bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Erbium Additions on the Solidification Behavior of γ-Tial
Authors: Bassler B. Timothy , Kral M. V. , Hofmeister W. H. , Bayuzick R. J. 
Published: April 2011

AbstractThe titanium-aluminum-erbium system has been studied using electromagnetic levitation and ultra high speed imaging in order to quantify the solidification velocity as a function of undercooling. Measurements were made on Ti-60 at% Al alloys with 0.25, 0.5, 1.0, and 2.0 at% Er additions. Boettinger and Aziz1 show that in ordered alloys it is thermodynamically possible at large enough interface velocities, corresponding to large undercoolings, to solidify a disordered phase with the same composition as the liquid. The result of the transition from ordered to disordered solidification is a discontinuity in the relationship between solidification velocity and melt undercooling. The experimental results for the solidification velocity as a function of melt undercooling will be presented and discussed for each alloy.
The Thermal Stability of a TiAl Based Alloy
Authors: Jin C. , Chen W. , Wang J. , Wan X. 
Published: April 2011

AbstractThe thermal stability of a TiAl based alloy was investigated through a series of high temperature exposures in air and vacuum. The microstructures were found to be thermally stable. The bending tests showed that both ductility and strength of air-exposed specimens decreased, but no significant variation was observed in those exposed in vacuum. The influence of alloy microstructure, thermal exposure temperature and time was also taken into account here.
A Study of Fibre/Matrix Interfaces in TiAl/Sic Composites
Authors: Djanarthany S. , Servant C. , Colin C. 
Published: April 2011

AbstractA continuous fibre reinforced SiC/TiAl composite has been prepared by arc spray and hot pressing. The as-fabricated fibre/matrix interface of monotapes and composites have been examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The arc-spray conditions result in a decohesion at the fibre/matrix interface.
In Situ Straining Tem Observation of Fracture behavior in Pst Crystals of TiAl
Authors: Chen Mingwei , Chen Da , Lin Dongliang 
Published: April 2011

AbstractCrack propagation process in TiAl alloy PST crystal has been investigated by in situ straining TEM observation. It has been found that the influence of lamellar boundaries on the fracture behaviors is connected with the types of interfaces (twin, pseudo-twin and α2/γ interfaces). Even though secondary microcracks always nucleate at α2/γ interfaces due to stress concentration, the crack growth is cleavage in α2 and γ phases rather than along interlamellae. When a crack meet γ/γ interfaces, its propagation can be inhibited and crack tips blunt by the slide of the interfaces. It also deserves to be mentioned that ductility of PST crystals has connection with the rate of crack propagation..
The Nature of Bonds in New Ternary Zirconium Silicide Intermetallic Compound of 16H Crystal Structure
Authors: Ikarashi Yukinori , Ishizaki K. , Bolsaitis P. , Ohnishi H. 
Published: April 2011

AbstractThe zirconium silicide intermetallic compounds of 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, new ternary zirconium silicide intermetallic compound of 16H crystal structure, Si3Y3Zr2, has been designed by substituting yttrium atoms into zirconium 6g point set sites.Near-neighbor diagrams are used to examine the bonds in Si3Y3Zr2, whose bonds are more symmetric than other 16H binary intermetallic compounds.Melting points of intermetallic compounds of 16H crystal structure depend upon the strain parameters of N4d-N4d(2-2) bonds. The melting point of Si3Y3Zr2 is estimated to be higher than that of Si3Zr5 (2500 K). It is predicted that Si3Y3Zr2 is a good material for high temperature structural applications.
Reaction Synthesis and Densification of MoSi2
Authors: Deevi Seetharama C. 
Published: April 2011

AbstractIn combustion synthesis, and in simultaneous reaction synthesis and hot pressing of Mo + 2 Si powders, a heterogeneous reaction occurs between liquid silicon and molybdenum powder. When the reactant mixture is heated at low-heating rates, Mo5Si3 is observed as a secondary phase along with MoSi2. Application of pressure during the reaction synthesis of MoSi2 eliminates the need to hot press a prealloyed powder. The technique can be applied to obtain composites and alloys of MoSi2 and various other transition metal silicides.
On Phenomenon of Superplasticity in Fe3AL with Large Grains
Authors: Shan Aidang , Lin Dongliang 
Published: April 2011

