bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fracture and Fatigue in a Zr-Based Bulk Metallic Glass
Authors: Gilbert C. J. , Schroeder V. , Ritchie R. O. 
Published: April 2011

AbstractThe fracture and fatigue properties of the Zr41.2Ti13.8Cu12.5Ni10Be22.5 (at.%) bulk metallic glass alloy have been examined. The plane-strain fracture toughness of the fully amorphous alloy was found to exceed 50 MPa√m, although results were sensitive to strain rate, showed significant variability and were influenced by the presence of residual stresses following processing. Fracture surfaces exhibited a characteristic vein morphology, consistent with micromechanical models for meniscus instabilities. Local melting was evident, consistent with the emission of light during rupture and very high local temperatures (>1000 K) measured during fracture. Upon partial or complete crystallization, the alloy was severely embrittled, with toughnesses dropping to ∼1 MPa√m and the hardness increasing by ∼10%. Under cyclic loading, crack-propagation behavior in the amorphous structure was similar to that observed in polycrystalline metals; the crack-advance mechanism was associated with alternating crack-tip blunting and resharpening, as evidenced by presence of fatigue striations. Conversely, the (unnotched) stress-life (S/N) properties were markedly different. Crack initiation and subsequent growth occurred quite readily due to the lack of microstructural barriers that would normally provide local crack-arrest points. This resulted in a very low fatigue limit of∼4% the ultimate tensile strength.
Environmental and Stress State Effects on Fracture and Fatigue Crack-Growth in Zr-Ti-Ni-Cu-Be Bulk Amorphous Metals
Authors: Flores Katharine M. , Suh Daewoong , Dauskardt Reinhold H. 
Published: April 2011

AbstractOur work has focused on the fracture and fatigue crack-growth mechanisms of a Zr41.25Ti13.75Ni10Cu12.5Be22.5 bulk metallic glass. These alloys exhibit failure strengths on the order of 2 GPa and toughnesses of 10–30 MPa√m with remarkably little plastic deformation. The effect of stress state on strength properties was studied in an effort to model fracture mechanisms. While fracture surfaces suggest significant plastic flow, failure strains are quite small and appear to be independent of stress state. Other methods of energy dissipation, including adiabatic heating, are discussed. Temperature increases of more than 20°C have been noted on the side face of the fracture sample at the crack tip during fracture. The micromechanics of fatigue crack growth are also considered and related to the batch chemistry, environment, and microstructure.
Superplastic Deformation and Viscous Flow in an Zr-Based Metallic Glass at 410°C
Authors: Nieh T. G. , Wang J. G. , Wadsworth J. , Mukai T. , Liu C. T. 
Published: April 2011

AbstractThe thermal properties of an amorphous alloy (composition in at.%: Zr-10Al-5Ti-17.9Cu-14.6Ni), and particularly the glass transition and crystallization temperature as a function of heating rate, were characterized using Differential Scanning Calorimetry (DSC). X-ray diffraction analyses and Transmission Electron Microscopy were also conducted on samples heat-treated at different temperatures for comparison with the DSC results. Superplasticity in the alloy was studied at 410°C, a temperature within the supercooled liquid region. Both single strain rate and strain rate cycling tests in tension were carried out to investigate the deformation behavior of the alloy in the supercooled liquid region. The experimental results indicated that the alloy did not behave like a Newtonian fluid.
Dynamic Failure Mechanisms in Beryllium-Bearing Bulk Metallic Glasses
Authors: Owen David M. , Rosakis Ares J. , Johnson William L. 
Published: April 2011

