bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of Defect Numbers and Distributions in Pecvd S102 Transparent Barrier Coatings on Pet
Authors: Sobrinho A. S. Da Silva , Czeremuszkin G. , Latrèche M. , Wertheimer M. R. 
Published: April 2011

AbstractTransparent ceramic barrier films are the object of increasing interest in packaging, pharmaceutical, optical, and electronics industries, since they can reduce the permeation rate of oxygen (OTR) and/or water vapor (WVTR) by several orders of magnitude. We prepare silicon dioxide (Si02) or nitride (“SiN”) barrier layers by plasma-enhanced chemical vapor deposition (PECVD). We have shown that OTR (and WVTR) decrease with increasing coating thickness, d, to a certain asymptotic minimum value, when d ≥ 50 nm; the residual permeation is attributed to the presence of microscopic defects in the coating. Since the coatings are transparent and very thin, the detection of defects and the analysis of their origin are very difficult.We have recently developed techniques based on reactive ion etching (RIE) in oxygen plasma to render visible micrometer- or sub-micrometer-sized defects in transparent barrier coatings on transparent polymers. These techniques can be used to better understand the origins of defects in these coatings on a microscopic scale, as well as for mapping and counting defect density on a macroscopic scale (tens of cm2 or more).In this article we present a correlation between measured 02 transmission rate (OTR) values and the number density and size distribution of defects in SiO2 barrier coatings. Excellent agreement between measured and calculated OTR values allows us to confirm that residual OTR is indeed controlled by pinhole defects; our results also compare well with published data for aluminized PET.
Monte Carlo Prediction of Alloy Structure
Authors: Good Brian S. , Bozzolo Guillermo , Noebe Ronald D. 
Published: April 2011

AbstractAs the performance demands on metal alloys of interest to the aerospace community continue to increase, the complexity of these alloys has tended to grow as well, with corresponding increases in the cost and time needed to develop future generations of materials. While the traditional empirical approach to designing these materials has proven effective, as the complexity of the materials grows, such methods will become less efficient, limiting prospects for further improvement. The incorporation of theoretically- and computationally-based input into the design process has the potential to both improve the quality of, and reduce the time to design, new materials.Among the most fundamental issues in new materials design, the prediction of the crystallographic structure of solids has long been a goal of researchers in the field of computer simulation. To become an effective tool for assisting in the process of alloy design, a computational scheme must make use of an energy method fast enough to allow consideration of a large number of candidate structures, and an efficient energy minimization scheme.In this work, we discuss our application of Monte Carlo methods, using the BFS semi-empirical energy method developed in our laboratory, to the problem of prediction of the crystallographic structure of multi-component metal alloys. Using a simple Metropolis Monte Carlo method in conjunction with an accurate and transferable method for computing energetics, we have investigated the crystallographic structure of a variety of fcc- and bcc-based intermetallic compounds, and have considered the influence of alloying additions in compounds having up to five constituents. We discuss the successes and limitations of the methodology, and the prospects for obtaining accurate prediction of physical properties from our results. We also emphasize the role of this type of methodology as part of a synergistic experimental-theoretical effort for alloy design.
The Abrasion of Aluminum, Platinum, and Nickel by Martian Dust as Determined by the Mars Pathfinder Wheel Abrasion Experiment
Authors: Ferguson Dale , Siebert Mark , Wilt David , Kolecki Joseph 
Published: April 2011

AbstractThe Mars Pathfinder Wheel Abrasion Experiment (WAE) spun a specially prepared wheel with strips of aluminum, platinum, and nickel, in the Martian soil. These materials were chosen because of their differing hardnesses, their ability to stick to anodized aluminum, and their comparative chemical inertness under Earth launch and Mars landing conditions. Abrasion of those samples was detected by the change in their specular reflectances of sunlight as measured by a photovoltaic sensor mounted above the wheel. The degree of abrasion occurring on the samples is discussed, along with comparisons to the abrasion seen in Earth-based laboratory experiments using Martian soil analogs. Conclusions are reached about the hardness, grain size, and angularity of the Martian soil particles, and the precautions which must be undertaken to avoid abrasion on moving parts exposed to the Martian dust.
Growth Competition During Double Recalescence in Fe-Cr-Ni Alloys
Authors: Matson D. M. 
Published: April 2011

