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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Structural and Phase Transformations in Superlocalization Band in Ni{sub 3}Ge Single Crystal

The paper studies the high-temperature plastic deformation in Ni{sub 3}Ge alloy single crystals localizing in a band a few tens of microns wide that reaches the shear strain of thousands of percent. The electron backscatter diffraction and synchrotron radiation techniques allow investigating the structure of the single crystal in the band of super-localized plastic deformation. It is shown that super-localization of plastic deformation occurs due to the formation of polycrystalline multi-level substructure in the initial single crystal. The grain size and grain misorientation bimodal distributions are determined in the polycrystalline substructure. Also, regions of amorphous state are observed in the super-localization band at high homologous temperature Т > 0.5T{sub m}. A partial destruction of the far atomic order is detected.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Investigation of the Process of Optical Damage of ZnGeP{sub 2} Crystals Using Digital Holography

A method of visualization of the process of optical damage of a ZnGeP{sub 2} single crystal using digital holography is suggested. The mechanism of the ZnGeP{sub 2} single crystal damage is investigated at energy density ~0.3–0.6 J/cm{sup 2}. The temperature in the damage channel during its formation is estimated. The data obtained allow the conclusion on the thermal nature of ZnGeP{sub 2} crystal damage to be made under the action of laser radiation with a wavelength of ~2.1 μm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Special Features of AgIn{sub 5}S{sub 8} Luminescence and Photoconductivity Under the Action of Laser Radiation

Luminescence spectra and relaxation curves of nonequilibrium photoconductivity of AgIn{sub 5}S{sub 8} single crystals under the action of Nd:YAG-laser radiation are experimentally investigated. It is shown that depending on the nature of excitation (one- or two-photon excitation), the emission lines of a free exciton with its phonon repetition and the emission caused by structural defects are observed in the luminescence spectrum. Investigation of the nonequilibrium photoconductivity relaxation curves shows the presence of two recombination channels with times τ ~ 2.7·10{sup –7} s and ~2·10{sup –6} s.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Influence of Melt Superheating Treatment on Solidification Characteristics and Rupture Life of a Third-Generation Ni-Based Single-Crystal Superalloy

The influence of melt superheating treatment on the melt properties, solidification characteristics, and rupture life of a third-generation Ni-based single-crystal superalloy was investigated to reveal the critical temperature range of melt structure evolution and its effect on rupture life. The results showed that the viscosity of superalloy decreased but the surface tension increased with increasing superheating temperature. Two characteristic temperature points where the melt viscosity and undercooling degree suddenly change were determined to be 1600 °C and 1700 °C, respectively. Similarly, the stability of the solidification interface firstly improved and then weakened with increasing superheating temperature. The dendrite arms were well refined and the segregation was reduced at 1700 °C. In addition, the rupture life obtained at 1100 °C and 137 MPa increased by approximately 30 pct, approaching the rupture life of the corresponding superalloy containing 2 pct Ru, with increasing superheating temperature from 1500 °C to 1700 °C. When the melt was further heated to 1800 °C, the rupture life decreased. The evolutions of solidification characteristics and rupture life with increasing melt superheating temperature were attributed to changes in the melt structure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of a High Magnetic Field on γ′ Phase for Ni-Based Single Crystal Superalloy During Directional Solidification

The effect of a high magnetic field on the γ′ phase of Ni-based single crystal superalloy during directional solidification is investigated experimentally. The results clearly indicate that the magnetic field significantly reduces the γ′ phase size. Further, the quenching experiment is carried out, and the results found that the length of mushy zone is obviously decreased under a high magnetic field. Based on both experimental results and nucleation mechanism, it is found that the decrease of γ′ phase size should be attributed to the fact that a high magnetic field causes the increase of temperature gradient in front of solid/liquid interface and leads to the increase of undercooling of γ′ phase.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Processing Parameters and Shape of Blade on the Solidification of Single-Crystal CMSX-4 Ni-Based Superalloy

