bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thin Film Fine Line Work of Adhesion by Microwedge Indentation
Authors: de Boer M. P. , Moody N. R. , Huang H , Gerberich W.W. 
Published: April 2011

AbstractThe mechanics for plane strain geometry are presented for thin film fine lines by considering the case of microwedge indentation of a fine line subject to no residual stress. The analysis is separated into three parts depending on the absence or presence of buckling. During indentation, unbuckled or double-buckled configurations may exist, while single-buckling may occur when the indenter tip is removed. A microwedge tip was employed in the indentation testing of unstressed rf-sputtered tungsten fine lines to demonstrate some of the analysis.
Scanning Scratch Tests for Evaluating the Adhesion of Thin Oxide Films on Stainless Steel
Authors: Haanappel V. A. C. , van Corbach H. D. , Fransen T. , Gellings P. J. 
Published: April 2011

AbstractAmorphous alumina films were deposited by metal-organic chemical vapour deposition (MOCVD) on stainless steel, type AISI 304. The MOCVD experiments were performed in nitrogen at low pressure (0.17 kPa (1.25 torr)).The effect of deposition temperature (200 − 380 °C), growth rate, film thickness, and post-deposition thermal treatment on the mechanical properties was studied. The experiments were performed with a scanning-scratch tester. The experiments are based on the estimation of the film adhesion to the substrate by determining a critical load, Lc: the load where the film starts to spall or to delaminate.The best mechanical properties were obtained with unannealed samples. After thermal annealing the critical load decreases. Regarding the unannealed samples, the critical load increased with increasing film thickness. The deposition temperature and the growth rate had no effect on the critical load.
Manipulation of Stresses in Metallic Thin Films by Alloying
Authors: Nandedkar A. S. 
Published: April 2011

AbstractAtomistic simulations were used to study the configurations of defects in copper aluminum alloy (2% copper, 98% aluminum). In the presence of free surface, the copper atoms migrated towards the surface. When the aluminum cell (about 2000 atoms) contained a dislocation, copper atoms segregated near the dislocation core on the compressional side. In presence of a grain boundary, copper atoms moved into the boundary plane. The segregation in these simulations resulted from reduction in localized strain near the structural defects.
Neural Network Processing of Optical Fiber Sensor Signals for Impact Location
Authors: Schindler Paul M. , Shaw John K. , May Russell G. , Claus Richard O. 
Published: April 2011

AbstractA system to detect and locate impacts by foreign bodies on a surface was developed and tested. Fiber optic extrinsic Fabry-Perot interferometer (EFPI) strain sensors were attached to or embedded in the surface, so that stress waves emanating from an impact could be detected. By employing an artificial neural network to process the sensor outputs, the impact location could be inferred to centimeter range accuracy directly from the arrival time data. In particular, the network could be trained to determine impact location regardless of material anisotropy. Results demonstrate that a back-propagation network identifiesimpact location for an anisotropic graphite/bismaleimide plate with the same accuracy as that for an isotropic aluminum plate.
Thermo-Electric Properties of Thin-Film Refractory Metal Thermocouples
Authors: Schinazi Robert G. , Lu Guo-Quan , Spaepen Frans 
Published: April 2011

AbstractThin-film thermocouples are well suited for “smart” processes where the mass of traditional two-lead thermocouples inhibits their wide utilization. However, currentthin-film thermocouples lack the robustness desired for abrasive environments. To addressthis issue, thin-film refractory metal thermocouples consisting of combinations of molybdenum, tantalum, tungsten, vanadium, or nickel were produced by ion-beam sputtering on an alumina substrate. To speed up the process of sampling a large number of material combinations, the thermocouples were made small, about 200 nm thick, 2.5 mm wide, and 12 mm long. An apparatus was fabricated to measure the thermo-electric responses of these short-length thermocouples. Materials design and heat-transfer issues relating to the applicationsand testing of these thermocouples are discussed.
Ba/sr Doped Electrostrictive Compositions for Actuator Design
Authors: Zhuang Zhiqiang , Jan Lijun , Kang S.B. , Gallois B. , Yang Z. , Du H. 
Published: April 2011

