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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Impact of Plate Thickness and Joint Geometry on Residual Stresses in 347H Stainless Steel Welds

Weldments of 347H stainless steel are potentially susceptible to stress relaxation cracking at elevated service temperatures. Mitigation of stress relaxation cracking susceptibility within a multipass weld requires a good understanding of welding practices and manufacturing techniques to control high tensile residual stresses. Here in this work, the dependence of residual stress distribution in 347H stainless steel on base plate thickness, joint geometry design, and preheating condition was systematically investigated by using three-dimensional finite element models. The finite element models were validated through good agreement between neutron diffraction measurements and calculated elastic strains. The single-V-groove welds with and without a preheating step all produced similar peak von Mises residual stresses, above 450 MPa, within both the fusion zone and heat-affected zone (HAZ). In plates thicker than 0.5 in. (12.7 mm), high tensile residual stress could be observed in a relatively large area, from the middle of the plate thickness to underneath the top surface. A double-V groove shifted the high tensile stress area to the middle thickness of the weld. A single-J-groove weld was able to confine the residual stress to a very small region near the middle thickness within the fusion zone and suppressed the von Mises residual stress within the HAZ to below 400 MPa.

14 SOLAR ENERGY↗
DOE OSTI2024

Cast Alumina-Forming Austenitic Stainless Steels for High Temperature Heat Treatment Furnace Rolls

Alloy developers worldwide have struggled to create creep-resistant alumina-forming, iron-based austenitic stainless steels for use as high-temperature structural alloys, but with limited success in balancing alloy cost, oxidation, and creep resistance. Here, this article describes the research and development of a novel cast alumina-forming austenitic stainless steel. This work won the prestigious Engineering Materials Achievement Award presented at IMAT 2023 in Detroit.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Microstructure and Mechanical Properties of Intercritically Treated Grade 91 Steel

Premature creep failures at the intercritical heat affected zone (ICHAZ) of creep-resistant steel weldments have been frequently reported. However, the creep degradation mechanism of different microstructure constituents in ICHAZ is complicated and needs further clarification. In this work, Grade 91 steel was intercritically heat-treated at a temperature (860 °C) between the critical temperatures AC1 and AC3, and a correlation between microstructure and mechanical properties of the heat-treated specimen was built. The effects of austenitization and tempering resulting from the intercritical treatment (IT) differentiated the local strain energies between the two microstructure constituents: newly transformed martensite (NTM) and over-tempered martensite (OTM). The formation of NTM grains led to a hardness increase from 247 HV0.5 in the base metal to 332 HV0.5 in the IT specimen. The ultimate tensile strength (UTS) increased from 739 MPa in the base metal to 1054 MPa in the IT specimen. Extensive growth of the OTM grains and rapid recovery of NTM grains took place simultaneously in the IT specimen during a typical tempering at 760 °C. These microstructure degradations led to a lowered hardness of 178 HV0.5, a reduced UTS of 596 MPa, and a poor creep resistance with a minimum creep strain rate of 0.49 %/h at 650 °C in an IT + tempering (ITT) specimen.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Synthesis of Nano-Oxide Precipitates by Implantation of Ti, Y and O Ions in Fe-10%Cr: Towards an Understanding of Precipitation in Oxide Dispersion-Strengthened (ODS) Steels

The properties of oxide dispersion-strengthened steels are highly dependent on the nature and size distribution of their constituting nano-oxide precipitates. A fine control of the processes of synthesis would enable the optimization of pertinent properties for use in various energy systems. This control, however, requires knowledge of the precise mechanisms of nucleation and growth of the nanoprecipitates, which are still a matter of debate. In the present study, nano-oxide precipitates were produced via the implantation of Y, Ti, and O ions in two different sequential orders in an Fe-10%Cr matrix that was subsequently thermally annealed. The results show that the oxides that precipitate are not necessarily favoured thermodynamically, but rather result from complex kinetics aspects related to the interaction between the implanted elements and induced defects. When Y is implanted first, the formation of nanoprecipitates with characteristics similar to those in conventionally produced ODS steels, especially with a core/shell structure, is evidenced. In contrast, when implantation starts with Ti, the precipitation of yttria during subsequent high-temperature annealing is totally suppressed, and corundum Cr 2 O 3 precipitates instead. Moreover, the systematic involvement of {110} matrix planes in orientation relationships with the precipitates, independently of the precipitate nature, suggests matrix restriction effects on the early stages of precipitation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Investigation of Microstructures and Tensile Properties of 316L Stainless Steel Fabricated via Laser Powder Bed Fusion

