bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bonding, Structure and Properties of Metal/Ceramic Interfaces
Authors: Howe James M. 
Published: March 2011

AbstractThis paper reviews the effects of chemical bonding, reaction, interfacial structure, fabrication, specimen geometry and testing conditions on the strength and fracture behavior of metal/ceramic interfaces. It is shown that a number of important properties of metal/ceramic interfaces such as the wetting behavior and work of adhesion can be qualitatively predicted from simple bonding models based on the elements in the metal and ceramic. In addition, the interfacial structure can often be predicted from principles of equilibrium thermodynamics and minimization of interfacial energy for relatively thick metal/ceramic layers. More quantitative description of interfacial structure employing atomistic calculations has been performed for simple interfaces and this area is progressing. The fracture behavior of metal/ceramic interfaces is a complicated process which depends on many factors such as the specimen geometry and loading conditions, strength of the interfacial bond, thermal, elastic and fracture properties of the metal and ceramic, thickness of the metal layer and testing environment. Advances in this area include the development of favorable specimen geometries for measuring interface properties and an understanding of the relationship among the phase angle of loading, crack trajectory and interface fracture energy for these geometries. Conversely, little is known about the stress corrosion and fatigue behavior of metal/ceramic interfaces although data on these time dependent failure modes are beginning to appear in the literature. Much progress has been made but considerably more work isneeded to understand the properties of metal/ceramic interfaces.
First principles study of interfacial adhesion: The Mo/MoSi2 Interface With and Without Impurities
Authors: Hong T. , Smith J. R. , Srolovitz D. J. 
Published: March 2011

AbstractAdhesive properties of the Mo(001)//MoSi2 (001) heterophase interface with and without C, O, B, S, and Nb impurities are calculated using a first principles local density functional approach. The adhesive energy and interfacial strength of the impurity-free interface are 10% to 15% smaller than the respective values for cleavage along the (001) planes of Mo and MoSi2. All of the impurities were found to decrease the Mo//MoSi2 adhesive energy. The substitutional impurities S and Nb decrease the interfacial strength, while the interstitial impurities C, O, and B increase it. All of the impurities increase the interfacial spacing in proportion to their covalent radii. The impurity effects on adhesion may be described in terms of competing bonding and strain effects.
Towards an Understanding of the Reaction Sequences in Brazed Joints: Investigation of the Ti-Cu-O Ternary at 945°C.
Authors: Kelkar G. P. , Carim A. H. , Spear K. E. 
Published: March 2011

AbstractThe joining of ceramics using active metal braze alloys is an attractive technique and has been used for a variety of material systems. The braze alloys usually contain an active element such as Ti which can reduce the ceramic and form a strong bond across the interface. Microstructural characterizations of brazed interfaces have been widely reported, though reasons for the formation of reaction products and their sequence is not clear due to the lack of thermodynamic information on the phases formed.The Ag-Cu-Ti/Al2O3 system contains an interface where Ti, the active element in the braze alloy, reduces Al2O3 to form layers of reaction products which include (Ti,Cu,Al)6O, an M6X type compound. In this study we have looked at the Ti-Cu-O system as a first step towards understanding the Ag-Cu-Ti/Al2O3 system. A section of the Ti-Cu-O ternary was investigated at 945°C. The system contains two M6X type compounds, Ti4Cu2O and Ti3Cu3O, which have independent single phase fields. A Ti activity diagram was generated from the available thermodynamic information and the knowledge of the ternary section. The two reaction sequences reported for such interfaces were analyzed based on the activity diagram.
Local Mechanical Stability of the Aluminum / Carbon (Amorphous) and Aluminum / SiO2 (Amorphous) Interface at Extrinsic Dislocations
Authors: McCarty E. D. , Hackney S. A. 
Published: March 2011

AbstractInterfaces between Al and amorphous C or amorphous Sio2 were prepared by sputter deposition of the ceramic phases onto the sputter cleaned surfaces of large grain Al. In situ TEM was used to study the behavior of the extrinsic dislocations (slip traces) at the metal/ceramic interface formed by the motion of Al lattice dislocations which intersect the interphase boundary plane. The proximity of the extrinsic lattice dislocation to the metal/ceramic interface places this interphase boundary under a highly localized stress. Relaxation behavior of extrinsic defects at the interface region is a function of the defect standoff distance from the interface, image stress and the applied stress. An experimental technique is proposed to estimate the minimum shear stress the various interfacial regions are able to withstand. Research supported by the Department of Energy.
Sintering of MoSi2
Authors: Petrovic J.J. , Idasetima J.S. 
Published: March 2011

