bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shape Memory Properties of an Iron Modified Nickel Aluminide Alloy
Authors: Horton J. A. , Liu C. T. , George E. P. 
Published: April 2011

AbstractThe ordered intermetallic NiAl with aluminum levels near 36% undergoes a B2 to martensite transformation. Shape memory alloys based on NiAl+Fe have the potential for transition temperatures of greater than 150°C. While binary alloys appear inherently brittle, alloying with iron and boron results in two phase alloys with L12and B2 phases and with about 7% room temperature tensile ductility. These alloys show a two-way shape memory effect over a range of transition temperatures with austenite peak temperature, Ap, between 100 to 200'C based on composition. Unfortunately, the B2 phase and its low temperature body centered tetragonal martensitic form are not stable and both can transform to Ni5Al3with a loss in ductility. These alloys with a constant tensile load show a two way shape recovery of up to 0.6% during temperature cycling between 100 and 200°C. A thorough survey of the shape memory properties of one such alloy with a composition of Ni-25.5 Al-16 Fe-0. 12 B (at.%) as a function of prior cold work, tensile loading and other training steps is presented. Nanoindentation was used to independently measure the mechanical properties of the two phases.
Review of Environmental Effects in Intermetallics
Authors: George E. P. , Liu C. T. 
Published: April 2011

AbstractThe recent progress made in our understanding of the phenomenology and mechanisms of environmental embrittlement in ordered intermetallics is reviewed by considering two model alloy systems of the L12and B2 crystal classes (Ni3Al and FeAl). The poor ductility commonly encountered when these alloys are tensile tested in ambient air is due mainly to environmental embrittlement, in the absence of which, both alloys are now known to be quite ductile. Both H2O and H2, at levels found in ordinary ambient air, are found to cause environmental embrittlement, with the former usually more deleterious. In the case of H2O, the micromechanism involves reaction with the intermetallic to form an oxide (or hydroxide) and simultaneous generation of atomic hydrogen which then enters the metal and causes embrittlement. In the case of H2, on the other hand, atomic hydrogen is generated as a result of the dissociation of physisorbed hydrogen molecules on the intermetallic surfaces. Consistent with the proposed embrittlement mechanism, ductility is found to increase with decreasing amounts of H2O (or H2) in the test environment, increasing strain rate, and decreasing (or increasing) temperature. Environmental embrittlement in Ni3Al (and other L12alloys) occurs predominantly intergranularly, whereas in FeAl (and other B2 alloys) it can also occur transgranularly—presumably because diffusion of hydrogen is fast enough through the bulk in the more open B2 structure but only so along grain boundaries in the L12structure. Microalloying with B, which segregates strongly to the grain boundaries, can overcome environmental embrittlement in L12alloys, but not in B2 alloys; in the latter, alloying additions probably have to be added at significantly higher (macroalloy) levels to affect the bulk properties. In neither alloy is environmental embrittlement the sole source of brittleness: depending on the alloy stoichiometry, and grain boundary character, a given grain boundary may be intrinsically weaker (or stronger) than the bulk, thereby influencing overall ductility.
Effect of Surface Treatment on the Formation of Oxygen Enriched Brittle Layer in A Ti3A1-Nb Alloy
Authors: Zhang B. , Wan X. , Li D. , Wang J. , Wang H. , Chen W. R. 
Published: April 2011

AbstractEffect of surface treatment on the formation of oxygen enriched brittle layer in a Ti3Al-Nb alloy was investigated. The results show that a mixed Ti2N and TiN layer was formed at the surface by the titanium nitride vapor deposit treatment, and this titanium nitride layer makes it possible to suppress the formation of the oxygen enriched brittle layer during thermal exposure. An Al2O3 film was formed at the surface of the alloy, when the surface treatment was conducted under a low partial pressure oxygen atmosphere. However, such surface treatment is not able to depress the formation of the oxygen enriched brittle layer during thermal exposure, due to the higher affinity of α2 phase for oxygen as well as the higher diffusivity of titanium in Al2O3.
Microstructure of the Intermetallic Compounds Al3(Ti1-XMx)
Authors: Kita K. , Itoh G. , Kanno M. 
Published: April 2011

