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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Effects of blended cements and carbonation on chloride-induced corrosion propagation

Highlights: • Corrosion propagation of blended cements was investigated for 1 year. • Carbonated and non‑carbonated mortars were evaluated. • Galvanostatic pulse and ER sensors were used to monitor corrosion. • Mortar properties were correlated with corrosion rates and corrosion damage. • Relationships between mortar properties and corrosion behaviour were established. Supplementary cementitious materials are known to refine the pore structure of concrete and accelerate the carbonation progress. The combination of the two processes can have both beneficial and disadvantageous effects on corrosion, especially when chlorides are also involved. In this study the corrosion properties of multiple blended cements were evaluated in carbonated and non‑carbonated states, with chlorides introduced through cyclic ponding. The examination involved monitoring the propagation phase, determining the microstructural properties of cements, and assessing the final corrosion damage. The results showed that the steel in the blended cements initially had a relatively high corrosion activity, which later decreased compared to the OPC. This stabilisation was presumably due to the beneficial changes to the pore structure. Carbonation had a significant impact on the corrosion, with carbonated mortars revealing shallower damage over a larger surface area. This effect was more pronounced for blended cements that exhibited greater susceptibility to carbonation.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Unconventional Molecular Weight Dependence of Charge Transport in the High Mobility n‐type Semiconducting Polymer P(NDI2OD‐T2)

The charge transport and microstructural properties of five different molecular weight (MW) batches of the naphthalenediimide‐thiophene copolymer P(NDI2OD‐T2) are investigated. In particular, the field‐effect transistor (FET) performance and thin‐film microstructure of samples with MW varying from M n = 10 to 41 kDa are studied. Unlike conventional semiconducting polymers such as poly(3‐hexylthiophene) where FET mobility dramatically drops with decreasing molecular weight, the FET mobility of P(NDI2OD‐T2)‐based transistors processed from 1,2‐dichlorobenzene is found to increase with decreasing MW. Using a combination of grazing‐incidence wide‐angle X‐ray scattering, near‐edge X‐ray absorption fine‐structure spectroscopy, atomic force microscopy, and resonant soft X‐ray scattering, the increase in FET mobility with decreasing MW is attributed to the pronounced increase in the orientational correlation length (OCL) with decreasing MW. In particular, the OCL is observed to systematically increase from <100 nm for the highest MW samples to ≈1 µm for the lowest MW samples. The improvement in OCL and hence mobility for low MW samples is attributed to the lack of aggregation of low MW chains in solution promoting backbone ordering, with the pre‐aggregation of chains in 1,2‐dichlorobenzene found to suppress longer‐range liquid crystalline order.

Nahid, Masrur M.↗
DOE OSTI2026

From Cryogenic to High Temperatures: A Microstructural Evolution of δ-phase Pu-Ga Alloys Investigated by Time-of-Flight High-resolution Neutron Diffraction

Phase stability and phase transformations in binary Pu alloys are critical for multiple applications. Long-term phase stability affects mechanical properties, microstructure, corrosion behavior, and structural integrity. A clear and detailed understanding of phase transformations and phase stability mechanisms is necessary to assess the behavior and response to unexpected stimuli. Gaining advanced knowledge on the behavior of Pu and Pu alloys at a variety of temperatures, pressures, and time will ensure better predictions and control on evolution outside laboratory measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure and Mechanical Property Inhomogeneities of a Modified AZ80 Magnesium Alloy Wide Plate Under Horizontal Flat Die Extrusion

In the present paper, inhomogeneities in the microstructure and mechanical properties of a modified AZ80 plate under industrial production conditions were investigated. The results indicated that the microstructure of the edge and middle region shows more homogeneous and fine recrystallized grains. Additionally, more coarse recrystallized grains existed between the edge and the middle region. The ultimate tensile strength and yield strength of the edge region of the plate are maximal (287 and 162 MPa), and those near the 1/8 W region are minimal (259 and 152 MPa). The grain size increased from 19.5 to 27.2 μm along the center layer to the surface layer. The ultimate tensile stress (yield stress) increases from 258 (121 MPa) to 284 MPa (176 MPa) in the direction from the surface layer to the middle layer. The microhardness decreased from the surface layer (72HV) to the center layer (64HV). The metal strain state and temperature distribution lead to different degrees of dynamic recrystallization, which causes the microstructure and mechanical properties of the plate.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Structure disorder degree of polysilicon thin films grown by different processing: Constant C from Raman spectroscopy