AbstractSolid solutions of lead zirconate titanate (PZT) and lead magnesium niobate (PMN) doped with barium/strontium were developed for use in miniature electrostrictive actuators. The microstructural features of the materials were determined by high-resolution transmission electron microscopy (HREM) and by x-ray diffractometry. The response and the strain hysteresis were measured by applying a sinusoidal or a rectangular voltage pulse. Pulses of variable amplitude and width were applied to the elements to study the switching behavior of 90° domain walls in the materials and to elucidate the initial zero-position “walk off” mechanism. The strain hysteresis or remanent strain of PZT decreased with increasing PMN concentration. A barium-doped PZT (Ba-PZT) composition containing 4 mole% of PMN exhibited ferroelectric relator behavior with a field-induced strain much larger than those of lead magnesium niobate (PMN) electrostrictive materials and a small remanent strain hysteresis.
Stresses Near the End of an Internal Electrode in Multilayer Electrostrictive Ceramic Actuators
Authors: Gong Xiao-Yan 
Published: April 2011

AbstractStresses near the end of an internal electrode in a multilayer electrostrictive ceramic actuator are studied in detail. A finite element program capable of overcoming two major difficulties is developed. The program solves both the mechanical and electrical coupling problem and the nonlinear electric field and electric displacement relationship for these materials. Results indicate that the stress difference between the coupled and the uncoupled cases can only be distinguished when a stress singularity is present. Tensile stresses are found both in front, and behind, the end of an internal electrode. The magnitude of the stresses is predetermined by the material constants.
In-Situ Observation of Microcracking in a Tial-Cr-V Alloy Under Compressive Stress
Authors: Pu Z. J. , Liu Y. Q. , Wu K. H. 
Published: April 2011

AbstractThe entire process of microcrack nucleation in a TiAl-Cr-V alloy with different microstructures is observed in situ by a scanning electronic microscope (SEM) during compressive deformation. The main results are summarized as follows: (1) In the fully lamellar microstructure, the microcracks nucleate mainly at the lamellar grain boundaries between soft-orientation and hard-orientation grains. (2) In the Widmanstatten structure, the microcracks distribute mainly at the intersection between two Widmanstatten plates. (3) In the duplex structure, the microcracks form at the lamella/ lamella and lamella/gamma boundaries. (4) In the nearly gamma structure, microcracks nucleate at gamma/gamma grain boundaries.
Tem and Computer Image Simulation Studies on the Dissociation of Superdislocations in Ll2 Al3Ti Alloy
Authors: Rong Yonghua , Wu Xiaohua , Chen Xiaofu , Chen Shipu , Hu Gengxiang 
Published: April 2011

AbstractTEM investigation associated with computer image simulations were conducted to determine the dislocation core structure in the Ll2 Al67MnsTi25 alloy deformed at room temperature. It is identified that the a<110> superdislocations dissociated into pairs of a/3<112> superpartials with SISF between them. The theoretical and experimental micrographs are in good agreement under various diffraction conditions. The unusual temperature dependence of flow stress at low temperature can be related to the SISF-type dissociation.
Structure-Property Relationships and Deformation Mechanisms in an Orthorhombic Based Ti-25Al-17Nb Alloy
Authors: Majumdar B. S. , Boehlert C. , Rai A. K. , Miracle D. B. 
Published: April 2011

AbstractThe microstructure-property relations were evaluated for a nominally Ti-25Al-17Nb orthorhombic alloy, in terms of the deformation and failure mechanisms of the constituent ordered phases (orthorhombic, alpha-2, and B2). The mechanisms were characterized through observation of slip traces, crack initiation sites, and TEM. Properties of interest were the room temperature elongation, fatigue crack growth (FCG) resistance, and creep resistance.
Localized Oxidation Near Cracks and Lamellar Boundaries in a Gamma Titanium Aluminide Alloy
Authors: Kameda J. , Gold C. R. , Lee E. S. , Bloomer T. E. , Yamaguchi M. 
Published: April 2011

