bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of CU and SI in Aluminum on Stress Change and on TiAl3 Formation in Al Alloy/TI Bilayer Films During Annealing
Authors: Brown Dirk D. , Besser Paul R. , Sanchez John E. , Korhonen Matt A. , Li Che-Yu 
Published: April 2011

AbstractInterconnect metallizations used in advanced integrated circuits typically use an Al-alloy sputterdeposited onto a Ti barrier layer. The Ti and Al react above ∼ 400°C to form TiAl3, which affects the stress evolution of the metal stack during thermal cycling. This paper describes results of thin film experiments performed on Ti/Al-alloy bilayer films. Two Al alloys were studied: Al-I%Cu and Al-0.5%Cu-1%Si. The rate of TiAl3 formation at 430°C was determined for both alloys and used to relate TiAl3 formation to the stress evolution of the film stacks during thermal cycling. The dominant effect of the TiAl3 intermetallic formation on stress arises from a change in the stress-temperature behavior of the film stack, due to a change in the yield behavior, effective modulus, and thermal expansion coefficient of the stack. The presence of Si in the Al-alloy markedly reduces both the rate of TiAl3 formation and the resulting change in composite stress.
Elastic Properties of Thin Films
Authors: White B. E. , POHL R. O. 
Published: April 2011

AbstractA technique has been developed for characterizing the disorder present in thin films through the measurement of their low temperature internal friction. The technique utilizes a substrate, in the form of a double paddle oscillator etched from a high purity silicon wafer, onto which the thin film of interest can be deposited. The oscillator possesses an internal friction of 3 × 10−8 at 4 K which is reproducible to within 1% upon thermally cycling to room temperature. This extremely small substrate internal friction coupled with the excellent reproducibility permits measurements of the internal friction of very thin amorphous films, with a 2 tun silica film producing a change in the internal friction of 4 × 10−9. By performing low temperature internal friction measurements on thin silica films with thicknesses ranging from 2 nm to 1000 nm, we have investigated the role of interacting defects in determining the universal nature of the anomalous low temperature thermal and elastic properties of amorphous solids. We have found no evidence for strong interactions between these tunneling defects. Other applications of the oscillator include monitoring of the crystallization of amorphous films through changes in the low temperature internal friction, internal friction measurements and vapor pressure measurements of quenched condensed rare gas solids and amorphous water ice, and internal friction studies of amorphous solids which can only be produced in thin film form.
On Separating Bonding Strength From Film and Substrate Properties
Authors: He Jia-Wen , Hendrix B. C. , Yi Mao-Zhong , Hu Nai-Sai 
Published: April 2011

AbstractBonding strength is commonly measured by various kinds of single cycle tests such as scratch tests or indentation tests. These tests all reflect complex composite properties - both plastic and elastic properties of the film and the substrate - as well as the bonding strength. In many cases experimental critical value of these single cycle tests is controlled by film or substrate strength or ductility rather than bonding strength. In these cases, the single cycle test should be evaluated in terms of the specific property which controls failure and should not be taken as a measure of “bonding strength.” However, the interfacial fatigue strength measured at 5X106 cycles is shown to be measurable over a large range of bonding strengths and composite properties. And further, this interface fatigue strength is insensitive to the composite properties. The complementary nature of these two types of tests is demonstrated for various TiN-based hard coatings on various steel and cemented carbide substrates.
Dielectric, Pyroelectric, and Thermal Properties of Solid Solutions of Ba (Ti,Zr)O3,Ba(Ti,Hf)03, Ba(Ti,Sn) 03 and (Ba,Nd)TiO3
Authors: Deb K. K. 
Published: April 2011

AbstractModified BaTiO3 ceramics are candidate materials for infrared sensors in nightvision equipment. Measurements of dielectric constants, dielectric losses, pyroelectric coefficient, and heat capacities as functions of temperature and frequency are performed. Crystallographic and grain size data are also presented. It is shown that additions of these impurities to BaTiO3 alters the temperature of phase transformations and, with it, dielectric and pyroelectric properties. The results of these measurements were compared with those of PZT and PbTiO3 ceramics, which are currently the favoredmaterials for uncooled detector arrays, as well as PbTiO3 and PZT thin films. It is concluded that these oxide ceramics offer the combination of preparative ease of property modification and show good performance at low impurity concentrations.
Modelling of Polydomain Smart Materials
Authors: Yu Yongsik , Roytburd Alexander 
Published: April 2011