In this study, a thorough investigation of the microstructures and tensile properties of 316L stainless steel fabricated via laser powder bed fusion (L-PBF) was done. 316L stainless steel specimens with two different thicknesses of 1.5 mm and 4.0 mm fabricated under similar conditions were utilized. Microstructural characterization was performed using optical microscopy (OM) and scanning electron microscopy (SEM) equipped with electron backscatter diffraction (EBSD). Melt pools and cellular structures were observed using OM, whereas EBSD was utilized to obtain the grain size, grain boundary characteristics, and crystallographic texture. The 1.5 mm thick sample demonstrated a yield strength (YS) of 538.42 MPa, ultimate tensile strength (UTS) of 606.47 MPa, and elongation to failure of 69.88%, whereas the 4.0 mm thick sample had a YS of 551.21 MPa, UTS of 619.58 MPa, and elongation to failure of 73.66%. These results demonstrated a slight decrease in mechanical properties with decreasing thickness, with a 2.4% reduction in YS, 2.1% reduction in UTS, and 5.8% reduction in elongation to failure. In addition to other microstructural features, the cellular structures were observed to be the major contributors to the high mechanical properties. Using the inverse pole figure (IPF) maps, both thicknesses depicted a crystallographic texture of {001} <101> in their as-built state. However, when subjected to tensile loads, texture transitions to {111} <001> and {111} <011> were observed for the 1.5 mm and 4.0 mm samples, respectively. Additionally, EBSD analysis revealed the pre-existence of high-density dislocation networks and a high fraction of low-angle grain boundaries. Interestingly, twinning was observed, suggesting that the plastic deformation occurred through dislocation gliding and deformation twinning.

316L stainless steel↗
DOE OSTI2022

Benchmarking a 9Cr-2WVTa Reduced Activation Ferritic Martensitic Steel Fabricated via Additive Manufacturing

Reduced activation ferritic (RAF) martensitic steels are promising candidates for the first wall of fusion reactors. However, current manufacturing capabilities call for these components to be made by welding wrought plates. This limits design freedom and necessitates the use of post-weld heat treatments (PWHT) in accordance with the boiler and pressure vessel code. Additive manufacturing (AM) can offer a unique solution to solve this challenge by leveraging the layer-wise deposition strategy to come up with temper bead deposition techniques to eliminate post-processing heat treatments (PPHT). However, it is necessary to benchmark the properties of RAF steels fabricated by AM with their wrought counterparts to identify the process-structure-property correlation, which is the goal of this study. The study demonstrates that while tensile properties at room temperature and high temperatures are satisfactory, the as fabricated and samples after PPHT have significant heterogeneity in tensile elongation. This has been attributed to the presence of discontinuities in the build. The as-fabricated samples have an average tensile strength of 1190 + 12 MPa and an average elongation of 15 + 5% at room temperature and 658 ± 20 MPa ultimate tensile strength (UTS) and 14 ± 7% at 600 °C. After the post-weld heat treatment, mechanical properties decrease to around 600–650 MPa and an elongation between 20–25% at room temperature to 300 MPa UTS and 25–28% elongation at 600 °C. The characterization of microstructures at various length scales demonstrates that the as-fabricated structure has a significant fraction of delta ferrite in a lath martensitic matrix. No precipitates could be identified in the as-fabricated structure. PPHT led to a decrease in the area fraction of delta ferrite and precipitation of M 23 C 6 and MX. Detailed characterization clearly demonstrates that the lack of precipitates in the as-fabricated structure could be due to the slow tempering response of the alloy. Finally, the needs to develop new alloys to achieve the objectives stated above are articulated.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Evaluation of Tungsten—Steel Solid-State Bonding: Options and the Role of CALPHAD to Screen Diffusion Bonding Interlayers

Critical aspects of innovative design in engineering disciplines like infrastructure, transportation, and medical applications require the joining of dissimilar materials. This study investigates the literature on solid-state bonding techniques, with a particular focus on diffusion bonding, as an effective method for establishing engineering bonds. Welding and brazing, while widely used, may pose challenges when joining materials with large differences in melting temperature and can lead to mechanical property degradation. In contrast, diffusion bonding offers a lower temperature process that relies on solid-state interactions to develop bond strength. The joining of tungsten and steel, especially for fusion reactors, presents a unique challenge due to the significant disparity in melting temperatures and the propensity to form brittle intermetallics. Here, diffusion characteristics of tungsten–steel interfaces are examined and the influence of bonding parameters on mechanical properties are investigated. Additionally, CALPHAD modeling is employed to explore joining parameters, thermal stability, and diffusion kinetics. The insights from this research can be extended to join numerous dissimilar materials for specific applications such as aerospace, automobile industry, power plants, etc., enabling advanced and robust design with high efficiency.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Stable, Ductile and Strong Ultrafine HT-9 Steels via Large Strain Machining

