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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

A New Alumina-Forming Ni-Co-Cr Base Alloy for Service in Gas Turbine Engine Combustors and Other High-Temperature Applications

HAYNES{sup ®} 233™ alloy based on the Ni-Co-Cr-Mo-Al system has been developed for service at high temperatures. The origins of 233 alloy can be traced to a couple of Haynes alloys: 230 alloy and 214 alloy. The former is a premier high-temperature alloy with superb creep strength and is widely accepted in the gas turbine industry. It is also chromia forming. The alumina-forming 214 alloy with its 4.5% Al content possesses outstanding oxidation resistance at high temperatures, but its creep strength above ~ 1800 °F (982 °C) is very poor. The new 233 alloy attempts to bridge this performance. This paper will present preliminary test results for 233 alloy from the products of the first production heats, including the tensile and creep properties of the alloy, microstructure, oxidation properties, as well as fabricability. These results will be compared and discussed with those of popular gas turbine alloys such as 230, 214, 617, and X alloys. The preliminary test results indicate that HAYNES 233 alloy has a unique combination of excellent oxidation resistance and creep-rupture strength while at the same time being readily fabricable. These properties make the alloy an attractive candidate for a wide variety of gas turbine and other high-temperature applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structural, Thermal, and Mechanical Characterization of a Thermally Conductive Polymer Composite for Heat Exchanger Applications

Polymer composites are being considered for numerous thermal applications because of their inherent benefits, such as light weight, corrosion resistance, and reduced cost. In this work, the microstructural, thermal, and mechanical properties of a 3D printed polymer composite with high thermal conductivity are examined using multiple characterization techniques. Infrared spectroscopy and X-ray diffraction reveal that the composite contains a polyphenylene sulfide matrix with graphitic fillers, which is responsible for the high thermal conductivity. Furthermore, differential scanning calorimetry determines that the glass transition and melting point of the composite are 87.6 °C and 285.6 °C, respectively. Thermogravimetric analysis reveals that the composite is thermally stable up to ~400 °C. Creep tests are performed at different isotherms to evaluate the long-term performance of the composite. The creep result indicates that the composite can maintain mechanical integrity when used below its glass transition temperature. Nanoindentation tests reveal that modulus and hardness of the composite is not significantly influenced by heating or creep conditions. These findings indicate that the composite is potentially suitable for heat exchanger applications.

36 MATERIALS SCIENCE↗
NASA NTRS2009

Pin Tool Geometry Effects in Friction Stir Welding

In friction stir welding (FSW) there is significant evidence that material can take one of two different flow paths when being displaced from its original position in front of the pin tool to its final position in the wake of the weld. The geometry of the pin tool, along with the process parameters, plays an important role in dictating the path that the material takes. Each flow path will impart a different thermomechanical history on the material, consequently altering the material microstructure and subsequent weld properties. The intention of this research is to isolate the effect that different pin tool attributes have on the flow paths imparted on the FSWed material. Based on published weld tool geometries, a variety of weld tools were fabricated and used to join AA2219. Results from the tensile properties and microstructural characterization will be presented.

Querin, J. A.↗
DOE OSTI2026

Coupling Microstructural Evolution Simulations to Material Property Degradation Predictions for Plasma-Facing Materials

