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Results for “Optical Microscopy”

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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Investigation on Explosive Welding of Zr{sub 53}Cu{sub 35}Al{sub 12} Bulk Metallic Glass with Crystalline Copper

A Zr{sub 53}Cu{sub 35}Al{sub 12} bulk metallic glass (BMG) was welded to a crystalline Cu using explosive welding technique. The morphology and the composition of the composite were characterized using optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy and transmission electron microscopy. The investigation indicated that the BMG and Cu were tightly joined together without visible defects, and a thin diffusion layer appeared at the interface. The captured jet at the end of the welding region mostly comes from the Cu side. Amorphous and partially crystallized structures have been observed within the diffusion layer, but the BMG in close proximity to the interface still retains its amorphous state. Nanoindentation tests reveal that the interface exhibits an increment in hardness compared with the matrix on both sides.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Novel technique for spatially resolved imaging of molecular bond orientations using x-ray birefringence

Birefringence has been observed in anisotropic materials transmitting linearly polarized X-ray beams tuned close to an absorption edge of a specific element in the material. Synchrotron bending magnets provide X-ray beams of sufficiently high brightness and cross section for spatially resolved measurements of birefringence. The recently developed X-ray Birefringence Imaging (XBI) technique has been successfully applied for the first time using the versatile test beamline B16 at Diamond Light Source. Orientational distributions of the C–Br bonds of brominated “guest” molecules within crystalline “host” tunnel structures (in thiourea or urea inclusion compounds) have been studied using linearly polarized incident X-rays near the Br K-edge. Imaging of domain structures, changes in C–Br bond orientations associated with order-disorder phase transitions, and the effects of dynamic averaging of C–Br bond orientations have been demonstrated. The XBI setup uses a vertically deflecting high-resolution double-crystal monochromator upstream from the sample and a horizontally deflecting single-crystal polarization analyzer downstream, with a Bragg angle as close as possible to 45°. In this way, the ellipticity and rotation angle of the polarization of the beam transmitted through the sample is measured as in polarizing optical microscopy. The theoretical instrumental background calculated from the elliptical polarization of the bending-magnet X-rays, the imperfect polarization discrimination of the analyzer, and the correlation between vertical position and photon energy introduced by the monochromator agrees well with experimental observations. The background is calculated analytically because the region of X-ray phase space selected by this setup is sampled inefficiently by standard methods.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Materials Based on Solid Solutions of Bismuth and Antimony Tellurides Formed by Rapid Melt Crystallization Methods

p-type Bi 0.5 Sb 1.5 Te 3 solid solutions prepared by hot pressing and the extrusion of powders prepared by rapid melt crystallization methods such as melt spinning and melt crystallization in a liquid are investigated. The morphology of the powders, the sample cleavage surface, and their microstructure are investigated using optical microscopy, scanning electron microscopy, and scanning tunneling microscopy. The mechanical properties of the samples are investigated by room-temperature compression tests. The Seebeck coefficient, electrical conductivity, and thermal conductivity of the materials are measured in the temperature range of 100–600 K. The highest limiting compressive strength σ B = 145 MPa at 300 K and maximal thermoelectric efficiency (ZT) max = 1.34 at 370 K are found for materials extruded from granules prepared by melt crystallization in water and ground in a ball mill.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Neutron irradiation effects on the corrosion of Zircaloy-4 in a pressurized water reactor environment - 2016-0085

