bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tailoring of Mechanical Properties in Microlaminates
Authors: Vill M. , Adams D. P. , Yalisove S. M. , Bilello J. C. 
Published: March 2011

ABSTRACTA multiscalar approach is used to demonstrate the ability to control strength and toughness in microlaminates composed of molybdenum and tungsten. Here, two different thickness scales are utilized; an alternating stack of molybdenum and tungsten layers having thicknesses on the nanometer scale are combined with a layer of molybdenum having a thickness on the micron scale. The stack of thin layers acts as a strong phase and the thick layer acts as a tough phase. Multilayers of two configurations were fabricated which had total thicknesses of 31μm and 50μm. The tough phase thickness was 5μm for the 31μm multilayer and 1μm for the other. The strong phase contained a stack of 29 alternating 4nm thick layers of molybdenum and tungsten. Uniaxial tensile testing was performed using a standard Instron tensile testing machine, followed by optical analysis of specimen fracture surfaces. Fracture toughness ranged from 2.4 to 9.5MPa(m)1/2, and tensile strengths were observed from 126MPa to 883MPa. Control of mechanical properties was demonstrated by an increase in the upper bound fracture toughness from 2.7 to 9.5MPa(m)1/2when the tough layer thickness was increased from 1μm to 5μm.
Stress Relaxation During Diffusional Phase Transformation Under Induced Thermal Stress
Authors: Zingu E C , Mofokeng B T 
Published: March 2011

ABSTRACTThermal mismatch between the expansion coefficients of a substrate and deposited thin film gives rise to extrinsic stress in the film. Different stress states are induced into the Co/Si thin film combination by depositing the multi-layers on Al and Si substrates respectively. Interdiffusion at 360°C is found to be influenced by the extrinsic stress in the films. The difference in Co2Si growth rate on different substrates is ascribed to the difference in composition (Co molar fraction) at the Co/Co2Si and Co2Si/Si interfaces due to different stress states.
Joining Ceramics Using Microwave Energy
Authors: Ahmad Iftikhar , Silberglitf Richard 
Published: March 2011

AbstractIn the past several years there has been an explosive growth in the use of microwave energy for the processing of a host of materials. Microwave energy provides rapid internal heating which results in an overall reduction in the processing time. The important features of microwave processing are described, as well as several applications.Microwave energy has been used by a few groups for the joining of alumina, mullite, silicon nitride and silicon carbide. The work performed by these groups will be reviewed. Typically, a single mode microwave applicator has been used to join ceramics at temperatures ranging between 1250°C - 1800°C. Microwave joining of ceramics was achieved in a matter of minutes, in contrast to hours reported by conventional methods. The strength of the joints was equal to or greater than the as-received materials. Joining of specimens of sintered silicon carbide (Hexoloy ™ ) using interlayers, and direct joining of reaction bonded silicon carbide (RBSC) to itself and Hexoloy™ has been accomplished recently. Both single mode and multimode microwave applicators were used and larger specimens of RBSC having complex shapes were joined using hybrid heating. The paper describes microwave joining apparatus, techniques and results.
Mechanisms of Wetting in Reactive Metal/Oxide Systems
Authors: Eustathopoulos N. , Drevet B. 
Published: March 2011

AbstractIt is shown that for metal/oxide systems with weak or moderate reactivity, wetting depends mainly on parameters related with the detailed chemistry and structure of interfacial reaction products rather than on parameters related with the intensity of interfacial reactions. Consequently, wetting can be promoted by alloying a metal matrix M with a reactive solute B capable of modifying in a favourable sense the metal/oxide interface. This can be achieved via two mechanisms depending on the value of the Wagner's interaction parameter εBo. When εBo<0 (moderate interactions between solute B and dissolved oxygen), the solute B can modify the liquid-side of the interface by adsorption, an effect that can be strongly enhanced by oxygen coming from dissolution of the oxide substrate. When εBo<<0 (strong O-B interactions in M), the solute B can lead to the formation, at the solid-side of the interface, of a new phase. When this new phase features metallic bonding wetting can be strongly improved.
Capacitor Discharge Weld Modelling Using Ultra High Speed Photography
Authors: Wilson R. D. , Hawk J. A. , Devletian J. H. 
Published: March 2011