AbstractThe understanding of dynamic failure mechanisms in bulk metallic glasses is important for the application of this class of materials to a variety of engineering problems. This is true not only for design environments in which components are subject to high loading rates, but also when components are subjected to quasi-static loading conditions where observations have been made of damage propagation occurring in an unstable, highly dynamic manner. This paper presents preliminary results of a study of the phenomena of dynamic crack initiation and growth as well as the phenomenon of dynamic localization (shear band formation) in a beryllium-bearing bulk metallic glass, Zr41.25Ti13.75Ni10Cu12.75Be22.5. Pre-notched and prefatigued plate specimens were subjected to quasi-static and dynamic three-point bend loading to investigate crack initiation and propagation. Asymmetric impact loading with a gas gun was used to induce dynamic shear band growth. The mechanical fields in the vicinity of the dynamically loaded crack or notch tip were characterized using high-speed optical diagnostic techniques. The results demonstrated a dramatic increase in the crack initiation toughness with loading rate and subsequent crack tip speeds approaching 1000 m s−1. Dynamic crack tip branching was also observed under certain conditions. Shear bands formed readily under asymmetric impact loading. The shear bands traveled at speeds of approximately 1300 m s−1 and were accompanied by intense localized heating measured using high-speed full-field infrared imaging. The maximum temperatures recorded across the shear bands were in excess of 1500 K.
Viscosity Measurements for La-Al-Ni liquid Alloys by an Oscillating Crucible Method
Authors: Yamasaki Tohru , Tatibana Tomohiro , Ogino Yoshikiyo , Inoue Akihisa 
Published: April 2011

AbstractThe viscosity of liquid lanthanum-based and aluminum-based La-Al-Ni alloys has been measured by an oscillating crucible method of the inverse suspending type in the temperature range from melting temperature (Tm) up to about 1400 K. In the case of La55Al45-xNix (x = 10∼40 at. %) alloys, the viscosity increased with increasing Ni content up to about 20 at. % Ni and then decreased with increasing the Ni content, while the activation energy for viscous flow decreased to a minimum value at about 20 at. % Ni. This composition is well consistent with that of the La-Al-Ni alloy having largest glass-forming ability.
In-Situ Electron Diffraction Study of Structural Change in the Super-Cooled Liquid Region in Amorphous La-Al-Ni Alloy
Authors: Ohkubo T. , Hiroshima T. , Hirotsu Y. , Ochiai S. , Inoue A. 
Published: April 2011

AbstractAtomic structures of an amorphous La55A125Ni20 alloy in the supercooled liquid state have been investigated by in-situ electron diffraction using a specimen-heating stage in TEM and the imaging-plate intensity recording. From the analysis of atomic pair distribution functions, changes in interatomic distances and coordination numbers were clearly observed at temperatures in the supercooled liquid state. From the reverse Monte Carlo simulations, structural units (icosahedral, Archimedean anti-prism and trigonal prism atomic clusters) typical of the metallic glass structure were found and increased in the supercooled liquid region. In addition, the deformation behavior was investigated using tensile test. The superplastic elongation was confirmed at optimum strain rates in the supercooled liquid region. From the TEM observation of tensile tested specimens with superplastic elongation, β-La (fcc) nano precipitates in the amorphous matrix were confirmed. The superplasticity in this alloy is thought to originate in viscous flow due to the glassy structure formation but is closely related to an additional flow mode with the microcrystalline precipitation from the amorphous state during the deformation.
Probing Slow Atomic Motions in Metallic Glasses using NMR
Authors: Tang X.-P. , Busch Ralf , Johnson William L. , Wu Yue 
Published: April 2011

AbstractWe report a nuclear magnetic resonance (NMR) study of slow atomic motions in Zr-Ti-Cu- Ni-Be bulk metallic glasses. The employed 9Be spin alignment echo technique is able to probe Be motions with jump rate below 0.1 Hz. It was found that the Be motion is spatially homogeneous. The jump rate follows a perfect Arrhenius temperature dependence. The measured activation enthalpy of 1.2 eV is nearly identical to that obtained by Be diffusivity measurement using elastic backscattering (EBS); this indicates that energy barriers are the same for short and long range Be motions. The present work provides direct experimental evidences that exclude vacancy-assisted and interstitial diffusion mechanisms for Be motions in these systems. The result is interpreted in terms of the spread-out free volume fluctuation mechanism.
Improved Conformality of CVD Titanium Nitride Films
Authors: Liu Xinye , LU Yuan Z. , Gordon Roy G. 
Published: April 2011