Reliable material performance is required for plasma-facing material (PFM) candidates. Previous research has shown that plasma and neutron radiation exposure induces microstructural changes in PFMs; changes in thermal and electrical conductivities and in material hardening and embrittlement were also observed after neutron irradiation. These material property changes will negatively impact the performance of the PFMs in a fusion reactor. Despite the well-known connection between material microstructure, properties, and performance, there is a need for validated modeling capabilities connecting PFM property degradation with microstructural evolution under fusion-relevant conditions. We are developing a simulation capability to couple plasma-induced microstructural evolution to material property degradation. Our approach relies on deliberate mapping between individual simulation models and experimental characterization for validation. The open-source Multiphysics Object-Oriented Simulation Environment (MOOSE) software was used for this simulation capability development. A MOOSE phase-field model was coupled with the cluster dynamics code, Xolotl, to predict microstructural evolution. Microstructure characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), and laser scanning confocal microscopy (LSCM) are used to validate these microstructural evolution simulations. Calculation of thermal and electrical conductivities with first principles simulations was performed for bulk material and for grain boundaries; these results are used within MOOSE models to calculate effective thermal and electrical conductivities as a function of grain characteristics. Thermoreflectance and four-probe techniques were employed to measure the thermal and electrical conductivities, respectively. A MOOSE crystal plasticity model was adapted to predict microstructure-sensitive deformation behavior, and X-ray diffraction (XRD) was used to collect bulk dislocation density data for validation. After individual simulation validation, these models are coupled to predict material property changes resulting from plasma exposure. We focused here on an experimental design to emphasize the separate effects of moderate thermal loads and plasma exposure using tungsten. Annealing of tungsten was performed under a protective environment for temperatures ranging from 500 C to 1500 C. The plasma exposure was completed in the Tritium Plasma Experiment at Idaho National Laboratory under a deuterium flux of 1e22 D/m^2-s. This incremental approach is employed to build confidence in the modeling capability: separate-effects tests ensure that the models capture key mechanisms from single environmental conditions before predicting PFM property degradation under combined loads. We will show our early results from coupling these simulation models to predict PFM property changes from microstructural evolution. Comparisons of the simulation results with preliminary validation data will be discussed.

36 - MATERIALS SCIENCE↗
NASA NTRS1987

Ultrasonic nondestructive evaluation, microstructure, and fracture toughness interrelations

Ultrasonic techniques for mechanical property characterizations are reviewed and conceptual models are advanced for explaining and interpreting the empirically based results. At present, the technology is generally empirically based and is emerging from the research laboratory. Advancement of the technology will require establishment of theoretical foundations for the experimentally observed interrelations among ultrasonic measurements, mechanical properties, and microstructure. Conceptual models are applied to ultrasonic assessment of fracture toughness to illustrate an approach for predicting correlations found among ultrasonic measurements, microstructure, and mechanical properties.

Vary, Alex↗
DOE OSTI2019

Microstructure Evolution and Mechanical Property of Low-Alloy Steel Used for Armor Layer of Flexible Pipe During Thermomechanical Process and Hot Rolling Process

In this paper, the thermomechanical process and hot rolling process were carried out to study the microstructure evolution and mechanical property of low-alloy steel used for armor layer of flexible pipes by analyzing continuous cooling transformation curve, microstructure morphology, grain characteristics, and strength. The experimental results indicate that deformation process promotes phase transformation process of both ferrite and bainite and induces the formation of fine grain. The density of low-angle grain boundary rises with increasing cooling rate. The dislocation concentration in grain becomes larger with the extended cooling rate. The microstructure of hot-rolled specimen consists of polygonal ferrite and granular bainite, which is consistent with one of the deformed specimens with similar cooling rate in dilatometer. The microstructure evolution provides effective data fundament for hot rolling process.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Hot Straining and Quenching and Partitioning of a TRIP-Assisted Steel: Microstructural Characterization and Mechanical Properties

Advanced high strength steels (AHSS), with yield strengths over 300 MPa and tensile strengths exceeding 600 MPa, are becoming more noticeable in vehicle manufacturing. A novel processing route of a TRIP-assisted steel was developed. Characterization and modelling techniques were used to establish correlations between processing, microstructure and mechanical properties. Quenching and partitioning (Q&P) and a novel process of hot straining (HS) and Q&P (HSQ&P) treatments have been applied to a TRIP-assisted steel in a Gleeble ®3S50 thermo-mechanical simulator. The heat treatments involved intercritical annealing at 800 oC and a two-step Q&P heat treatment with a partitioning time of 100 s at 400 oC. The effects of high-temperature isothermal deformation on the carbon enrichment of austenite, carbide formation and the strain-induced transformation to ferrite (SIT) mechanism were investigated. Carbon partitioning from supersaturated martensite into austenite and carbide precipitation were confirmed by means of atom probe tomography (APT). Austenite carbon enrichment was clearly observed in all specimens, and in the HSQ&P samples it was slightly greater than in Q&P, suggesting an additional carbon partitioning to austenite from ferrite formed by the SIT phenomenon. By APT, the carbon accumulation at austenite/martensite interface was clearly observed. The newly developed combined process is promising as the transformation induced plasticity can contribute to the formability and energy absorption, contributing to fill the gap of the third generation of high-strength steels.