Beyond the current commercial materials, refining the grain size is among the proposed strategies to manufacture resilient materials for industrial applications demanding high resistance to severe environments. Here, large strain machining (LSM) was used to manufacture nanostructured HT-9 steel with enhanced thermal stability, mechanical properties, and ductility. Nanocrystalline HT-9 steels with different aspect rations are achieved. In-situ transmission electron microscopy annealing experiments demonstrated that the nanocrystalline grains have excellent thermal stability up to 700 °C with no additional elemental segregation on the grain boundaries other than the initial carbides, attributing the thermal stability of the LSM materials to the low dislocation densities and strains in the final microstructure. Nano-indentation and micro-tensile testing performed on the LSM material pre- and post-annealing demonstrated the possibility of tuning the material’s strength and ductility. The results expound on the possibility of manufacturing controlled nanocrystalline materials via a scalable and cost-effective method, albeit with additional fundamental understanding of the resultant morphology dependence on the LSM conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Through-Thickness Microstructure Characterization in a Centrifugally Cast Austenitic Stainless Steel Nuclear Reactor Primary Loop Pipe Using Time-of-Flight Neutron Diffraction

The US code of Federal Regulations mandates regular inspection of centrifugally cast austenitic stainless steel pipe, commonly used in primary cooling loops in light-water nuclear power plants. These pipes typically have a wall thickness of ~8 cm. Unfortunately, inspection using conventional ultrasonic techniques is not reliable as the microstructure strongly attenuates ultrasonic waves. Work is ongoing to simulate the behavior of acoustic waves in this microstructure and ultimately develop an acoustic inspection method for reactor inspections. In order to account for elastic anisotropy in the material, the texture in the steel was measured as a function of radial distance though the pipe wall. Experiments were conducted on two 10 × 12.7 × 80 mm radial sections of a cast pipe using neutron diffraction scans of 2 mm slices using the HIPPO time-of-flight neutron diffractometer at the Los Alamos Neutron Science Center (LANSCE, Los Alamos, NM, USA). Strong textures dominated by a small number of austenite grains with their (100) direction aligned in the radial direction of the pipe were observed. ODF analysis indicated that up to 70% of the probed volume was occupied by just three single-grain orientations, consistent with grain sizes of almost 1 cm. Texture and phase fraction of both ferrite and austenite phases were measured along the length of the samples. These results will inform the development of a more robust diagnostic tool for regular inspection of this material.

42 ENGINEERING↗
NASA NTRS1928

Welding of high chromium steels

A brief description is given of different groups of high chromium steels (rustless iron and stainless steels) according to their composition and more generally accepted names. The welding procedure for a given group will be much the same regardless of the slight variations in chemical composition which may exist within a certain group. Information is given for the tensile properties (yield point and ultimate strength) of metal sheets and welds before and after annealing on coupons one and one-half inches wide. Since welds in rustless iron containing 16 to 18 percent chromium and 7 to 12 percent nickel show the best combination of strength and ductility in the 'as welded' or annealed condition, it is considered the best alloy to use for welded construction.

IRON - STAINLESS↗
NASA NTRS1952

Effects of Cyclic Loading on Mechanical Behavior of 24S-T4 and 75S-T6 Aluminum Alloys and SAE 4130 Steel

An investigation was conducted to determine the effects of cyclic loading on the mechanical behavior of 24S-T4 and 75S-T6 aluminum alloys and SAE 4130 steel. Specimens of the three materials were subjected to various numbers of prior fatigue cycles both below and above the fatigue limits. Special slow-bend tests were employed to show the effects of prior cycles of fatigue stressing on the transition temperature to brittle fracture for SAE 4130 steel and on the energy-absorption capacity of the aluminum alloys. Micrographic studies were made to observe and measure crack formation and propagation and additional special tests were conducted to supplement the results of the slow-bend tests. These included Charpy impact tests, mirohardness surveys, tension tests, and fretting-corrosion studies.

