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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

MiR-326 antagomir delays the progression of age-related cataract by upregulating FGF1-mediated expression of betaB2-crystallin

Highlights: • FGF-1 upregulates the expression of an anti-cataract protein βB2. • miR-326 inhibits FGF-1 expression and thereby decreases βB2 level. • miR-326 antagomir delay cataract progression via the function of miR-326. Age-related cataract, the most common cause of blindness worldwide, has been found closely associated with β-crystallin B2 (βB2 or CRYBB2). MicroRNAs (miRNAs) are the primary epigenetic regulators important for various biological processes. However, the role of miRNAs in the progression of lens cataract remains to be elucidated. In this study, we found a novel signal cascade miR-326–fibroblast growth factor 1 (FGF1)–βB2 modulating the progression of lens cataract. In brief, miR-326 exacerbated but its antagomirs attenuated H{sub 2}O{sub 2}-induced apoptosis of HLEC-B3 human lens epithelial cells. Dual-luciferase reporter assay and Western blot showed that miR-326 inhibited FGF1 expression by directly targeting its mRNA 3′-UTR. Consistent with this result, miR-326 antagomir enhanced FGF1 protein level. In addition to FGF1, miR-326 antagomir also enhanced βB2 expression and this enhancement was abolished by transfection of HLEC-B3 cells with FGF1 shRNA. These data demonstrated that miR-326 antagomir increased βB2 expression via upregulating FGF1, which was further confirmed by the studies in a rat model of selenite-induced cataract. This work suggests that miR-326 antagomir might be a promising candidate to prevent progression of age-related cataract.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Identification of a rare homozygous c.790C>T variation in the TFB2M gene in Korean patients with autism spectrum disorder

Highlights: • TFB2M have been known to critical in mitochondrial DNA gene expression. • We identified a variation of TFB2M gene sequence in Korean autism patients. • The variation caused increased mitochondrial DNA gene expression. • Increased mitochondrial biogenesis resulted in ROS production and damaged cells. • Structural changes of variant TFB2M seems to delay unloading of DNA from TFB2M. Mitochondrial dysfunction and subsequent enhanced oxidative stress is implicated in the pathogenesis of autism spectrum disorder (ASD). Mitochondrial transcription factor B2 (TFB2M) is an essential protein in mitochondrial gene expression. No reports have described TFB2M mutations and variations involved in any human diseases. We identified a rare homozygous c.790C>T (His264Tyr) variation in TFB2M gene in two Korean siblings with ASD by whole-exome sequencing. The roles of the TFB2M variation in the pathogenesis of ASD were investigated. Patient fibroblasts revealed increased transcription of mitochondrial genes and mitochondrial function in terms of ATP, membrane potential, oxygen consumption, and reactive oxygen species (ROS). Overexpression of the TFB2M variant in primary-cultured fibroblasts demonstrated significantly increased transcription of mitochondrial genes and mitochondrial function compared with overexpression of wild-type TFB2M. Molecular dynamics simulation of the TFB2M variant protein suggested an increase in the rigidity of the hinge region, which may cause alterations in loading and/or unloading of TFB2M on target DNA. Our results suggest that augmentation of mitochondrial gene expression and subsequent enhancement of mitochondrial function may be associated with the pathogenesis of ASD in Korean patients.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Analysis of phase stability and chemical segregation in the Mo-V alloys using a generalized embedded atom method potential

A new interatomic potential for the Mo-V system is introduced to facilitate the study of phase stability and mechanical properties at lower temperatures. This potential is based on a generalization of the embedded atom method and includes contributions from embedding energy, explicit two- and three-body interactions and nonlocal many-body interaction terms. The parameters of the potential are optimized by using data from ab initio density functional theory (DFT) calculations. The potential is rigorously validated across a range of physical properties, such as elastic constants, equation of states, phonon dispersion curves, point defect properties and melting temperatures for different compositions. Even though our potential is trained on a small dataset, its accuracy is comparable to available machine learning potentials for Mo and V. Furthermore, our results show that an ordered B2 phase is stable at low temperatures in alloys containing 50% V, but the solid solution phase is stable above 800 K. However, such long-range ordering is not observed in V-rich or Mo-rich alloys. In addition, our results show that V segregates to dislocation cores and grain boundaries.