Ariza, Edwan Anderson↗
DOE OSTI2019

Effect of Different Heat Treatments on the Microstructural Evolution and Mechanical Properties of Ni-Cr-Si Alloy Fabricated by Laser Additive Manufacturing

Ni-Cr-Si alloy samples were fabricated on mild steel via laser additive manufacturing technology. The microstructural evolution and mechanical properties of the samples were studied systematically in as-deposited conditions and under three different types of heat-treated conditions. The scanning electron microscopy, energy-dispersive x-ray spectroscopy and x-ray diffraction results showed that the structures of the as-deposited samples were mainly dendritic matrices of γ(Ni, Fe), continuous interdendritic eutectics of γ + Ni{sub 3}B and discrete Cr-rich carbides and borides. After solid solution treatment, carbides (Cr{sub 7}C{sub 3}) and borides (CrB) precipitated on the boundary of the eutectic structure, distributing discretely in the matrix. In the solution plus aging heat-treated conditions, the interdendritic eutectics formed Ni{sub 3}Fe intermetallic compounds with a layered distribution. After annealing, the grains were refined, and the hard phases (CrB) were uniformly dispersed along the grain boundary. Among the tested samples, the as-deposited specimens exhibited the highest microhardness and good wear ability at room temperature; however, the wear resistance of the as-deposited sample obviously decreased at 250 °C. The mechanical properties of the specimens were not greatly improved by solution treatment or solution plus aging treatment. The sample subjected to annealing treatment exhibited excellent wear resistance both at room temperature and at a service temperature of 250 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure, Texture, and Mechanical Properties of Continuously Extruded and Rolled AZ31 Magnesium Alloy Sheets

It is difficult to fabricate magnesium alloy sheets at room temperature due to their hexagonal close-packed structure. In this paper, we proposed a new process that can be used to fabricate AZ31 magnesium alloy sheets with fine-grained microstructure and good mechanical properties. AZ31 magnesium alloy sheets with dimensions of 160 mm × 8 mm were obtained successfully by a continuous extrusion technique. The extruded sheets were then rolled by two different rolling routes, Route 1: the extruded sheet was heated at 350 °C and then rolled without heating of rolls and Route 2: the sheet was rolled without any previous heating by heating rolls at 280 °C. The microstructure and texture evolution as well as mechanical properties of the continuously extruded and rolled sheets were examined experimentally. The magnesium alloy sheets with relatively fine grains of 4.5-8.3 µm were obtained by continuous extrusion followed by rolling processes. The tensile strength of continuously extruded AZ31 Mg alloy sheets can be effectively increased by rolling using heating rolls (Route 2), while the ductility was enhanced by rolling heated sheets (Route 1). The mixed microstructure, consisting of refined DRX grains and deformed grains, contributes to enhancement in tensile strength of the sheet samples rolled by Route 2 due to grain-boundary strengthening and work hardening. Lower temperature and larger rolling reduction are two main factors for improving the tensile strength of AZ31magnesium alloy sheets.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The effect of neutron irradiation on conventional and nanocrystalline nickel: NSUF Work Package UA-22PN080501 Milestone M3UA-22PN0805012 (Final Report)

