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At least 1,459 records · Page 81
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Superconducting Performance, Structure, Microstructure, and Trapped Field of Top-Seeded Melt-Processed Bulk Y{sub 3}Ba{sub 5}Cu{sub 8}O{sub x}

The sintering temperature for the production of Y{sub 3}Ba{sub 5}Cu{sub 8}O{sub 18} (Y-358) preform powders synthesized in sol-gel spontaneous combustion technique was optimized. A large single-grain bulk Y-358 crystal was fabricated employing a top-seeded melt-growth technique utilizing the optimally sintered preform powders (i.e., at 900 {sup ∘}C for 12 h). Structural, microstructural, elemental, and magnetic properties were investigated by means of X-ray diffraction, scanning electron microscopy, and SQUID, respectively. The structural characterization indicated that the sample is highly textured in (00l) direction. The Y-358 phase fractions were estimated in both preform powders and bulk sample using Rietveld refinement. The onset of superconducting transition is observed at 92.5 K, and the curve is very sharp indicative of the high quality of the produced bulk sample. The field dependence of critical current density (J{sub c}) was determined at 77 K, and the self-field J{sub c} was found to be ∼26 kA/cm{sup 2}. A magnetic field of 0.27 T was trapped by the sample at 77 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of the Laser Scan Rate on the Microstructure, Magnetic Properties, and Microhardness of Selective Laser-Melted FeSiB

FeSiB alloys have been fabricated by selective laser melting (SLM) using a laser scan rate of 0.1–1.5 m/s, laser power of 90 W, scan line spacing of 40 μ m, and layer thickness of 50 μ m. X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, atomic force microscopy, profilometer, microdurometer, and vibrating sample magnetometer have been used to investigate the structural, microstructural, roughness, microhardness, and magnetic property changes during the laser melting process. The produced samples exhibit a nanocomposite structure consisting of nanocrystalline α-Fe{sub 0.95}Si{sub 0.05} and Fe{sub 2}B phases embedded into an amorphous ε-FeSi-type matrix. The selective laser-melted samples show high density, low surface roughness, higher microhardness values (1654–2273 Hv), and soft magnetic properties (M{sub s} = 188.6–199 emu/g and H{sub c} = 43.8–73 Oe).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effects on Glass Forming Ability, Microstructure, Crystallization Behaviors, and Magnetic Properties of Si Substituting for P in Fe-Rich Fe{sub 86}B{sub 13−x}Si{sub x}P{sub 1}Cu{sub 0.6}Hf{sub 0.4} Alloys

In the paper, we have studied the effects on glass forming ability (GFA), microstructure, crystallization behaviors, and saturation magnetization (M{sub s}) of Si substitution for P in Fe-rich Fe{sub 86}B{sub 12}Si{sub x}P{sub 1−x}Cu{sub 0.4}Hf{sub 0.6} alloys. The amorphous structure is identified by X-ray diffraction first, and the patterns with Si addition less than x = 0.75 only show one halo scattering peak at 2θ = 45°; further, the ribbons with entirely amorphous structure have been fabricated successfully and the alloys have a good GFA. Then, by differential scanning calorimetry testing, the curves show two separated exothermic peaks and the ribbons will go through a two-step crystallization before reaching stable state; further, the first peak is ensured by the crystallization of a-Fe phase while the second peak is ensured by the precipitation of FeB or Fe(BP) compounds. As Si was added, the apparent activation energy of the first crystallization (E{sub a1}) and the second crystallization (E{sub a2}) shows an increased tendency first and then decreases slightly. By comparison, as x = 0, x = 0.25, and x = 0.5, the ribbons easily form Hf{sub 3}P{sub 2} compounds during the first crystallization process simultaneously, where the ribbons of x = 0.75 and x = 1.0 are easier to finish the first crystallization for forming the uniform a-Fe phase entirely. By vibrating sample magnetometer testing, with the addition of Si, M{sub s} value shows an increased trend and reaches to the maximum about 177.5 emu/g (x = 1.0), and which shows an increased trend in the subsequent annealing process and reaches to the maximum 206.3 emu/g (x = 0), 212.3 emu/g (x = 0.25), 214.2 emu/g (x = 0.5), 214.9 emu/g (x = 0.75), and 208.3 emu/g (x = 1.0) as the annealing temperature higher than T{sub p1} but less than T{sub x2}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Influence of Packing Atmosphere on the Microstructures and Transport Properties of Bi-2223/AgAu Tapes

