bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Temperature Deformation of Nb-18 Al
Authors: Marieb T. N. , Kaiser A. D. , Nutt S. R. , Anton D. L. , Shah D. M. 
Published: March 2011

ABSTRACTSpecimens of Nb-18 at. % Al were bend-tested at 20° C, 1200° C, and 1600° C, and the deformed microstructures were characterized using TEM to determine phase distributions and slip systems. Material deformed at 20° C showed brittle fracture and was characterized by large grains of a Nb-Al phase showing B2 ordering. Lamellar colonies of heavily dislocated massively transformed Nb3Al (A15) were present at grain boundaries. The slip system for dislocations in Nb3Al, was determined to be {100}/<001>, with defects typically extending in <011> directions. Fracture at 1200° C was ductile, and TEM observations revealed a bcc Nb-Al(ss) matrix with second phase growth of Nb3Al and α -Al2O3. The Nb3Al phase contained total dislocations and slip-induced planar defects on {100} planes terminating in partial dislocations. In tilting experiments, the planar defects exhibited stacking fault contrast consistent with a displacement vector of R=a/4<100>. Fracture at 1600° C was also ductile, and the deformed material consisted of a niobium matrix with equiaxed inclusions of alumina resulting from internal oxidation during deformation. The creep resistance reported previously was attributed to a combination of dispersion hardening of the refractory metal matrix and inherent creep resistance of Nb3Al.
Electron Microscopic Observation on the Structure of Ni(Cu)AI Martensite
Authors: Kang Seung-Hyuk , Jeon Seung-Jun , Lee Hu-Chul 
Published: March 2011

ABSTRACTIn an effort to seek a way to toughen NiAL intermetallic compounds, deformation characteristics of copper containing NiAL martensite were studied by electron microscopy. Martensite plates with fine {111} <112> internal twins were well developed across the grains in as extruded alloys. Initial linear work hardening up to 7 % strain was observed and the migration of twin interface and martensite plate interfaces were suggested as major deformation modes at this stage. Increase in strain hardening rate after 7 % strain was associated with the development of dislocation structure and growth of new strain induced twins within the internal twin free martensite plates.
Effect of Ta on the Structure and Dynamics of γ/α2 Interfaces in Tial
Authors: Singh S. R. , Howe J. M. 
Published: March 2011

ABSTRACTThe structure of γ/α interfaces in binary and Ta-containing TiAl alloys were analyzed by HRTEM and image simulations. Growth of α2 was found to be due to a ledge mechanism, consisting of Shockley partial dislocations on alternate (111)γ planes. The interface is atomically flat between the ledges and addition of Ta was found to transform arrays of growth ledges in the binary alloy into islands on the plate faces in the Ta-containing alloy. These islands of α2 on the γ/α2 interfaces were 4–7nm wide and increased in size with decreasing ageing temperature. The height of the ledges and islands were always a multiple of the c-parameter (0.46nm) of the α2 phase. The islands were bounded by 90°(edge) and 30° screw) Shockley partial dislocations. The 30° partial dislocation cores were localized whereas the 90° partial dislocation cores appeared to be highly delocalized due to presence of a high density of kinks, which in one case was found to be about 0.65nm−1.These results are interpreted in terms of the growth mechanisms and morphology of the α2 phase.
Deformation and Defects in C36 Laves Phases
Authors: Livingston J. D. , Hall E. L. 
Published: March 2011

ABSTRACTMgNi2and MgCu0.4Zn1.6, two C36 Laves phases, were plastically deformed at elevated temperatures, and, the deformation-induced defects were studied by TEM. Extensive faulting was observed, consistent with the low stacking-fault energy of the C36 structure. HREM revealed multi-layer faults with a variety of stacking sequences.
Micromechanisms of Deformation and Fracture in a Ti3Al-Nb Alloy
Authors: Akkurt A.S. , Liu G. , Bond G.M. 
Published: March 2011