AbstractCapacitor discharge welding (CDW) is a rapid solidification joining process where high cooling rates (106 K/s) are obtained as a result of the large weld surface area to small weld volume. The objective of this study, directed by the U.S. Bureau of Mines and the Oregon Graduate Institute of Science and Technology, was to use ultra-high speed photography to quantify transient arc behavior during the CDW cycle. The simple cylindrical geometries of the CD welds have been used to formulate analytical models which are compared to the high speed photographs of the welding process. The high speed photographs were analyzed with respect to welding time and process weld variables and compared to predicted values from the analytical model. The detailed photographic analyses revealed that material is continuously ejected as a plasma from the weld area due to induced magnetic forces, rather than having the liquid metal squeezed out of the weld upon contact. It was found that welding time was controlled by tip length and drop height. Results from high speed photographs found the arc travel speed around tube welds to be 109m/s. Finally, the high speed photographs revealed that the velocity of arc propagation during ignition was fast enough to allow the CDW process to be modelled as onedimensional heat flow.
Self-Propagating, High Temperature Synthesis As A Technique To Join Metals
Authors: Hawk J. A. , Petty A. V. , Dogan C. P. , Rawers J. C. 
Published: March 2011

AbstractSelf-propagating, high temperature synthesis (SHS) can be used to bond both similar and dissimilar metals. A unique feature of this technique is the ability to stack either metal foils or metal foils and powder, and to process them to form two-dimensional, layered composites with a “graded” intermetallic interface between layers. This process can also be used to modify a surface for corrosion or wear resistance. To date Bureau of Mines research has focused on making iron-, titanium-, and nickel-aluminum composites. The elemental metal foils are stacked and placed in a hot press, and the temperature is raised until the composite sandwich undergoes the SHS reaction. At approximately 660°C (i.e., the melting point of aluminum), the aluminum reacts with the transition metal to form intermetallic phases. The SHS process is mass and energy limited; i.e., mass transport controls the chemical reaction rates, while the energy liberated by the chemical reaction is distributed to the surroundings by heat conduction, convection and radiation.
A Novel Brazing Technique for Aluminum and Other Metals
Authors: Timsit Roland S. , Janeway B. J. 
Published: March 2011

AbstractIn the novel brazing technique, the aluminum components in the joint assembly are coated with a powder mix consisting of elemental Si and a potassium fluoroaluminate flux. During brazing at −600°C in nitrogen gas, the flux melts and removes the native Al2O3 surface film from the coated aluminum components. This action allows the silicon to diffuse into the aluminum to generate in-situ a layer of Al-Si filler metal of eutectic composition.The liquid metal then flows into thejoint and yields a metallurgical bond on cooling.This brazing technique maybe exploited with aluminum using intermediary elements other than Si. The technique may also be used for joining other metals.
Indirect-Bonded Metallization of Aluminum Nitride
Authors: Norton M. Grant 
Published: March 2011

AbstractThe use of aluminum nitride (AIN) as a substrate and packaging material for microcircuit applications is of present interest due to its many advantageous physical properties. A limitation to the widespread use of AIN is the lack of an adequate metallization system. The most common method of achieving high-integrity metallized ceramics is through the use of indirect-bonded metallizations. A wide range of intermediate bonding materials are used, for example glasses, oxide mixtures, and active metals. In this paper, the indirect-bonded metallization of AIN will be reviewed and discussed. Requirements which must be considered in producing successful metallizations include; wetting of the substrate and the metal by the intermediate phase and the reactivity between the intermediate phase and the substrate. The reactions which occur in many of the systems considered can be predicted by examination of thermodynamic data.
A Joining Technique Using Multilayer Lead-Indium-Gold Composite Deposited In High Vacuum
Authors: Lee Chin C. , Wang Chen-Yu , Chen Yi-Chia , Matijasevic Goran 
Published: March 2011