Flat, low-stress, boron-doped polysilicon thin films were prepared on single crystalline silicon substrates by low pressure chemical vapor deposition. It was found that the polysilicon films with different deposition processing have different microstructure properties. The confinement effect, tensile stresses, defects, and the Fano effect all have a great influence on the line shape of Raman scattering peak. But the effect results are different. The microstructure and the surface layer are two important mechanisms dominating the internal stress in three types of polysilicon thin films. For low-stress polysilicon thin film, the tensile stresses are mainly due to the change of microstructure after thermal annealing. But the tensile stresses in flat polysilicon thin film are induced by the silicon carbide layer at surface. After the thin film doped with boron atoms, the phenomenon of the tensile stresses increasing can be explained by the change of microstructure and the increase in the content of silicon carbide. We also investigated the disorder degree states for three polysilicon thin films by analyzing a constant C. It was found that the disorder degree of low-stress polysilicon thin film larger than that of flat and boron-doped polysilicon thin films due to the phase transformation after annealing. After the flat polysilicon thin film doped with boron atoms, there is no obvious change in the disorder degree and the disorder degree in some regions even decreases.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructure and mechanical properties of resistance-spot-welded joints for A5052 aluminum alloy and DP 600 steel

The microstructure and mechanical properties of resistance-spot-welded A5052 aluminum alloy and DP 600 dual-phase steel joint were studied. The fusion zone (FZ) and heat-affected zone (HAZ) of DP 600 exhibited lath martensite and ferrite-martensite structures, respectively. The microstructure of FZ and HAZ in the A5052 side was composed of cellular crystals and the boundary region of FZ exhibited a columnar crystal morphology. A Fe{sub 2}Al{sub 5} intermetallic compound (IMC) layer with 3.3 μm thickness was found adjacent to the DP 600 side, whereas a needle-shaped Fe{sub 4}Al{sub 13} IMC layer with length of 0.67 μm to 15.8 μm was found adjacent to the aluminum alloy side. The maximum tensile shear load of the A5052/DP 600 joint was 5.5 KN, with a corresponding molten nugget diameter of 6.3 mm. The fracture morphology of the optimized A5052/DP 600 joint was mainly an elongated dimple fracture accompanied by cleavage fracture. - Highlights: •A5052 and DP 600 with large gaps in properties were investigated by RSW. •The microstructures of RSW joints in DP 600/A5052 were examined detailedly. •The micro/macro-characteristics and strength relations of joints were analyzed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Dynamic fragmentation of cellular, ice-templated alumina scaffolds

Here, we examine the dynamic failure of ice-templated freeze-cast alumina scaffolds that are being considered as biomimetic hierarchical structures. Three porosities of alumina freeze-cast structures were fabricated, and a systematic variation in microstructural properties such as lamellar width and thickness was observed with changing porosity. Dynamic impact tests were performed in a light-gas gun to examine the failure properties of these materials under high strain-rate loading. Nearly complete delamination was observed following impact, along with characteristic cracking across the lamellar width. Average fragment size decreases with increasing porosity, and a theoretical model was developed to explain this behavior based on microstructural changes. Using an energy balance between kinetic, strain, and surface energies within a single lamella, we are able to accurately predict the characteristic fragment size using only standard material properties of bulk alumina.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of intermediate annealing time on microstructure, texture and mechanical properties of Al-Mg-Si-Cu alloy