Oxygen partial pressure was the key factor to tune the phase evolution mechanism of Bi-2223 system. In order to investigate the influence of packing atmosphere on the phase formation rate of Bi-2223, microstructures‚ and the current capacity of final tapes‚ 37-filamentary Bi-2223/AgAu tapes were fabricated by powder-in-tube (PIT) process, and the powder packing process operated in the glove box under different atmosphere of pure O{sub 2}‚ air, and N{sub 2}–7.5%O{sub 2}, with the oxygen partial pressure of 100%‚ 25%, and 7.5%, respectively. With different packing atmosphere, the phase formation rate of Bi-2223 increased obviously during the first heat treatment process (HT1). While, based on the same HT1 process, the maximum Bi-2223 phase content was obtained in the tapes with packing atmosphere of N{sub 2}–7.5%O{sub 2}‚ which should be attributed to the suitable Bi-2223 content and distribution. Due to the improvement of superconducting phase content and better texture structure, the critical current density increased with decreasing oxygen partial pressure of packing atmosphere and the maximum value of 19.9 kA/cm{sup 2} was reached. Moreover‚ the in-field current capacities of these Bi-2223/AgAu tapes have also been enhanced with low oxygen partial pressure in packing atmosphere, attributed to the improvements of intergrain connectivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Influence of Annealing on Microstructure, Electrochemical, and Magnetic Properties of Co-Doped SrTiO{sub 3} Nanocubes

Effect of annealing on microstructure, electrochemical, and magnetic properties of Co-doped SrTiO{sub 3} nanocubes obtained by the hydrothermal method was studied. X-ray diffraction (XRD) results of all as-prepared and annealed Co-doped SrTiO{sub 3} samples revealed a cubic perovskite structure with the second phases of SrCO{sub 3} and Co{sub 3}O{sub 4}in as-prepared and annealed SrTi{sub 0.90}Co{sub 0.10}O{sub 3} samples, respectively. Agglomerated nanocubes could be clearly observed in all as-prepared and annealed Co-doped samples by scanning electron microscope (SEM) and transmission electron microscope (TEM). X-ray absorption near edge spectroscopy (XANES) results suggested the presence of Co{sup 2+} cations in as-prepared Co-doped SrTiO{sub 3} samples, while both of Co{sup 2+} and Co{sup 3+} cations were found in annealed Co-doped SrTiO{sub 3} samples. The cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) results of as-prepared and annealed SrTi{sub 1-x}Co{sub x}O{sub 3} (x = 0.05, 0.075 and 0.10) electrodes revealed pseudocapacitor behavior of the Faradaic redox reaction type. The specific capacitance (Csc) was affected by the increase of Co content in all as-prepared and annealed Co-doped SrTiO{sub 3} samples with an excellent cycling stability after 200 cycle test of 97.24% and the highest value of 75.28 F g{sup −1} at 1 A g{sup −1} in an annealed SrTi{sub 0.925}Co{sub 0.075}O{sub 3} electrode. Magnetization measurements at room temperature using vibrating sample magnetometer (VSM) revealed diamagnetic behavior of as-prepared SrTiO{sub 3} sample, whereas paramagnetic behavior was observed in all as-prepared Co-doped SrTiO{sub 3} samples. After annealing, undoped sample exhibited paramagnetic behavior, whereas ferromagnetic behavior was observed in all Co-doped SrTiO{sub 3} samples with the increase of saturation magnetization (M{sub s}) at 10 kOe from 0.58 to 1.63 emu/g and the coercive field (H{sub c}) from 43.71 to 123.87 Oe, suggested to originate from the face-center exchange (FCE) mechanism.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Implications of theoretical analysis to explore the functional core dimension in one-rod core microstructured optical fibers

A new development in optical fiber technology that has attracted interest for multitude of novel and potential applications is an all-in-silica microstructured optical fibre (MOF) with one-rod core. We aim to estimate the functional core dimension for one-rod core triangular MOF (T-MOF) from its geometrical characteristics by using an alternative analytical field model. Moreover, to scrutinize the validity of the choice of effective core dimension (by adapting V-parameter, i.e., the normalized frequency) for T-MOF, we have explored the rudimentary propagation characteristics of the T-MOF in single mode guidance realm. We made comparisons with those which are based on the experimental and numerical studies. Relative errors are also reported.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

The Influence of Microstructure on Oxidation Rate Of V–Cr–Ta–Zr Alloy During Its Chemical-Heat Treatment

Using the methods of scanning (electron backscatter diffraction) and transmission electron microscopy, an investigation of the influence of microstructure of a V–Cr–Ta–Zr alloy on the rate of surface oxide scale formation in the course of its chemical-heat treatment using oxidation in air is performed. It is shown that a preliminary plastic deformation, ensuring a multiple increase in the density of dislocations and misorientation boundaries, results in a 10% thicker surface oxide layer and a respective increase in the concentration of oxygen in the alloy during the final stage of its chemical-heat treatment. The role of this factor in developing the chemical-heat treatment regimes is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Special Aspects of Microstructure, Deformation and Fracture of Bioinert Zirconium and Titanium-Niobium Alloys in Different Structural States