36 MATERIALS SCIENCE↗
DOE OSTI2010

In situ biomonitoring of juvenile Chinook salmon (Onchorhynchus tshawytscha) using biomarkers of chemical exposures and effects in a partially remediated urbanized waterway of the Puget Sound, WA

In situ biomonitoring has been used to assess the effects of pollution on aquatic species in heavily polluted waterways. In the current study, we used in situ biomonitoring in conjunction with molecular biomarker analysis to determine the effects of pollutant exposure in salmon caged in the Duwamish waterway, a Pacific Northwest Superfund site that has been subject to remediation. The Duwamish waterway is an important migratory route for Pacific salmon and has received historic inputs of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Juvenile pre-smolt Chinook salmon (Oncorhynchus tshawytscha) caged for 8 days in the three contaminated sites in close proximity within the Duwamish were analyzed for steady state hepatic mRNA expression of 7 exposure biomarker genes encompassing several gene families and known to be responsive to pollutants, including cytochrome P4501A (CYP1A) and CYP2K1, glutathione S-transferase {pi} class (GST-{pi}), microsomal GST (mGST), glutamylcysteine ligase catalytic subunit (GCLC), UDP-glucuronyltransferase family 1 (UDPGT), and type 2 deiodinase (type 2 DI, or D2). Quantitation of gene expression was accomplished by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) in assays developed specifically for Chinook salmon genes. Gill PAH-DNA adducts were assessed as a chemical effects biomarker using {sup 32}P-postlabeling. The biomarkers in the field-caged fish were analyzed with respect to caged animals maintained at the hatchery receiving flow-through water. Chemical analysis of sediment samples from three field sampling sites revealed relatively high concentrations of total PAHs in one site (site B2, 6711 ng/g dry weight) and somewhat lower concentrations of PAHs in two adjacent sites (sites B3 and B4, 1482 and 1987 ng/g, respectively). In contrast, waterborne PAHs at all of the sampling sites were relatively low (<1 ng/L). Sediment PCBs at the sites ranged from a low of 421 ng/g at site B3 to 1160 ng/g at site B4, and there were no detectable waterborne PCBs at any of the sites (detection limit=10 ng/L). There were no significant differences (p<0.05) in biomarker gene expression in the Duwamish-caged fish relative to controls, although there was a pattern of gene expression suppression at site B3, the most heavily PAH-enriched site. The lack of a marked perturbation of mRNA biomarkers was consistent with relatively low levels of gill PAH-DNA adduct levels that did not differ among caged reference and field fish, and which were also consistent with relatively low waterborne concentrations of chemicals. The results of our study suggest a low bioavailability of sediment pollutants in caged juvenile Chinook potentially reflecting low waterborne exposures occurring at contaminated sites within the Duwamish waterway that have undergone partial remediation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Effect of Basic Residue on the Kinetics of Peptide Fragmentation Examined Using Surface-Induced Dissociation Combined with Resonant Ejection

In this work, resonant ejection coupled with surface-induced dissociation (SID) in a Fourier transform ion cyclotron resonance mass spectrometer is used to examine fragmentation kinetics of two singly protonated hexapeptides, RYGGFL and KYGGFL, containing the basic arginine residue and less basic lysine residue at the N-terminus. The kinetics of individual reaction channels at different collision energies are probed by applying a short ejection pulse (1 ms) in resonance with the cyclotron frequency of a selected fragment ion and varying the delay time between ion-surface collision and resonant ejection while keeping total reaction delay time constant. Rice-Ramsperger-Kassel-Marcus (RRKM) modeling of the experimental data provides accurate threshold energies and activation entropies of individual reaction channels. Substitution of arginine with less basic lysine has a pronounced effect on the observed fragmentation kinetics of several pathways, including the b2 ion formation, but has little or no effect on formation of the b5+H2O fragment ion. The combination of resonant ejection SID, time- and collision energy-resolved SID, and RRKM modeling of both types of experimental data provides a detailed mechanistic understanding of the primary dissociation pathways of complex gaseous ions.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2013

Five-Year Outcomes, Cosmesis, and Toxicity With 3-Dimensional Conformal External Beam Radiation Therapy to Deliver Accelerated Partial Breast Irradiation