Long-time Advanced Test Reactor (ATR) corrosion weight-gain data from non-fueled α-processed Zircaloy-4 cladding coupons are presented herein. The data were generated in pressurized loops that simulated pressurized water reactor (PWR) chemistry, temperature, and neutron flux conditions. High neutron flux and high-fluence post-transition corrosion rates were accelerated over out-of-flux post-transition corrosion rates by more than 40 times at 270 deg. C and more than 30 times at 310 deg. C We conclude in large part that the acceleration was caused by irradiation-induced changes to the base metal. The effect that irradiation has on the base metal and its effect on corrosion has been shown in the past to be carried over into post-irradiation tests in autoclave environments, but its impact was shown in this study to be accentuated in the in-reactor environment, in which sustained corrosion accelerations were much greater than observed in the postirradiation tests (in non-irradiation environments). This suggests some aspect of the radiation environment potentially acts synergistically with the corrosion film formed from the irradiation-damaged base metal to further accelerate in-reactor corrosion rates. We also present results from detailed microstructural examinations of thick (more than 25 μm) oxide films formed on α-processed Zircaloy-4 grown in a 360 deg. C autoclave and in the reactor. The examinations consisted of optical microscopy, field emission gun scanning electron microscopy, focused ion beam microscopy, analytical electron microscopy, and X-ray diffraction, with a focus on the evolution of the microstructure of the intermetallic precipitates in the oxide films during exposure to autoclave water or to the corroding environment under neutron irradiation. The film microstructure suggests that the water environment was closer to the oxide-metal interface in the films grown in the reactor than in the autoclave-grown corrosion films examined, but it was not obvious from the microstructural examinations how the radiation environment facilitated that effect. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of environmental exposure on autogenous self-healing of cracked cement-based materials

Despite abundant literature on self-healing of cement-based materials, there is dearth of information on how environmental exposure affects self-healing. In this study, self-healing of cracks in cement mortar under different environmental exposure was investigated. Pre-cracked mortar specimens were submerged in water, while identical specimens were exposed to cyclic temperature and relative humidity. Change in crack width was examined using optical microscopy. SEM coupled with energy dispersive X-ray analysis was used to identify healing compounds. Mercury Intrusion Porosimetry, water absorption and permeability were employed to assess porosity. X-ray computed tomography was deployed to explore healing of internal cracks. No significant self-healing occurred in specimens exposed to cyclic T and RH. Although crack self-healing was identified in submerged specimens, X-ray μCT demonstrated that it was limited to exposed surface of specimens. This warrants further research to bridge the gap between laboratory findings on self-healing and actual field performance of ageing civil infrastructure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Hot Deformation Behavior and Microstructural Evolution of Antibacterial Austenitic Stainless Steel Containing 3.60% Cu

Hot deformation behavior of as-cast antibacterial austenitic stainless steel containing 3.60% copper was investigated in a temperature range of 900-1150 °C and strain rate range of 0.01-20 s{sup −1}. At strain rates higher than 1 s {sup −1}, the flow stress curves were corrected considering adiabatic heating. Kinetic analysis indicated that the hot deformation activation energy of steel was 376.02 kJ mol{sup −1}. The microstructural evolution under different temperatures was observed by optical microscopy. The nucleation sites for recrystallization and different orientations and twin ratios under different strain rates were analyzed by electron backscatter diffraction. The results showed that hot deformation was dominated by continuous dynamic recrystallization in the high-temperature and high-strain-rate region (1050-1150 °C, 1-20 s{sup −1}). On increasing the temperature and strain rate, the degree of recrystallization and twinning increased simultaneously. These phenomena promoted one another. Thus, the volume fraction of the recrystallized and twinned grains increased with the addition of Cu.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Improvement of the quality of graphene-capped InAs/GaAs quantum dots

In this paper, we study the transfer of graphene onto InAs/GaAs quantum dots (QDs). The graphene is first grown on Cu foils by chemical vapor deposition and then polymer Polymethyl Methacrylate (PMMA) is deposited on the top of graphene/Cu. High quality graphene sheet has been obtained by lowering the dissolving rate of PMMA using vapor processing. Uncapped as well as capped graphene InAs/GaAs QDs have been studied using optical microscopy, scanning electron microscopy, and Raman spectroscopy. We gather from this that the average shifts Δω of QDs Raman peaks are reduced compared to those previously observed in graphene and GaAs capped QDs. The encapsulation by graphene makes the indium atomic concentration intact in the QDs by the reduction of the strain effect of graphene on QDs and the migration of In atoms towards the surface. This gives us a new hetero-structure graphene–InAs/GaAs QDs wherein the graphene plays a key role as a cap layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The effect of Sn addition on phase stability and phase evolution during aging heat treatment in Ti–Mo alloys employed as biomaterials