The characteristics of microstructure, deformation and fracture of Zr – 1 wt% Nb and Ti – 45 wt% Nb bioinert alloys in the coarse- and ultrafine-grained states are investigated. It is shown that the ultrafine-grained structure formed in them ensures excellent mechanical properties of the alloys and affects the stages of the stress-strain curves and the behavior of the maximum temperature vs. deformation time plot. The formation of an α-phase in the Ti – 45 wt% Nb ultrafine-grained alloy suppresses the linear stage VI characterized by a constant strain hardening coefficient. In stage VII, the strain hardening coefficient rapidly becomes negative, which indicates the material softening prior to its failure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Microstructural Changes and Kinetics of Reduction of Hematite to Magnetite in CO/CO{sub 2} Gas Atmospheres

The microstructures of porous magnetite formed on gaseous reduction of dense hematite have been examined using high-resolution scanning electron microscopy. It has been shown that cellular pores are formed on reduction in the temperature range 573 K to 973 K (300 °C to 700 °C). Dendritic shaped gas pores are formed on reduction at temperatures between 1073 K and 1273 K (800 °C and 1000 °C). The apparent chemical reaction rate constant for the reduction of hematite to magnetite in CO/CO{sub 2} gas mixtures has been derived from measurements of product thickness against reaction time; the rate constant is described by the relation φ{sub CO} = 0.232exp(76,000/RT) µm s{sup −1} atm{sup −1}.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Formation Mechanisms and Microstructure Characterization of Al/Al{sub 3}Ni In-situ Composite by Compound Casting

The Compound casting method was used to produce an Al/Ni bimetal composite. The mechanisms of formation of the reinforcing intermetallic phases were studied and the produced bimetal composite’s microstructure was then characterized. The results showed that the Al/Ni interface consisted of two intermetallic layers including Al{sub 3}Ni{sub 2} and Al{sub 3}Ni. It is suggested that the Al{sub 3}Ni reinforcing particles of the composite originated from two sources. (1) Some Al{sub 3}Ni particles detached from the Al{sub 3}Ni layer formed at the interface between the Ni core and the Al melt and dispersed in the liquid Al and (2) Al-Al{sub 3}Ni eutectic phase, which formed during the solidification process. The increase in the temperature led to the formation of more reinforcing particles and extended the depth of dispersion of the particles in the Al matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Effect of Melt Ultrasound Treatment on the Microstructure and Age Hardenability of Al-4 Wt Pct Cu/TiC Composite

In the present work, Al-4 wt pct Cu/TiC composite was synthesized by the molten salt route that contains submicron-sized TiC particles in the Al-4 wt pct Cu matrix. The concentration of the TiC particle in the base alloy is 7.5 wt pct. Melt ultrasound treatment was done by remelting the as-cast composite at 1023 K (750 °C) in a view to refine the size of TiC particles to nanoscale and distribute them evenly in the matrix. The microstructure and age hardenability of the untreated and ultrasound-treated composites were investigated. The TiC particles accelerate the precipitation kinetics of CuAl{sub 2} phase in Al-4 wt pct Cu alloy. In the present study, the hardness obtained for untreated Al-4 wt pct Cu/TiC composite is 120 VHN within 5 hours of peak aging time, which is higher than the hardness of the monolithic Al-4 wt pct Cu, which is 104 VHN at 35 hours of peak aging time. Melt ultrasound treatment of Al-4 wt pct Cu/TiC composite shows no significant effect on the distribution and refinement of TiC particles in the matrix. However, it partially disintegrates the TiC into Al{sub 3}Ti and Al{sub 4}C{sub 3} particles. The ultrasound-treated composite showed an improved hardness of about 132 VHN at 5 hours of peak aging, in comparison to that of the untreated composite, by forming denser and homogeneous CuAl{sub 2} precipitates.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Properties of 5083 Al/1060 Al/AZ31 Composite Plate Fabricated by Explosive Welding

A 5083 Al/1060 Al/AZ31 composite plate was fabricated by explosive welding. The microstructure and properties of the composite plate were investigated after explosive welding. The results showed that all bonding interfaces were wavy interfaces. With an increasing distance from the detonation point, the wavelength and the amplitude also increased. The EDS results indicated that a 5-μm diffusion layer was observed at the 1060 Al/AZ31 layer, including the Mg{sub 2}Al{sub 3} phase. Adiabatic shear bands and twin structures were observed in AZ31. The shear bond strength of the 5083 Al/1060 Al interface was 60 MPa, and the shear bond strength of the 1060 Al/AZ31 interface was 84 MPa.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructures, Martensitic Transformation, and Mechanical Behavior of Rapidly Solidified Ti-Ni-Hf and Ti-Ni-Si Shape Memory Alloys