ABSTRACTThe object of this study has been to gain a greater understanding of deformation and fracture processes in a Ti-24Al-11Nb (at %) alloy. The in-situ TEM deformation technique has been used to observe these processes as they occur. Material characterization studies revealed the existence of three different crystal structures in the material (α2,B2 and orthorhombic (0)). Slip is first initiated in the B2 and 0 phases. Although dislocations are observed in the α2 phase in the deformed material, they are seen only in high-stress regions and only in some laths. While numerous dislocations may be injected into the corresponding grain and phase boundaries, slip does not easily propagate into the α2 phase. Cracks are seen to originate most frequently in the regions transformed fully to α2 laths, and sometimes in the regions that contain α2 laths at prior β grain boundaries. Failure of grain or phase boundaries in the B2 or 0 phases where no α2 is present is not observed. Crack branching in the α2 phase is common, particularly in the vicinity of phase boundaries. Crack propagation in the B2 and 0 phases occurs by plastic thinning, and cracks formed in the α2 lath regions are either stopped in phase boundaries or blunted in the neighboring 0 or B2 grains.
Tough, Ductile High-Temperature Intermetallic Compounds: Results of a Four-Year Survey.
Authors: Fleischer R.L. , Briant C.L. , Field R.D. 
Published: March 2011

ABSTRACTA four-year survey of high-temperature intermetallic compounds has been aimed at identifying potentially useful structural materials for aerospace and aircraft engine applications. Since the good properties of high strength and stiffness at high temperatures are typically negated by brittleness at ambient temperature, new materials must have roomtemperature toughness or ductility. Screening has been done of 90 binary compounds with 20 different crystal structures, and 130 ternary or higher-order alloys. Testing typically included hardness vs. temperature, elastic modulus determination, and toughness evaluation via a room-temperature chisel test. Four alloy systems, including only two types that are of the simplest structures, showed substantial room-temperature toughness: Al-Ru, Ru-Sc, Ir-Nb, and Ru-Ta. Of these the last and the first are the most promising. Special features of the Ru- Ta (L1o) alloys are their room-temperature impact resistance and high-temperature strength. AIRu (B2) alloys can be tougher than the L1o structures and most are also ductile in compression at room temperature. Alloying experiments with B, Cr, and Sc show beneficial effects on ductility, oxidation resistance, and high-temperature strength.
Room Temperature Strength and Fracture of FeAl And NiAl.
Authors: Nagpal P. , Baker I. , Liu F. , Munroe P.R. 
Published: March 2011

ABSTRACTThe yield strengths (σy) of FeA1 and NiAl of various aluminum concentrations were measured as a function of grain size, d, and the results fitted to σy=σo+ kd−1/2. It was found that for NiAl the lattice resistance (σo) and Hall-Petch slope (k) have minima at the stoichiometric composition and increase with decreasing aluminum concentration, whereas for FeAl these parameters have maxima at the stoichiometric composition and decrease off this composition. In tension tests, iron-rich FeAl was shown to be ductile whereas the stoichiometric alloy is brittle. In contrast, stoichiometric NiAl shows ductility but off-stoichiometric compositions are brittle. The fracture modes of the FeAl and NiAl are predominantly intergranular at the stoichiometric compositions and become increasingly transgranular with decreasing aluminum concentration.
On the High Temperature Behavior of Niobium Aluminide intermetallics
Authors: Rodriguez A. B. , Barth E. P. , Tien J. K. 
Published: March 2011

ABSTRACTA basic characterization of the mechanical and physical properties of a Niobium Aluminide intermetallic, NbAl3 , was undertaken. Four ingots of material were vacuum arc-melted, yielding a two phase microstructure in each case. Physical testing including coefficient of thermal expansion measurement was performed on the most promising ingot. Elastic modulus of this compound was measured in compression. Elevated temperature microindentation measurements have been performed to gain insight into the deformation behavior as a function of temperature. Microindentation measurements have also been used to study the time-dependent deformation of NbAl3.
Ductility and Strength in Mo Modified TiAl
Authors: Maeda T. , Okada M. , Shida Y. 
Published: March 2011

ABSTRACTAn investigation has been made on the effect of ternary additions of Mo and other elements on the room temperature tensile ductility and high temperature strength, including creep rupture strength in TiAl based alloys. Mo modified Ti-rich TiAl in an annealed condition exhibited higher tensile ductility at room temperature than other well-known Cr or Mn modified alloys, this resulting from the refinment of mean grain size in the duplex structure of lamellar (γ+α2) and single phase (γ) rather than the crystalline tetragonality of the γ phase. Moreover, creep strength in as cast Ti-rich TiAl is improved with the addition of Mo, and lowered with the addition of Mn. These results suggest that Mo modified Ti-rich TiAl can enhance, the potential of TiAl as a high temperature material more than other ternary modified TiAl.
The Fatigue Behavior of γ/α2 Titanium Aluminides
Authors: Dowling W.E. , Donlon W.T. , Allison J.E. 
Published: March 2011