AbstractPolydomain materials with periodic (modulated) domain structures are of potential practical importance since they can possess unique and desirable mechanical and physical properties. A twin related domain formation can be a result of constrained structural, ferroelectric or ferromagnetic transformations. The thermodynamic theory on the deformation of layer composites containing a polydomain (polytwin) ferroelectric component is analyzed. The deformation of the layer composite under different directional electric fields and constraints is calculated.
A New Superfluid Leak Tight Low Temperature Valve Using a Magnetostrictive Actuator
Authors: Hahn Inseob , Barmatz M. , Clark A. 
Published: April 2011

AbstractLow temperature valves play an important role in many research and development applications. Conventional low temperature valves primarily use actuation mechanisms depending on either gas or mechanical pressure. These actuation mechanisms usually require inconvenientoperating procedures such as a gas handling system or manual operation. We developed a superfluid leak tight low temperature valve that can be activated by a magnetostrictive material. All that is required to activate this magnetostrictive valve is a magnetic field produced by a simple power supply and coil. This new valve consists of separate valve and actuator units. The valve unit is designed to be normally closed using a spring. The stemof the valve is made of a hard 440c stainless steel ball while the seat uses a softer 304 stainless steel.
Thermo-Mechanical Ni50Ti50/Si Composite Thin Film Switch
Authors: Kim T. , Su Quanmin , Wuttig Manfred 
Published: April 2011

AbstractThe mechanical properties of Ni50Ti50 deposited on Si and 3C-SiC substrates were studied focussing on the interaction of the film and substrate. This interaction determines the transformation characteristics through interface accommodation and mechanical constraints exerted by the substrate stiffness. Substrate stiffness, controlled by the film/substrate thickness ratio, was found to have a substantial influence on the output energy of the film/substrate composite. A switch type composite based on this knowledge was fabricated and tested.
Properties of Piezoelectric Pzt Thin Films for Microactuator Applications
Authors: Damjanovic D. , Brooks K. G. , Kholkin A. , Kohli M. , Maeder T. , Muralt P. , Setter N. 
Published: April 2011

AbstractThe piezoelectric properties of lead zirconate titanate (PZT) thin films deposited on thick silicon substrates and thin silicon membranes were investigated using optical interferometry. The effect of the geometrical constraints and clamping effects on the piezoelectric response is discussed. The study of the dielectric permittivity and the loss as a function of the amplitude of the alternating electric field reveals that extrinsic contributions to the dielectric permittivity become active at large fields. The DC electric field has the effect of freezing out the extrinsic contributions. The influence of the dielectric loss on the piezoelectric properties is discussed.
Present and Future Applications of Shape Memory and Superelastic Materials
Authors: Duerig T.W. 
Published: April 2011

AbstractThe utility of superelastic Ni-Ti alloys in the medical industry has been rather dramatically demonstrated in recent years. A great number of devices are now in production, and still others are staged to enter production during the next few years. This surge in interest from the medical community stems from an increased acceptance of Ni-Ti because of its biocompatibility, advances in micromachining techniques and trends towards less-invasive surgical techniques. In addition, there are a variety of new developmental concepts that will have a major influence on this and other markets during the next 5 years of commercialization. This review will highlight many of the properties of Ni-Ti by illustration in a variety of recent medical applications, and then discuss some of the newer developmental concepts. Medical applications that will be presented here include guidewires, laparoscopic surgical instruments, implants, stents, retrieval baskets, and bone anchors. Some of the new concepts and capabilities that are reviewed include microvalves made from thin films, high temperature alloys, fatigue resistant composites, and robotic actuators with tactile feedback.
Phase Stability and Site Substitution in NB-AL Compounds
Authors: Sluiter M. , Takahashi M. , Kawazoe Y. 
Published: April 2011

AbstractThe site preferences of Ta, Mo, and W in A15 Nb3Al, the phase stability of off-stoichiometric A15 Nb3Al, and the atomic order of the Nb2Al D8b (σ) phase are investigated by performing electronic structure calculations based on the local density approximation. Mo, W, and Ta are found to have a preference for the Nb sublattice. Ta has the strongest site preference. It was shown that some recently proposed ground states for off-stoichiometric A15 phases are unlikely to occur in the Nb-Al system. Moreover, it was shown that the atomic order in the D8b Nb2Al phase contributes significantly to its stability.
The C14-to-C15 Transformation in Cr2Hf
Authors: Kumar K. S. , Hazzledine P. M. 
Published: April 2011