Purpose: To report the interim results from a study comparing the efficacy, toxicity, and cosmesis of breast-conserving treatment with accelerated partial breast irradiation (APBI) or whole breast irradiation (WBI) using 3-dimensional conformal external beam radiation therapy (3D-CRT). Methods and Materials: 102 patients with early-stage breast cancer who underwent breast-conserving surgery were randomized to receive either WBI (n=51) or APBI (n=51). In the WBI arm, 48 Gy was delivered to the whole breast in daily fractions of 2 Gy, with or without additional 10 Gy to the tumor bed. In the APBI arm, patients received 37.5 Gy in 3.75 Gy per fraction delivered twice daily. Toxicity results were scored according to the Radiation Therapy Oncology Group Common Toxicity Criteria. Skin elasticity was measured using a dedicated device (Multi-Skin-Test-Center MC-750-B2, CKelectronic-GmbH). Cosmetic results were assessed by the physician and the patients as good/excellent, regular, or poor. Results: The median follow-up time was 5 years. No local recurrences were observed. No significant differences in survival rates were found. APBI reduced acute side effects and radiation doses to healthy tissues compared with WBI (P<.01). Late skin toxicity was no worse than grade 2 in either group, without significant differences between the 2 groups. In the ipsilateral breast, the areas that received the highest doses (ie, the boost or quadrant) showed the greatest loss of elasticity. WBI resulted in a greater loss of elasticity in the high-dose area compared with APBI (P<.05). Physician assessment showed that >75% of patients in the APBI arm had excellent or good cosmesis, and these outcomes appear to be stable over time. The percentage of patients with excellent/good cosmetic results was similar in both groups. Conclusions: APBI delivered by 3D-CRT to the tumor bed for a selected group of early-stage breast cancer patients produces 5-year results similar to those achieved with conventional WBI.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Annealing effect for the Al 0.3 CoCrFeNi high-entropy alloy fibers

High-entropy alloy fibers with excellent performance potential are desired for functional applications. A previous study on the Al 0.3 CoCrFeNi high-entropy fiber reported a tensile fracture strength of 1200 MPa and elongation of 8% at room temperature (Acta Mater. 123 (2017) 285). Here, the goal is to improve the ductility of Al 0.3 CoCrFeNi high-entropy fiber by manipulating the microstructure through annealing. Al 0.3 CoCrFeNi fibers at Φ1.0 mm and Φ1.6 mm diameters were annealed at 900 °C for 10 min, 30 min, 300 min and 720 min, respectively. The resulting microstructure is a fine face-centered cubic (FCC) structure with grain sizes less than ~3 μm, which were strengthened by dense NiAl-type ordered body-centered cubic (B2) precipitation. Finally, the fibers achieved a fracture strength greater than 900 MPa with an elongation of over 25% at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Reliable thermodynamic estimators for screening caloric materials

Reversible, diffusionless, first-order solid-solid phase transitions accompanied by caloric effects are critical for applications in the solid-state cooling and heat-pumping devices. Accelerated discovery of caloric materials requires reliable but faster estimators for predictions and high-throughput screening of system-specific dominant caloric contributions. We assess reliability of the computational methods that provide thermodynamic properties in relevant solid phases at or near a phase transition. Here, we test the methods using the well-studied B2 FeRh alloy as a “fruit fly” in such a materials genome discovery, as it exhibits a metamagnetic transition which generates multicaloric (magneto-, elasto-, and baro-caloric) responses. For lattice entropy contributions, we find that the commonly-used linear-response and small-displacement phonon methods are invalid near instabilities that arise from the anharmonicity of atomic potentials, and we offer a more reliable and precise method for calculating lattice entropy at a fixed temperature. Then, we apply a set of reliable methods and estimators to the metamagnetic transition in FeRh (predicted 346 ± 12 K, observed 353 ± 1 K) and calculate the associated caloric properties, such as isothermal entropy and isentropic temperature changes.