ABSTRACTAxial load controlled high cycle fatigue experiments were conducted on the γ/α2 alloy, Ti-48A1-1V-0.2C (at%), at 23 and 815°C. Four different microstructures, produced through thermomechanical processing, were evaluated to examine the influence of grain size and α2 content on fatigue behavior. The load controlled fatigue life was significantly reduced by increasing grain size and unaffected by α2 content at both 23 and 815°C. Although, α2 content did not greatly influence high cycle fatigue life, the room temperature crack initiation and fast fracture was changed from transgranular to partially intergranular as the volume fraction of α2 was reduced in the fine grain size material. The fatigue strength at 107 cycles (FS) to ultimate tensile strength (UTS) ratio was 0.8 to 0.9 at 23°C and 0.5 to 0.6 at 815°C for all microstructures examined. Low tensile ductility, high work hardening rate and the difficulty in forming strain local-izations all aided the high FS/UTS ratio. The dislocation microstructures produced by fatigue at room temperature were examined in the fine grained high α2 (ductile) microstructure. They consisted of loop patches of all <110] regular dislocations without any <101] or <011] super dislocations because of the large difference in CRSS for these dislocation. The inability to nucleate and move superdislocations inhibited the formation of persistent slip bands as is often found in high and intermediate stacking fault FCC metals.
Cyclic Deformation Of B2 Aluminides
Authors: Hartfield-Wünsch S.E. , Gibala R. 
Published: March 2011

ABSTRACTA study has been undertaken to understand the cyclic deformation behavior of singlephase B2 aluminides. The alloys chosen for this study were rapidly solidified powder extrusions of Fe60 Al40 (at.%) and Ni50 A130 Fe20 (at.%). These alloys were chosen to compare the cyclic deformation behavior of a material that deforms by <111> slip and thus meets the von Mises criterion for slip system compatibility (Fe60Al40) with one that deforms by <100> slip and does not meet the von Mises criterion (Ni50A130Fe20). Fully reversed tension/compression tests were run in plastic strain control at room temperature. Rapid cyclic hardening was observed for the Fe60Al40 alloy. However, intergranular failure occurred before saturation was reached at all plastic strain amplitudes. The Ni50A130Fe20 alloy displays no tensile ductility , with failure occurring before completion of the first cycle. For the Ni50A130Fe20 alloy, a lower extrusion temperature during materials processing, and compressive prestrain both increase the cyclic accumulated plastic strain to failure, as well as the monotonic tensile ductility. This made cyclic deformation of the Ni50Al30Fe20 alloy possible. In this alloy, limited cyclic hardening is followed by saturation. For both the Fe60Al40 and Ni50 Al30Fe20 alloys, significant ductility enhancement was achieved by the application of thin nickel films. All cyclic deformation results are compared to similar monotonic tension results and are discussed in terms of the dislocation substructures observed.
Flow and Fracture Behavior of NiAl in Relation to the Brittle-Toductile Transition Temperature
Authors: Noebe R.D. , Bowman R.R. , Cullers C.L. , Raj S.V. 
Published: March 2011

ABSTRACTNiAl has only three independent slip systems operating at low and intermediate temperatures whereas five independent deformation mechanisms are required to satisfy the von Mises criterion for general plasticity in polycrystalline materials. Yet, it is generally recognized that polycrystalline NiAl can be deformed extensively in compression at room temperature and that limited tensile ductility can be obtained in extruded materials. In order to determine whether these results are in conflict with the von Mises criterion, tension and compression tests were conducted on powder-extruded, binary NiAl between 300 and 1300 K. The results indicate that below the brittle-to-ductile transition temperature (BDTT) the failure mechanism in NiAl involves the initiation and propagation of cracks at the grain boundaries which is consistent with the von Mises analysis. Furthermore, evaluation of the flow behavior of NiAl indicates that the transition from brittle to ductile behavior with increasing temperature coincides with the onset of recovery mechanisms such as dislocation climb. The increase in ductility above the BDTT is therefore attributed to the climb of <001> type dislocations which in combination with dislocation glide enable grain boundary compatibility to be maintained at the higher temperatures.
The Compression Creep Behavior of Ni3Al-X Single Crystals
Authors: Miura Seiji , Hayashi Tohru , Takekawa Mitsuhiro , Mishima Yoshinao , Suzuki Tomoo 
Published: March 2011