AbstractThe rapid solidification of a Fe- 12wt%Cr- 16wt%Ni alloy was investigated under containerless processing conditions using both ground-based electromagnetic levitation equipment and aboard the shuttle Columbia using the TEMPUS facility. A high-speed digital video technique was used to image growth of the metastable ferritic phase and the stable austenitic phase into the undercooled melt. Above a critical undercooling, the metastable phase nucleates first. After a delay, a second thermal rise is observed during transformation to the stable phase. Double recalescence events were observed at temperatures consistent with the To, temperature of the bcc phase thus defining a value of the critical undercooling for metastable nucleation which is significantly lower than previously predicted. For a given liquid temperature the velocity of the stable fcc phase is greater than that of the metastable bcc phase. The velocity for growth of the stable phase into the semi-solid which forms during primary metastable recalescence was also measured and found to be independent of the initial undercooling. A model based on competitive growth of the two phases successfully predicts the limit where double recalescence events may be detected.
The Isothermal Dendritic Growth Experiment: Evolution of Teleoperational Control of Materials Research in Microgravity
Authors: Lacombe J.C. , Koss M.B. , Lupulescu A.O. , Frei J.E. , Glicksman M.E. 
Published: April 2011

AbstractExactly one year ago, the Isothermal Dendritic Growth Experiment (IDGE) completed its third and final orbital space flight aboard the United States Microgravity Payload (USMP) on STS-87. The IDGE conducted 180 experiments on dendritic growth in 5-9's succinonitrile (SCN), a BCC material used on USMP-2 and USMP-3, and over 100 experiments on 4-9's pivalic acid (PVA), an FCC material used on USMP-4. IDGE film and telemetry data provide benchmark tip velocity and radii versus supercooling for critically testing transport theory and the interfacial physics of diffusion-limited dendritic growth. Post-flight application of optical tomography is providing the first tip shape data allowing quantitative tests of three-dimensional phase field calculations. Several new discoveries were made during each flight concerning the behavior of dendrites at low driving forces, and the influences of time-dependent pattern features and noise. A summary of these scientific highlights will be provided.The IDGE instrument was upgraded on each successive flight, improving its optics and electronics, especially the capability for teleoperational control. Near real-time, full gray-scale video was accommodated on USMP-4, allowing investigation of non-steady-state features and time-dependent growth dynamics. A short example of video from space will be shown. USMP-4 science was teleoperated by a student cadre for 16 days from a remote site established by NASA at RPI. This operational experience provides valuable insights, which will be drawn upon for future microgravity experiments to be conducted on the International Space Station.
Vapor Grown Carbon Fiber Reinforced Aluminum Matrix Composites for Enhanced Thermal Conductivity
Authors: Ting J.-M. , Tang C. , Lake P. 
Published: April 2011

AbstractAluminum matrix composites reinforced with high thermal conductivity vapor grown carbon fiber (VGCF) were developed for improved thermal efficiencies in electronic devices. The carbon fiber was heat treated to increase its thermal conductivity. Various aluminum matrix composites were fabricated by the densification of fiber preforms using a pressure casting technique. Uniformity of the density was examined using optical microscopy. A scanning electron microscope equipped with a microprobe was utilized to examine the mechanical integrity of the composite. Mechanical properties, including tension, compression and flexural properties, were measured. While the results of the mechanical property measurements indicate moderate values, the composite exhibited remarkable thermal conductivity that reached 642 W/m.K, three times that of aluminum, at a fiber volume fraction of 36.5%, following closely the rule of mixture.
Large Scale Teleoperation on the Lunar Surface
Authors: Konesky Gregory 
Published: April 2011