Increases in life expectancy and improvements in necessary healthcare attach great importance to the development of biomaterials. Ti alloys containing β stabilizing elements are often used as biomaterials due to their high specific strength, high corrosion resistance, unusual biocompatibility and low elastic moduli, which benefit bone tissues close to an implant. This study deals with phase stability in β Ti–Mo–Sn alloys processed under different conditions and was performed according to the following steps: a study of the effect of Sn content (a) on phase stability in Ti–Mo alloys, (b) on the suppression of α″ and ω phase precipitation; (c) on α-phase precipitation during aging heat treatments and (d) on mechanical properties, including the elastic modulus, as measured using tensile tests and acoustic techniques. The alloys were prepared by arc melting under a controlled atmosphere followed by homogenization heat treatment and hot rolling. Optical microscopy, scanning and transmission electron microscopy, X-ray diffraction and differential scanning calorimetry were employed for characterization purposes. Samples were also submitted to solution treatment above the β transus temperature and aging heat treatments under a controlled atmosphere. The results suggest that Sn suppresses the formation of the ω and α″ phases in Ti–Mo system. - Highlights: • Sn addition to Ti alloys decreases elastic modulus by suppressing ω phase precipitation. • Sn addition decreases the temperature of martensite decomposition. • Sn addition decreases the temperature of α phase precipitation and β transus. • Mechanical strength decreases with increasing Sn content.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Formation and mechanism of nanocrystalline AZ91 powders during HDDR processing

Grain sizes of AZ91 alloy powders were markedly refined to about 15 nm from 100 to 160 μm by an optimized hydrogenation-disproportionation-desorption-recombination (HDDR) process. The effect of temperature, hydrogen pressure and processing time on phase and microstructure evolution of AZ91 alloy powders during HDDR process was investigated systematically by X-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy, respectively. The optimal HDDR process for preparing nanocrystalline Mg alloy powders is hydriding at temperature of 350 °C under 4 MPa hydrogen pressure for 12 h and dehydriding at 350 °C for 3 h in vacuum. A modified unreacted core model was introduced to describe the mechanism of grain refinement of during HDDR process. - Highlights: • Grain size of the AZ91 alloy powders was significantly refined from 100 μm to 15 nm. • The optimal HDDR technology for nano Mg alloy powders is obtained. • A modified unreacted core model of grain refinement mechanism was proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Free surface effects on the recrystallization of compressed, stable, Al-Mn single crystals

Highlights: • The free surface provokes high frequency nucleation. • The free surface and surface ‘quality’ do not modify the orientations of the recrystallized grains. • The misorientation relations across recrystallization front are similar for all sections of both orientations. The free surface effect on the grain crystallography and morphology during recrystallization has been studied in stable Goss {110}001 and brass {110}112 - oriented single crystals of Al-1%wt.Mn alloy. The samples were plane strain compressed up to a strain of about 0.5 to develop a homogeneous structure comprising two sets of symmetrical microbands and then lightly annealed. The variation of recrystallization after annealing was then analysed by optical microscopy and SEM/EBSD on different cross-sections. The results are discussed in terms of the misorientation angle and axis distributions. The free surface provokes high frequency nucleation leading to a small grain size compared to internal sections of the bulk sample. However, the free surface and surface ‘quality’ do not modify the orientations of the recrystallized grains, i.e. similar groups of recrystallized grain orientations were observed for all sections. This leads to a strong misorientation relation between deformed/recovered area orientations and the limited number of groups of recrystallized grain orientations, basically the same as those observed during bulk recrystallization of similar crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Austenitizing Temperature on the Microstructure and Mechanical Properties of an Fe-Cr-Ni-Mo-Ti Maraging Stainless Steel