ABSTRACTCompressive creep behavior is investigated in ternary Ni3Al single crystals containing Ti, Si, Hf and Cr with stress axes parallel to the crystallographic orientation near [001]. Then a comparison is made with the results of high temperature compression tests under a constant strain rate for the same orientation where plastic behavior is characterized by a distinct yield drop followed by steadystate deformation. It is found that the deformation mechanism for the two cases is identical, namely octahedral viscous flow being expressed by the state equation of the power-law type with a stress exponent of about 3 to 4. The effect of offstoichiometry on the creep resistance is then examined in Ni3(Al,5 at%Ti) alloys with different Ni concentrations. The results support the observation in the polycrystalline compound where the creep resistance increases with Ni concentration on both sides of stoichiometry exhibiting a discontinuity at stoichiometry. Finally, the apparent activation energy in the power-law type state equation for the steady state creep deformation is estimated for all the ternary alloys examined. They are in general in good agreement with that for diffusion of ternary elements in Ni3Al. However, the relative magnitude of the value can not simply be compared since the activation energy depends on deviations from stoichiometry.
The Strain Rate Sensitivity of Ni3(Al,Ta) Single Crystals.
Authors: Bonneville J. , Martin J.L. 
Published: March 2011

ABSTRACTIn order to obtain more complete information about the strain rate sensitivity of the flow stress of L12alloys, Ni3Al,Ta) single crystals have been deformed in compression, over a range of temperatures (293–1273K), at two different strain rates and in stress relaxation experiments.During the stress relaxation tests, at almost all the temperatures (except T~470K), a logarithmic decrease of the stress as a function of time has been observed. This is in fair agreement with the classical frame work of the thermal activation theory of dislocation glide. Thus, the corresponding apparent activation volumes have been determined and the nonmonotonic variation of this activation parameter with the temperature indicates that it is necessary to consider more than one plastic deformation process. These new results are discussed in terms of the previously published models which account for the plastic behaviours of the L12compounds.
High-Temperature Ductility of Intermetallic Nickel Aluminide (IC-218LZr)
Authors: Mirshams A.R. , Baldwin R.H. , Sikka V.K. 
Published: March 2011

ABSTRACTThis paper reports the results of uniaxial and compression tests on IC-218LZr extruded bars at temperatures from 700 to 1000°C in air. Tensile results indicate reduction in ductility at temperatures between 750 to 900°C. However, the results show improvement in ductility above 950°C. Compression test results do not show a decrease in the ductility in the temperature range.
First-Principles Investigation of Mechanical Behavior of B2 Type Aluminides: Feal and Nial
Authors: Fu C. L. , Yoo M. H. 
Published: March 2011

ABSTRACTFirst-principles calculations of the elastic constants, shear fault energies, and cleavage strength of NiAl and FeAl are presented. For NiAl, we find that the dissociation of <111> superdislocations into partial dislocations is unlikely, because of a high antiphase boundary energy and a weak repulsive elastic force between partial dislocations. FeAl has a high ideal cleavage strength as a result of the directional d-bond formation at the Fe sites. The strong ordering behavior of NiAl is explained in terms of the Al-to-Ni charge transfer and the repulsive interaction between Al atoms. The spontaneous glide decomposition of the <111> superdislocations in NiAl is also discussed.
High Temperature Properties of Refractory Intermetallics
Authors: Anton D.L. , Hartford CT E. , Shah D.M. , Whitney Pratt , Hartford CT E. 
Published: March 2011

AbstractOn the basis of creep strength, ultimate tensile strength and oxidation resistance, seven intermetallic compounds with melting temperatures above 1600°C have been selected as possible candidate materials for high temperature structural applications in advanced aero-turbines. These compounds, Nb3Al, Cr3Si, Co2Nb, Cr2Nb, MoSi2, Mo5Si3 and Nb2Al, have been evaluated and their properties reported herein. All seven of the compounds displayed excellent creep resistance at 1200°C with Mo5Si3 and Nb2Al being the strongest. Nb3Al, with the precipitation of the niobium solid solution displayed the greatest low temperature toughness. The greatest ultimate tensile strengths were observed for Co2Nb and MoSi2, while MoSi2 was by far the most oxidation resistant.
High Temperature Deformation of Single Crystalline Cr3Si (A15) Intermetallic Compound
Authors: Chang C. Steve , Pope D. P. 
Published: March 2011