36 MATERIALS SCIENCE↗
DOE OSTI2019

High strength and high ductility in a novel Fe 40.2 Ni 11.3 Mn 30 Al 7.5 Cr 11 multiphase high entropy alloy

In the present study, a novel Fe 40.2 Ni 11.3 Mn 30 Al 7.5 Cr 11 high entropy alloy displaying an excellent com- bination of high strength and high ductility has been developed. The b.c.c.þB2/f.c.c. dendritic- interdendritic microstructure was characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy, and the alloy’s mechanical properties were examined using Vickers hardness measurements and room-temperature tensile tests. The phase stability of Fe 40.2 Ni 11.3 Mn 30 Al 7.5 Cr 11 was investigated by annealing the alloy between 1173 Ke1273 K, and the presence of both Ni-rich, b.c.c. needle-shaped precipitates and Cr-rich, s phase particles was observed for the 1173 K annealed specimen. The s phase precipitates contributed to the rapid age-hardening effect in the material annealed at 1173 K. A further increase in ageing temperature to 1223 K and 1273 K led to the dissolution of the s phase and a reduction in the volume fraction of the b.c.c./B2 dendrites, which led to a consequent drop in room-temperature yield strength from the as-cast value of ~593 MPae~486 MPa and ~228 MPa for the specimens annealed at 1223 K and 1273 K, respectively. An accompanying increase in ductility was observed from ~22% for the as-cast alloy to ~27% and ~40% after annealing the material at 1223 K and 1273 K, respectively. Post-deformation transmission electron micrographs revealed that the f.c.c interdendrites accommodated plastic strain via wavy slip and moreover, deformed before the b.c.c. dendritic regions, which were reinforced by B2 particles and acted as obstacles to moving dislocations. Finally, the discovery of a multi-phase HEA that contains 11% Cr and good mechanical properties has relevant high-temperature structural applications especially in cases that require suitable corrosion resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Machine learning reveals sequence-function relationships in family 7 glycoside hydrolases

Family 7 glycoside hydrolases (GH7) are among the principal enzymes for cellulose degradation in nature and industrially. These important enzymes are often bimodular, including a catalytic domain and carbohydrate binding module (CBM) attached via a flexible linker, and exhibit an active site that binds cello-oligomers of up to ten glucosyl moieties. GH7 cellulases consist of two major subtypes: cellobiohydrolases (CBH) and endoglucanases (EG). Despite the critical importance of GH7 enzymes, there remain gaps in our understanding of how GH7 sequence and structure relate to function. Here, we employed machine learning to gain data-driven insights into relationships between sequence, structure, and function across the GH7 family. Machine-learning models, trained only on the number of residues in the active-site loops as features, were able discriminate GH7 CBHs and EGs with up to 99% accuracy, demonstrating that the lengths of loops A4, B2, B3, and B4 strongly correlate with functional subtype across the GH7 family. Classification rules were derived such that specific residues at 42 different sequence positions each predicted the functional subtype with accuracies surpassing 87%. A random forest model trained on residues at 19 positions in the catalytic domain predicted the presence of a CBM with 89.5% accuracy. Our ML results recapitulate, as top-performing features, a substantial number of the sequence positions determined by previous experimental studies to play vital roles in GH7 activity. We surmise that the yet-to-be-explored sequence positions among the top-performing features also contribute to GH7 functional variation and may be exploited to understand and manipulate function.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Understanding formation mechanisms of intermetallic compounds in dissimilar Al/steel joint processed by resistance spot welding

Here, this paper confirmed the formation mechanism of intermetallic compounds (IMCs) in Al/steel resistance spot welds with transmission electron microscopy, electron backscatter diffraction, nanoindentation and thermodynamic calculations. In particular, the formation of AlFe with BCC_B2 structure, which is not commonly seen in welds, was identified. The formation mechanism of IMCs at the high welding energy region is described as follows. Al 13 Fe 4 first nucleates from the Al side, followed by Al 5 Fe 2 growth with Fe atoms accumulating at the Al 13 Fe 4 grain boundaries. Then, Al 5 Fe 2 grains grow continuously to coarse columnar grains, and AlFe forms at the interface of Al 5 Fe 2 grains and the ferrite phase. Lastly, the needle-like Al 13 Fe 4 forms in the cooling process. At the middle welding energy region, only equiaxed Al 5 Fe 2 and small Al 13 Fe 4 grains are formed at the interface because of the lower diffusion rates of Al and Fe, hence postponing the growth of Al 5 Fe 2 and Al 13 Fe 4 . At the low welding energy region, only sporadic Al 5 Fe 2 and Al 13 Fe 4 grains are formed surrounded by the Al phase.