AbstractThree alloys, single-phase Cr2Hf, a two-phase alloy consisting of Cr solid solution and Cr2Hf, and a two-phase alloy consisting of Hf solid solution and Cr2Hf were cast and heat treated. The C14-to- C15 transformation of the Laves phase, Cr2Hf was studied as a function of heat treatment. According to the existing phase diagram, the Cr2Hf phase exhibits a C14 structure at elevated temperature but transforms to the C15 structure at lower temperatures. Such transformations are known to be extremely sluggish. In the present study, the Cr2Hf phase was found to retain the C14 structure at room temperature in all three compositions in the cast or cast and forged conditions; upon subsequent heat-treatment at various temperatures and time-at-temperatures, however, the C14 structure decomposes to a variety of higher order structures including the 16H, 10H, and 4H structures. These superstructures can be viewed as containing various percentages of the cubic and hexagonal stacking. The C15 structure was not observed for any of the conditions considered.
Fracture Toughness, Fracture Planes and BDT in Stoichiometric Feal and Nial Single Crystals
Authors: Specht Petra , Brede Markus , Neumann Peter 
Published: April 2011

AbstractFracture toughness data of stoichiometric FeAl and NiAl single crystals were measured in four-point-bending tests and the crystallographic orientations of the resultant fracture surfaces were determined.For FeAl single crystals unexpectedly high fracture toughness values were measured even at low temperatures (17 MPa [001] at 77K). However, these crystals failed in a brittle manner for temperatures up to 300K. The crystallographic orientation of the fracture surfaces were strongly dependent on the environment due to hydrogen embrittlement.The NiAl specimens were precracked and the fracture toughness was measured in the weakest crystal orientation. The fracture surfaces were similar to those obtained in previous investigations. Although the room temperature (RT) KIC-value was the highest for pure weak-oriented NiAl (7.5 MPa [001]) the BDT temperature was found in the same region where it occurs for the hard orientation (673K to 693K). The onset of the BDT will be discussed.
Rapid Solidification Joining of Intermetallics using Capacitor Discharge Welding
Authors: Wilson R. D. , Alman D. E. , Hawk J. A. 
Published: April 2011

AbstractCapacitor Discharge Welding (CDW) is a rapid solidification joining process capable of cooling rates greater than 106 K/s. The Bureau of Mines is investigating the CDW process as a method of joining TiAl, Fe3A1 and MoSi2. Experimental results show that the fusion zone of the CDW welds is less than 0.1 mm wide, is uniform in composition, and has a cellular solidification microstructure. This paper compares the CDW microstructure of several intermetallics to the microstructures obtained from the gas tungsten arc welding.
Influence of Ni5Zr Particles on Fatigue Property of Ni3Al Alloy
Authors: Li Gang , Guo Jian-Ting , Wang Zhong-Guang 
Published: April 2011

AbstractIn this investigation, the influence of second phase particles on high cycle fatigue behavior of Ni3Al alloy is studied. A single phase Ni3Al-B alloy and a Ni3Al-B/Zr alloy with a few second phase particles (Ni5Zr) at the grain boundaries are selected for investigation. High cycle fatigue tests at room temperature with R (minimum stress/maximum stress) 0.1 are conducted in air and at 30 Hz. The results show that the second phase particles are detrimental to high cycle fatigue resistance. It may be explained in terms of the second phase particles promoting fatigue crack initiation. The characteristics of fracture surfaces are examined by Scanning Electron Microscopy (SEM).
Fracture Toughness of Multiphase Intermetallics
Authors: Chan Kwai S. 
Published: April 2011

AbstractAn overview of recent advances in ductile-phase toughening of multiphase intermetallics is presented. The fracture characteristics of aluminides, silicides, chromides, and their composites are reviewed to elucidate relationships between microstructure, toughening mechanism, and fracture resistance. The roles of crack-tip blunting, trapping, bridging, and interface delamination in instigating fracture resistance are considered. Prospects for improving fracture toughness are discussed in conjunction with relevant microstructural variables such as the volume fraction, size, morphology, constraint, and work-of-fracture of the ductile phase.
High Temperature Creep of Alpha-2 Ti-34mo1%Al Polycrystals
Authors: Oikawa Hiroshi , Fukuda Toshihiko , Ohtsuka Makoto 
Published: April 2011