AbstractHigh temperature compression tests were performed on Cr 3Si single crystalline and poly crystalline samples. Slip systems were determined to be of the {001}<010> type based on an analysis of slip traces and Laue spots. Single crystals show significant compressive ductility at temperatures above 0.7Tm. The implication of cube slip on the ductility of A15-type intermetallic compounds is discussed.
Miniaturized Disk-Bend Testing of Ni3 Al: Effect of Stoichiometry and Boron Content
Authors: Li H. , Ardell A. J. 
Published: March 2011

ABSTRACTThe results of miniaturized disk-bend tests on samples of Ni 3Al of different stoichiometry and boron content are presented. The yield strengths and ductilities of alloys containing 24, 25 or 26 %Al. either boron-free or doped with 0.3 or 0.35 %B, were measured. Specimens 3 mm in diameter and approximately 200 μm thick were tested, some of these having been cut from the grip sections of previously tested tensile bars. The yield strengths were in excellent agreement with the results obtained from the uniaxial tensile tests. The load-displacement curves for the brittle alloys (all but the boron-doped 24 %Al alloy) exhibited a maximum load corresponding to crack initiation. The shapes of the deformed specimens confirmed the assumption that they deform as if they were clamped even though they are not. The fracture surfaces of the brittle alloys are consistent with intergranular failure. Nevertheless, the ductility of the alloys increases with decreasing Al content and decreasing grain size, even for the boron-free alloys which are all brittle. The fracture stress of the boron-doped 26 %Al alloy is about 30% greater than that of the boron-free alloy. It is argued that this is most likely a consequence of the depletion of aluminum at grain boundaries, coupled with boron segregation. Independent evidence suggests that this should increase the cohesive strength of grain boundaries in the boron-doped 26 %Al alloy.
Miniaturized Disk-Bend Testing and Microstructure of 3.8 Mev Zr3+ Irradiated Zr3Al
Authors: Chen F. C. , Ardell A. J. , Pedraza D. F. 
Published: March 2011

ABSTRACTThe mechanical behavior of Zr3Al irradiated with 3.8 MeV Zr3+, ions has been investigated using a miniaturized disk bend test (MDBT). The samples tested were 3 mm in diameter and either nominally 100 or 250 μ m thick. They were irradiated at 250 °C to peak doses varying from 0.0041 to 2 displacements per atom (dpa). The yield stresses, σy, of the thin specimens were independent of dose, within experimental error, and comparable to that of unirradiated Zr3 Al. However, for the thick specimens σy was significantly larger for the irradiated material, possibly increasing to a maximum at a peak dose between 0.02 and 0.06 dpa. The relative insensitivity of σy of the thin specimens to irradiation, compared to the thick ones, is a surprising result for which we have no satisfactory explanation. Examination by transmission electron microscopy showed that Zr3Al begins to undergo chemical disorder at a dose of only 0.02 dpa and Is nearly completely disordered at 0.41 dpa. Electron diffraction indicates the presence of satellite reflections along 〈110〉 in {001} diffraction patterns. The nature of the defects responsible for these has not yet been determined, although rather similar effects have been observed in electron and Kr+-ion irradiated Zr3Al and attributed to elastic softening of the lattice. The possible roles of these defects, as well as disordering, are discussed.
Ternary Alloying of Gamma Titanium-Aluminides for Hot-Workability
Authors: Masahashi Naoya , Mizuhara Y. , Matsuo M. , Hashimoto K. , Kimura M. , Hanamura T. , Fujii H. 
Published: March 2011

ABSTRACTA Microstructurally controlled γ(TiAl)-based alloy containing β(bcc) has shown remarkable tensile properties at high temperatures. It exhibits over 450% tensile elongation at 1473K. The strain rate sensitivity factors are calculated to be over 0.3 above 1273K. A specific texture is not observed from transmission X-ray photograph. TEM observation reveals that the precipitated β phase located at grain boundaries elongates uniformly along γ grain boundaries and causes large ductility. We propose β/γ dual phase alloys as high temperature deformable materials.
Spray Forming of MoSi2 and MoSi2-Based Composites
Authors: Tiwari R. , Herman H. , Sampath S. 
Published: March 2011

ABSTRACTVacuum plasma spraying has been used to fabricate dense MoSi2 and TiB2-reinforced MoSi2-based composites. The spray-formed deposits have high hardness and fracture toughness as compared to that achieved by other processing techniques. Annealing of the spray formed MoSi2 leads to a decrease in hardness and an increase in fracture toughness. Reinforcement with TiB2 leads to toughening and strengthening of the spray-formed MoSi2.