Highlights: • Long intermediate annealing time could be beneficial to the improvement of deep drawability. • Long intermediate annealing time could give rise to more particles with a larger average size. • As intermediate annealing time increases, strength will change and it has no positive correlation with annealing time, • A particle dissolution model is proposed to illustrate the variation of the strengths with intermediate annealing time. - Abstract: The effect of intermediate annealing time on the microstructure, texture and mechanical properties of Al-Mg-Si-Cu alloys was studied by mechanical properties, microstructure and texture characterization in the present study. The results show that the intermediate annealing time has some influence on the microstructure, recrystallization texture, and final mechanical properties. After the pre-aging treatment and natural aging treatment (T4P treatment), in contrast to the sheet with short intermediate annealing time, the sheet with long intermediate annealing time possesses higher plastic strain ratio r value. Strength has no positive correlation with annealing time, and when applying the annealing time of 16 h, the strength is highest. Before solution treatment, the sheet with long intermediate annealing time has more particles with a larger average size, compared with the sheet with short intermediate annealing time. After solution treatment, they possess the similar recrystallization equiaxed grain structure and recrystallization texture. The sheet with short intermediate annealing time is comprised of Cube{sub ND} {001} <310>, Goss {110}<001> and P {011}<122> orientations, while the sheet with long intermediate annealing time possesses weak texture including Cube{sub ND} {001}<310>, Goss {110}<001> and {015}<751> orientations. Finally, a particle dissolution model during solution treatment is proposed to explain the variation of strength with annealing time.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Oxygen deficiency induced deterioration in microstructure and magnetic properties at Y{sub 3}Fe{sub 5}O{sub 12}/Pt interface

Transport efficiency of pure spin current across the ferromagnetic films adjacent with a nonmagnetic metal is strongly dependent on the spin mixing conductance, which is very sensitive to atomic-level interface conditions. Here, by the means of advanced electron microscopy techniques, atomic structure, electronic structure, and magnetic properties at Y{sub 3}Fe{sub 5}O{sub 12} (YIG)/Pt interface are detailed characterized to correlate the microstructure and magnetic properties with interfacial transport properties. It is found that the order-disorder structure transformation at the interface is accompanied with oxygen deficiency, thus the reduced iron valence and the break of magnetic atom-O-magnetic atom bridges, which is responsible for superexchange interaction and magnetic order. It is also found that the magnetic moment of interfacial iron ions is decreased. The disorder interfacial layer with suppressed magnetism finally contributes to the declined spin transport efficiency. Our results provide the knowledge to control and manipulate the interfacial structure and properties in order to obtain higher spin transport efficiency.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Understanding Microstructure Variability in Vapor-Deposited Energetic Materials by Using Phase-Field Methods

Critical components, such as detonators, in Sandia's stockpile contain heterogeneous materials whose performance and reliability depend on accurate, predictive models of coupled, complex phenomena to predict their synthesis, processing, and operation. Ongoing research in energetic materials has shown that microstructural properties, such as density, pore-size, morphology, and specific surface area are correlated to their initiation threshold and detonation behavior. However, experiments to study these specific characteristics of energetic materials are challenging and time consuming. Therefore, in this work, we turn to mesoscale modeling methods that may be capable of reproducing some observed phenomena to refine and predict outcomes beforehand. Even so, we have no physics-based modeling capability to predict how the microstructure of an energetic material will evolve over near- and long-term time scales. Thus, the goal of this work is to (i) identify any knowledge gaps in how the underlying microstructure forms and evolves during the synthesis process, and (ii) develop and test a mesoscale phase-field model for vapor deposition to capture critical mechanisms of microstructure formation, evolution, and variability in vapor-deposited energetic materials, such as processing conditions, material properties, and substrate interactions. Based on this work, the phase-field method is shown to be a valuable tool for developing the necessary models containing coupled, complex phenomena to investigate and understand the synthesis and processing of energetic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effect of the overlapping factor on the microstructure and mechanical properties of pulsed Nd:YAG laser welded Ti6Al4V sheets

The effect of the overlapping factor on the microstructures and mechanical properties of pulsed Nd:YAG laser welded Ti6Al4V alloy sheets was investigated by microstructural observations, microhardness tests, tensile tests and fatigue tests. A microstructural examination shows that by increasing the overlapping factor, the grains in the fusion zone become coarser, and the width of the heat affected zone increases. As overlapping factor increases, the width of region composed completely of martensite α′ and the secondary α phase in the heat affected zone increases, consequently the gradient of microstructure along the direction from the fusion zone to base metal decreases, so does the gradient of microhardness. The results of tensile and fatigue tests reveal that the joints made using medium overlapping factor exhibit better mechanical properties than those welded with low and high overlapping factors. Based on the experimental results, it can be stated that a sound weld of Ti6Al4V alloy can be obtained if an appropriate overlapping factor is used. - Highlights: • The weld quality of Ti6Al4V alloy under various overlapping factors was assessed. • Tensile and fatigue tests were conducted with as-welded specimen. • Localized strain across the weld was measured using DIC photogrammetry system. • A sound weld of Ti6Al4V alloy is obtained by using right overlapping factor.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effects of rejuvenation modes on the microstructures and mechanical properties of metallic glasses

