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At least 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Enhanced piezoelectric properties in (Ba1-xCax)(Ti0.90Sn0.10)O3-0.08Dy2O3 lead-free ceramics

Highlights: • MPB exists in the BCTSD ceramics with x = 0.06–0.10. • BCTSD ceramics exhibit typical diffuse phase transition behavior, which is not sensitive to the amount of Ca{sup 2+} ions. • Remarkable improvement on piezoelectric properties (d{sub 33} = 675 pC/N, k{sub p} = 55%) were achieved at x = 0.06. - Abstract: (Ba{sub 1-x}Ca{sub x})(Ti{sub 0.90}Sn{sub 0.10})O{sub 3}-0.08Dy{sub 2}O{sub 3} ceramics (BCTSD-x, x = 0.02–0.10) were fabricated by conventional solid state sintering method. The effect of Ca{sup 2+} ions addition on the phase structure, microstructure, and electric properties of ceramics were studied. X-ray diffraction analysis reveals the replacement of Ba{sup 2+} ions in the perovskite structure by Ca{sup 2+} ions. Rhombohedral phase and tetragonal phase coexist in the composition with x = 0.06–0.10. Both d{sub 33} and K{sub p} of the ceramics increase with increasing Ca concentration, and attain maximum values of 675 pC/N and 55.0%, respectively, for x = 0.06. All the ceramics present typical diffuse phase transition behavior, and the feature is not sensitive to the amount of Ca{sup 2+} ions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Development of a silicon carbide ceramic based counter-flow heat exchanger by binder jetting and liquid silicon infiltration for concentrating solar power

A silicon carbide ceramic counter-flow heat exchanger with integrated headers was printed by binder jetting additive manufacturing process. Multiple phenolic binder infiltration cycles (3 or 5) followed by pyrolysis were conducted to increase the net carbon content of the printed SiC specimens. Subsequently, to attain full densification, silicon melt infiltration was used. The microstructure and mechanical properties were comprehensively characterized on the densified material. The chemical compositions and visual distribution of the various regions in the specimens were determined via scanning electron microscopy, while X-ray diffraction and synchrotron µ-computed tomography were used to provide a quantitative assessment of the volume fractions of the identified phase regions. Microhardness measurements showed dependence on the local microstructure. The fracture strength of the material was correlated with the specimen density and agreed with the reported values in the literature. High-temperature exposure at 750 °C for up to 200h did not degrade the strength for the specimens with three phenolic-binder infiltrations; however, the strengths degraded for ones with five phenolic-binder infiltrations. The associated fracture toughnesses of the specimens were ~3.4 MPam 1/2 at room temperature and 750°C, and the thermal conductivities varied from >150 W/mK at room temperature to ~45 W/mK at 750°C. Hence, this study validated the use of the binder-jetting printed SiC ceramic materials for high-temperature heat exchanges. Lastly, we also present in this work the first successful fabrication of a binder-jetting printed one-piece dense SiC ceramic heat exchanger body with unblocked channels that can be used for the flow of heat transfer fluids.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Neutron Diffraction Residual Stress Characterization of Large-Scale Components by WA-DED

Two large scale 316L stainless steel cylindrical shells were fabricated by wire arc directed energy deposition (WA DED). Residual stresses were measured by neutron diffraction, and the microstructure and mechanical properties of the printed material were characterized. Longitudinal and transverse residual stresses were compressive at the inner diameter, near neutral at mid wall, and tensile at the outer diameter; radial (through thickness) residual stresses were relatively low in magnitude, and peak tensile residual stresses occurred at the outer diameter surface along the longitudinal direction. The printed 316L SS exhibited a heterogeneous microstructure with finely dispersed δ ferrite, and demonstrated high yield and tensile strengths with large elongation and ductile fracture at ambient temperature and at 250 °C. These results indicate that the outer diameter surface and near surface regions—where tensile residual stress is highest—are the most vulnerable to residual stress–sensitive failure modes, such as stress corrosion cracking and fatigue.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Stochastic Design Optimization of Microstructural Features Using Linear Programming for Robust Design

Microstructure design can have a substantial effect on the performance of critical components in numerous aerospace applications. However, the stochastic nature of metallic microstructures leads to deviations in material properties from the design point and alters the performance of these critical components. In this paper, a novel stochastic linear programming (LP) methodology is developed for microstructure design accounting for uncertainties in desired properties. The metallic microstructure is represented using a finite element discretized form of the orientation distribution function (ODF). The inverse LP problem solves the mean values and covariance matrix of the ODFs to maximize the mean values of a property, given the statistical constraints on other properties. The highlight is an analytical uncertainty quantification model via a Gaussian distribution to model propagation of microstructural uncertainties to the properties. Examples illustrate maximization of the yield strength and magnetostriction of a galfenol alloy when constrained by uncertainties in a set of stiffness constants.