AbstractA joining technique for electronic devices has been developed. This technique uses a leadindium- gold multilayer composite solder deposited directly on GaAs wafers in high vacuum to prevent indium oxidation. The gold layer on the composite further protects the indium layer from oxidation in atmosphere. The GaAs dies are bonded to a gold-coated alumina substrate at a process temperature of 250°C. Nearly perfect joints are achieved as verified by a scanning acoustic microscope (SAM). SEM and EDX results indicate that the alloy joint consists of AuIn2 grains embedded in an In-Pb solid solution phase, as predicted from the Au- In-Pb phase diagram. Compared to lead-tin solder, indium-lead solder has been shown by others to exhibit much better fatigue resistance and have much less of a scavenging effect. Thermal shock as well as shear tests confirm that a good die attach is obtained with the leadindium- gold composite.
Diffusion Bonding of Advanced Aerospace Metallics
Authors: Dunford David V. , Wisbey Andrew 
Published: March 2011

AbstractAdvanced aluminium and titanium alloys, metal matrix composites (MMC's) and intermetallic compounds are of considerable interest to the aerospace industry. These materials offer significant mechanical improvements over many conventional materials. Appropriate joining technologies are being developed to utilise the advantages these materials offer in aerospace applications. Diffusion bonding offers considerable potential as a joining process. This keynote paper will review diffusion bonding with reference to these advanced metallic systems.
Reliability Factors in Ceramic/Metal Joining
Authors: Suganuma Katsuaki 
Published: March 2011

AbstractThis paper reviews the processing factors in joining ceramics to metals concerning the reliability. Thermal expansion mismatch has a great influence not only on the absolute value of strength but also on the reliability of joints. Large thermal stress increases the scatter of joint strength because of the presence of defects induced during joining process. One should insert an appropriate interlayer to relax the stress between a ceramic and a metal. Surface roughness also has some influence on the reliability. A roughly ground bond face leads large scatter in strength. Scratches must be removed before joining. Unjoined area reduces joint strength especially in solid-state joining. In brazing, the homogeneity in the braze layer should be also controlled carefully. A slight applied pressure during brazing can preserve the integrity of joints.
Interface Science of Controlled Metal/Metal and Metal/Ceramic Interfaces Prepared using Ultrahigh Vacuum Diffusion Bonding
Authors: King Wayne E. , Campbell G. H. , Coombs A. W. , Johnson G. W. , Kelly B. E. , Reitz T. C. , Stoner S. L. , Wien W. L. , Wilson D. M. 
Published: March 2011

AbstractWe have designed, constructed, and are operating a unique capability for the production of highly controlled homophase and heterophase interfaces: an ultrahigh vacuum diffusion bonding machine. This machine is based on a previous design which is operating at the Max Planck Institut für Metallforschung, Institut für Werkstoffwissenschaft, Stuttgart, FRG. In this method, flat-polished single or polycrystals of materials with controlled surface topography can be heat treated up to 1500°C in ultrahigh vacuum. Surfaces of annealed samples can be sputter cleaned and characterized prior to bonding. Samples can then be precisely aligned crystallographically to obtain desired grain boundary misorientations. Material couples can then be bonded at temperatures up to 1500°C and pressures up to 10 MPa. Results are presented from our initial work on Mo grain boundaries and Cu/Al2O3 interfaces.
Interfacial Reactions Between Titanium and Borate Glass
Authors: Brow R. K. , Saha S. K. , Goldstein J. I. 
Published: March 2011

AbstractInterfacial reactions between the melts of several borate glasses and titanium have been investigated by analytical scanning electron microscopy (ASEM) and by x-ray photoelectron spectroscopy (XPS). A thin titanium boride interfacial layer is detected by XPS after short (30 minutes) thermal treatments. ASEM analyses after longer thermal treatments (8–120 hours) reveal boron-rich interfacial layers and boride precipitates in the Ti side of the interface.
Combustion Synthesis of Molybdenum Disilicide and its Composites
Authors: Deevi Seetharama C. 
Published: March 2011

AbstractA combustion wave originating from an exothermic reaction between Mo and Si propagates through the reactants converting Mo-2Si mixture to Mosi2. X-ray analysis of the product confirmed that the product is single phase Mosi2 with no second phase or reactants when combustion synthesis experiments were carried out in argon. The oxygen content of the product was 0.22 wt.%. When the mixture was reacted under pressure in a hot press, the product obtained was also Mosi2, and a theoretical density up to 92% could be achieved. Heating of a mixture of Mo and Si with C leads to the formation of Mosi2 with a dispersed SiC phase.
Thermo-Chemical Synthesis of Nanostructured Chromium Silicide / Silicon Carbide and Molybdenum Silicide / Silicon Carbide Composite 'Powders
Authors: Luo Ping , Strutt Peter R. , Gonsalves Kenneth E. 
Published: March 2011