Even though nanocrystalline materials (20-100 nm) present an unprecedented potential, scientific knowledge related to the effect of neutron irradiation on the mechanical properties and microstructure is still scarce. Most of the past studies were conducted using ion irradiation which may not have the same effect as neutron irradiation because of the smaller irradiation volume and the higher dose rate. To reach a firm conclusion on the potential of nanocrystalline materials for nuclear reactor applications, extensive study of model metals with different stacking fault energy (SFE) is required to elucidate their behavior in radiation environments. Nanocrystalline copper and nickel are typically chosen because they are commonly used as model FCC metals in studies of radiation effects. Nickel is an FCC metal with a high stacking-fault energy (~125 mJ/m 2 ) compared to copper (~45 mJ/m 2 ). Hence, microcrystalline and nanocrystalline nickel samples were irradiated in the INL’s Advanced Test Reactor (ATR), as a part of FY08 North Carolina State University NSUF Irradiation Experiment# 96 to evaluate the irradiation behavior of these materials. The objective of this FY20 NSUF project# 19122 is to perform PIE (at PNNL NSUF facility) on previously ATR-neutron irradiated (1.2 and 2.6 dpa; 80-89°C) nanocrystalline and microcrystalline nickel samples to investigate the changes in mechanical properties and microstructures and evaluate whether nanocrystalline nickel is relatively more radiation resistant compared to conventional microcrystalline nickel. To perform PIE at PNNL, sixteen neutron irradiated specimens (microcrystalline and nanocrystalline) were transferred from the NSUF Nuclear Fuels and Materials Library at INL. Experimental techniques such as SEM/EBSD, XRD, TEM, Vickers microhardness and tensile testing were employed to characterize the effect of neutron irradiation on the microstructure and mechanical properties of nanocrystalline nickel and compared them with corresponding characteristics of microcrystalline nickel.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Microstructural stability and mechanical properties of the as-cast and heat-treated newly developed TiNbCrTa refractory complex concentrated alloy

In this study, a TiNbCrTa refractory complex concentrated alloy (RCCA) was prepared using vacuum arc remelting. The microstructural evolution and mechanical properties of both as-cast and heat-treated RCCA samples were analyzed. Heat treatment (HT) was performed at 800–1200 °C for 1 h in a vacuum-sealed environment. These samples exhibited a formation of Cr 2 Nb and Cr 2 Ti Laves phases. A variation in elemental distribution was observed, with interdendritic (ID) regions showing higher fractions of Ti and Cr, while the dendritic regions had a greater concentration of Ta and Nb. Micro-segregation at the IDs was confirmed through energy dispersive x-ray spectroscopy mapping, which inferred the formation of Cr- and Ti-rich phases during HT at 800–1200 °C. High-temperature HT at 1200 °C for 1 h led to the evolution of the hcp omega phase. Prolonged HT at 1200 °C for 96 h resulted in the evolution of a Cr-rich Laves phase (Cr 2 Ta), which was homogeneously distributed within the microstructure, indicating an unstable microstructure. Furthermore, despite prolonged HT, a variation in the elemental distribution persisted due to the presence of dendritic and ID regions. Electron backscattered diffraction analysis revealed the presence of bcc and hcp phases in the dendritic and ID regions, respectively, of the as-cast and HTed samples. The as-cast samples demonstrated a high compressive strength of approximately 2 GPa. Micro-hardness values increased with the HT temperature up to 1000 °C. Further increases under HT conditions did not significantly reduce the microhardness value, whereas prolonged HT at 1200 °C led to an increase in the microhardness value. Overall, the newly developed TiNbCrTa RCCA exhibited high-strength behavior even after the phase transformation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Cooling rate and dendrite spacing control in direct metal deposition printed Cu-Fe alloys