42 ENGINEERING↗
DOE OSTI2018

Recrystallization Behavior and Super-Elasticity of a Metastable β-Type Ti-21Nb-7Mo-4Sn Alloy During Cold Rolling and Annealing

Based on the d-electron alloy design theory, a new metastable β-type titanium alloy for biomedical applications, Ti-21Nb-7Mo-4Sn (wt.%) was designed in this article. This theory predicted this alloy was a metastable single β-type titanium alloy with low elastic modulus at room temperature, and the β-phase transition (β to α″) would be easy to occur during the cold rolling. The evolution of microstructure and mechanical properties of this alloy during cold rolling plus annealing were investigated by means of x-ray diffraction, optical microscope, transmission electron microscope and mechanical properties test. The results indicate that only β phase can be identified in this alloy before cold rolling, while a large amount of lath martensite (α″ phase) appears after cold rolling due to stress-induced martensitic transformation, which is in accordance with the prediction of the d-electron alloy design theory. The recrystallization nucleation occurs preferentially in the martensite lath region during the subsequent annealing process, and this region forms a large number of nano-crystals and microcrystals, showing that cold rolling plus annealing can become a new process for refining grains. Compared with casting and cold rolling samples, the annealing materials at 923 K for 10 min have excellent comprehensive mechanical properties with lower elastic modulus (58 GPa) and higher elastic recovery rate (35.39%).

36 MATERIALS SCIENCE↗
NASA NTRS1986

Analytical Ultrasonics in Materials Research and Testing

Research results in analytical ultrasonics for characterizing structural materials from metals and ceramics to composites are presented. General topics covered by the conference included: status and advances in analytical ultrasonics for characterizing material microstructures and mechanical properties; status and prospects for ultrasonic measurements of microdamage, degradation, and underlying morphological factors; status and problems in precision measurements of frequency-dependent velocity and attenuation for materials analysis; procedures and requirements for automated, digital signal acquisition, processing, analysis, and interpretation; incentives for analytical ultrasonics in materials research and materials processing, testing, and inspection; and examples of progress in ultrasonics for interrelating microstructure, mechanical properites, and dynamic response.

Vary, A.↗
DOE OSTI2020

Influence of geochemical reactions on the creep behavior of Mt. Simon sandstone

The capture and subsurface storage of carbon dioxide is a sustainable option that is currently pursued worldwide to mitigate greenhouse gas effect. However, predicting the long-term mechanical integrity of CO 2 underground storage systems remains a challenge. To address that question, it is essential to understand the influence of fluid-rock chemo-mechanical interactions on the long-term and on the time-dependent mechanical properties. In turn, the long-term mechanical response and the time-dependent mechanical behavior can be represented by the creep response. We investigate the impact of CO 2 -induced geochemical reaction on the creep response of Mt. Simon sandstone with a 50–400 micron grain size. We perform static and dynamic flow experiments on Mt. Simon sandstone specimens under geological conditions, at a temperature of T = 50 - 53 °C and for CO 2 pressures of P = 8:62; 17:2 MPa under both static flow and dynamic flow-through conditions. After aging, we employ creep indentation testing, high-resolution SEM-EDS, computer vision, machine learning, and micromechanics modeling to probe changes on the microstructure and mechanical properties. Following both static and dynamic flow-through experiments, we observe a 10–22% decrease in quartz volume fraction and an increase in both the microporosity (7–28%) and nanoporosity (60–65%). Additional CO 2 -induced microstructural changes include an enlargement of pore throats and the formation of channels. These observations point to the presence of CO 2 -induced K-feldspar dissolution and clay dissolution reactions. Here, the macroscopic creep behavior is logarithmic and the macroscopic creep modulus varies depending on the microporosity and the relative quartz and feldspar content. As a result of these geochemical reactions and of the related microstructural changes, a 55-60% decrease in the macroscopic logarithmic creep modulus is predicted.