The effect of mold withdrawal velocity, heater and pouring temperatures and the thickness of blade root on the solidification parameters and shape of the liquidus isotherm as well as microstructure of single-crystal CMSX-4 nickel-based superalloy, manufactured by the Bridgman method, has been analyzed in the article. The temperature gradient G, solidification rate v and location of the liquidus isotherm were determined in relation to the radiation baffle on the basis of temperature measurements conducted in nine test points along the height of castings (140 mm) with different thicknesses of root (27, 15 and 7 mm) and withdrawal velocities of 3 and 5 mm/min. The increase of root thickness, relative to the airfoil, resulted in the rise of inhomogeneity of solidification parameters as well as the primary dendrite arm spacing and unsteady state solidification along the whole blade height. However, in the case of blade with constant thickness, the steady-state solidification was created at the distance of 65 to 130 mm from its base. The increase of mold withdrawal velocity caused the decrease of temperature gradient. However, the solidification rate was different from the mold withdrawal velocity, especially in the root and middle part of the airfoil. The increase of heater temperature resulted in a rise of temperature gradient and reduction of the curvature of the liquidus isotherm, whereas the pouring temperature did not affect the solidification parameters in the blade. Particularly unfavorable conditions of the solidification process could occur in the middle part of the airfoil and root because of the lowest value of G/v and the largest primary dendrite arm spacing.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Formation Mechanism of Stray Grain of Nickel-Based Single-Crystal Superalloy Under a High Magnetic Field During Directional Solidification

We investigate the formation mechanism of stray grain of nickel-based single-crystal superalloy under a high magnetic field. It was shown that the high magnetic field induced the formation of stray grains on the side that the dendrite diverges the wall. In addition, results showed a sloping solid/liquid interface and a further increased sloping magnitude under a high magnetic field. Further, the formation process of stray grain in the high magnetic field is analyzed in detail.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Interaction Between Graphene-Coated SiC Single Crystal and Liquid Copper

The wettability of graphene-coated SiC single crystal (C{sub Gn}/SiC{sup sc}) by liquid Cu (99.99%) was investigated by a sessile drop method in vacuum conditions at temperature of 1100 °C. The graphene layer was produced via a chemical vapor deposition routine using 4H-SiC single crystal cut out from 6″ wafer. A dispensed drop technique combined with a non-contact heating of a couple of materials was applied. The Cu drop was squeezed from a graphite capillary and deposited on the substrate directly in a vacuum chamber. The first Cu drop did not wet the C{sub Gn}/SiC{sup sc} substrate and showed a lack of adhesion to the substrate: the falling Cu drop only touched the substrate forming a contact angle of θ{sub 0} = 121° and then immediately rolled like a ball along the substrate surface. After settling near the edge of the substrate in about 0.15 s, the Cu drop formed an asymmetric shape with the right and left contact angles of different values (θ{sub R} = 86° and θ{sub L} = 70°, respectively), while in the next 30 min, θ{sub R} and θ{sub L} achieved the same final value of ~ 52°. The second Cu drop was put down on the displacement path of the first drop, and immediately after the deposition, it also did not wet the substrate (θ = 123°). This drop kept symmetry and the primary position, but its wetting behavior was unusual: both θ{sub R} and θ{sub L} decreased in 17 min to the value of 23° and next, they increased to a final value of 65°. Visual observations revealed a presence of ~ 2.5-mm-thick interfacial phase layer reactively formed under the second drop. Scanning electron microscopy (SEM) investigations revealed the presence of carbon-enriched precipitates on the top surface of the first Cu drop. These precipitates were identified by the Raman spectroscopy as double-layer graphene. The Raman spectrum taken from the substrate far from the drop revealed the presence of graphene, while that obtained from the first drop displacement path exhibited a decreased intensity of 2D peak. The results of SEM investigations and Raman spectroscopy studies suggest that the presence of graphene layer on the SiC substrate suppresses but does not completely prevent chemical interaction between liquid Cu drop and SiC. Both chemical degradation (etching) and mechanical degradation of the graphene layer during drop rolling due to high adhesion of the Cu drop to the SiC substrate are responsible for mass transfer through the 2nd drop/substrate interface that in turn results in significant changes of structure and chemistry of the drop and the interface.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Universal Mechanism of Viscoplastic Deformation of Metallic Materials Far from Thermodynamics Equilibrium