AbstractA variety of Fe3Al alloys including Fe-25Al, Fe-28Al, Fe-28Al-4Cr and Fe-28Al-2Ti (all in atomic percent) have been investigated by tensile test to find if these alloys could have superplasticity at elevated temperatures, the results revealed that all these alloys exhibited large elongations when the temperature is higher than 600°C. At 850°C , under appropriate initial strain rate, the elongation is all above 300%. For Fe-28Al-2Ti, the maximum elongation reached 585%. Maximum m values are all above 0.3. Initial grain sizes are bigger than 100μm but became finer after deformation. Fracture happened with necking but no cavities were found under optical microscope. Characteristics of this phenomenon were summarized and discussed.
The Effect of Y and Zr on the Oxidation of NiA1
Authors: Schumann Eckart , Yang J. C. , Rühle M. , Graham M. J. 
Published: April 2011

AbstractThe effect of Y and Zr on the oxidation behaviour of NiAl has been investigated using high resolution SIMS and analytical TEM. 18O tracer experiments in conjunction with SIMS showed that Y and Zr reduce the outward transport of cations during the growth of the AI2O3scale. Complementary STEM-EDS measurements revealed segregation of Y and Zr at the metal/oxide interface as well as the grain boundaries in the AI2O3scale. The amounts of segregation at both the interface and grain boundary were calculated to be less than one monolayer.
Oxidation of Some Intermetallic Compounds and Intermetallic Matrix Composites
Authors: Jackson M. R. , Rowe R. G. , Skelly D. W. 
Published: April 2011

AbstractOxidation resistance (1000-1400°C) was characterized for intermetallics M2Al, M3Al, M2Cr, and M5Si3 (M=Nb, Nb+Ti), and metal-toughened intermetallic composite systems. Aluminides were poorest in oxidation, and Laves phases were best. Substitution of Ti for Nb was beneficial for each intermetallic. Addition of metal to produce two-phase castings had differing effects on oxidation, depending on the metal and intermetallic. Modulus and expansion were also measured.
The Microstructure of Nb3Al-Mo Intermetallics
Authors: Passa E. , Tsakiropoulos P. 
Published: April 2011

AbstractThe microstructure of arc melted ingots and melt-spun ribbons of Nb-18A1, Nb-18Al-(20–40) Mo (at%) were studied. Rapid quenching from the melt refined the grain size by at least two orders of magnitude. In the binary alloy ingots and ribbons the Nb3Al (A15) and B2 phases were present. Molybdenum exhibited complete solid solubility in the bcc Nb-Al solid solution as well as in the Nb3Al (A15 phase). The former was the only phase present in the ribbons of the ternary alloys, while Nb3Al was detected only in the ingots. B2 phase was formed in the alloy with 20 at% Mo and the A2 phase was present in the alloy with 40 at% Mo. Furthermore, Mo addition increased the room temperature microhardness of the Nb-Al solid solution by ≈7 Kgmm−2/ at%Mo.
Phase Stability and Mechanical Properties of Multi-Phase Alloys Based on the B2 CoA1 and the E21 Co3AlC
Authors: Kimura Yoshisato , Takahashi Masaru , Miura Seiji , Mishima Yoshinao 
Published: April 2011

AbstractThe Co-Al-C ternary phase diagram has been experimentally examined for the Co-corner with a particular interest in phase relations among B2 type intermetallic compound, the E21 type Co3AlC, and cobalt primary solid solution, denoted as (Co). Reaction scheme, liquidus surface, isothermal sections and isoplethals at constant concentration were determined. Mechanical properties of the B2/E21/(Co) three-phase alloys were investigated by compression tests carried out at a temperature range from 77 to 1273 K, and by tensile tests at room temperature. It has been revealed that both excellent ambient temperature ductility and sufficient high temperature strength can be achieved by proper choice of alloy compositions.
Deformation Microstructures of C15 Cr2Nb Laves Phase Intermetallic Compounds
Authors: Yoshida M. , Takasugi T. , Hanada S. 
Published: April 2011

AbstractThe Cr2Nb intermetallic compounds with C15 Laves structure, which are considered to be attractive candidate as extremely high temperature structural materials, are deformed by compression test. The Cr2Nb intermetallic compounds are deformable at temperatures above 1473 K. The Burgers vector of dislocations activated at temperatures above BDTT are determined to be 1/2<011= which is split into a pair of 1/6<112= (i.e. the Shockley partials) connected by the stacking fault (SF). Also, the morphological feature of the activated dislocations and the SF energy are evaluated.
Effects of Angular Dependent Terms in the Interatomic Potential on Defect Properties in TiAl
Authors: Panova Julia , Farkas Diana 
Published: April 2011