The influence of austenitizing temperature on the microstructure and mechanical properties of an Fe-Cr-Ni-Mo-Ti maraging stainless steel was investigated. The grain size, Laves phase, and retained austenite in steels given different solution treatments were observed using optical microscopy, scanning electron microscopy, and x-ray diffraction. Relationships with mechanical properties were measured by tensile testing. The grain growth rate was relatively slow at temperatures of 800-1000 °C then rapidly increased at higher temperatures. Low-temperature austenitization augmented the retention of austenite, the fraction of which decreased with an increase in austenitizing temperature. The Laves phases, which precipitated in austenite during austenitization at 800-900 °C, were preserved after quenching. The solution treatment had a significant effect on the final tensile properties of the steel after aging, due to the presence of retained austenite and Laves phase reducing its strength.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of the Microstructure on Magnetic Stray Fields of Low-Carbon Steel Welds

This study examines the relationship between the magnetic mesostructure with the microstructure of low carbon steel tungsten inert gas welds. Optical microscopy revealed variation in the microstructure of the parent material, in the heat affected and fusion zones, correlating with distinctive changes in the local magnetic stray fields measured with high spatial resolution giant magneto resistance sensors. In the vicinity of the heat affected zone high residual stresses were found using neutron diffraction. Notably, the gradients of von Mises stress and triaxial magnetic stray field modulus follow the same tendency transverse to the weld. In contrast, micro-X-ray fluorescence characterization indicated that local changes in element composition had no independent effect on magnetic stray fields.

42 ENGINEERING↗
DOE OSTI2018

Study of Morphology and Magnesium Purity, Formed by Vapor Phase Through Silicothermic Reduction

This article describes the influence of temperature profile on the morphology and impurity distributions of magnesium vapor condensation during silicothermic reduction of calcined dolomite. The formation of magnesium crystals was comprehensively analyzed by optical microscopy, scanning electron microscopy (SEM), and inductively coupled plasma (ICP). The results showed that the temperature changed the morphology and purity of condensation products in the condenser. When the temperature of the condenser zone was lower than 250 °C, the magnesium vapor condensation was fine and noncompacted. The crystal growth of magnesium occurred in the range of 250 °C and 380 °C. It was found that crystal magnesium became coarser and denser at higher temperatures. Based on the analysis of crystallized magnesium, the impurity distributions decreased at temperatures higher than those of the condenser. Furthermore, this indicates that the impurity contents with less than 0.04 pct were distributed randomly through the condenser.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High-Temperature Interaction of Liquid Gd with Y{sub 2}O{sub 3}

The sessile drop method combined with contact heating procedure was applied for the investigation of high-temperature interaction between liquid Gd and Y{sub 2}O{sub 3} substrate. Real-time behavior of Gd sample in flowing inert gas (Ar) atmosphere upon heating to and at temperature of 1362 °C was recorded using high-speed high-resolution CCD camera. The results evidenced that molten Gd wets Y{sub 2}O{sub 3} substrate (the contact angle θ < 90°) immediately after melting of metal sample observed at T = 1324 °C (T{sub m} = 1312 °C). During the first 3 min of the sessile drop test, the contact angle dropped from θ = 52° to θ = 24° and then stabilized at the final value of θ{sub f}{sup *} = 33°. The solidified Gd/Y{sub 2}O{sub 3} couple was subjected to structural characterization using optical microscopy, scanning electron microscopy coupled with x-ray energy-dispersive spectroscopy. The results evidenced that the wettability in the Gd/Y{sub 2}O{sub 3} system has a reactive nature and the leading mechanism of the interaction between liquid Gd and Y{sub 2}O{sub 3} is the dissolution of the ceramic in the liquid metal responsible for the formation of a deep crater in the substrate under the drop. Therefore, the final contact angle θ{sub f}*, estimated from the side-view drop image, should be considered as an apparent value, compared to the more reliable value of θ{sub f} = 70° measured on the cross section of the solidified couple.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Morphology and kinetics of polymorphic transformations in K{sub 0.965}Rb{sub 0.035}NO{sub 3} single crystals