AbstractWe demonstrate a novel approach to improving the step coverage of thin films made by chemical vapor deposition (CVD). Titanium nitride (TiN) films were deposited by atmospheric pressure CVD using tetrakis(diethylamido)titanium vapor (TDEAT) and ammonia gas (NH3) carried in nitrogen gas. Trimethylamine (NMe3) gas was added during some of the depositions. The substrates were patterned silicon wafers having holes with aspect ratio of 3.5 through a silicon dioxide layer. We discovered that the step coverage was significantly increased for TiN films made with NMe3. At 320 °C, the step coverage was increased from 70% to nearly 100%. Within the range of deposition temperatures used in our study, 320 °C to 370 °C, the amount of improvement increased as the deposition temperature decreased. The trimethylamine did not increase the resistivity or the impurity levels in the films, but it did reduce the growth rate slightly. We suggest that the trimethylamine adsorbs onto the surface, temporarily blocking some of the sites on which growth could take place. Thus the effective sticking coefficients for the precursors are decreased, and the step coverage is increased.
Characterization of Low-Temperature PECVD Silicon Dioxide Films
Authors: Deenapanray P. N. K. , Lengyel J. , Tan H. H. , Petravic M. , Durandet A. , Williams J. S. , Jagadish C. 
Published: April 2011

AbstractSilicon dioxide (SiOx, x ≤ 2) films were plasma-deposited at a pressure of 1 Torr and low substrate temperature (≤ 300°C) by N20/lSiH4 flow. Deposition rates in the range 20–50 nm/min were achieved at 20 W rf source power. Deep level transient spectroscopy showed that no significant defect levels were introduced in the Si substrates at this low source power. The effects of flowrate ratio, R, of N2O/SiH4 and substrate temperature on film properties were determined using ex-situ spectroscopic ellipsometry, prism coupler, Rutherford backscattering spectroscopy (RBS), secondary ion mass spectrometry (SIMS), Fourier transform infrared spectroscopy (FTIR) and chemical etching (P-etch). Near-stoichiometric oxide layers were obtained for R ≥ 1, and a decrease in deposition rate with increasing R was observed. The increase in refractive index for R ≤ 1 has been correlated to compositional changes in the thin films. Complementary results were obtained from FFIR and P-etch measurements. Nitrogen was present in the films deposited using R = 4.4, for which the depostion rate showed an Arrhenius-like relationship to substrate temperature. No OH-related bands were observed in our films.
The characteristics of dc glow discharge and its effects on enhancement of diamond nucleation in HF-CVD system
Authors: Xu Z. , Narayan R. J. , Narayan J. , Sankar J. 
Published: April 2011

AbstractWe have investigated enhancement of diamond nucleation due to electrode biasing and compared these results with those obtained using substrate biasing. The electrode biasing results in near-surface dc glow discharge with characteristic negative glows and dark regions on both sides of the electrode (cathode). We have studied systematically diamond nucleation density as a function of substrate location with respect to the electrode and gas pressure. Using scanning electron microscopy and Raman spectroscopy, we have determined that a significant enhancement up to 109 cm-2 in diamond nucleation is achieved when the substrate is located in the negative glow region of the near-surface dc glow discharge. It is also found that gas pressure enhances nucleation site density but the quality of diamond decreases. The optimization of these parameters in obtaining high-quality diamond films is discussed.
The Thermochemical Surface Modification of the Iron-Carbon Alloys
Authors: Timofeeva Larissa A. , Dobrotvorskaya Maria V. , Stepanenko Victor M. 
Published: April 2011

AbstractIron and steel samples have been treated in overheated salt -water vapor environment (oxy-doping technique). SEM and optical microscope images of modified surface demonstrated that coating with three distinct layers was deposited. XPS, XRD and SEM + EDA studies were used for the composition evaluation, and non-uniform distribution of dopants was found. Tribological properties were determined, and it was found improvement of working characteristics in 2–10 times. Thermally enhanced difflusion model describing the coating formation was discussed.
Multilayer Coatings and Optical Materials for Tuned Infrared Emittance and Thermal Control
Authors: Martin P. M. , Johnston J. W. , Bennett W. D. 
Published: April 2011