AbstractIntermetallic silicides and silicon carbide composites are potential useful materials in high temperature applications requiring superior strength combined with enhanced fracture toughness. This paper presents results obtained on these materials in nanostructured form, since structural reduction to this scale offers a way for achieving unique properties.Chromium silicide / silicon carbide and molybdenum silicide / silicon carbide composite powders were readily synthesized by thermal conversion from spray dried precomposites at 1250°C. Basically, the process involves spray drying the aqueous chemical solution to a precomposite, followed by thermal conversion in a tube furnace reactor. The phases present in the composites are hexagonal Cr5−XSi3−XCX+Y (Cr5Si3Cx) / cubic β-SiC and tetragonal MoSi2, hexagonal Mo5Si3CXx/ cubic β-SiC. The volume fraction of these phases can be controlled through the solution preparation of the precursors. Characterization of composite powders include x-ray diffraction spectrometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Particle size distribution of the synthesized chromium silicide and silicon carbide composite was conducted by a computerized image analyzer and the statistical result was obtained.
Microcracking, Strain Rate and Large Strain Deformation Effects in Molybdenum Disilicide
Authors: Hardwick D. A. , Martin P. L. 
Published: March 2011

AbstractHigh purity molybdenum disilicide was deformed in compression to strains ranging from 5 to >50%. The deformation was accomplished at temperatures in the range 1200°-1400°C and at strain rates from 10−3 to 10−5 sec−1. The strength of this high purity material was found to be at least twice that of MoSi2 produced by the hot pressing of commercial powder. Microstructural examination revealed that subgrain formation resulted from modest strains (≈10%) while dynamic recrystallization was observed following large strains. Transmission microscopy revealed a significant change in the dislocation substructure after straining as the temperature was increased from 1300°C to 1400°C.
High Temperature Oxidation Behavior of Strucflural Siucides
Authors: Ramberg C. E. , Beatrice P. , Kurokawa K. , Worrell W. L. 
Published: March 2011

AbstractThe factors which control the formation of a protective silica (SiO2) layer on structural silicides at high temperature are summarized. The thermodynamic and kinetic conditions under which both silica and a metal oxide can form are also described. Molybdenum disilicide (MoSi2) forms highly protective silica scales and has the best oxidation resistance at high temperatures. Although the preparation method has little influence, the heating rate and the structure of the silica layer have significant effects on the oxidation behavior of MoSi2.
Surface Oxidation Mechanisms of Molybdenum Disilicide in High-Temperature Combustion Environments
Authors: Lin Wen-Yi , Speyer Robert F. 
Published: March 2011

AbstractThe stability of MoSi2 was studied at 1600°C in combustion products with an incoming gas to air ratio of 1:6.7 and compared to results in a 1:10 environment. Oxidation was investigated using periodic weight measurements and characterization using XRD, SEM, and EDS. Passive oxidation was observed; MoSi2 was oxidized by H2O and CO2 to form Mo5 Si3 and SiO2. The amorphous silica product formed a surface layer and reduced the oxidation rate as it coarsened. MoO3(g) did not form which was in agreement with the thermodynamic (SOLGASMIX-PV) prediction that it would only form in the presence of molecular oxygen. A good agreement was observed between the measured and calculated weight gains based on the surface layer thickness.
Characterization of Structure and Mechanical Properties of MoSi2-SiC Nanolayer Composites
Authors: Kung H. , Jervis T. R. , Hirvonen J-P. , Nastasi M. , Mitchell T. E. 
Published: March 2011