AbstractThe popular success of the Mars Pathfinder mission, especially in terms of individual access to “live”pictures over the internet, demonstrates substantial mass appeal of space exploration on a personal level. Teleoperation provides an inexpensive approach to remote presence, but is distance-limited due to finite signal propagation times. The proximity of the Lunar surface permits near real-time teleoperation, and through a Virtual Reality approach, presents a sense of “being there” without the difficulty of getting there (and back).While limited single user teleoperated Lunar Rovers concepts have been proposed (Luna Corp., Inc.), an on-going and economically self supporting venture would require simultaneous teleoperation of many vehicles on a large scale. In addition, each vehicle would carry several simultaneous stereoscopic remote viewing television camera heads, whose position is controlled by the head movements of Earth bound viewers. The overall concept is similar to a small fleet of touring busses, although some smaller scout vehicles may be included, as well as a tow truck. An access fee structure for Earth bound teleoperators provides for return on investment.Technical issues for an on-going operation in the Lunar environment include temperature extremes, high vacuum, solar radiation, micrometeorites, abrasive nature of Lunar dust and its capacity to electrostatically attach to surfaces are discussed, as are their impact on vehicle design and operation. Optical data links are considered to handle bandwidth requirements of 500 simultaneous users. The economics of scale, on multiple levels, demonstrates the feasibility of large scale teleoperation. Various base-line studies are presented.
Dislocation Dynamics in Ni3Al: Experiments and Computations
Authors: Bhate N. , Kumar S. , Phillips R. , Clifton R. J. 
Published: April 2011

ABSTRACTA modified electrolytic etchant has been successfully used to observe dislocation etch-pits on {100} surfaces of single crystal Ni3AI containing Hf and B additions. Four-point bending tests have been used to obtain the dependence of dislocation velocity on resolved shear stress at room temperature. A comparison with earlier studies reveal that the rate of change of dislocation velocity with resolved shear stress, to a first approximation, is independent of alloying. Atomic level simulations have been performed using the embedded atom method (EAM) to study dislocation core structures and frictional stress in Ni3Al.
Effect of Off-Stoichiometry on the Deformation Behavior of Ni3AI Binary Polycrystals
Authors: Matterstock B. , Conforto E. , Kruml T. , Bonneville J. , Martin J. L. 
Published: April 2011

ABSTRACTPolycrystals of binary Ni3Al with different compositions are deformed in compression between 300K and 1300K. They exhibit a strength anomaly with peak temperatures between 800K and 950K. Below the peak, the aluminium rich compounds are the strongest ones while the nickel rich compounds are the weakest ones. As the aluminium content increases, the complex stacking fault energy, measured through weak beam experiments, increases as well. This confirms the cross slip mechanism of mobile dislocation exhaustion through Kear-Wilsdorf lock formation. A ‘ductile-to-brittle transition’ is observed at 1000K. Fracture occurs along grain boundaries, the strength of which decreases as environmental effects are enhanced at high temperatures.
Atomistic Studies of Jogged Screw Dislocations in γ-TiAl Alloys
Authors: Chen K. Y. , Li M. , Zhou S. J. 
Published: April 2011

ABSTRACTThe behavior of jogged screw dislocations in γ-TiAl alloys have been investigated with largescale molecular dynamics (MD) simulations. We find a new mechanism for formation of pinning points in jogged screw dislocations. We also find that the critical height for the jogs in ±[110] directions on the (001) plane to move nonconservatively is between 3r0 and 4r0, where r0 is the nearest neighbor distance of aluminum atoms. Interstitials and vacancies are created during the nonconservative motions of the jogs. In addition, the formations of dislocation dipole and loops around the jogs are also observed.
Thermal Defects in B2 Iron Aluminide
Authors: Collins Gary S. , Peng Luke S.-J , Wei Mingzhong 
Published: April 2011

ABSTRACTThermal defects in B2 FeAl samples with compositions between 49.5 and 54.7 at.% Fe were investigated using perturbed angular correlation of gamma rays (PAC). Vacancies on the Fe-sublattice were detected through quadrupole interactions induced at adjacent 111In/Cd probe atoms on the Al-sublattice. Five high-frequency quadrupole-interaction signals were detected (greater than 50 Mrad/s) that are attributed to complexes involving 1, 2, 3, 4 and (with less certainty) 5 Fe-vacancies in the first neighbor shells of the probes. These attributions are based on (1) a comparison between measured quadrupole interaction parameters and point-charge calculations of electric-field gradients for possible vacancy-probe complexes; and (2) numerical simulation of the evolution of site fractions of probes in the complexes at lower temperatures. Measurements were made at temperatures up to 950 C. Assuming that the equilibrium high-temperature is the triple defect (2 Fe-vacancies and one Fe-antisite atom), measurements over the range 600–900 °C yield a formation enthalpy of 1.1(1) eV for the triple defect. Below about 600 °C, Fe-vacancies are quenched-in with a fractional concentration of the order of 1 at.% close to stoichiometry. However, quenched-in vacancies continue to jump over short distances and trap next to the impurity probes atoms in day-long measurements down to 200 °C. Simulations of site fractions below 700 °C were used to determine binding enthalpies of vacancies with probe complexes. Binding enthalpies obtained for the first four vacancies were 0.23, 0.23, 0.15 and 0.18 eV. Simulations in the range 200–700 °C suggest a negative value for the formation entropy. The negative value indicates either that triple defects stiffen the B2 lattice or that repulsive defectdefect interactions become important at the high defect concentrations in FeAl.
Stoichiometric and Off-Stoichiometric Alloying in Silicide Compound Ti5Si3 By Nb or Cr Additions
Authors: Zhang Lanting , Wu Jiansheng 
Published: April 2011