58 GEOSCIENCES↗
DOE OSTI2018

Wear Resistance Enhancement of Ti-6Al-4 V Alloy by Applying Zr-Modified Silicide Coatings

Zr-modified silicide coatings were prepared on Ti-6Al-4 V alloy by pack cementation process to enhance its wear resistance. The microstructure and wear properties of the substrate and the coatings were comparatively investigated using GCr15 and Al{sub 2}O{sub 3} as the counterparts under different sliding loads. The obtained Zr-modified silicide coating had a multilayer structure, consisting of a thick (Ti,X)Si{sub 2} (X represents Al, Zr and V elements) outer layer, a TiSi middle layer and a Ti{sub 5}Si{sub 4} + Ti{sub 5}Si{sub 3} inner layer. The micro-hardness of the coating was much higher than the substrate and displayed a decrease tendency from the coating surface to the interior. Sliding against either GCr15 or Al{sub 2}O{sub 3} balls, the coatings showed superior anti-friction property to the Ti-6Al-4 V alloy, as confirmed by its much lower wear rate under each employed sliding condition.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Proton irradiation effects in Molybdenum-Carbide-Graphite composites

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) has prompted the investigation of novel materials for beam-intercepting devices, and in particular for the collimators responsible for protecting the machine from beam losses. The HL-LHC collimation system will inevitably experience increased levels of radiation damage and undergo changes in their crucial physio-mechanical properties. Graphite-matrix composite materials containing molybdenum carbide particles, along with small amounts of titanium carbide, were developed with the objective of enhanced in-beam performance and tested under proton irradiation. The physical degradation observed in early grades of molybdenum carbide compounds, even after modest proton fluences, has prompted the development of advanced compounds. In this work, we examine the effects of proton irradiation on the microstructural and thermophysical properties of new grades of Molybdenum-carbide-graphite compounds up to fluences of ~2 × 10 20 p/cm 2 . Here, we employ a combination of precision dilatometry and high-energy X-ray diffraction to quantify the dimensional stability and crystallographic phase evolution both pre- and post-irradiation. Our results reveal that these new compounds exhibit superior resilience to radiation damage than their predecessors.

36 MATERIALS SCIENCE↗
NASA NTRS1995

Low Cost Fabrication of Silicon Carbide Based Ceramics and Fiber Reinforced Composites

A low cost processing technique called reaction forming for the fabrication of near-net and complex shaped components of silicon carbide based ceramics and composites is presented. This process consists of the production of a microporous carbon preform and subsequent infiltration with liquid silicon or silicon-refractory metal alloys. The microporous preforms are made by the pyrolysis of a polymerized resin mixture with very good control of pore volume and pore size thereby yielding materials with tailorable microstructure and composition. Mechanical properties (elastic modulus, flexural strength, and fracture toughness) of reaction-formed silicon carbide ceramics are presented. This processing approach is suitable for various kinds of reinforcements such as whiskers, particulates, fibers (tows, weaves, and filaments), and 3-D architectures. This approach has also been used to fabricate continuous silicon carbide fiber reinforced ceramic composites (CFCC's) with silicon carbide based matrices. Strong and tough composites with tailorable matrix microstructure and composition have been obtained. Microstructure and thermomechanical properties of a silicon carbide (SCS-6) fiber reinforced reaction-formed silicon carbide matrix composites are discussed.

Singh, M.↗
NASA NTRS2007

Development of GRCop-84 for Rocket Engine Applications

GRCop-84 (Cu-8 at.% Cr-4 at.% Nb) has been under development at the NASA Glenn Research Center for several years. The alloy possesses a unique combination of good thermal conductivity, high elevated temperature strength, long creep lives and long low cycle fatigue lives. The alloy is also more oxidation resistant than pure copper and most competitive alloys. The combination of properties has attracted attention from major rocket engine manufacturers who are interested in the alloy for the combustion chamber liner in their next generation of regeneratively cooled engines. It is also a strong candidate for various components in hypersonic vehicles, which also experience very high heat flux conditions. This presentation will discuss the alloy design strategies used to develop GRCop-84 and the various processing routes available for manufacturing components. The microstructure and mechanical properties of the alloy will be reviewed, as well as the results of actual hot fire testing of subscale rocket combustion chambers. The use of environmental and thermal barrier coatings to extend the performance to even higher levels will also be discussed.