AbstractInteratomic potentials of the Embedded Atom and Embedded Defect types were used to study the effect of the angular dependent term in the Embedded Defect potential on the properties of defects in TiAl. The defect properties were computed with interatomic potentials developed with and without angular dependent terms. It was found that the inclusion of the angular dependent terms tends to increase the energies of the APB’s and lower the energies of stacking faults. The effects of the angular term on the relaxation around vacancies and antisites in TiAl was also studied, as well as the core structure of several dislocations in this compound.
Ni-Enrichment and its Influence on the Structure Chemistry and Bonding of Grain Boundaries in Ni3Al
Authors: Subramanian S. , Muller D. A. , Silcox J. , Sass S. L. 
Published: April 2011

AbstractSmall angle [001] twist boundaries and [001[(110) tilt boundaries in B-free and B-doped Ni-rich Ni3AI (76 at. pet. Ni) were examined using conventional electron microscopy techniques as well as annular dark field (ADF) imaging, X-ray Fluorescence (XRF) and spatially resolved electron energy loss spectroscopy (EELS) in an UHV scanning transmission electron microscope. The interface structure consists of periodically spaced pairs of a/2<10> partial dislocations, linked by an antiphase boundary (APB). An analysis of the separation of the partials gives APB energies which are lower than in bulk Ni3Al and which decrease with increasing misorientation angle. EELS, XRF and ADF imaging demonstrate that the APBs are Ni-rich. The observations on the APB chemistry and energy taken together lead to the conclusion that Ni-enrichment occurs to lower boundary energy by decreasing the number of high energy Al-Al bonds across the APB. These results on small angle boundaries lead to the suggestion that Ni-enrichment also occurs at large angle boundaries to decrease the number of high energy bonds across the interface.
Some Unusual Properties of the Fine Structure of Dislocations in Ni3Al Deformed at High Temperature
Authors: Veyssiére Patrick , Horton J. A. 
Published: April 2011

AbstractIn Ni3Al polycrystals deformed at 850°C and quenched rapidly, surface defects exhibit two kinds of behaviour. On the one hand, dislocation coupling by antiphase boundary (APB) and complex stacking fault (CSF) is of normal magnitude for this alloy composition. On the other hand, separations are dramatically decreased in both cases. A method to visualize antiphase boundaries using a weakly excited superlattice reflection is introduced.
Grain Boundary Melting and Hot Cracking in Weld Haz of A Two-Phase Ni3Al Alloy Containing Zr
Authors: Li Huaxin , Chaki T.K. 
Published: April 2011

AbstractGrain boundary melting and its effect on hot cracking in the weld heat-affected zone (HAZ) have been investigated in the investment cast billet of a two-phase (γ + γ′) nickel aluminide alloy (Ni74.48Al16.98Cr8.02Zr0.51B0.10), designated as IC-218. Due to enrichment of Zr, which can form eutectic alloys with Ni, the dendritic boundaries melted incipiently at 1150°C. Under thermal stresses during welding the molten layers often opened up producing liquation cracks at the boundaries in the HAZ. Annealing at 1100°C in argon for 23 h prior to welding reduced the incipient melting temperature to 1125°C and increased the propensity of liquation cracking in the HAZ.
Effect of Crystallographic Orientation on The Fracture Toughness of NiAl Single Crystals
Authors: Shrivastava S. , Ebrahimi F. 
Published: April 2011

AbstractIn the present study, single-edge notched bend specimens of NiAl single crystals were tested in {100}<010>, {101}<101=, and {101}<010} orientations before and after heat-treating the notched specimens at 1000°C for one hour. The fracture toughness data for the non heat-treated specimens were found to be consistent with the previous results. An increase in the fracture toughness of NiAl was observed in all orientations studied upon heat-treating the notched specimens. The toughness ratio for the two orientations obtained from the heat-treated notched specimens was found to be 1.2. This ratio is in agreement with the reported stress analysis considering the crack kinking in {100} oriented specimens. A detailed SEM analysis revealed that the electric discharge machine (EDM) cutting of the notch caused the formation of sharp microcracks at the notch front and also created internal stresses in the vicinity of the notch. The increase in toughness upon heat treatment is attributed to the modification of EDM damage.
Fracture Behaviour of Two-Phase γ-Titanium Aluminides
Authors: Appel Fritz , Lorenz Uwe , Zhang Tao , Wagner Richard 
Published: April 2011