42 ENGINEERING↗
DOE OSTI2011

Indentation Schmid factor and orientation dependence of nanoindentation pop-in behavior of NiAl single crystals

Instrumented nanoindentation techniques have been widely used to characterize the small-scale mechanical behavior of materials. The elastic-plastic transition during nanoindentation is often indicated by a sudden displacement burst (pop-in) in the measured load-displacement curve. In defect-free single crystals, the pop-in is believed to be the result of homogeneous dislocation nucleation because the maximum shear stress corresponding to the pop-in load approaches the theoretical strength of the materials and because the statistical distribution of pop-in stresses is consistent with what is expected for a thermally activated process of homogeneous dislocation nucleation. This paper investigates whether this process is affected by crystallography and stress components other than the resolved shear stress. A Stroh formalism coupled with the two-dimensional Fourier transformation is used to derive the analytical stress fields in elastically anisotropic solids under Hertzian contact, which allows the determination of an indentation Schmid factor, namely, the ratio of maximum resolved shear stress to the maximum contact pressure. Nanoindentation tests were conducted on B2-structured NiAl single crystals with different surface normal directions. This material was chosen because it deforms at room temperature by {110}<001> slip and thus avoids the complexity of partial dislocation nucleation. Good agreement is obtained between the experimental data and the theoretically predicted orientation dependence of pop-in loads based on the indentation Schmid factor. Pop-in load is lowest for indentation directions close to <111> and highest for those close to <001>. In nanoindentation, since the stress component normal to the slip plane is typically comparable in magnitude to the resolved shear stress, we find that the pressure sensitivity of homogeneous dislocation nucleation cannot be determined from pop-in tests. Our statistical measurements generally confirm the thermal activation model of homogeneous dislocation nucleation. That is, the extracted dependence of activation energy on resolved shear stress is almost the same for all the indentation directions considered in this study, except for those close to <001>. Because very high pop-in loads are measured for orientations close to <001>, which implies a large contact area at pop-in, there is a higher probability of activating pre-existing dislocations in these orientations, which may explain the discrepancy near <001>.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Analysis of several high-resolution infrared bands of perdeutero-spiropentane, C5D8

Perdeutero-spiropentane (C5D8) has been synthesized and infrared spectra were taken from 400 to 4000 cm-1 at low sample pressures in a 22 meter multipass cell. The spectral resolution (0.0015 cm-1) reveals thousands of individual rovibrational transitions for several fundamental bands occurring in the spectral region of 500 to 1100 cm-1. C5D8 ground state constants reported in a previous study of a ?15 parallel band at 1054 cm-1 [1] were improved significantly in the present work by adding combination-differences derived from ?16 parallel and ?24 perpendicular band analyses. The larger data set at higher J values also allowed determination of the ground state K? = 2 splitting constant (?2? = 0.76(2) ×10-9 cm-1). For ?16, the band origin is 847.16933(5) cm-1 and changes in upper state rotational constants are ?A = –0.0013411(5) and ?B = –0.0002021(1) (in units of cm-1). Overlapping, and in Fermi resonance with ?16, is a second parallel band which, from Gaussian calculations at the anharmonic level, is assigned as the b2 combination ?8+?12, with band origin of 840.5434(1) and ?A = –0.0003500(7) and ?B = –0.0003502(1) cm-1. For ?24 analogous values are 556.41453(2) and ?A = –0.00032295(9) and ?B = –0.00016782(4) cm-1. The analyses also yields accurate values for the changes in both quartic and sextic centrifugal distortion constants and, for ?24, values for the l-doubling constants q+ and q-. Theoretical calculations of the rovibrational parameters aided in the analysis and the numerical values are in good agreement with experimental results.