AbstractDespite the fundamental nature of sintering and its importance as a low cost fabrication process, little information exists on the sintering behavior of the structural silicide Mosi2. The sintering of commercial Mosi2 powders in the range of 1-10 μm was investigated as a function of sintering temperature, sintering time, and sintering atmosphere. Initial densities for uniaxially cold pressed powders were in the range of 47-56% theoretical. A maximum sintered density of 90% of theoretical was achieved for 1 μm Mosi2 powders after sintering for 100 hours at 1600 °C in an argon atmosphere. Larger 10 μm Mosi2 powders achieved lower sintered densities under these conditions. Avenues to optimize the sintering behavior of Mosi2 are suggested.
Combustion Synthesis of MoSi2 and MoSi2-Composites
Authors: Monroe K. , Govindarajan S. , Moore J.J. , Mishra B. , Olson D.L. , Disam J. 
Published: March 2011

AbstractMosi2 and Mosi2-composites are potential candidate materials for both high-temperature coatings and structural components. The application of combustion synthesis and hot pressing in the production of dense Mosi2 and Mosi2- composites, i.e., Mosi2-SiC, Mosi2 -Mo, is currently being studied. Selection of compositions was based on oxidation resistance, thermal expansion, thermodynamic stability, and compatibility. Functionally-graded materials (FGM's) of these composite material systems are also currently being studied.
Synthesis of High-Temperature Silicides Via Rapid Solid-State Metathesis
Authors: Jacubinas Richard M. , Kaner Richard B. 
Published: March 2011

AbstractMosi2 has a very favorable combination of materials properties, including a high melting point (2020°C), high strength at elevated temperatures, and resistance to high temperature oxidation and corrosion. These properties make it a good candidate for a hightemperature structural material; however, it has very poor ductility. A great deal of research has focused on improving the ductility of this alloy through various preparative routes. We have synthesized Mosi2, as well as WSi2, TaSi2, and NbSi2, using rapid solid-state metathesis reactions between a high oxidation state metal halide and an alkaline earth silicide. These reactions take advantage of the large exothermic heat of formation of the alkaline earth halide and can reach temperatures as high as the melting point of the product silicides. In addition, this approach yields crystalline products in seconds. The synthetic technique will be discussed along with characterization results.
Synthesis and Properties of MoSi2/SiC Processed by Low Pressure Plasma Co-Injection and Deposition
Authors: Lawrynowicz D.E. , Wolfenstine J. , Nutt S. , Lavernia E.J. , Bailey D.E. , Sickinger A. 
Published: March 2011

AbstractLow-pressure plasma deposition (LPPD) and co-injection has been used to fabricate a MoSi2 composite reinforced with 15 µm SiC particles. The microstructure and creep behavior of the LPPD processed composite are reported and discussed. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the structure of the composite to be lamellar and energy dispersive X-ray analysis (EDAX) identified the phases present in the material as: MoSi2, Mo5Si3, SiO2, and SiC. Density characterization revealed a porosity of less than 1.0 vol. %, indicating a nearly fully dense material. A high concentration of SiO2 (∼8.0 vol. %) present in the MoSi2/SiC composite may be attributed to possible contamination of the starting powders before or during LPPD. Sublimation of SiC during co-injection led to a low volume fraction (< 2.0 vol. %) of reinforcement in the composite. The creep rate of the LPPD MoSi2/SiC was higher relative to that of MoSi2/SiC composites fabricated by powder metallurgy (PM) techniques. On the basis of the results of this study it has become evident that alternative processing methods such as LPPD insitu processing may be better suited for the fabrication of elevated volume fraction MoSi2/SiC composites.
A Review of Creep of Silicides and Composites
Authors: Sadananda K. , Feng C.R. 
Published: March 2011