STEELS↗
NASA NTRS1990

A porous stainless steel membrane system for extraterrestrial crop production

A system was developed in which nutrient flow to plant roots is controlled by a thin (0.98 or 1.18 mm) porous (0.2 or 0.5 microns) stainless steel sheet membrane. The flow of nutrient solution through the membrane is controlled by adjusting the relative negative pressure on the nutrient solution side of the membrane. Thus, the nutrient solution is contained by the membrane and cannot escape from the compartment even under microgravity conditions if the appropriate pressure gradient across the membrane is maintained. Plant roots grow directly on the top surface of the membrane and pull the nutrient solution through this membrane interface. The volume of nutrient solution required by this system for plant growth is relatively small, since the plenum, which contains the nutrient solution in contact with the membrane, needs only to be of sufficient size to provide for uniform flow to all parts of the membrane. Solution not passing through the membrane to the root zone is recirculated through a reservoir where pH and nutrient levels are controlled. The size of the solution reservoir depends on the sophistication of the replenishment system. The roots on the surface of the membrane are covered with a polyethylene film (white on top, black on bottom) to maintain a high relative humidity and also limit light to prevent algal growth. Seeds are sown directly on the stainless steel membrane under the holes in the polyethylene film that allow a pathway for the shoots.

NASA Discipline Number 61-20↗
NASA NTRS2017

Cryogenic Thermal Emittance Measurements on Small-Diameter Stainless Steel Tubing

The Mid Infrared Instrument aboard the James Webb Space Telescoep includes a mechanical cryocooler which cools its detectors to their 6 K operating temperature. The refrigerant flows through several meters of approximately 2 mm diameter 304L stainless steel tubing, with some sections gold plated, and some not, which are exposed to their environment. An issue of water freezing onto the tube surfaces is mitigated by a running a warm gas through the lines to sublimate the water. To model the effect of this process on nearby instruments, an accurate measure of the tube emittance is needed. Previously we reported the abosprtance of the gold plated stainless steel tubing as a function of source temperature (i.e. its environment). In this work the thermal emittance of the uncoated tubing is measured as a function of its temperature between 100 and 300 K. This value leads to an accurate prediction of the minimum length of time required to thermally recycle the system. We report the technique and present the results.

cryogenic↗
NASA NTRS2017

Cryogenic Thermal Emittance Measurements on Small-Diameter Stainless Steel Tubing

The Mid Infrared Instrument aboard the James Webb Space Telescope includes a mechanical cryocooler which cools its detectors to their 6 K operating temperature. The refrigerant flows through several meters of 2 mm diameter 304L stainless steel tubing, with some sections gold plated, and some not, which are exposed to their environment. An issue of water freezing onto the tube surfaces is mitigated by running a warm gas through the lines to sublimate the frozen water. To model the effect of this process on nearby instruments, an accurate measure of the tube emittance is needed. Previously we reported the absorptance of the gold plated stainless steel tubing as a function of source temperature (i.e. its environment). In this work the thermal emittance of the uncoated tubing is measured as a function of its temperature between 100 and 280 K. These values lead to an accurate prediction of the minimum length of time required to thermally recycle the system. We report the technique and present the results.

stainless steel↗
DOE OSTI2020

Ab initio Study of the Mechanism for the Initiation of Localized Corrosion on Stainless Steel

Stainless steels are widely used as primary piping material in PWR’s because of their high corrosion resistance largely due to the formation of a passive film of metal oxides, such as chromium (e.g., Cr2O3). However, upon exposure to aggressive ions like chlorides (Cl-), stainless steel becomes susceptible to localized corrosion due to the breakdown of the passive film. It is therefore essential to gain fundamental insights into the mechanism of the passive film breakdown (depassivation) to develop a tailored design to minimize localized corrosion. This project investigates the initial stages of the depassivation of the Cr passive film using density functional theory (DFT), a quantum based computational method.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Detecting Thermally-Induced Spinodal Decomposition with Picosecond Ultrasonics in Cast Austenitic Stainless Steels

Destructive techniques to monitor nuclear reactor component health may not always be available during service, as they are time-consuming and often require pre-installed inspection coupons. Non-destructive evaluation (NDE) techniques can bridge this gap by rapidly identifying the state of mission-critical reactor components, via inference between NDE-measurable material properties and those of ultimate interest, such as ductility and toughness. Here, we demonstrate one such inference about the health of thermally aged cast austenitic stainless steels. Observations of surface acoustic wave peak (SAW) splitting correlate with spinodal decomposition-induced embrittlement as destructively measured by Charpy impact energy. Elastodynamic calculations and molecular dynamics simulations of the effects of spinodal decomposition on elastic moduli support that the new acoustic modes present are due to stiffening in the δ-ferrite domains. Finally, this discovery enables one to probe structure-property relationships in materials in a greatly accelerated manner, suggesting that similar inference methods can be used to determine material fitness-for-service, or to quickly uncover new structure-property relationships.

304-type stainless steel↗