The article gives results of structure formation in metallic materials after different types of deformation: tungsten after rolling, nickel after thermal cycling and nickel single crystal after rolling, aluminum single crystal after cyclic tension and aluminum alloys (D16, 2024-T3) after impulsive load. We used optical and electron microscopy methods for investigation of deformation structure formation and molecular dynamics method for computer modeling of the processes of plastic deformation (LAMMPS software). The following quantitative parameters were calculated during the simulation: energy of pair interaction, temperature, total cumulative pressure, stress tensor and pressure tensor. The study shows that the plastic flow of metallic materials with any initial structure at certain loading stage can be carried out by homogeneous mass transfer through channels with a liquid-like structure, from which follows that the dislocation mechanism of plastic deformation of crystals has a limited field of application. The main role has a synergistic structure formation in the conditions of distance from thermodynamic equilibrium. The relaxation processes proceed intensively after and during the process of destruction. The results of modeling have shown the possibility of forming channels of hydrodynamic flow without the participation of defects in the initial material.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Base Metal Misorientation on Single-Crystal Superalloy Transient Liquid-Phase Bonded Joints

In this paper, experiments and theoretical analysis were conducted to elucidate the internal relation between base metal misorientation and the characteristics of DD5 single-crystal superalloy TLP joints. The alloy was bonded at 1513 K for 10 h in vacuum environment. High-temperature creep rupture tests were carried out to determine the joint’s quality. Results revealed that base metal misorientation exerted a remarkable influence on DD5 alloy TLP joints. The joints of base metals with [001] orientation were used in this research. When the misorientation was smaller than 9°-10°, the single crystallization of joints can be realized and joints can achieve excellent mechanical properties. When the misorientation was more than 10°, there would be second-phase particles distributed in grain boundaries, thus resulting in poor mechanical property of joint; moreover, the characteristics of joint did not change with base metal misorientation in this case.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Detwinning on the Shape Memory Effect in Ni{sub 55}Fe{sub 18}Ga{sub 27} Single Crystals

Deformation mechanisms, one-way and two-way shape memory effects were studied in the mode of compression in the [011] single crystal of the Ni{sub 55}Fe{sub 18}Ga{sub 27} alloy where the detwinning occurred during deformation and in the [001] single crystal where the detwinning was forbidden. It was found that the [001] and [011] crystals deformed by different mechanisms during compression to 5% (reorientation was in [001] crystal, and the reorientation and detwinning were in [011] crystal) and from 15 to 20% (the 14 M → L1{sub 0} transition was in [001] crystal and plastic deformation of 14 M phase was in [011]). The compression of both single crystals from 5 to 15% occurred due to the same mechanisms: the 10 M ↔ 14 M transformation and the plastic deformation of the 14 M martensite. The 14 M and L1{sub 0} phases were stable under load, and they transformed to the 10 M martensite on unloading. It was shown that the crystal orientation and detwinning hardly affected the value of the one-way shape memory effect since both crystals were in the 10 M martensite after preliminary deformation. In this case, the transformation of 10 M martensite to the austenite on heating was accompanied by a strain of about 5% and this was the maximum value of the shape memory effect. It was found that the detwinning significantly affected the temperature ranges of strain recovery. In the [011] crystal, the strain recovered in a very narrow interval on heating (1-2°C), whereas in the [001] crystal the shape memory effect was observed in “normal” temperature range (~ 10°C). The detwinning resulted in the formation of a large oriented internal stress during the preliminary deformation that increased the value of the two-way shape memory effect that was observed in [011] crystals in comparison with the [001] crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Corrosion and Electrochemical Behavior of Sn-2Ag-0.5Cu Lead-Free Solders Solidified with Magnet Stirring