AbstractSmall punch (SP) tests on single grained titanium aluminide (Ti-48 at.%Al) specimens with 12° and 80° lamellar orientations with respect to the tensile stress axis were conducted at 1123 K in air. Brittle cracks readily extended through the thickness in the 80° lamellar structure. In a SP specimen with the 12° lamellar structure load-interrupted at the strain of 0.43%, surface cracks with the depth of 15–25 μm were formed along lamellar boundaries. Local oxidation behavior on partly sputtered surfaces in the load-interrupted 12° lamellar specimen was examined using scanning Auger microprobe (SAM). Oxygen enriched regions were observed near cracks and some lamellar layers. The mechanisms of high temperature oxygen-induced cracking are discussed in terms of the local oxidation near cracks and lamellar boundaries.
Microstructure and Mechanical Properties of The L12/L21 Two-Phase Alloys In The Quaternary Co-Al-Ni-Ti System
Authors: Matano Takeo , Kimura Yoshisato , Miura Seiji , Mishima Yoshinao 
Published: April 2011

AbstractAn attempt is made to develop a two-phase alloy consisting of the Ll2 and L21(Heusler) phases in the Co–Al–Ni–Ti quaternary sytem exhibiting a high elevated temperature strength as well as some room temperature ductility as a new class of heat resisting structural materials. The idea behind this approach is expectations for the L21 phase to provide high elevated temperature strength, whereas the Ll2 phase provides some room temperature ductility. Compositional optimization in the room temperature ductility of the Ll2 (Co,Ni)3(Al,Ti) is first carried out and then, based on the result, several L12/L21 two phase alloys are designed. It is found that a few to several per cent room temperature bend ductility is obtained in such two-phase alloys.
First-Principles Study of Intermetallic Phase Stability in the Ternary Ti-Al-Nb Alloy System
Authors: Asta Mark , Ormeci Alim , Wills John M. , Albers Robert C. 
Published: April 2011

AbstractThe stability of bcc-based phases in the Ti-Al-Nb alloy system has been studied from first-principles using a combination of ab-initio total energy and cluster variation method (CVM) calculations. Total energies have been computed for 18 binary and ternary bcc superstructures in order to determine low temperature ordering tendencies. From the results of these calculations a set of effective cluster interaction parameters have been derived. These interaction parameters are required input for CVM computations of alloy thermodynamic properties. The CVM has been used to study the effect of composition on finite-temperature ordering tendencies and site preferences for bcc-based phases. Strong ordering tendencies are observed for binary Nb-Al and Ti-Al bcc phases as well as for ternary alloys with compositions near Ti2AlNb. For selected superstructures we have also analyzed structural stabilities with respect to tetragonal distortions which transform the bcc into an fcc lattice. Instabilities with respect to such distortions are found to exist for binary but not ternary bcc compounds.
Site Occupation of Excess Al Atoms in Off-Stoichiometric γ-Tial: Measurement of Debye-Waller Factors
Authors: Swaminathan S. , Jones I. P. , Maher D. M. , Fraser H. L. 
Published: April 2011

AbstractIn recent years, the determination of x-ray structure factors and hence the electron charge density distribution in TiAl has received considerable attention. Experimental assessment of electron charge densities requires accurate values of the Debye-Waller (D-W) factors. This work attempts to determine the Debye-Waller factors from measurements of an Al rich off-stoichiometric single crystal of TiAl using the four circle x-ray diffraction method. The results suggest an ordered substitution of the excess Al atoms on the Ti-sublattice. This result is consistent with previous site occupancy studies.
Evolution of Dislocation Structures in Cyclically Deformed NiAl-Fe
Authors: Kallingal C. G. , Matsugi K. , Stoloff N.S. , Rajan K. 
Published: April 2011

AbstractThe microstructures of NiAl-Fe (Ni, 50.3at % Al, 0.28 at% Fe) polycrystals tested in HCF (high cycle fatigue) below and above the DBTT (ductile to brittle transition temperature) viz., 673 K, 823 K, 873 K and 928 K at different stress amplitudes were observed by transmission electron microscopy. The microstructure consisted of low energy dislocation networks and dislocation cells. The fundamental features of the dislocation structures are described. Misorientation angles between cells were measured from Kikuchi patterns obtained from cells through microdiffraction. The misorientations across the cell walls were found to increase with increase in the stress amplitude to which the material was subjected during cycling. The mechanisms for the formation and evolution of these structures are discussed on the basis of existing theoretical models. The implications of these substructures on the mechanical properties are also discussed.
Phase Decomposition and Deformation of L12-Ordered Co-Rich Co3Ti
Authors: Nemoto M. , Tian W. H. , Hayashi K. 
Published: April 2011