AbstractA review of creep behavior of molybdenum disilicides and their composites is presented. Creep rates of these silicides are compared with those of other high temperature materials such as superalloys, ceramic-ceramic composites, intermetallics including aluminides (nickel and titanium), berylides (vanadium and niobium), and refractory metals(molybdenum and tungsten). Creep rates of silicides are shown to be very sensitive to grain size even in the power-law creep regime with grain size exponent of the order of five and above. In addition, the results show that with increase in volume fraction of reinforcements there is a decrease in creep rates for volume percentages less than 25%. To achieve significant improvement in creep strength volume percentages of reinforcements greater than 25% are required. This weakening effect at low volume percentages is related to accompanying decrease in grain size with the addition of reinforcements. Addition of carbon to MoSi2 eliminated the silica present at grain boundaries and converted it to SiC. The SiC thus formed, inhibited grain growth during hot pressing. Thus although addition of carbon enhanced creep resistance, its effect is masked by the accompanying decrease in grain size. Thus, grain size plays a dominant role in the creep of molydisilicide composites. It is shown that among all the materials molybdenum disilicides possess very high creep resistance comparable to ceramic-ceramic composites.
Plasticity Enhancement Processes in MoSi2-Base Materials
Authors: Gibala R. , Chang H. , Czarnik C.M. 
Published: March 2011

AbstractLow temperature plasticity enhancement processes observed in body-centered cubic metals and B2 ordered alloys can be observed in MoSi2 in appropriate stress-temperature-strain rate regimes. We illustrate effects of surface films (ZrO2) and dispersoids (TiC) in enhancing plasticity of MoSi2 in the ductile-to-brittle transition range of temperatures, 900-1400°C. We also show, through experiments involving high temperature (1300°C) prestrain, that effective operation of dislocation generation processes can extend the low temperature range to which MoSi2 can be plastically deformed. These results illustrate that approaches to enhance toughness of MoSi2 need not be limited to ductile phases characterized by weak interfaces.
Creep Behavior of MoSi2-SiC Composites
Authors: Butt Darryl P. , Maloy Stuart A. , Kung H. , Korzekwa David A. , Petrovic John J. 
Published: March 2011

AbstractUsing a cylindrical indenter, the indentation creep behavior of hot pressed and HIPed MoSi2-SiC composites containing 0-40% SiC by volume, was characterized at 1000-1200°C, 258-362 MPa. The addition of SiC affects the creep behavior of MoSi2 in a complex manner by pinning grain boundaries during pressing, thus leading to smaller MoSi2 grains; by obstructing or altering both dislocation motion and grain boundary sliding; and by increasing the overall yield stress of the material. Comparisons are made between indentation and compressive creep studies. It is shown that under certain conditions, compressive creep and indentation creep measurements yield comparable results after correcting for effective stresses and strain rates beneath the indenter.
Creep Rupture of MoSi2/SiCp Composites
Authors: French Jonathan D. , Wiederhorn Sheldon M. , Petrovic John J. 
Published: March 2011

AbstractWe studied the creep rupture of a series of MoSi2 materials reinforced with SiC particles. Particulate contents were in the range of 0 to 40 volume percent. Temperature and stress ranges were 1050°C to 1200°C and 10 MPa to 50 MPa, which gave failures ranging from 1 hour to 1500 hours. The creep curves show an extensive tertiary regime, accounting for 25-95% of the total lifetime. Tertiary creep increases with increasing stress and temperature. Cavitation occurs throughout the creep life, and tertiary creep is associated with the linkage of cavities into large cracks. The creep life improves with increasing SiC particle content, with a concurrent loss of creep ductility. Significant improvement occurs only when the particle content is greater than 30 volume percent. Our studies suggest that the creep and creep rupture behavior of MoSi2 can be further improved by increasing the content of SiC particles.
The Temperature and Strain Rate Dependence of the Flow Stress in MoSi2 Single Crystals
Authors: Maloy S.A. , Mitchell T.E. , Petrovic John J. , Heuer A.H. , Lewandowski J.J. 
Published: March 2011

AbstractThe temperature dependence of the flow stress and deformation mechanisms of single crystal MoSi2 have been determined for compression along three different orientations, [001], [021] and [771], at two different strain rates, 1 × 10−5/s and 1 × 10−4/s, and at temperatures between 900 and 1600°C. The flow stress along [021] is slightly higher than that along [771] while both orientations gave a much lower flow stress than that along [001]. Along [021], slip occurs on the {110} 1/2<111> slip system between 1000 and 1200°C, while at 1300-1400°C, slip occurs on the {013}<100> slip system. Along [771], deformation occurs by the [001]<100> slip system while cross-slip onto {013} and [011] planes is observed at 1000-1300°C except that slip occurs on the {013{1/2<331> slip system at 1000-1100°C for faster strain rates. Along [001], slip occurs on the {013}1/2<331> system at 900-1100°C while slip is observed on the {011} 1/2<111> system at 1300-1600°C. Strain rate jump tests from 1×10−5/s to 5x10−5/s at 1 100°C revealed a stress exponent of 7 along [771] and 20 along [021], while a rate jump test from lx10−5/s to 2x 10−5/s along [001] at 1400°C gave a stress exponent of 3.9.
The Effect of Grain Size and SiC Particulates on the Strength and Ductility of MoSi2
Authors: Ghosh Amit K. , Basu Ajoy 
Published: March 2011