This study systematically investigates the effects of three rejuvenation modes, namely biaxial loading, thermal pressure loading, and cryogenic thermal cycling, on the microstructures and mechanical properties of Cu 64 Zr 36 metallic glasses (MGs) using molecular dynamics (MD) simulations. The simulation results demonstrate that biaxial tension application during loading results in a rejuvenated glassy state with high strength. Specifically, we find that the yield stress, Young's modulus, and shear modulus of the rejuvenated glass obtained by biaxial tensile loading decreased by 2.8%, 2.1%, and 2.7%, respectively, compared to an as-cast MG reference. We also find that MGs achieve the greatest degree of rejuvenation, at the expense of strength, with the use of thermal pressure loading. Interestingly, the application of cryogenic thermal cycling results in a rejuvenated state with a lower strength drop compared to thermal pressure loading. Furthermore, analysis of the potential energy and medium-range-order (MRO) size indicates that the microstructures of MGs achieves a high-energy ordered glass state after thermal pressure loading, but a high-energy disordered glass state after biaxial tensile loading and cryogenic thermal cycling. Furthermore, these findings provide meaningful insights into the effect of rejuvenation modes on the microstructures and mechanical properties of MGs, as well as useful guidelines for designing MGs with high strength and superior plasticity for prospective applications in industry.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Gas sensing properties of magnesium doped SnO{sub 2} thin films in relation to AC conduction

Conducting magnesium doped (0 to 1.5 wt %) tin oxide thin films prepared by Spray Pyrolysis technique achieved detection of 1000 ppm of LPG. The films deposited at 304 °C exhibit an enhanced response at an operating temperature of 350 °C. The microstructural properties are studied by means of X-ray diffraction. AC conductivity measurements are carried out using precision LCR meter to analyze the parameters that affect the variation in sensing. The results are correlated with compositional parameters and the subsequent modification in the charge transport mechanism facilitating an enhanced LPG sensing action.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Effects of Sc Addition on the Microstructure and Mechanical Properties of Be-Al Alloy Fabricated by Induction Melting

This study investigated the alloying effects of 0.4 wt.% Sc on the microstructure, mechanical properties, and fracture behavior of a cast Be-Al alloy prepared by vacuum induction melting. The micromechanics of Sc-containing secondary-phase particles (SPs) were characterized by nanoindentation, and the fracture behavior of the alloy was investigated via tensile fractography and optical metallography. The addition of 0.4 wt.% Sc significantly modified the alloy microstructure by decreasing the secondary dendritic arm spacing (SDAS), weakening the dendritic structure of Be, and producing an equiaxed/cellular alloy microstructure with refined Be grains. Sc alloying increased the Vickers hardness by 36%, elastic modulus by 28%, yield strength by 35%, ultimate strength by 52%, but decreased the elongation from 3.6 to 2.9%. Sc-containing SPs had a higher elastic modulus, yield strength, microhardness, and a lower plasticity index than the Be and Al matrices, resulting in interface separation during the fracture process. SPs located at the Be/Al interfaces did not act as microcrack sources for the matrices, whereas highly faceted SPs within the Be grains induced microcrack formation and decreased the elongation. The failure mode of the cast Be-Al-0.4Sc alloy still involved the brittle cleavage failure of Be regions and ductile dimple failure of Al regions, which was not the case with the cast Be-Al alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructures and Mechanical Properties of Resistance Spot-Welded Steel/Aluminum Alloy Joints with Process Tapes

The microstructure and mechanical property of resistance spot-welded joints of steel and aluminum were studied by using process tapes. The steel/aluminum joint consists mainly of aluminum nugget and interface zone. The liquid nugget solidification has an epitaxial growth characteristic, and the interface zone displays a double-layer structure, Fe{sub 2}Al{sub 5} layer at steel side and Fe{sub 4}Al{sub 13} layer at aluminum nugget side. Compared with joints without process tape, the joint nugget diameter and tensile shear load increased by 35.45 and 10.98%, respectively, and its indentation ratio decreased by 56.25% due to the process tapes increasing heat input, producing larger nugget diameter and continuous interface layer, and protecting against deep indentation. The joining area of intermetallic layer and aluminum nugget is weak link in the joint. It is favorable to use the process tapes for improving welding quality, raising joint strength, and energy saving.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Characterization of geopolymer fly-ash based foams obtained with the addition of Al powder or H{sub 2}O{sub 2} as foaming agents