In this work, the microstructure and mechanical properties of rapidly solidified Ti{sub 50−x/2}Ni{sub 50−x/2}Hf{sub x} (x = 0, 2, 4, 6, 8, 10, and 12 at.%) and Ti{sub 50−y/2}Ni{sub 50−y/2}Si{sub y} (y = 1, 2, 3, 5, 7, and 10 at.%) shape memory alloys (SMAs) were investigated. The sequence of the phase formation and transformations in dependence on the chemical composition is established. Rapidly solidified Ti-Ni-Hf or Ti-Ni-Si SMAs are found to show relatively high yield strength and large ductility for specific Hf or Si concentrations, which is due to the gradual disappearance of the phase transformation from austenite to twinned martensite and the predominance of the phase transformation from twinned martensite to detwinned martensite during deformation as well as to the refinement of dendrites and the precipitation of brittle intermetallic compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure, Corrosion and Magnetic Behavior of an Aged Dual-Phase Stainless Steel

In the present work, the effect of the precipitation phenomena on corrosion and magnetic behavior of an aged dual-phase stainless steel was investigated. Aging treatment caused the precipitation of the σ phase, chromium carbides and secondary austenite, which was accompanied by the shifting of the δ/γ interfaces inside the δ ferrite grains. Aging between 700 and 850 °C strongly deteriorated the pitting corrosion resistance of the studied material. Magnetic investigation of the aged material using the vibration sample magnetic technique revealed the sensitivity of the intrinsic magnetic properties to the smallest microstructural change. This was confirmed by the Eddy current technique that led also to the evaluation of the aging-induced localized corrosion.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Experimental Investigation of Microstructure and Phase Transitions in Ag-Cu-Zn Brazing Alloys

Microstructure and phase transitions of selected brazing alloys from the Ag-Cu-Zn ternary system were investigated. Four ternary alloys with silver content in the compositional range from 25 to 60 wt.% were studied using x-ray diffraction (XRD) and scanning electron microscopy coupled with the energy-dispersive spectroscopy (SEM–EDS). Phase transitions of the investigated alloys were measured using differential scanning calorimetry (DSC). Experimentally obtained results were compared with the results of a thermodynamic calculation of the phase equilibria according to the CALPHAD method. The experiments confirmed the optimized thermodynamic parameters for the calculations from the thermodynamic assessment in literature. Phase compositions, liquidus and solidus temperatures were confirmed by the EDS and DTA methods. Additionally, the calculated solidification paths and predicted phase transformations were in agreement with the SEM images.

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 OSTI2018

Effect of Different Thermomechanical Processes on the Microstructure, Texture, and Mechanical Properties of API 5L X70 Steel

A commercial API 5L X70 steel plate was subjected to different thermomechanical processes to propose a novel thermomechanical rolling path to achieve improved mechanical properties. Scanning electron microscopy, electron backscatter diffraction, and x-ray texture analysis were employed for microstructural characterization. The results showed that strain-free recrystallized {001} ferrite grains that developed at higher rolling temperature could not meet the American Petroleum Institute (API) requirements. Also, refined and work-hardened grains that have formed in the intercritical region with high stored energy do not provide suitable tensile properties. However, fine martensite–austenite constituents dispersed in ferrite matrix with grains having predominantly {111} and {110} orientations parallel to the normal direction that developed under isothermal rolling at 850 °C provided an outstanding combination of tensile strength and ductility.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructural and Mechanical Properties of Hot Roll Bonded Titanium Alloy/Low Carbon Steel Plate

In this paper, a titanium alloy and low carbon steel were bonded via hot rolling in a vacuum, and the effect of roll bonding temperature and reduction ratio on the microstructural and mechanical properties of the plate was studied. When the bonding temperature was between 850 and 1050 °C, the shear strength of the interface increased with an increasing reduction ratio from 18 to 70%. At a bonding temperature of 950 °C and at a rolling reduction ratio of 70%, the best bonding strength was obtained, and a shear fracture occurred on the low carbon steel matrix. At 1050 °C, brittle compounds, i.e., TiC, FeTi, and Fe{sub 2}Ti, formed at the interface, which decreased the bonding strength. The large reduction ratio can break up compounds at the interface and extrude fresh metal for bonding, thereby increasing the bonding strength.

36 MATERIALS SCIENCE↗