In this study, permanent magnet stirring (PMS) was applied to modify the crystallographic texture and corrosion resistance of Sn-2Ag-0.5Cu (SAC205) solders. The results indicate that PMS transforms the lamellar structure into equiaxed grains. Following the initiation corrosion process, the crystallographic texture shows a new class of grains that consists of single-crystal morphology with {111}{sub Sn} facets before applying PMS. This could result in severe corrosion of β-Sn crystals with non-uniform corrosion rate caused by the orientation effect of (111). The corrosion rate for SAC205 solder, measured by immersion tests in 3.5% NaCl solution at 25 °C, was significantly decreased from 31 to 8 mpy after applying PMS. This change in corrosion resistance of SAC205 solder can be attributed to the improved anodic and cathodic reaction activities caused by the modification of microstructure and crystallographic texture. The mechanism of pitting and sequential corrosion events is fully explained and discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Hot Corrosion Performance of Single-Crystal CMSX-4 and CMSX-486 Superalloys in the Mixture of Na{sub 2}SO{sub 4}-NaCl Melts

A modification in the chemistry of single-crystal CMSX-4 to produce CMSX-486 superalloy has been reported in the literature to be accomplished without degradation in high-temperature mechanical performance. However, adequate attention has not yet been focussed on the hot corrosion response of the alloy considering its chemical composition modification. This paper reports for the first time that a considerable degradation in the hot corrosion resistance of CMSX-4 occurs by the modification of its chemistry. Corrosion tests at different salt concentrations and temperatures showed that the hot corrosion resistance of CMSX-486 is worse than the conventional CMSX-4 alloy. The difference in the corrosion resistance characteristics of the two alloys is attributable to the nature of the protective oxide layer formed on the materials during hot corrosion. Characterization using various advanced techniques revealed that the oxide layer formed on CMSX-486 consists of less amount of protective and coherent Al{sub 2}O{sub 3} and Cr{sub 2}O{sub 3} film than CMSX-4, and this is the reason for its poor hot corrosion resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Exploiting Acoustic Anisotropy to Detect Recrystallization in a Ni Single Crystal Using Ultrasonic Nondestructive Inspection

Ultrasonic inspection was used to detect regions of recrystallization (RX) within a single crystal of Ni. RX can produce polycrystalline regions within single-crystal (SX) materials. Because RX regions act as initiator sites for failure by fatigue-crack growth in otherwise SX Ni-based superalloys, RX is an issue of direct concern for the service life of high-performance turbine blades. Detection and discrimination of RX regions in single-crystal materials are significant challenges for current nondestructive inspection technologies. The present study leverages the elastic anisotropy of single crystals, which produces acoustic anisotropy, to ultrasonically detect and characterize RX regions produced within single-crystal specimens. Single crystals of pure Ni were processed to create controlled regions of RX. These specimens were ultrasonically examined in an immersion tank using a high-resolution, polyvinylidene fluoride transducer to detect acoustic impedance changes across the boundaries between different crystals (i.e., grains) within the RX region. Data from time-of-flight and absolute peak amplitude measurements were used to create acoustic images that were compared against electron microscope images of the RX regions. The ultrasonic inspection technique described here successfully detected not only the locations of RX regions, but also the approximate sizes and shapes of the RX regions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Fatigue Failure Characteristics of Single-Crystal Fe-3%Al Alloy