AbstractMonolithic MoSi2 and MoSi2 reinforced with SiC particulate reinforcements have been produced with widely varying grain sizes. Monotonic compression behavior of these materials has been examined in the temperature range of room temperature to 1200°C. Based on these results, the ductile-to-brittle transition temperature at low deformation rate of MoSi2 and its composite appears to be near 900°C and may decrease slightly with decreasing grain size. Tension and compression creep behavior of these materials were also studied between 1100 and 1400°C. Creep strength of the matrix decreases with decreasing grain size even in the nominally dislocation climb-glide regime. While 20 vol% SiC particulates provide a reasonable amount of creep strengthening of the fine grain MoSi2 matrix, strengthening due to coarser grain size can be significantly higher in these materials. These results parallel those on other intermetallics.
Brittle Composites Modeling: Compazisons with MoSi2/ZrO2
Authors: Chen S. P. , Lesar R. , Rollett A. D. 
Published: March 2011

AbstractWe have calculated the mechanical properties of brittle composites with spring-network (SN) model. The composites that we studied involve the transformation toughening effects and the accompanying micro-cracking. Our simulation results are consistent with experiments of MoSi2 toughened with ZrO2. By monitoring the stress changes due to the transformation and micro-cracking we are able to separate, for the first time, the contributions from these two competing effects. We also found that the fracture toughness of the composite increases as the modulus, interfacial cohesion of particle increases.
Design and Synthesize of New Ternary Zirconium Silicide Intermetallic Compounds with the 16H Crystal Structure
Authors: Ikarashi Yukinori , Ishizaki Kozo 
Published: March 2011

AbstractThe zirconium silicide intermetallic compounds with the 16H crystal structure are good materials for high temperature structural applications, because of their high melting point and low density. Their shortcoming is low ductility. To increase ductility, the coordination numbers are increased to increase isotropy of bondings, and to have more metallic nature of bonds.Combination of elements, silicon, zirconium and other atoms for ternary silicides are selected by theoretical consideration of the coordination numbers. As the coordination numbers increase, the atomic bonds increase metallic properties, and their ductility increases. Higher coordination numbers are obtained by substituting yttrium atoms onto zirconium 6g point set sites.
Cyclic Oxidation Resistance of MoSi2/20v% Nb Composites
Authors: Alman D.E. , Stoloff N.S. 
Published: March 2011

AbstractThe effect of Nb morphology on the 1200°C cyclic oxidation resistance of MoSi2/2Ov%Nb composites was investigated. Niobium was incorporated into MoSi2 as particles, random short fibers and continuous aligned fibers. After oxidation, it was found all that the composites had lost weight and essentially disintegrated. This was due to spalling of both the Nb2O5 scale and the MoSi2 matrix. The spalling of the matrix was a result of cracks originating from the oxidized Nb and propagating through the MoSi2 matrix. These cracks arose from two sources: (1) the volume expansion associated with the transformation of Nb to Nb2O5 and (2) the difference in thermal expansion between Nb2O5 and MoSi2. Composites with smaller diameter Nb reinforcements did not disintegrate as rapidly as composites with larger sized Nb reinforcements. This was attributed to the effect of reinforcement size on CTE mismatch cracking.
Thermal Fatigue of MoSi2 and a MoSi2-10 vol% TiC Composite
Authors: Kush M. T. , Holmes J. W. , Gibala R. 
Published: March 2011