AbstractA systematic study of the structure-mechanical properties relationship is reported for MoSi2-SiC nanolayer composites. Alternating layers of MoSi2 and SiC were synthesized by DCmagnetron and if-diode sputtering, respectively. Cross-sectional transmission electron microscopy was used to examine three distinct reactions in the specimens when exposed to different annealing conditions: crystallization and phase transformation of MoSi2, crystallization of SiC, and spheroidization of the layer structures. Nanoindentation was employed to characterize the mechanical response as a function of the structural changes. As-sputtered material exhibits amorphous structures in both types of layers and has a hardness of 11GPa and a modulus of 217GPa. Subsequent heat treatment induces crystallization of MoSi2 to form the C40 structure at 500°C and SiC to form the a structure at 700°C. The crystallization process is directly responsible for the hardness and modulus increase in the multilayers. A hardness of 24GPa and a modulus of 340GPa can be achieved through crystallizing both MoSi2 and SiC layers. Annealing at 900°C for 2h causes the transformation of MoSi2 into the Cllb structure, as well as spheroidization of the layering to form a nanocrystalline equiaxed microstructure. A slight degradation in hardness but not in modulus is observed accompanying the layer break-down.
Electrochemical Protection of Molybdenum and Molybdenum Disilicide in Molten Soda-Lime-Silicate Glass Environment
Authors: Sundaram S. Kamakshi , Speyer Robert F. 
Published: March 2011

AbstractElectrochemical corrosion of Mo and MoSi2 in a molten soda-lime-silicate glass environment was studied using a two electrode cell with Pt as the counter electrode. XRD, SEM, and EDS were used to characterize the corroded specimens. When Mo was given a cathodic bias (∼ 0.8V), the specimen surface oxidized to MoO2(s). With reverse bias, Mo ions were interpreted to have been removed into the glass melt. For MoSi2, Mo5 Si3 interfacial layers were observed for both cathodic and anodic corrosion. Mo5 Si3 debris particles (∼4 µm) were seen floating into the glass en masse under a cathodic bias, but not when the bias was reversed. This was interpreted to be a result of an inherent negative charge of debris particles.
Microstructural Evolution in Compositionally Tailored MoSi2/SiC Composites
Authors: Riddle S.E. , Jayashankar S. , Kaufman M.J. 
Published: March 2011

AbstractCompositionally tailored MoSi2/SiC composites with silicon carbide content ranging from 0 to 60 volume percent were synthesized through a novel processing scheme involving the mechanical alloying of elemental molybdenum, silicon, and carbon. The effects of important processing parameters such as the nominal powder composition and the processing temperature on the microstructural evolution during mechanical alloying and subsequent heating are described based on the results obtained from DTA and XRD.
Effect of Deformation Processing on Mechanical Properties of Nb-10 a/o Si In-Situ Composite
Authors: Weiss I. , Thirukkonda M. , Srinivasan R. 
Published: March 2011

AbstractNb-10 a/o Si alloy is an in-situ composite. The microstructure of the cast alloy consists of pro-eutectic Nb dendrites distributed in a matrix of eutectic Nb3Si + Nb phases. The microstructure of the as-cast alloy was modified by multiple hot extrusions producing an oriented composite. Extensive grain size refinement occurred in both the Nb and Nb3Si phases. The ductile primary (pro-eutectic) Nb particles were aligned along the extrusion direction. Bend strength and fracture toughness measured by three point bend and four point bend tests, respectively, showed that both the yield strength and fracture toughness of the alloy increases considerably following this thermomechanical processing. These improvements have been attributed to the changes in size, morphology and spacing of the constituent phases and their microstructural refinement.
Influence of Tungsten Alloying Additions on the Mechanical Properties and Texture of Tantalum
Authors: Gray G.T. , Bingert S.R. , Wright S.I. , Chen S.R. 
Published: March 2011

AbstractTantalum, like all bcc metals, exhibits deformation behavior which is substantially influenced by alloying, temperature, and strain rate. Recently, the mechanical response, in particular the highstrain- rate response, of tantalum and tantalum alloys has received increased interest for ballistic applications. In this paper, recent results on the influence of tungsten alloying additions on the mechanical response and starting crystallographic texture of tantalum-tungsten alloys are presented. The stress-strain behavior of three tantalum alloys containing 2.5, 5, and 10 wt.% W has been investigated as a function of loading path, tension and compression, and strain rate, 10−3 to 8000 s−l The yield strength and work-hardening rate were found to increase with increasing tungsten alloying content compared to unalloyed-Ta. Based on measurements of the surface and centerline textures of the Ta-W alloys, no systematic effect of tungsten content on texture was documented. However, due to variations in mechanical behavior between through-thickness and in-plane properties the need for complete through-thickness texture measurements is indicated.