AbstractMany thermal control applications require thin film coatings that emit or absorb strongly at near infrared and infrared wavelengths. One of the primary applications for these coatings is thermal control for surfaces and structures of spacecraft, which are exposed to solar radiation during at least 60% of their orbit, causing wide temperature fluctuations. Another recent application for this type of coating is infrared emissive imaging employing a fiber optic infrared scene projector. While single layer coatings can provide high emissivity in a broad wavelength band, multilayer coatings can be used to obtain higher emissivities over a narrow wavelength band. This band can be tuned to a specific range of temperatures and wavelengths. Coatings developed for thermal control have a reflective base layer, either ZrN or a refractory metal boride or silicide. These materials have increased durability compared to metal layers. The multilayer coating deposited over the based layer consists of an A1203/SiO2 stack with high emittance at 300 K (9.8 μm), and solar reflectance near 0.6. Multilayer tuned infrared absorber/emitter coatings are applied to fiber optic infrared scene projectors. The coatings consists of a three layer Si3N4/Cr/Si3N4 absorber tuned at the 1.06 μtm laser wavelength, and a six layer Cr/dielectric/Cr/dielectric/Cr/dielectric coating which emits strongly in either the 3 - 5 jim or the 8 - 12 μm infrared wavelength bands. Absorption bands of the coatings are independently tunable. All coatings are deposited by reactive DC and RF magnetron sputtering onto 2.5-in fiber optic faceplates. Either Si3N4, Si, or ZnS thin film dielectric materials were used in the emitter coatings. With an input laser power of 15 W, the coatings emit at a black body temperature 529 K, which compared well with predicted performance.
Micro- And Nano-Mechanical Behavior of Diamondlike Carbon Containing Foreign Atoms Prepared by Pulsed Laser Deposition
Authors: Wei Q. , Narayan R. J. , Sharma A. K. , Sankar J. , Oktyabrsky S. , Narayan J. 
Published: April 2011

AbstractWe have prepared diamondlike carbon (DLC) films using KrF excimer pulsed laser (248 nm). The DLC films were deposited on Si (100) substrates and Cu and Ti were incorporated into the films through adopting a new target design. Visible Raman spectroscopy analysis of G-peak was correlated to internal stress changes in the DLC films due to incorporation of foreign atoms. Reduction of internal stresses in the presence of foreign atoms was established. This is consistent with adhesion studies that showed significant improvement in adhesion of DLC films containing dopants. Nanohardness and Young's modulus of DLC films containing Ti and Cu showed some decrease as compared to pure DLC. The experimental results are discussed in terms of the effect of dopants on the short range environment of the continuous random network (CRN) of DLC.
Nitrogen Implantation Effects on the Chemical Bonding and Hardness of Boron and Boron Nitride Coatings
Authors: Jankowski Alan , Felter Thomas , Patterson Robert , Hayes Jeffrey , Anders Simone , Stamler Thomas , Poker David 
Published: April 2011

AbstractBoron nitride (BN) coatings are deposited by the reactive sputtering of fully dense, boron (B) targets utilizing an argon-nitrogen (Ar-N2) reactive gas mixture. Near-edge x-ray absorption fine structure analysis reveals features of chemical bonding in the B ls photoabsorption spectrum. Hardness is measured at the film surface using nanoindentation. The BN coatings prepared at low, sputter gas pressure with substrate heating are found to have bonding characteristic of a defected hexagonal phase. The coatings are subjected to post-deposition nitrogen (N+ and N2+) implantation at different energies and current densities. The changes in film hardness attributed to the implantation can be correlated to changes observed in the B ls NEXAFS spectra.
Laser Assisted Deposition of Carbon Nitride Coatings
Authors: Kumar Ashok , Alexandrescu R. 
Published: April 2011

AbstractWe have investigated the growth of carbon nitride (CNx) coatings on various substrates using laser assisted methods such as pulsed laser deposition (PLD) and laser chemical vapor deposition (LCVD). It has been shown that the both techniques produce good quality thin films of CNx. In PLD, a laser beam (λ= 248 nm) has been used to ablate the pyrolytic graphite target in nitrogen atmosphere, where as CO2 laser was used to irradiate carbon-nitrogen containing mixtures such as C2H2/N20/NH3 in LCVD method. A comparative analysis will be presented in terms of structural properties of CNx films prepared by both techniques.
Property and Processing Comparison of Optical Coatings Made by Ion Assisted Evaporation and Magnetron Sputtering
Authors: Pawlewicz W. T. 
Published: April 2011