AbstractConstant-stress compressive creep tests were carried out on an Al-rich a2 single-phase material, which had equiaxed-grains of 60μim in grain size, at 1050∼1250 K under 100∼500MPa. The type of the primary creep stage and the microstructures developed during creep depend greatly on the creep condition. The minimum creep-rate, however, can be represented by one set of parameters over the whole range of experimental condition. The stress exponent is 5.0±0.2 and the (modulus-compensated) activation energy is 360 ± 10kJ/mol. The Dorn-type plot of the minimum creep rate reveals that the normalized creep strength of fine-grained Ti-34mol%Al is not greatly different from that of disordered solid-solution hardened alloys.
The Strain Rate Sensitivity of Polycrystalline and Single Crystal NiAl
Authors: Lee Tsang-Sheau , Hon Wei-Pirn , Yang Sy-Cherng , Hsu Shu-En , Chin Stephen , Anton Donald L. 
Published: April 2011

AbstractThe compressive and tensile strain rate sensitivities of polycrystalline and single crystal NiAl have beem evaluated at 877°C which is well above the static DBTT. Samples were prepared to specific grain sizes by hot press consolidation of appropriate powder sizes and minimizing post-consolidation thermal exposures. NiAl single crystals were grown in the near [100] orientation using a modified Bridgeman technique. The use of high oxygen content powders to fabricate polycrystalline NiAl with very fine grain sizes resulted in increased strengths but did not debit ductility. The yield and tensile strength of polycrystalline NiAl as a function of grain size generally follows a Hall-Petch type relationship. A tensile strain rate effect was found at strain rates of 1 to 10−4 sec−1. The strain rate sensitivity exponent, m, in the equation σ = Cεm is in the range 0.10 to 0.13. The highest strain rate (1 sec−1) resulted in significantly higher strengths and little or no observed tensile ductility. Cleavage-type transgranular fractures were found on samples tested at the highest strain rate (1 sec−1) and ductile fractures were found on samples tested at the lower strain rates (10−1 and 10−4 sec−1). Compression testing at strain rates of 10−5 to 10−3 sec−1 also indicated an effect of strain rate on strength.
The Temperature and Strain Rate Dependence of the Flow Stress of Single Crystal Nial Deformed Along <110>
Authors: Maloy Stuart A , Gray George T 
Published: April 2011

AbstractSingle crystal NiAl and Ni-49.75Al-0.25Fe have been deformed along <110> at temperatures of 77, 298 and 773K and strain rates of 0.001/s, 0.1/s and 2000/s. The flow stress of <110> NiAl is rate and temperature sensitive. A significant decrease in the work hardening rate is observed after deformation at 77K and a strain rate of 2000/s. Coarse {110} slip traces are observed after deformation at a strain rate of 2000/s at 77K, while no slip traces were observed after deformation under all other conditions. TEM observations reveal distinct {110} slip bands after deformation at 77K and a strain rate of 2000/s.
Thermally Activated Processes and Dislocation Mobilities in Two-Phase γ-Titanium Aluminides
Authors: Appel Fritz , Sparka Ulf , Wagner Richard 
Published: April 2011

AbstractThe processes controlling the dislocation mobility in two-phase γ-titanium aluminides have been investigated over a wide temperature range by determining the activation volumes and activation energies of thermally activated dislocation glide processes. The deformation tests are supplemented by electron microscope observations. Accordingly, at room temperature the mobility of ordinary dislocations is determined by a combination of localized pinning and lattice friction. Additional glide resistance arises from dislocation dipoles and debris defects, which are trailed and terminated at jogs in 1/2 <110] screw dislocations. Dislocation climb processes start above 900 K and seem to initiate the transition from brittle to ductile material behaviour.
What Determines the Peak-Temperature in Binary Ni3Al?
Authors: Karnthaler C. Rentenberger , Karnthaler H.P. 
Published: April 2011