Ellis, David L.↗
DOE OSTI2018

Structure, Ferroelectric, and Magnetoelectric Properties of Bulk PZT–NiFe{sub 1.9}Co{sub 0.02}O{sub 4–δ} Composites

The phase composition, microstructure, and dielectric, ferroelectric, magnetic, and magnetoelectric properties of bulk ceramic (1 – x)PZT–xNiFe{sub 1.9}Co{sub 0.02}O{sub 4–δ} composites with 3–0 connectivity have been studied. Using X-ray diffraction and electron microscopy, it has been established that the ferrimagnetic (spinel- like) and ferroelectric (tetragonal perovskite-like) phases separately exist in the composites of all compositions. The simultaneous existence of ferroelectric and ferrimagnetic properties in the composites is confirmed by measuring their P(E) and σ(B) hysteresis loops and studying the temperature dependences of dielectric and magnetic properties. The synthesized composites have high magnetoelectric characteristics: their voltage coefficient at x = 0.4 is 215 mV/A at a frequency of 1 kHz and 130 V/A at an electromechanical resonance frequency of 380 kHz.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2019

Simulating Space Weathering in the Transmission Electron Microscope via Dynamic in Situ Heating and Helium Irradiation of Olivine

The chemical composition, microstructure, and optical properties of grains on the surfaces of airless bodies are predominantly altered by micrometeorite impacts and solar wind irradiation. These processes drive space weathering and result in the formation of features including chemically-altered, amorphous grain rims, Fe nanoparticles (npFe), and vesiculated grain textures. These characteristics have been identified in returned samples from the surfaces of the Moon and asteroid Itokawa. In order to advance our understanding of the formation of these microstructural and chemical features in returned samples, we have simulated space weathering processes for a variety of materials via laboratory experiments. These experiments include ion irradiation to simulate solar wind exposure and laser irradiation and in situ heating to simulate micrometeorite impacts. While these experiments have provided considerable insight into the formation mechanisms of many space weathering features, they are predominantly static and typically performed separately. Here we present results from the simulated space weathering of olivine grains via He irradiation and dynamic heating, both performed in situ inside the transmission electron microscope (TEM). These experiments allow for the real-time observation of chemical and microstructural changes resulting from the superposed effects of ion irradiation and pulsed heating.

Thompson, M. S.↗
DOE OSTI2023

Multi-fidelity Uncertainty Quantification for Homogenization Problems in Structure-Property Relationships from Crystal Plasticity Finite Elements

Crystal plasticity finite element method (CPFEM) has been an integrated computational materials engineering (ICME) workhorse to study materials behaviors and structure-property relationships for the last few decades. These relations are mappings from the microstructure space to the materials properties space. Due to the stochastic and random nature of microstructures, there is always some uncertainty associated with materials properties, for example, in homogenized stress-strain curves. For critical applications with strong reliability needs, it is often desirable to quantify the microstructure-induced uncertainty in the context of structure-property relationships. However, this uncertainty quantification (UQ) problem often incurs a large computational cost because many statistically equivalent representative volume elements (SERVEs) are needed. In this article, we apply a multi-level Monte Carlo (MLMC) method to CPFEM to study the uncertainty in stress-strain curves, given an ensemble of SERVEs at multiple mesh resolutions. By using the information at coarse meshes, we show that it is possible to approximate the response at fine meshes with a much reduced computational cost. We focus on problems where the model output is multi-dimensional, which requires us to track multiple quantities of interest (QoIs) at the same time. In conclusion, our numerical results show that MLMC can accelerate UQ tasks around 2.23x, compared to the classical Monte Carlo (MC) method, which is widely known as ensemble average in the CPFEM literature.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Investigation of the temperature-dependent failure processes in PVD Cr-coated ZIRLO nuclear fuel cladding using in situ X-ray micro-tomography imaging

In this work, an accident tolerant fuel cladding system with Cr coating deposited using physical vapour deposition (PVD) method onto commercial Optimized ZIRLO™ was studied. The cladding tubes were machined into C-rings and loaded to failure under compression with real-time synchrotron micro-X-ray computed tomography (XCT) imaging at room temperature (RT), 345 °C, 650 °C and 950 °C in argon (Ar) atmosphere. The mechanical behaviour and failure processes were found strongly temperature-dependent where the Cr coating showed brittle fracture at RT and 345 °C, ductile fracture at 650 °C and a reversion to brittle fracture at 950 °C. Nanoindentation measurements and scanning electron microscopy (SEM) imaging were conducted on the materials after high temperature testing. It was found that recrystallisation of the Cr coating occurred at elevated temperatures, which significantly affected its local properties hence the failure behaviour at different temperatures. This work represents the first in situ 3D XCT observation of progressive failure processes in PVD Cr-coated ZIRLO claddings up to 950 °C providing critical insights into its brittle-to-ductile transition (BDTT) behaviour and subsequent ductile-to-brittle reversion with the increase in temperature. Moreover, results are compared with other PVD Cr-coated Zircaloy materials from open literature; the influences of the coating microstructure and local properties on the failure stress/strain and fracture processes are discussed.