AbstractThe Co3Ti phase hardens appreciably by the fine precipitation of disordered fee Co-rich phase upon aging after quenching from solution annealing temperature. Transmission electron microscope(TEM) observations revealed that the precipitates are platelet in shape, lying nearly parallel to the {100} planes of the L12-ordered matrix, and perfectly coherent with the matrix lattice at the beginning of aging. The high temperature strength increases appreciably with the fine precipitation of disordered Co-rich phase over the whole temperature range investigated. TEM observations of the underaged and deformed alloys revealed that superdislocations are pinned by precipitates indicating an attractive interaction between dislocations and precipitates. At the overaged state, thin twins are introduced in the fee Co-rich precipitates during deformation.
Simulations of Creep in Ductile-Phase Toughened Nb5Si3/Nb In-Situ Composites
Authors: Henshall G. A. , Strum M. J. , Subramanian P. R. , Mendiratta M. G. 
Published: April 2011

AbstractThe primary and steady-state creep behavior of ductile-phase toughened Nb5Si3/Nb in-situ composites has been simulated using analytical and finite element (FE) continuum techniques. The microstructure of these composites is complex, consisting of large, elongated primary dendrites of the ductile (Nb) solid-solution phase in a eutectoid matrix with the silicide as the continuous phase. This microstructure has been idealized to facilitate the modeling; the effects of these idealizations on the predicted composite creep rates are discussed. Further, it has been assumed that the intrinsic creep behavior of each phase within the composite is the same as that of the corresponding bulk material. Thus, the experimentally measured creep properties of the bulk Nb5Si3 and (Nb) phases have been analyzed to provide the required material constants in the creep constitutive equation. Model predictions of the steady-state composite creep rate have been compared with the experimental results for a Nb-10 at.% Si alloy. While accurate at low stress, the models underpredict the composite creep rate at large stresses because the composite stress exponent is underpredicted. In the case of primary creep, the models somewhat over-predict the composite creep strain but are reasonably accurate given uncertainties in the primary creep data. Finally, FE predictions of the tensile stress distributions within the composites have been shown to be qualitatively consistent with the cracking observed experimentally during tertiary creep.
Microstructure and Growth Mechanism of Al2O3/Al Ceramic Matrix Composite Made by Directed Oxidation of Al Alloys
Authors: Qin C-D. , Lai M.O. , Cotterell B. , Shi S. 
Published: April 2011

ABSTRACTSince the Lanxide process was advanced for forming of Al2O3 ceramic composite by directed oxidation of Al alloys, much work has been done with various mechanisms being proposed. The mechanisms have claimed that only certain dopants are essential to the growth process. Nevertheless, no united consensus has yet been reached. In the present work, Al alloy containing 5% Mg was oxidised in air for 12 hours at 1150°C with or without surface dopants of MgO or Pd. The resultant composites showed very different microstructures. Without any surface doping, the alloy did not develop any portion of composite as the initial intimate oxide film stops further oxidation. This intimate oxide film can either be broken off by mechanical means or penetrated by reaction with surface dopants, so that the composite can grow and develop. The results show that the previously reported incubation time is not only related to reaction processes but also to the initial mechanical disturbances. Doping with Pd made the composite darker in colour as the grains of the alumina ceramic matrix and inclusions of Al metal are finer. This shows that Pd may make the top oxide layer less intimate, and more nucleation sites are therefore available for oxidation. A new model is presented for oxide sustained growth based on the existence of oxygen active top surface layer and the capillary flow of molten metal around ceramic phase.
Hot-Isostatic Pressing of Silicon Carbide Based Multiphase Composed Materials
Authors: Jiang Dongliang , She Jihong 
Published: April 2011