Polymorphic transformations in K{sub 0.965}Rb{sub 0.035}NO{sub 3} single crystals have been investigated by optical microscopy and X-ray diffraction. The equilibrium temperature between modifications II and III of the crystal studied is determined to be T = 452 ± 0.5 K. It is found that polymorphic transformations are of the single crystal ↔ single crystal type and occur with the formation and growth of nuclei of new crystals in matrix ones at II ↔ III transformations. An empirical dependence of the growth rate of modification III on temperature is established in the form ϑ = ϑ = (–0.478ΔT + 0.712ΔT{sup 2}–0.00041ΔT{sup 3}) × 10{sup –2} cm/s (ΔT = T{sub tr}–T{sub 0}, where T{sub tr} is the transformation temperature and T{sub 0} is the equilibrium temperature)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Immobilization of Radioactive Wastes Using Geopolymers - 19483

This work explores an encapsulation and immobilization technology for spent radioactive ion exchange (IX) resins using geopolymer materials as a matrix. Geopolymer-IX resin composites with different IX resin loadings were prepared by mixing an aluminosilicate material (metakaolin), sodium hydroxide and inactive IX resin (Amberlite IRN 150) and curing the mixture at room temperature with or without γradiation applied using an external radiation source. The metakaolin and sodium hydroxide reacted to form a geopolymer framework encapsulating the IX resin beads. The IX resin loading capacity and the encapsulation efficiency of the geopolymer material were investigated by examining the morphology and distribution of resins within the geopolymer framework using optical microscopy, and by measuring the compressive strengths of the geopolymer-IX resin composites. These properties of the geopolymer-IX resin composites were compared with those of ordinary Portland cement (OPC)-IX resin composites. The geopolymer matrix allowed for a higher IX resin loading capacity than OPC. The geopolymer-IX resin composite was stable under γ-radiation for 28 d. In leaching tests performed with encapsulated Sr-loaded IX resins, the ability of the geopolymer to prevent leaching of Sr{sup 2+} into solution was greatly superior to that of OPC. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Ultrafast carrier capture and Auger recombination in single GaN/InGaN multiple quantum well nanowires

Ultrafast optical microscopy is an important tool for examining fundamental phenomena in semiconductor nanowires with high temporal and spatial resolution. In this paper, we used this technique to study carrier dynamics in single GaN/InGaN core–shell nonpolar multiple quantum well nanowires. We find that intraband carrier–carrier scattering is the main channel governing carrier capture, while subsequent carrier relaxation is dominated by three-carrier Auger recombination at higher densities and bimolecular recombination at lower densities. Finally, the Auger constants in these nanowires are approximately 2 orders of magnitude lower than in planar InGaN multiple quantum wells, highlighting their potential for future light-emitting devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Adiabatic Shear Localization and Microstructure in Ultrafine Grained Aluminum Alloy at Cryogenic Temperature

Adiabatic shear localization plays an important role in the deformation and failure of ultrafine grained 6061 aluminum alloy processed by friction stir processing. To understand the effects of temperature and strain on adiabatic shear localization in the ultrafine grained 6061 aluminum alloy, it has been investigated dynamic mechanical behavior of ultrafine grained 6061 aluminum alloy under the controlled shock loading experiments. Deformation characteristics and microstructures in the shear band were performed by optical microscopy and transmission electron microscopy. The shear band in the ultrafine grained aluminum alloy is a long and straight band distinguished from the matrix. The width of the shear band decreases with increasing nominal strain. The results show that the grains in the boundary of the shear band are highly elongated along the shear direction and form the elongated cell structures (0.2 μ in width), and the core of the shear band consists of a number of recrystallized equiaxed grains 0.2-0.3 μ in diameters and the second phases distribute in both the boundary and the inner of the equiaxed new grains. The calculated temperature in the shear band is about 692 K. Rotational dynamic recrystallization mechanism is responsible for the formation of the microstructure in the shear band.

36 MATERIALS SCIENCE↗