Over the last several decades, additive manufacturing (AM) has been primarily used for rapid prototyping or to create novel geometries that would be difficult or impossible to create by normal manufacturing methods. More recently, research has been focused on expanding the list of materials that can be made through additive manufacturing, opening a greater range of material properties for this manufacturing method. Due to the unusual conditions during AM, including the high cooling rates and voxel by voxel method of production, AM parts often have anisotropic material microstructures and properties. In this investigation, the laser power, composition, and nozzle head speed during direct metal deposition of copper-iron alloys was varied to understand how the grain structure within the printed parts could be changed and controlled. The resulting dendrite spacing was measured and compared to calculated cooling rates from Gaussian beams on flat plates under similar material and laser properties, which resulted in a cooling rate to dendrite spacing relationship following an inverse square root, as is found in other dendritic systems [Young and Kerkwood, Metall. Trans. A 6, 197–205 (1975)]. Thus, it is demonstrated that in the Cu-Fe system, dendrite spacing can be controlled through manipulation of printing parameters.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Probing Microstructure-induced Swelling & Thermal Property Changes in Ion-Irradiated Oxide Fuels using Laser-generated Surface Acoustic Waves

Radiation of fuel rods with neutrons during a fission reaction in a nuclear reactor is known to affect the material microstructure of the fuel as a result of fission fragment damage, and lead to the formation of atomic-level defects such as voids, dislocation loops, and lattice swelling from fission-gas release. A consequence of the radiation-induced damage in nuclear fuels is the drastic alteration of material properties, in particular, the reduction of the thermal conductivity – a key parameter that governs the transport of thermal energy released from fissile fuel atoms to the surrounding coolant. Swelling can induce high stresses and ultimate failure of the cladding. A fundamental understanding of the role of radiation-induced damage on the thermal transport and mechanical properties of nuclear fuels is therefore critical for efficient, reliable and safe operation of a nuclear power plant. As opposed to conventional post-irradiation examination techniques that are often time-consuming and require significant sample preparation, laser-based characterization methods have emerged as promising non-contact, non-destructive tools to measure the evolution of microstructure-induced material property changes. Moreover, laser methods offer the promise of in-situ characterization while the material is being irradiated. This project aims to develop an improved understanding of the impact of radiation-induced changes to material microstructure on the thermal and elastic properties of nuclear materials. A laser ultrasonic technique, known as the transient grating (TG) spectroscopy method, is used to simultaneously measure thermal diffusivity and elastic properties in unirradiated and ion-irradiated oxide nuclear fuel samples. The results will complement on-going investigations on electron- and phonon-mediated thermal transport in nuclear materials and will provide foundational work for incorporating the influence of defects in fuel performance codes.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Effect of Y/Zr Ratio on Inclusions and Mechanical Properties of 9Cr-RAFM Steel Fabricated by Vacuum Melting

This study investigates the inclusions, microstructures, tensile properties, and impact toughness of reduced-activation ferritic/martensitic (RAFM) steels with different Y/Zr ratio contents. An optical microscope and a scanning electron microscope (SEM) were employed to determine the size and number of inclusions, and SEM and transmission electron microscope were employed to examine the inclusion types. The increase in Y/Zr ratio influenced the prior austenite grain size owing to the pinning effect of the inclusions. The result of this examination showed that the mechanical properties of the steel are closely related to the refinement of prior austenite grain size and as well as the fine submicron-sized inclusions. The average prior austenite grain sizes of the alloys were 14.5, 13.5, and 13.4 μm for the steels with different Y/Zr ratio contents (i.e., 1/2, 5/3, and 11/2, respectively). Moreover, the submicron-sized inclusions in the alloys achieved densities of 4.71 × 10{sup 16}, 4.49 × 10{sup 16}, and 3.84 × 10{sup 16}/m{sup 3}. The ductile-to-brittle transition temperature (DBTT) decreases when the Y/Zr ratio increases to 5/3. However, the DBTT increases when the Y/Zr ratio reaches 11/2 owing to inclusion coarsening. The RAFM steel with Y content of approximately 0.005 wt.% and Zr content of 0.002 wt.% was verified to exhibit an optimized combination of microstructures, tensile properties, and impact toughness.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Welding Combined Plastic Forming on Microstructure Stability and Mechanical Properties of Friction Stir-Welded Al-Cu Alloy