AbstractIn Ni3Al alloys the yield stress increases with increasing temperature up to a maximum stress, reached at the temperature TP. Below TP glide occurs on primary octahedral planes whereas above TP glide on primary cube planes is dominating. Therefore this change of glide planes was considered to determine TP.TEM investigations were carried out to study the mechanisms that control TP in Ni3Al specimens with [001] compression axis. In this case no shear stresses are acting on any of the cube glide systems. The TEM results show a pronounced change of the dislocation structure on the {111} glide planes below and above the peak. The breakdown of the barriers (locked screw dipoles) starts when the diffusion is high enough to facilitate their annihilation. The dynamic recovery of the locked screws occurs by multiple cross-slip via octahedral planes. It is proposed that, in this and other ordered alloys, the value of TP is diffusion controlled.
Activation Volumes in the Yield Strength Anomaly Domain of Ni3(Al,Ta).
Authors: Spätig P. , Bonneville J. , Martin J.-L. 
Published: April 2011

AbstractNi3(Al,Ta) single crystals have been deformed in compression in the temperature range of the flow stress anomaly (293–780K). The strain-rate sensitivity (SRS) of the flow stress has been characterised by using a technique of repeated stress relaxations that allows for the measurement of the true (or effective) activation volume (Veff). When measured at the conventional critical resolved shear stress (CRSS), Veff exhibits as a function of temperature a sharp discontinuity close to 470K. When the temperature is held constant (420K), the discontinuity of Veff occurs along the stress-strain curve at approximately 3% strain; the stress for both discontinuities is approximately the same. These results suggest a change in the rate controlling mechanism that is dependent on stress as much or more than temperature.
The Yield Stress Anomaly in Fe-Al Alloys: The Role of the Local Climb Locking Mechanism
Authors: Morris David G. , Peguiron David 
Published: April 2011

AbstractA detailed examination of the variation of yield stress with temperature in an Fe3Al alloy shows a maximum at a temperature of about 500°C, slightly below the critical temperature for loss of DO3 order. At this temperature the dislocations present in the material change from being <111= superdislocations separated by APB to being single dislocations with Burgers vector <100=. At slightly lower temperatures the superdislocations become pinned by a local climb process involving point defect transfer between the partial dislocations.Analysis of the forces between the dislocations which induce the local climb locking process allows an estimation of the role which will be played by variations in composition of the Fe-Al alloy considered, changes in deformation rate and orientation of the applied stress.Examination of data available in the literature shows that each of the three aspects discussed, namely the influence of variations in ordered state, in Al content over the range 25% to 50%, or additions of alloying elements such as Si, straining at very fast or at slow rates, and stressing along different crystallographic axes, is completely consistent with the model proposed.
Near-Transus Processing (NTP) of Powder Metallurgy Tial-Based Alloys
Authors: Fuchs G. E. 
Published: April 2011

AbstractAlloys based on the intermetallic compound γ-TiAl are rapidly being developed for elevated temperature structural applications. In order to produce an alloy, by either I/M or P/M techniques, with useful engineering properties, it is necessary to control the microstructure by heat treatment and/or hot working. By combining consolidation with the heat treatment, unique microstructures can be produced in powder metallurgy (P/M) materials. The effect of processing on the microstructures and tensile and creep properties are discussed.
A Preliminary Investigation of the Cr3Si-Mo Pseudo-Binary Phase Diagram
Authors: Dickerson R. M. , Raj S. V. , Locci I.E. 
Published: April 2011

AbstractAn investigation was undertaken to study the phase relations in Cr3Si alloyed with Mo varying from 10 to 83.5 wt. % of the material. Specimens were prepared from arc-melted buttons that were subsequently heat treated at 1673 K for 200 h and air quenched to room temperature to preserve the high temperature microstructures. Alloys containing more than 20 wt. % Mo were primarily two-phase materials of M3Si and M5Si3, where M is (Cr,Mo). Three alloys contained less than 5 % of a third phase, which also had the M5Si3 crystal structure. Differential thermal analysis (DTA) was performed on several specimens at temperatures up to 2073 K in order to determine a solidus curve for the M3Si phase. Since only one DTA peak was observed in each alloy, the M5Si3 phase must melt above 2073 K, the maximum temperature examined. A preliminary pseudo-binary phase diagram for (Cr,Mo)3Si and a portion of the 1673 K isothermal section of the Cr-Mo-Si ternary phase diagram are presented.