AbstractIon Assisted Evaporation and Magnetron Sputtering are the two most important Physical Vapor Deposition processes used for optical coatings today. Each has advantages and limitations, and each is best for different coating applications. This paper provides a brief but comprehensive comparison of the two. Starting with introductory process descriptions, the paper compares Ion Assist and Sputtering feature-by-feature and ranks them in scorecard fashion. Features examined include: adatom energetics, reactivity, materials compatibility, thickness uniformity, deposition rate, substrate temperature, durability, environmental stability, refractive indices, absorption, scatter, mechanical stress control, and scalability (chamber and substrate size). The comparison is illustrated with examples from the author's twenty-four years of optical coating experience at three companies, with more than forty coating chambers (small, medium and very large), in research, development and production coating environments.
Preparation And Characterization Of Carbon Nitride Thin Films By Electron Cyclotron Resonance (Ecr) Sputtering Method
Authors: Aoi Yoshifumi , Tani Youji , Hisa Masaaki , Kamijo Eiji 
Published: April 2011

AbstractCrystalline carbon nitride films were deposited by electron cyclotron resonance (ECR) plasma sputtering method using a carbon target and a nitrogen gas atmosphere. The deposited films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and X-ray diffraction (XRD). Nitrogen content of the deposited film was varied with substrate selfbias potential and substrate temperature. Bonding states of nitrogen and carbon in the deposited filns were different according to the substrate temperature, sp3 C-N bonds were observed for the film deposited at 600 °C. Crystallization of carbon nitride thin film was observed hen the deposition was carried out an elevated substrate temperature.
The Oxidation of Ni and Ni-20Cr Deposited with Chromia Thin Films VIA Combustion CVD
Authors: Alexiou A. E. , Hendrick M. R. , Hampikian J. M. 
Published: April 2011

AbstractChromia thin films were deposited onto substrates of Ni and Ni-20Cr by gaseous fuel combustion chemical vapor deposition. The chemical precursor utilized to achieve chromia films was aqueous 0.27M chromium nitrate, and the depositions took place within the flame at temperatures between 200 and 550°C. Amorphous coatings were deposited between 200 and 375°C, whereas crystalline coatings of chromia (eskolaite) were deposited between 400 and 550°C. The eskolaite deposition rate was approximately five times faster than the amorphous chromia. Chromia coatings containing 2 wt% yttria were also formed. The deposition temperature necessary to form crystalline chromia/yttria coatings was slightly higher (∼50°C) than those containing chromia only. The ability of the various coatings to provide oxidation protection was characterized using thermogravimetric analysis (TGA). The eskolaite coatings that are at least 1 im thick reduce the oxidation mass gain/area of Ni-20Cr by nearly a factor of ten and the parabolic constant by an order of magnitude, whereas the amorphous chromia coatings that are 0.6 μm thick do not demonstrate such an improvement. Yttria-doped chromia coatings further reduce the parabolic constant by two orders of magnitude, consistent with expectation. Characterization of the coatings was accomplished using a variety of techniques, including SEM, TEM, EDS, and XRD.
Mullite Diffusion Barriers for SiC-C/C Composites Produced by Pulsed Laser Deposition
Authors: Fritze H. , Schnittker A. , Witke T. , Rüscher C. , Weber S. , Scherrer S. , Schultric B. , Borchardt G. 
Published: April 2011

AbstractPulsed Laser Deposition (PLD) allows the ablation of nonconductive and high melting point target materials and the preparation of films with complex composition. High energy impact leads to melting and evaporation of the target material in a single step. In case of mullite ablation, the flux of the metal components is stoichiometric. Under reduced pressure the oxygen content in the layers decreases. However, after a short oxidation treatment, the formation of mullite in the coating is completed, as confirmed by IR spectroscopy and XRD investigations. For a commercial Si-SiC precoated C/C material, the effectiveness of additional PLD mullite layers as outer oxidation protection is tested in the temperature range 773 K < T < 1873 K. Mullite coatings with a thickness of 2.5 pm improve the oxidation behaviour significantly. Because of SiO2 formation at the mullite-SiC interface, all samples exhibited a mass increase upon oxidation. For oxidation durations of three days, only amorphous SiO2 is formed at the mullite-SiC interface. The inward diffusion of oxygen across the outer mullite-containing layer controls the kinetics of the reaction, as was deduced from 18O diffusivity measurements in PLD mullite layers. At temperatures close to the eutectic temperature (1860 K), mullite can seal defects. The calculated oxidation rates resulting from the diffusion parameters in SiO2 and mullite are close to the thermogravimetric data.