A new tailor-welded process, which combines stages of welding, plastic forming, and heat treatment strengthening, was developed to produce a friction stir-welded (FSW) Al-alloy joint. The Al-Cu sheets were FSW under different welding parameters and then were plastic-deformed. The microstructural evolution and mechanical properties of the FSW joint were investigated by scanning electron microscopy and tensile tests. It was found that high heat input during FSW and low solution temperature suppress the abnormal grain growth (AGG) of the joint due to the differential in grain size and grain boundary energy. The microstructure heterogeneity of the FSW joint is effectively improved, as no AGG occurs. The retention of fine equiaxed grains and the increase in the density of precipitates result in excellent mechanical properties. The increase in the strength and micro-hardness of the joint mainly depends on the plastic deformation prior to aging treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2020

An additively manufactured AlCuMnZr alloy microstructure and tensile mechanical properties

In this study, selective laser melting (SLM) was used to fabricate an AlCuMnZr alloy. The microstructural features that resulted from additive manufacturing (AM) were significantly refined compared to the corresponding cast alloy features. A combination of fine equiaxed and columnar grains along with in-situ formation of θ' precipitates during AM leads to enhanced yield strength (up to 300°C) in the as-fabricated AM alloy. The refinement of brittle intermetallics and a bimodal grain size distribution leads to improved tensile elongation in the AM alloy. The results illustrate the microstructural advantages that can result from additive processing over conventionally processed microstructures.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Theoretical Correlation of Elemental Distribution of Nd and Pr in Ce-Fe-B Microstructure With Hard Magnetic Properties

Relatively resource-rich but property inferior-Ce-Fe-B magnet can be improved by partial replacement of Ce by Nd and/or Pr. In addition to the amount of Nd/Pr, their distribution profile in microstructure plays an important role. From our first principles density functional theory (DFT) calculation, the substitution energy of Ce by Pr/Nd is negative in Ce 2 Fe 14 B (2:14:1) while that for laves phase, CeFe 2 is positive, implying that Nd/Pr stabilize 2:14:1 and suppress the formation of the CeFe 2 phase. Further, micromagnetic simulation indicates that homogenized distribution of Nd/Pr improves squareness of demagnetization curve, while core (Ce-rich)-shell (Nd/Pr-rich) 2:14:1 grain structure enhances coercivity. Magnetic properties of Ce-Fe-B can be optimized by manipulating distribution profile of chemical element in microstructure based on their subtle difference in thermodynamic property, which is an effective pathway to design optimized chemical composition and processing route for high-performance magnet.

36 MATERIALS SCIENCE↗
NASA NTRS2003

Challenges and Opportunities in Reactive Processing and Applications of Advanced Ceramic Materials

Recently, there has been a great deal of interest in the research, development, and commercialization of innovative synthesis and processing technologies for advanced ceramics and composite materials. Reactive processing approaches have been actively considered due to their robustness, flexibility, and affordability. A wide variety of silicon carbide-based advanced ceramics and composites are currently being fabricated using the processing approaches involving reactive infiltration of liquid and gaseous species into engineered fibrous or microporous carbon performs. The microporous carbon performs have been fabricated using the temperature induced phase separation and pyrolysis of two phase organic (resin-pore former) mixtures and fiber reinforcement of carbon and ceramic particulate bodies. In addition, pyrolyzed native plant cellulose tissues also provide unique carbon templates for manufacturing of non-oxide and oxide ceramics. In spite of great interest in this technology due to their affordability and robustness, there is a lack of scientific basis for process understanding and many technical challenges still remain. The influence of perform properties and other parameters on the resulting microstructure and properties of final material is not well understood. In this presentation, mechanism of silicon-carbon reaction in various systems and the effect of perform microstructure on the mechanical properties of advanced silicon carbide based materials will be discussed. Various examples of applications of reactively processed advanced silicon carbide ceramics and composite materials will be presented.

Singh, Mrityunjay↗