To obtain a better understanding of the mechanical properties and failure characteristics of the single-crystal Fe-3%Al alloy (SC), tensile and fatigue properties of the SC and polycrystalline Fe-3%Al alloy (PC) have been investigated. The tensile strength and fracture strain for the SC samples were different depending on the loading direction, i.e., 〈111〉, 〈110〉 and 〈100〉, which could be explained by the Schmid factor. Fatigue strength for the SC samples was basically correlated with their tensile strength. Different fatigue properties were obtained for the PC sample, e.g., the high fatigue strength was obtained in the early fatigue stage, and significant reduction in the fatigue strength was appeared in the later fatigue stage, e.g., low endurance limit at 10{sup 7} cycles. The reason for this was caused by the material brittleness due to the accumulated dislocation at the grain boundaries. Because the high ductile SC samples made severe plastic deformation ahead of the crack tip, the crack growth rate did not enhance even if the high stress intensity factor range was applied in Region II (da/dN versus ΔK). The crack growth rate dropped just before the final fracture. Effective stress intensity factor range was estimated using the crack closure model, but the crack growth rate is found to be affected strongly by the slip system of SC sample.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Topological Characterization of Coordination-Driven Self-assembly Complexes: Applications of Ion Mobility-Mass Spectrometry

Coordination-driven self-assembly (CDSA) is increasingly used to synthesize coordination complexes containing metal-centered electron acceptors and typically nitrogen-containing electron donors. Characterization of the structures obtained from CDSA via crystallographic or spectroscopic means is limited due to difficulties in forming single crystals for X-ray studies and overlapping precursor and product signals in NMR. Here, we employ ion mobility-mass spectrometry (IM-MS), which provides a direct measure of size and shape of the CDSA complexes, to study the intact reaction products of a rhomboid-shaped complex. This approach negates the need for product isolation and crystallization and allows for tracking of the product distribution as a function of time. A potential challenge of IM-MS is that the size/shape of the observed CDSA complexes can vary with internal energy; however, we show that proper tuning of the instrument reduces the effects of collisional activation thereby allowing for retention of ion conformations that reflect solution-phase ion structures. .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

The crystal structure of a new calcium aluminate phase containing formate

A new calcium aluminate phase containing formate ions was synthesized and its crystal structure determined. This new phase is indicated as M-phase and was firstly observed in Portland cement pastes hydrated in presence of Ca-formate and in excess of water. The crystal structure of the M-phase was successfully solved in the R-3 space group of the trigonal system on the basis of synchrotron X-ray single crystal diffraction data. The structural model was confirmed by Rietveld refinement of the powder diffraction data acquired on the synthesized pure sample. The crystal structure of the M-phase is similar to that of ettringite, being characterized by columns of AlO{sub 6} octahedra alternating with groups of three edge-sharing CaO{sub 7} polyhedra. The formate ions (HCOO){sup −} share two oxygens with Ca polyhedra and are located in the interspace between the columns. The crystal structure of the M-phase testifies the strong interaction occurring between small organic molecules as formate and the calcium aluminate components of Portland cement.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nanostructural evolution of Al(OH)3 gel formed by the cubic and orthorhombic ye'elimite clinkers of calcium sulfoaluminate cements in an ultra-wide hydration temperature range

This paper investigated the influence of hydration temperature on the nanostructure of the AH{sub 3} phase formed in calcium sulfoaluminate cements. Orthorhombic ye'elimite (st-ye'elimite) and cubic ye'elimite (ss-ye'elimite) were hydrated in an ultra-wide temperature range (5–220 °C). Results showed that the AH{sub 3} phase formed by ss-ye'elimite was always microcrystalline in nature at various curing temperatures (5–130 °C), and transformed into the AlOOH phase at 150 °C and above. However, the AH{sub 3} phase formed by st-ye'elimite grew from a microcrystal to a favorable crystal as the temperature increased, and transformed into the AlOOH phase at 170 °C and above. The nanostructure of hydration products was further investigated using TEM/SAED analysis together with FE-SEM images, directly evidencing that the formed AFm-12 phase was single-crystal in nature, and the formed AH{sub 3} phase was microcrystalline at low temperatures and grew into single-crystal hexagonal prisms with the preferred growth direction along [001] direction at high temperatures.

36 MATERIALS SCIENCE↗