AbstractTitanium aluminides with a lamellar microstructure consisting of the intermetallic phases ֱ2 (Ti3Al) and γ(TiAl) suffer from brittleness at ambient temperatures but exhibit at the same time a relatively high fracture toughness. This discrepancy indicates particular processes stabilizing crack propagation in the lamellar microstructure. In this context, the toughening mechanisms were investigated in (α2 + γ) TiAl alloys which contained different volume fractions of lamellar colonies. The fracture toughness for crack propagation parallel or across the lamellar interfaces was estimated by using chevron-notched bending bars. Electron microscope studies were performed to characterize the related processes of crack tip plasticity. Special emphasis was paid to the crystallography of crack propagation and to the interaction of crack tips with lamellar interfaces. Accordingly, the lamellar morphology derives some of its toughness from interface-related processes which stabilize crack propagation by deflecting the crack tip and providing the necessary dislocation sources for crack tip shielding in the process zone ahead of the crack tip.
In Situ Straining Experiments On Fe70AL30 Single Crystals
Authors: Molenat G. , Rösner H. , Nembach E. 
Published: April 2011

AbstractWith an aim to contributing to the understanding of the mechanical properties of Fe3Al-based intermetallic alloys, Fe-30 at. % Al single crystals have been strained in a transmission electron microscope below and in the temperature range of the yield stress anomaly (at 300K and 573K respectively).
A Potential Method for Densifying Reactive Sintered NI3AL
Authors: Hu Chen-Ti , Chiou Wen-Chen 
Published: April 2011

AbstractA potential method to produce Ni3Al+0. 1B PM products of large dimension and as sheets, rods, tubes or other shapes with simple laboratory facilities is presented. The method includes multi-stage sintering and interstage cold deformation to collapse and to eliminate the sintering pores; most important of all, a thermally absorbing material must keep contact with the powder compacts during the preliminary reactive sintering stage to decrease the maximum temperature of the specimen and to develope the Ni2Al3 phase. The found Ni2Al3 regions with some special characteristics can be used to sustain the deformation of cold rolling more than 30% without failure. The monolithic Ni76Al24B0.1 phase is obtained after the second stage of sintering at 1200°C for 4h. At meantime, common reactive sintered specimens without a thermally absorbing material contacting were also studied and compared side by side.
Phase Stability, Point Defects and Site Preference of Feal and Nial with Ternary Additions
Authors: Fu C.L. , Zou J. 
Published: April 2011

AbstractFirst-principles calculations have been used to investigate the defect properties and the site preference of FeAl and NiAl with ternary additions. It is found that a “triple-defect” structure model becomes invalid in describing the defect structure of FeAl (which is weakly ordered). The calculated mono-vacancy concentration on the Fe sites is lower than available experimental values by an order of magnitude, which may suggest the formation of defect complexes or the need of sufficiently long annealing time to anneal out quenched-in vacancies. For the site preference of ternary additions in FeAl, Cr and Ti are found to occupy Al sublattices, whereas Ni has a distinct preference for the Fe sites. The substitutional behavior of ternary elements in FeAl is consistent with the trend in the calculated heat-of-formation. For Fe addition in Al-rich NiAl, Fe atoms occupy Ni sublattices exclusively. The site preference of Fe addition in Ni-rich NiAl is dependent on alloy composition and temperature. At low temperatures, Fe atoms are found to preferentially occupy Al sublattices in Ni-rich alloys.
In-Situ Processing and Characterization of Mosi2/Sic Formed by Reactive Low-Pressure Plasma Deposition
Authors: Lawrynowicz D. E. , Wolfenstine J. , Lavernia E. J. , Nutt S. R. , Bailey D. E. , Sickinger A. , Hirt A. M. 
Published: April 2011

AbstractLow-pressure plasma deposition (LPPD) was used to synthesize an in-situ MoSi2/SiC composite using 100% methane (CH4) as a powder carrier gas. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) identified MoSi2, Mo5Si3, Mo5Si3C, Si02, and SiC as the phases present in the composite. XRD and XPS revealed ∼6 vol% SiC in the as-sprayed material. Annealing of the as-sprayed composite increased the SiC content to ∼8 vol% while reducing the Si02 volume fraction. Transmission electron microscopy studies revealed a fine homogeneous distribution of SiC and/or carbide particles at prior splat boundaries in the MoSi2 matrix. Wavelength dispersive spectroscopy (WDS) confirmed the increased presence of carbon in the in-situ materials. Fracture toughness measurements yielded values on the order of 10 MPa m½ for annealed composites. The creep behavior of the LPPD reactive spray composite dramatically improved compared to unreinforced LPPD MoSi2. Additionally, the creep behavior was shown to be equal to or better than that of powder metallurgy MoSi2/SiC composites containing higher percentages of SiC.
Particles Cellulation Composite (PCC): Dispersion Morphology of SiC Particles in Si3N4/SiC Composites
Authors: Yamada K. , Kamiya N. 
Published: April 2011