Recent innovations in geopolymer technology have led to the development of various different types of geopolymeric products, including highly porous geopolymer-based foams, which are formed by the addition of foaming agents to a geopolymer fly-ash based matrix. These agents decompose, or react with the liquid matrix or oxygen in the matrix, resulting in the release of gases which form pores prior to the hardening of the gel. The hardened structure has good mechanical and thermal properties, and can therefore be used for applications in acoustic panels and in lightweight pre-fabricated components for thermal insulation purposes. This study presents the results of the pore-forming process in the case when two different foaming agents, i.e. aluminium powder amounting to 0.07, 0.13 and 0.20 mass. % and H{sub 2}O{sub 2} amounting to 0.5, 1.0, 1.5 and 2.0 mass. %, were added to a fly-ash geopolymer matrix. The physical, mechanical, and microstructural properties of the thus obtained foams, and the effects of the type and amount of the added foaming agent, are presented and discussed. Highly porous structures were obtained in the case of both of the investigated foaming agents, with overall porosities up to 59% when aluminium powder was added, and of up 48% when H{sub 2}O{sub 2} was added. In the latter case, when 2% of the H{sub 2}O{sub 2} foaming agent was added, finer pores (with diameters up to 500 μm) occurred in the structure, whereas somewhat larger pores (some had diameters greater than 1 mm) occurred when the same amount of aluminium powder was added. The mechanical properties of the investigated foams depended on their porosity. In the case of highly porous structures a compressive strength of 3.3 MPa was nevertheless achieved for the samples containing 0.2% of aluminium powder, and 3.7 MPa for those containing 2.0% of H{sub 2}O{sub 2}. - Highlights: • Preparation of geopolymer foams based on fly ash with the addition of Al powder or H{sub 2}O{sub 2} as foaming agents • Determination of density, porosity and mechanical properties of such foams • Characterization of foaming process by means of X-ray micro-tomography (μcT)

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Deformation Temperature on the Microstructure and Mechanical Properties of High-Strength Low-Alloy Steel During Hot Compression

The microstructure and mechanical properties of high-strength low-alloy steel were investigated at deformation temperatures of 800-1100 °C and strain rates of 0.1-10 s{sup −1} using an MMS-200 thermal mechanical simulator. The results indicated that the increased deformation processes observed between the starting and finishing temperatures during hot compression testing caused a polygonal ferrite transformation in the material. The polygonal ferrite grain sizes increased with increasing transformation temperatures and gradually grew larger at higher deformation temperatures. Widmanstätten ferrite and acicular ferrite were also formed at high temperatures from 1000-1100 °C, which accordingly led to an increase in Vickers microhardness. In addition, the flow stress in the material increased with an increase in the strain and a decrease in the deformation temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A Comparative Study of the Efficacy of Local/Global and Parametric/Nonparametric Machine Learning Methods for Establishing Structure–Property Linkages in High-Contrast 3D Elastic Composites

Reduced-order structure–property (S-P) linkages play a pivotal role in the tailored design of materials for advanced engineering components. There is a critical need to distill these from the simulation datasets aggregated using sophisticated, computationally expensive, physics-based numerical tools (e.g., finite element methods). The recent emergence of materials data science approaches has opened new avenues for addressing this challenge. In this paper, we critically compare the relative merits of the application of four distinct machine learning approaches for their efficacy in extracting microstructure-property linkages from the finite element simulation data aggregated on high-contrast elastic composites with different microstructures. The machine learning approaches selected for the study have included different combinations of local/global and parametric/nonparametric approaches. Furthermore, the nonparametric approaches selected for this study are based on Gaussian Process (GP) models that allow for a formal treatment of uncertainty quantification in the predicted values. The predictive performances of these different approaches have been compared against each other using rigorous cross-validation error metrics. Furthermore, their sensitivity to both the dataset size and dimensionality has been investigated.

36 MATERIALS SCIENCE↗