Yuan, Guanjie↗
DOE OSTI2018

Understanding the Deformation Mechanisms of FeNiMnAlCr High Entropy Alloys

The aim of this project was to understand the microstructure and mechanical properties of Fe-Ni-Mn-Al-Cr high entropy alloys. High entropy alloys are defined as materials containing five or more elements with each element constituting 5-35 atomic percent of the alloy. We performed several different tasks in this project. 1) We showed that reducing the crystal or grain size in single-phase Fe40Ni11Mn35Al8Cr6 containing either 1.1 atomic percent carbon added or with no carbon added produced a substantial increase in strength with a small reduction in ductility. The finer grain size material was produced by cold rolling followed by heating to recrystallize the microstructure. The changes in strength and ductility were related to observed changes in deformation structure as determined by transmission electron microscopy. We also examined how the deformation behavior changed with temperature from -200°C to 200°C. 2) We showed that heating Fe36Ni18Mn33Al13 with and without 1.26 at.% carbon led to ordered body-centered cubic precipitates forming in the materials, which were both initially two-phase. The heat treatment again led to substantial increases in strength with some reduction in ductility. 3) We examined whether titanium additions (2 atomic percent) to Fe42Ni18Mn33Al13 could improve the mechanical properties. We examined both as-cast material and material that had been recrystallized to produce a fine grain size. In both cases ordered body-centered cubic precipitates were present. Again, the recrystallization and resulting reduction in grain size increased the yield strength and reduced the ductility. We also showed, using high-resolution electron microscopy, that contrary to some predictions, having an alloy containing a range of atoms with different atomic diameters produced no lattice distortions. 4) We used scanning electron microscopy and transmission electron microscopy coupled with energy dispersive x-ray spectroscopy to show that carbides formed during intermediate temperature (≤800oC) heating of carbon-doped Fe40Ni11Mn35Al8Cr6. In addition to forming within the grains, the carbides coated the grain boundaries. This produced an increase in strength but a drastic reduction in ductility. However, we showed by hot rolling we could get both high strength and high ductility for this material. The work led to nine publications in referred journals and contributed to the education of two Ph.D. students. In addition, ten presentations (six of which were invited) at conferences, at a university and at a national laboratory in Germany.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Simulated Fission Gas Behavior in Silicide Fuel at LWR Conditions

As a promising candidate for the accident tolerant fuel (ATF) used in light water reactors (LWRs), the fuel performance of uranium silicide (U 3 Si 2 ) at LWR conditions needs to be well-understood. However, existing experimental post-irradiation examination (PIE) data are limited to the research reactor conditions, which involve lower fuel temperature compared to LWR conditions. This lack of appropriate experimental data significantly affects the development of fuel performance codes that can precisely predict the microstructure evolution and property degradation at LWR conditions, and therefore evaluate the qualification of U 3 Si 2 as an AFT for LWRs. Considering the high cost, long timescale, and restrictive access of the in-pile irradiation experiments, this study aims to utilize ion irradiation to simulate the inpile behavior of the U 3 Si 2 fuel. Both in situ TEM ion irradiation and ex situ high-energy ATLAS ion irradiation experiments were employed to simulate different types of microstructure modifications in U 3 Si 2 . Multiple PIE techniques were used or will be used to quantitatively analyze the microstructure evolution induced by ion irradiation so as to provide valuable reference for the development of fuel performance code prior to the availability of the in-pile irradiation data.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1992

The influence of chromium on structure and mechanical properties of B2 nickel aluminide alloys

Major obstacles to the use of NiAl-based alloys and composites are low ductility and toughness. These shortcomings result in part from a lack of sufficient slip systems to accommodate plastic deformation of polycrystalline material (von Mises Criterion). It has been reported that minor additions of chromium to polycrystalline NiAl cause the predominant slip system to shift from the usual. If true, then a major step toward increasing ductility in this compound may be realized. The purpose of the present study was to verify this phenomenon, characterize it with respect to chromium level and Ni to Al ratio, and correlate any change in slip system with microstructure and mechanical properties. Compression and tensile specimens were prepared from alloys containing 0 to 5 percent chromium and 45 to 55 percent aluminum. Following about one percent strain, transmission electron microscopy foils were produced and the slip systems determined using the g x b = 0 invisibility criterion. Contrary to previous results, chromium was found to have no effect on the preferred slip system of any of the alloys studied. Possible reasons for the inconsistency of the current results with previous work are considered. Composition-structure-property relationships are discerned for the alloys, and good correlation are demonstrated in terms of conventional strengthening models for metallic systems.

Cotton, James Dean↗