluate their effects on the tensile behavior of LP-DED 15-5 PH SS. Scanning electron microscopy was used to characterize the microstructural features and the fracture surfaces. Tensile tests were performed to evaluate the mechanical properties at cryogenic and room temperatures. Reduction in area of CA-H1150 treated specimens after tensile tests was significantly higher than CA-H900 ones, while the ultimate tensile and yield strengths of CA-H900 specimens were higher compared to the CA-H1150 ones. The mechanical behavior of the LP-DED 15-5 PH SS in various heat treatment conditions is discussed based on their microstructures and fracture surfaces.

Laser powder directed energy deposition (LP-DED)↗
DOE OSTI2022

On the thermal coarsening and transformation of nanoscale oxide inclusions in 316L stainless steel manufactured by laser powder bed fusion and its influence on impact toughness

The thermal evolution of nanoscale oxide inclusions in 316L stainless steel (SS) manufactured by laser powder bed fusion additive manufacturing (AM) was explored. The size, chemical composition, morphology, and distribution of the oxides were characterized as the function of heat treatment conditions. The study revealed the mechanistic driving force of the rapid oxide coarsening during recrystallization. Ostwald ripening governs oxide coarsening. The active grain boundary-oxide interaction at the early stage of recrystallization accelerated oxide coarsening via enhanced solute diffusion along grain boundaries. Pipe diffusion along dislocation cellular boundaries has a negligible contribution to oxide coarsening. At high temperatures (T> 1065 °C), although lattice diffusion primarily controlled the oxide growth, the contribution from the grain-boundary diffusion was necessary. The transformation from MnSiO 3 to CrMn 2 O 4 took place in the un-recrystallized grains but was not observed when recrystallization started. The interaction of grain boundary and oxides during recrystallization resulted in a high fraction of oxides accumulated at grain boundaries. While oxide coarsening does not significantly alter the toughness value, grain-boundary oxides promote microvoid formation and intergranular fracture under Charpy impact in the recrystallized AM 316L SS.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Accelerated creep profiling: a high-throughput thermal- and stress-gradient approach applied to additive and wrought stainless steel

Here, this study investigates logarithmic creep behavior at temperatures near room temperature in wrought and additively manufactured (AM) 316 L austenitic stainless steel. A novel high-throughput (HiTp) methodology employed thermal gradients to obtain stress- and temperature-dependence of creep behavior. The findings, based on 104 two-week creep tests, reveal significant differences in creep response between wrought and AM materials. Compared to the wrought material, the AM material exhibited a higher activation energy and a lower activation volume. These differences were attributed to the materials’ distinct microstructural features, e.g., dislocation cell structures and precipitate distributions, which alter the susceptibility to dislocation glide creep, particularly at stresses below the yield stress. The HiTp methodology provides both an accelerated determination of low-temperature creep mechanisms, offering critical data for the design and optimization of alloys in near-ambient, high stress applications.

316 L Stainless steel↗
DOE OSTI2021

In situ high-energy X-ray study of deformation mechanisms in additively manufactured 316L stainless steel

A key structural material planned to be used in the core of the Transformational Challenge Reactor is the additively manufactured 316L stainless steel (AM 316L SS). While the deformation of conventionally-manufactured 316 SS have been extensively studied, the deformation mechanism of AM 316L SS is less known. Here the room-temperature tensile behavior of AM 316L SS was studied in situ using high-energy X-ray diffraction and X-ray tomography. Diffraction yielded the lattice strains and the dislocation densi-ties of the AM 316L SS, which were compared to those of a conventionally processed 316H SS. It was found that while the conventional 316H SS had three distinct deformation stages, namely stage II ather-mal hardening, stage III dynamic recovery, and stage IV, the AM 316L experienced only the stages III and IV after an initial transitional period. The plastic instability stresses (PIS), i.e. the true ultimate tensile strength, were nearly the same in both materials. The AM 316L had very low dislocation barrier strength throughout the plastic deformation, which, in combination with the invariant PIS, explained its high dis-location storage capability and the attractive combination of strength and ductility. Tomography revealed morphological changes of the built-in pores in the AM 316L during deformation and fracture, and it was concluded that large pores close to the surface might have significant roles in the necking stage.

316 stainless steel↗
DOE OSTI2024

Corrosion Testing Of Additively Manufactured Stainless Steel 316H In Molten Salt Environments