AbstractInduction heating of disk shaped specimens was used to study thermal fatigue behavior of hot pressed MoSi2, hot pressed and hot isostatically pressed (HIPed) MoSi2, and a MoSi2-10 vol% TiC particulate composite. Specimens were subjected to 5 s, 30 s, and 300 s heating and cooling cycles between temperature limits of 700°C and 1200°C. Specimens of both the hot pressed and the hot pressed and HIPed polycrystalline MoSi2 material failed by transgranular cracking on the initial temperature ramp of the 5 s and 30 s cycles. Only when the severity of the thermal cycle was reduced (300 s heating/300 s cooling) was thermal fatigue cracking avoided in the HIPed MoSi2. In sharp contrast, the MoSi2-10% TiC composite remained uncracked when subjected to the severe 30 s heating/30 s cooling cycle. The fatigue results are discussed with reference to the initial microstructure of the specimens and the stress-strain history of the specimens which was obtained by a thermoelastic finite element analysis.
Fabrication and Characterization of a Functionally Gradient Mo-MoSi2 Composite
Authors: Agarwal Gaurav , Lin Wen-Yi , Speyer Robert. F. 
Published: March 2011

AbstractFor the application of immersed combustion-radiant tubes in glass melters, a Mo-MoSi2 functionally gradient composite was developed. A gradient profile mixture with varying amounts of powders of these two compounds was hot pressed at 1650°C and 17.4 MPa. Mo5Si3, and Mo3Si reaction products were detected by XRD in the hot pressed composite. Limited cracking was apparent in regions where pure Mo regions applied tensile stresses to regions rich in Mo3Si product. Cyclic heat treatments in a reducing atmosphere showed no signs of further CTE mismatch induced cracking, but did indicate a propensity to creep under load at ∼ 1400°C. A functionally gradient material with MoSi2 on all exterior surfaces showed excellent oxidation protection to the Mo center.
Development of High-Strength-Fabricable Tantalum-Base Alloys
Authors: Buckman R. W. 
Published: March 2011

AbstractIn the 1950s, Ta-7.5%W and the Ta-2.5%W were the only tantalum alloys of commercial significance. An intensive alloy development effort occurred between 1958 and 1968 in response to Air Force and Navy aerospace needs for high-temperature, oxidation-resistant alloys for rocket and air-breathing engines and airframe applications. Compatibility with oxidation-resistant coatings, high-temperature short-time strength, fabricability and weldability were of prime importance. These programs led to the development of Ta-10w%W, Ta-30w%Nb-7.5w%V, T-111(Ta-8w%W-2w%Hf), and T-222(Ta-10w%W-2.5w%Hf-O.Olw%C). T-111, with its demonstrated compatibility with liquid alkali metals, and combination of strength, fabricability and weldability, was selected by NASA as the baseline reference alloy for space nuclear power systems studies. Significant quantities of T- 111 and T-222 were produced in the 1960s. Today, however, production is limited to unalloyed tantalum and the tantalum-tungsten binaries because of the demand of the chemical industry for materials with outstanding acid corrosion resistance. To again produce T-11 and T-222 on a commercial basis will require relearning by the refractory metal alloy producers. The current lack of experience in the refractory metal industry with these high temperature alloys will necessitate recovery of the expertise needed for the United States to effectively compete in this technology arena.
Synthesis and Properties of In-Situ MoSi2/SiC Composites
Authors: Jayashankar S. , Riddle S.E. , Kaufman M. J. 
Published: March 2011

AbstractCompositionally-tailored, silica-free, MoSi2/SiC composites with SiC content ranging from 0 to 40 percent were synthesized through a novel processing scheme involving mechanical alloying and in-situ reactions for the formation of the reinforcement. Room temperature indentation fracture toughness and hardness measurements were obtained from these silica-free composites and were compared with values obtained from silica-containing, conventionally-processed MoSi2/SiC composites.
Mechanical Working of Refractory Alloys Produced by Melting Processes
Authors: Hughes John R. 
Published: March 2011

AbstractThe elements generally considered to be the “major” refractory metals are niobium (Nb) and tantalum (Ta) from group VA of the periodic table, and molybdenum (Mo) and tungsten (W) from group VIA. By virtue of their high melting points, these metals and their alloys constitute an important class of materials. When they are produced by melting processes, the resulting ingots usually have large grain sizes, which need to be refined during mechanical working. While the unalloyed refractory metals have varied room-or-low-temperature applications, they require alloy additions, in many cases substantial, to meet the requirements of most of their hightemperature applications. This often results in high flow stresses at elevated working temperatures, and a concomitant decrease in low-temperature ductility. As BCC materials, the refractory metals have ductile-to-brittle transition temperatures, which vary widely from one metal to another and with other metallurgical variables. All of these factors must be taken into account in order to develop successful processing schedules for the refractory metals.