ABSTRACTDispersion morphology of fine SiC particles in Si3N4/xSiC (x=0, 10, 20, 30wt%, average size: 0.03/µ m) composites was statistically analyzed, and typical properties of the composites such as creep, electric and thermal conductivity were investigated. The dispersion morphology of SiC particles was analyzed by observing the ECR-plasma etched surface of the sintered composites using scanning electron microscopy. SiC particles in Si3N4/SiC composites were distributed both within Si3N4 grains and on Si3N4 grain boundary, but 90% or more of them was located on the grain boundary. For the composites with 20-30wt%SiC, the SiC particles on the grain boundary clearly formed a three-dimensional network structure surrounding a few or more Si3N4 crystalline grains.A Si3N4/SiC composite with a three-dimensional network structure of SiC particles, named particles cellulation composite (PCC), was artificially made by pressing the granulated Si3N4 powder (less than 500 µ m diameter) discontinuously coated with SiC particles (average size: 0.4 µ m). The creep deformation of PCC was reduced to about 60%.of that of the composites with SiC particles randomly dispersed. Electrical and thermal properties were also improved. These results suggest that the formation of three-dimensional network structure by the second phase particles in a composite would considerably improve its mechanical property as well as electrical and thermal properties.
Structure and Formation Kinetics of Mosi2 Composites Formed by Reactive Vapor Infiltration Process
Authors: Hillig W.B. , Ramakrishnan R.M. , Broglio M. , Patibandla N. 
Published: April 2011

ABSTRACTReactive Vapor Infiltration is a convenient new process for producing high purity MoSi2 matrix composites by reacting compacted mixed Mo + MoSi2 powders ranging from 0 to 80 wt. % MoSi2 with H2 + SiCl4 vapors at temperatures from 1000 to 1400°C. Consideration must be taken of the volumetric increase that accompanies this conversion. The kinetics of the advance of the MoSi2 growth layer and the gravimetric uptake are given as a function of temperature and the composition. The parabolic growth rate constant was independent of composition at least up to 30% MoSi2 composition, but then showed a strong, linear increase with increasing MoSi2 content. There appeared to be a levelling off of rate above 70% MoSi2. The corresponding gravimetric rate constant was relatively insensitive to the starting MoSi2 content. This behavior is at variance with a simple one-dimensional diffusive growth model. Possible reasons for this variance are offered.
Elevated Temperature Fiber Push-Out Testing
Authors: Eldridge J.I. 
Published: April 2011

ABSTRACTThe potential use of fiber-reinforced composite materials for high temperature applications makes the development of interface test methodology at those high temperatures very desirable. A facility for performing high temperature fiber push-out tests will be described with emphasis on critical issues in experimental procedure. Examples from several composite systems illustrate the temperature dependence and environmental sensitivity of fiber debonding and sliding. Interpretation of the temperature dependence will be made primarily in terms of changes in residual stresses along with additional effects due to changes in matrix ductility and interfacial wear. Examples will show that high temperature fiber push-out testing can often distinguish between chemical and frictional fiber/matrix bonding in cases where room temperature only testing cannot.
Optimization of Bundle Infiltration in the Forced Chemical Vapor Infiltration (FCVI) Process
Authors: Matlin W.M. , Stinton D.P. , Besmann T.M. , Liaw P.K. 
Published: April 2011

ABSTRACTA two-step forced-flow, thermal-gradient, chemical vapor infiltration process (FCVI) was proposed to reduced processing time while maintaining uniformly high densities. GTCVI, a finite-volume computer code developed specifically for the FCVI process was used to model thermal gradient effects on processing time and density. An optimum thermal gradient was determined and used to process material with uniformly infiltrated bundles.
In-Situ Measurement of Bending Strength of TiC Whiskers in the Scanning Electron Microscope
Authors: Seino Yutaka , Shin Shoichiro , Nagai Satoshi 
Published: April 2011

ABSTRACTThe three–point bending strength of TiC whiskers was measured in a scanning electron microscope. The whisker samples have ∼ 50µm length and 2∼4µm diameter and are commercially available as reinforcements for composite materials. The distribution of the bending strengths of the whiskers showed a double peak around 5.2GPa and 30.4GPa, respectively. The difference in these values is attributed to differences in the cleavage strength of two crystal planes depending on whisker growth direction.