ABSTRACTTitanium silicide Ti5Si3 whose melting temperature is 2130°C bears the potential for very hightemperature application. This paper reports our results on the alloying behaviour of Nb or Cr addition to this compound. Total energy calculation shows that the substitution of Ti by Nb or Cr atoms in Ti5Si3 crystal stiffens the bonding between the atoms. In experiment, two means of alloying are considered: stoichiometric and off-stoichiometric alloying. Stoichiometric alloying in Ti5Si3 results in compounds consisting of single Ti5Si3 phase while off-stoichiometric alloying yields hypereutectic microstructure with Ti5Si3 being the primary phase. The Ti5Si3 phase in both cases dissolves certain amount of Nb or Cr alloying element and its composition agrees with the stoichiometric composition of (Ti,Nb) 5Si3 or (Ti,Cr) 5Si3 The moduli of the stoichiometric alloys increase with the increase of alloying element addition, indicating an enhancement in Ti5Si3crystal.
Processing, Microstructure, and Properties of Multiphase Mo Silicide Alloys
Authors: Liu C. T. , Schneibel J. H. , Heatherly L. 
Published: April 2011

ABSTRACTMultiphase Mo silicide alloys containing T2 (Mo5SiB2), Mo3Si and Mo phases were prepared by both melting & casting (M&C) and powder metallurgical (PM) processes. Glassy phases are observed in PM materials but not in M&C materials. Microstructural studies indicate that the primary phase is Mo-rich solid solution in alloys containing ≤(9.4Si+13.8B, at. %) and T2 in alloys with ≥(9.8Si+14.6B). An eutectic composition is estimated to be close to Mo–9.6Si–14.2B. The mechanical properties of multiphase silicide alloys were determined by hardness, tensile and bending tests at room temperature. The multiphase alloy MSB-18 (Mo–9.4Si–13.8B) possesses a flexure strength distinctly higher than that of MoSi2 and other Mo5Si3 silicide alloys containing no Mo particles. Also, MSB-18 is tougher than MoSi2 by a factor of 4.
Influence of Ni Addition on Mechanical Properties and Fracture Behaviors of Ir-15Nb Two-Phase Refractory Superalloys
Authors: Gu Yuefeng , Yamabe-Mitarai Y. , Ro Y. , Yokokawa T. , Harada H. 
Published: April 2011

ABSTRACTIr-based alloys with fcc-L12 two-phase coherent structure, which are called “refractory superalloys”, have good potentiality as structure materials used at ultra-high temperatures up to 2000 °C. Preliminary results showed that the refractory superalloys failed predominately by brittle intergranular fracture at room temperature even though they showed higher strength at that temperature. This paper will present the influence of nickel (Ni) addition on mechanical properties and fracture behaviors of one of these alloys, Ir-15at%Nb. The results indicated that Ni addition was beneficial to the compression ductility and strength of two-phase Ir-15at%Nb alloy when Ni content was below the optimum content.
The Influence of Microstructure on Superplastic Behaviours of γ-TiAl Alloys
Authors: Sun J. , Wu J. S. , Hu G. X. , He Y. H. , Huang B. Y. 
Published: April 2011