Nibler, Joseph W.↗
DOE OSTI2016

Phase stability and microstructures of high entropy alloys ion irradiated to high doses

The microstructures of Al x CoCrFeNi (x = 0.1, 0.75 and 1.5 in molar ratio) high entropy alloys (HEAs) irradiated at room temperature with 3 MeV Au ions at the highest fluence of 105, 91, and 81 displacement per atom, respectively, were studied. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) analyses show that the initial microstructures and phase composition of all three alloys are retained after ion irradiation and no phase decomposition is observed. Furthermore, it is demonstrated that the disordered face-centered cubic (FCC) and disordered body-centered cubic (BCC) phases show much less defect cluster formation and structural damage than the NiAl-type ordered B2 phase. This effect is explained by higher entropy of mixing, higher defect formation/migration energies, substantially lower thermal conductivity, and higher atomic level stress in the disordered phases

36 MATERIALS SCIENCE↗
DOE OSTI2015

Atomistic study on the site preference and lattice vibration of Gd{sub 3−x}Y{sub x}Co{sub 29}T{sub 4}B{sub 10} (T=Al and Ge)

The effects of the Y substitution for Gd on the structural stability and the site preference of intermetallics Gd{sub 3−x}Y{sub x}Co{sub 29}T{sub 4}B{sub 10} (T=Al and Ge) are studied by using a series of interatomic pair potentials. The calculated results show Y can stabilize Gd{sub 3−x}Y{sub x}Co{sub 29}T{sub 4}B{sub 10} with the tetragonal structure, and Y substitute for Gd with a strong preference for the 2b sites. The calculated lattice parameters are in good agreement with the experimental data. Furthermore, the total and partial phonon densities of states are evaluated for the Gd{sub 3−x}Y{sub x}Co{sub 29}T{sub 4}B{sub 10} compounds with the tetragonal structure. A qualitative analysis is carried out with the relevant potentials for the vibrational modes, which makes it possible to predict some properties related to lattice vibration. - Graphical abstract: The lattice cell of Gd{sub 3}Co{sub 29}T{sub 4}B{sub 10} consists of 92 atoms, or two Gd{sub 3}Co{sub 29}T{sub 4}B{sub 10} formula units, with fourteen distinct kinds of site. Rare-earth atoms occupy 2b and 4d sites, Co atoms occupy the Co1(2c), Co2(8i1), Co3(8i2), Co4(8i3), Co5(8j1), Co6(8j2) and Co7(16k), T atoms occupy the T(8i) sites, and B atoms occupy the B1(2c1), B2(2c2), B3(8i) and B4(8j) sites. - Highlights: • The application of the pair potentials obtained from lattice-inversion method. • The lattice vibrations for Gd{sub 3−x}Y{sub x}Co{sub 29}T{sub 4}B{sub 10} (T=Ge and Al) are first evaluated. • The Y atoms should prefer the 2b site of Gd{sub 3−x}Y{sub x}Co{sub 29}T{sub 4}B{sub 10} compounds. • The total and partial phonon densities of states are evaluated for the Gd{sub 3−x}Y{sub x}Co{sub 29}T{sub 4}B{sub 10} compounds with the tetragonal structure. • A qualitative analysis is carried out with the relevant potentials for the vibrational modes.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Tribological properties of self-lubricating NiAl/Mo-based composites containing AgVO{sub 3} nanowires