ABSTRACTSilicon carbide (SiC) based ceramic composites with improved fracture toughness and increased flexure strength have been developed by incorporating some other non-oxide and oxide particles or some whiskers and fibres. Hot-Isostatic Pressing (HIP) has been identified as an important technology for strengthening carbide by surface modification. In this paper, Hot-pressed SiC-TiC with different densities and HIP-SiC/SiC(w) composites were post HIPped under a N2-pressure of 200MPa at 1850°C for lh. The results showed that the open pores were closed and physical and mechanical properties such as density, flexure strength and toughness were obviously improved. For the SiC-TiC composites, the final density can be reached above 98% theoretical density, flexure strength and fracture toughness were increased by 100% and 30-50%, respectively. For the SiC/5vol%-SiC(w) composites, the final flexure strength and fracture toughness were increased from 595 MPa and 6.7 MPa m1/2 to 920MPa and 8.5 MPa m1/2 separately. A possible reaction-HIP densification mechanism for SiC ceramics with open pores is proposed.
Forced Chemical Vapor Infiltration of Tubular Geometries: Modeling, Design, and Scale-Up
Authors: Stinton D.P. , Besmann T.M. , Matlin W.M. , Starr T.L. , Curtain W.A. 
Published: April 2011

ABSTRACTThe development of thick-walled, tubular ceramic composites has involved investigations of different fiber architectures and fixturing to obtain optimal densification and mechanical properties. The current efforts entail modeling of the densification process in order to increase densification uniformity and decrease processing time. In addition, the process is being scaled to produce components with a 10 cm outer diameter.
Experimental Investigation of Interface Properties in SiC Fiberreinforced Reaction-Bonded Silicon Nitride Matrix Composites
Authors: Eldridge J.I. , Bhatt R.T. 
Published: April 2011

ABSTRACTInterfacial properties of 1-D SiC/RBSN composites were measured by the matrix crack spacing method and by the fiber push-out method, and the results were compared. The composites consisted of 8 to 33 vol% of aligned SCS-6 SiC fibers (142 μm diameter) in a relatively porous (20 to 40 vol%) Si3N4 matrix. The effects of fiber volume fraction and test temperature on the interfacial properties have been investigated. The advantages and limitations of both methods in evaluating the interface properties of fiber-reinforced ceramic matrix composites and the factors influencing the interfacial measurements are discussed.
Effect of Oxidation on the Mechanical Properties of Nextel™ 312/BN/Blackglas™ Composites
Authors: Vaidyanathan K. Ranji , Cannon W. Roger , Danforth Stephen C. , Tobin Albert G. , Holmes John W. 
Published: April 2011

ABSTRACTPreceramic polymers are attractive precursor materials for the production of low cost continuous fiber reinforced ceramic composites (CFCC) into near net shape components. Currently, CFCC components based upon a Blackglas™ matrix reinforced with Nextel™ 312 fibers with a BN rich surface layer are being investigated for gas turbine engine applications. The effects of oxidation on tensile and bend properties were investigated after exposure to flowing air at 600°C for 20–1000h. A significant reduction in the tensile properties accompanied by increases in fiber pull-out was observed after oxidation for 96 hours. After 500 hours oxidation, strength decreased by 50% relative to as-prepared composites. These results indicate that oxidation beyond 200 hours may be embrittling the composite.
Nickel-Alumina Composites: In Situ Synthesis by a Displacement Reaction, and Mechanical Properties
Authors: Jones Steven A. , Burlitch James M. , Üstündag Ersan , Yoo Jeannie , Zehnder Alan T. 
Published: April 2011

ABSTRACTNickel-alumina composites have the potential to be high performance materials. Alumina, with its excellent oxidation resistance, combined with a ductile phase such as nickel may provide a tough material with a lower density and higher Young's modulus, overall, a higher specific modulus than typical Superalloys. Dense, interpenetrating Ni-Al2O3 composites were synthesized using a displacement reaction between NiO and aluminum. The resulting composites were characterized in terms of their mechanical properties such as hardness, flexure strength, fracture toughness and elastic constants. The synthesis, characterization, and mechanical properties, as well as the effect of the interpenetrating microstructure on the toughening mechanisms and other properties will be discussed.