ABSTRACTIn this work, superplastic behaviours in Ti-33A1–3Cr-0.5Mo (wt%) γ-TiAl alloys with two different initial microstructures of near gamma (NG) and duplex (DM) structure were investigated with respect to the effect of testing temperatures and strain rates. At 1050°C and a strain rate of 8×10–5 S–1, a maximum elongation of 570% was observed for NG-TiAl and a maximum elongation of 467% for DM-TiAl. The relations of flow stress and strain rate sensitivity vs. strain rates at different temperatures were also determined by incremental strain rate tests. The results showed that the value of strain rate sensitivity is higher and the flow stress is lower for NG than those for DM at the same condition. The microstructural evolution during superplastic deformation was examined and correlated to the mechanical properties for these two alloys. The influence of microstructure on the superplastic behaviours of γ-TiAl alloys, and possible superplastic deformation mechanisms were finally discussed.
Fragmentation of α2 Plates in a Fully Lamellar TiAl During Creep
Authors: Wang J. G. , Hsiung L. M. , Nieh T. G. 
Published: April 2011

ABSTRACTThe fragmentation and spheroidization of α2 laths in a fully-lamellar TiAl alloy during creep were examined. Three possible mechanisms, Rayleigh's perturbation model, subgrain boundary groove mechanism and intersection of deformation twins with α2 lamellae were presented and discussed. During creep deformation, the pile-up of interfacial dislocations leads to a change of planar interface, which, in turn, causes a difference in local chemical potential, and further results in the spheroidization of α2 lamellae. On the other hand, the deformation of the α2 phase is expected to be induced by the high local stress concentration introduced by the pile up of interfacial dislocations. The dynamic recovery process may lead to the formation of subgrain boundaries in the α2 lamellae, which results in the spheroidization and termination of α2 lamellae with the aid of diffusion during creep.
The Effects of Nanostructure on the Strengthening of NiAl
Authors: Chen T. , Thadhani N. N. , Hampikian J. M. 
Published: April 2011

ABSTRACTThe relationship between microhardness and grain size was investigated for nanocrystalline and coarse-grained stoichiometric intermetallic NiAl. The nanocrystalline NiAl specimens were synthesized through mechanical alloying with a high-energy Spex 8000 shaker mill and consolidated by shock compaction at a peak pressure of 4–6 GPa, to 83% dense compacts. The nanocrystalline NiAl compacts were also sintered at 1073, 1173 and 1473 K for 2 h. The Vickers hardness of consolidated and sintered NiAl was determined by microhardness testing, and the grain size and microstructure were investigated with transmission electron microscopy. It was found that the hardness values increased with decreasing grain size of the NiAl alloy. The Vickers hardness values were approximately 650±16, 690±6, 800±43 HV, respectively for NiAl with grain-sizes corresponding to approximately 27±18, 11±6 and 9±6 nm. The possible strengthening mechanisms operating in NiAl are discussed.
Equilibrium Defects and Concentrations in Nickel Aluminide
Authors: Bai Bin , Collins Gary S. 
Published: April 2011

ABSTRACTPerturbed angular correlation of gamma rays was applied to determine properties of equilibrium defects in B2 NiAl near the stoichiometric composition. Point defects were detected through quadrupole interactions they induce at In probe atoms on the Al sublattice. Well-resolved signals were observed for probe atoms having zero, one or two Ni-vacancies (VNi) in the first neighbor shell. The fractions of probes in different sites are analyzed using a thermodynamic model to determine defect properties as follows. The equilibrium high-temperature defect is determined to be the triple defect combination (two VNi and one Ni-antisite atom) through the variation of the vacancy concentration with composition and not, for example, the Schottky vacancy pair. The binding enthalpy of VNi with a probe atom was determined to be in the range 0.18–0.24 eV. Site fractions were measured for three samples having 50.03, 50.14 and 50.91 at.% Ni at temperatures up to 1300 C. Vacancy concentrations were deduced from the site fractions and binding enthalpy. The equilibrium constant for formation of the triple defect was determined as a function of temperature from the vacancy concentrations and sample compositions. The formation enthalpy was found to be in the range 1.65–1.83 eV, depending on the binding enthalpy. The formation entropy was found to be -3.2(4) kB. The large, negative value of the formation entropy probably cannot be explained in terms of a binding entropy, and we speculate that triple defects harden the B2 lattice, perhaps by disrupting the well-known 1/3 <111> ‘soft mode’ lattice instability in B2 and bcc materials.