Silver vanadate (AgVO{sub 3}) nanowires were synthesized by hydrothermal method and self-lubricating NiAl/Mo-AgVO{sub 3} composites were fabricated by powder metallurgy technique. The composition and microstructure of NiAl/Mo-based composites were characterized and the tribological properties were investigated from room temperature to 900 °C. The results showed that NiAl/Mo-based composites were consisted of nanocrystalline B2 ordered NiAl matrix, Al{sub 2}O{sub 3}, Mo{sub 2}C, metallic Ag and vanadium oxide phase. The appearance of metallic Ag and vanadium oxide phase can be attributed to the decomposition of AgVO{sub 3} during sintering. Wear testing results confirmed that NiAl/Mo-based composites have excellent tribological properties over a wide temperature range. For example, the friction coefficient and wear rate of NiAl/Mo-based composites containing AgVO{sub 3} were significantly lower than the composites containing only metallic Mo or AgVO{sub 3} lubricant when the temperature is above 300 °C, which can be attributed to the synergistic lubricating action of metallic Mo and AgVO{sub 3} lubricants. Furthermore, Raman results indicated that the composition on the worn surface of NiAl-based composites was self-adjusted after wear testing at different temperatures. For example, Ag{sub 3}VO{sub 4} and Fe{sub 3}O{sub 4} lubricants were responsible for the improvement of tribological properties at 500 °C, AgVO{sub 3}, Ag{sub 3}VO{sub 4} and molybdate for 700 °C, and AgVO{sub 3} and molybdate for 900 °C of NiAl-based composites with the addition of metallic Mo and AgVO{sub 3}. - Highlights: • NiAl/Mo-AgVO{sub 3} nanocomposites were prepared by mechanical alloying and sintering. • AgVO{sub 3} decomposed to metallic Ag and vanadium oxide during the sintering process. • NiAl/Mo-AgVO{sub 3} exhibited superior tribological properties at a board temperature range. • Phase composition on the worn surface was varied with temperatures. • Self-adjusted action was responsible for the improvement of tribological properties.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Synthesis and microstructure characterization of Ni-Cr-Co-Ti-V-Al high entropy alloy coating on Ti-6Al-4V substrate by laser surface alloying

Ni-Cr-Co-Ti-V-Al high-entropy alloy coating on Ti-6Al-4V was synthesized by laser surface alloying. The coating is composed of a B2 matrix and (Co, Ni)Ti{sub 2} compounds with few β-Ti phases. Focused ion beam technique was utilized to prepare TEM sample and TEM observations agree well with XRD and SEM results. The formation of HEA phases is due to high temperature and rapid cooling rate during laser surface alloying. The thermodynamic parameters, ΔH{sub mix}, ΔS{sub mix}and δ as well as Δχ, should be used to predict the formation of the BCC solid solution, but they are not the strict criteria. Especially when Δχ reaches a high value (≥ 10%), BCC HEA will be partially decomposed, leading to the formation of (Co, Ni)Ti{sub 2} compound phases. - Highlights: •Preparing HEA coating on Ti-6Al-4V by laser surface alloying is successful. •The synthesized HEA coating mainly consists of BCC HEA and (Co, Ni)Ti{sub 2} compounds. •FIB technology was used to prepare the sample for TEM analysis. • ΔH{sub mix}, ΔS{sub mix}and δ as well as Δχ, should be all used to predict the formation of solid solution.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure characterization and thermal stability of TC11/Ti2AlNb joints during thermal exposure

Highlights: • Mechanical properties of TC11/Ti{sub 2}AlNb deteriorate due to coarsening of O and α{sub s}. • Thermal stability of α{sub s} phase is lower than that of O phase during exposure. • A relationship was found between the reduction of area and phase thickness. - Abstract: TC11/Ti{sub 2}AlNb welding joints undergoing hot deformation were thermally exposed at the range of 500–700 °C for 100, 200 and 500 h. In present research, typical microstructures of five different zones of the joints were investigated, fusion zone, two interfaces and two base alloys included. The microstructures of fusion zone, Ti{sub 2}AlNb-based alloy and the interface between them were characterized by the coarsening of O phase during thermal exposure, while those of TC11 alloy and the interface between it and fusion zone featured the coarsening of α{sub s} phase. The transformation from B2 to β and O phase was stifled below 600 °C and Ti{sub 2}AlNb-based alloy thus was verified to be stable at this temperature range. α{sub s} phase was stable during exposure at 500 °C. When exposed above 600 °C, α{sub s} phase coarsened by at least 52% with the extension of holding time. Due to the low thermal stability of α{sub s} phase compared with that of O phase, the fracture position of the samples tested at room temperature moved from fusion zone to TC11 alloy when temperature rose. In spite of different thermal exposure conditions, the samples tested at 300 and 500 °C all fractured at TC11 alloy for the severe coarsening of α{sub s} phase. The decrease of interfacial area resulting from the coarsening of O and α{sub s} phases facilitated the dislocation slipping and the strength of joints thus deteriorated. The mechanical properties of TC11/Ti{sub 2}AlNb joints measured at room temperature, 300 and 500 °C were all correlated with the lamellar thickness of O and α{sub s} phases.

36 MATERIALS SCIENCE↗