The development of a new ASTM standard for evaluating the corrosion resistance of additive manufactured (AM) stainless steel (SS) 316H in chloride molten salts is critical for the use of these materials in extreme environments such as molten salt reactors (MSRs). This report pertains to a work package of the Advaned Materials and Manufacturing Technologies (AMMT) developing a systematic methodology to link changes in AM fabrication parameters, namely surface finishing, porosity, microstructure, and chemical heterogeneity, to corrosion performance in NaCl-MgCl2 salt, a proposed secondary coolant for MSRs. During Fiscal Year 2024, Idaho National Laboratory investigators in the AMMT program, utilized SS316H bars, fabricated with laser bed powder fusion at Los Alamos National Laboratory, to establish and optimize the workflow for evaluating these process-to-performance relationships. Standard practices for specimen preparation were established using these specimens, with particular focus on descaling and sectioning methods that align with ASTM guidelines. A comprehensive experimental design for static corrosion testing was developed, with pre- and post-exposure analysis utilizing optical microscopy and scanning electron microscopy. So far standard descaling techniques were optimized, one static corrosion test was conducted on the LANL AM SS316H specimens, and pre- and post-corrosion practices were established. In addition, the work package yielded a review paper on corrosion testing gaps for AM materials in nuclear applications and submitted a proposal for a rapid-turnaround experiment to the Nuclear Science User Facilities Program to investigate the combined effects of proton irradiation and corrosion on AM SS316H. This work package establishes a foundation for evaluating processing-to-performance relationships for AM SS316H in harsh conditions, contributing to the safe and efficient design of components for next-generation nuclear reactors. The creation of a standardized methodology and the generation of relevant publications and future research pathways represent significant strides towards integrating AM materials into critical applications where corrosion resistance is paramount.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Deformation and Fracture Behavior of Additively Manufactured 316L Stainless Steel

Tensile deformation and fracture behavior of an additively manufactured (AM) 316L stainless steel (SS) in the as-built, stress-relieved, and solution-annealed conditions was investigated using in situ tensile testing in a scanning electron microscope with an electron back scattering diffraction (SEM–EBSD) detector. Analyses were performed to discuss the characteristic deformation and fracture process of the fine-grained AM 316L SS with and without relaxation heat treatment. The as-built 316L showed the highest strength, and both post-build heat treatments lowered the strength of the alloy. Regardless of the post-build processing, the AM 316L SS showed overall higher strength but slightly lower ductility when compared to the wrought (WT) 316L SS. Analysis of EBSD data indicated that the characteristic microstructural features from AM, such as the complex and fine grain morphology, dislocation network, pores, and silicon-rich oxides, evolved and exerted various roles during the tensile deformation and fracture processes. Further, it was obvious that the interaction of dislocation slips with oxide particles and cavities (or pores) resulted in an accelerated cracking in AM 316L SS. Overall, however, their influence on mechanical behavior was limited, as the genuinely high ductility of 316L SS could help avoid any premature or brittle fracture.

36 MATERIALS SCIENCE↗
DOE OSTI2022

3D In-situ Stop Action Study of Recrystallization in Additively Manufactured 316L Stainless Steel: Reconstruction Optimization and Observations

A volume of an additively manufactured 316L stainless steel sample has been tracked during its recrystallization using near-and far-field High Energy Diffraction Microscopy (HEDM) and absorption tomography at Advanced Photon Source beamline 1-ID. A nearfield compatible in situ furnace allows monitoring of Bragg diffraction signals as they evolve out of a weak and diffuse background while the sample temperature is approximate to 1250 degrees C. The sample is rapidly cooled to room temperature after observation of significant signal evolution and ti similar to 0.035 mm(3) is mapped by the near-field method. Four cycles of heat treatment follow the structure from a state of small, isolated grains through impingement of domains to near completion of recyrstallization. Here, the experiment and reconstructions are described, and recrystallized fractions, twin domains, and distributions of grain boundary types are discussed.

Liu, He↗
NASA NTRS1972

Materials data handbook: Stainless steel alloy A-286

A summary of the materials property information for stainless steel alloy A-286 is presented. The scope of the information includes physical and mechanical properties at cryogenic, ambient, and elevated temperatures. Information on material procurement, metallurgy of the alloy, corrosion, environmental effects, fabrication, and bonding is developed.

Muraca, R. F.↗
NASA NTRS1978

Automatic welding of stainless steel tubing

The use of automatic welding for making girth welds in stainless steel tubing was investigated as well as the reduction in fabrication costs resulting from the elimination of radiographic inspection. Test methodology, materials, and techniques are discussed, and data sheets for individual tests are included. Process variables studied include welding amperes, revolutions per minute, and shielding gas flow. Strip chart recordings, as a definitive method of insuring weld quality, are studied. Test results, determined by both radiographic and visual inspection, are presented and indicate that once optimum welding procedures for specific sizes of tubing are established, and the welding machine operations are certified, then the automatic tube welding process produces good quality welds repeatedly, with a high degree of reliability. Revised specifications for welding tubing using the automatic process and weld visual inspection requirements at the Kennedy Space Center are enumerated.

Clautice, W. E.↗
NASA NTRS1986

Thermal conductance of pressed aluminum and stainless steel contacts at liquid helium temperatures

The thermal conductance of aluminum and stainless steel 304 sample pairs with surface finishes ranging from 0.1 to 1.6 microns rms roughness was investigated over a temperature range from 1.6 to 6.0 k. The thermal conductance follows a simple power law function of temperature, with the exponent ranging from 0.5 to 2.25, increases asymptotically with increasing applied force, and exhibits an anomaly for surface finishes in the 0.4 micron region.

Salerno, L. J.↗
NASA NTRS1988

Photodesorption from stainless steels

The photodesorption by low-energy photons from three types of stainless steels is examined. For all these systems both CO and CO2 were observed to photodesorb with high yields: about 0.001 molecules/photon for CO2 and about 0.0001 molecules/photon for CO at 250 nm. The observed threshold energies were found to be the same for all systems at E0 = 2.92 eV for CO2 and E0 = 2.92-3.10 eV for CO.

Mesarwi, A.↗