AbstractAn attempt was made to change the crystal structure of the intermetallic compound Al3Ti from DO22 to Ll2, by replacing Ti with several alloying elements. The alloying elements chosen in this study were Sc, Er and Lu with which Al forms intermetallic compounds having LI, structure. Ingots weighing about 50g of Al3(Ti1-xMx) — M represents alloying element and the x value is 0, 0.25 or 0.5 — were melted in an argon plasma arc furnace. X-ray diffraction, energy dispersive spectroscopy and scanning electron and optical microscopy were carried out to examine the microstructurc in relation to the kind and amount of alloying elements. Microstructural observation revealed the occurrence of an Ll2 phase in all M bearing alloys. Compression tests were also carried out to assess the ductility of these alloys. The results showed that the Sc alloying is effective to increase the room temperature ductility of Al3Ti.
New Gas Atomizing Technique for Nb3Al Intermetallic Alloy
Authors: Murahashi Noriaki , Kohmoto Hiroaki , Kohno Tohru 
Published: April 2011

AbstractPlasma-Melt-Gas-Atomizing (PMGA) technique has been developed to produce rapidly solidified powders of intermetallic alloys for ultra-high temperature structural applications. Using this technique, rapidly solidified Nb3Al powders have been produced. These powders consist mainly of supersaturated solid solution of Al in Nb (A2), while the conventional cast structure consists of ordered A 15, and may be a good source for most powder metallurgical applications. Furthermore, a unique technique to control the powder size distribution is currently under development. In-situ measurement method of the atomized powder size distribution has been examined by using phase Doppler particle analyzer to control final powder size distribution by the feedback from the in-situ measurement data to the control system of the Plasma-Melt-Gas-Atomizer.
The Mechanics of Cross-Slip in L12Alloys
Authors: Saada Georges , Shi Xiaoli , VeyssiÈre Lem Patrick 
Published: April 2011

AbstractRelationships between the microstructural organization in Ll2alloys and the flow stress anomaly are discussed. Attention is paid to the origin of friction on the cube plane, to the stability of Kear-Wilsdorf (KW) locks and to the fine structure of kinks. The difficulty of dislocation multiplication and the easiness of their annihilation are outlined. Directions for a future model of the flow stress anomaly based on a close analysis of the microstructure are given.
The Influence of Mo on the Physical and Mechanical Properties of Single Crystalline Nial
Authors: Hu J. , Levit V. , Kaufmann M. J. 
Published: April 2011

AbstractThe room and elevated temperature (300°C and 600°C) tensile properties of single crystalline NiAl with and without molybdenum additions have been investigated. It is shown that 0.2at% molybdenum has a considerable influence on the mechanical properties of NiAl and this influence is sensitive to heat treatment. At room temperature, the ductility of the Mo-doped alloy was higher than the binary NiAl after appropriate heat treatment. Furthermore, the elongations observed are highest at 300°C and are related to greater uniformity of deformation.
Defect Recovery and Ordering in Ni3A1+B
Authors: Karnthaler H. P. , Kozubski R. , Pfeiler W. , Rentenberger C. 
Published: April 2011

AbstractDefect recovery andlong-range ordering(LRO) in Ni76Al24+0.19at.%B (400 wt.ppm) were studied by means of residual resistometry, TEM methods and microhardness testing. The material was cold-rolled with intermediate annealings and the samples were prepared from sheets exhibiting effective thickness reductions of 8 and 14%, respectively, achieved in the final rolling step.By TEM two recovery processes were observed. Firstly,superlattice intrinsic stacking faults(SISF) of large density recovered almost completely in the temperature regime between 443 and 700 K showing that they are bounded by dislocations of opposite sign. This indicates that most of the SISF are formed by pulling out dipoles and not by dislocation interactions as recently suggested. Secondly, the recovery of antiphase-boundary (APB) dissociated superlattice dislocations occurred by the annihilation of dipoles within the whole temperature regime leading finally to a loss of all dislocations at 1273 K.Despite some excess disorder caused by cold-rolling, the mechanical deformation did not influence qualitatively the LRO processes.
Monitoring of Deformation Induced Microcracking in Polycrystalline NiAl
Authors: Wanner A. , Schietinger B. , Bidlingmaier T. , Zalkind H. , Arzt E. 
Published: April 2011

AbstractMicrocracking in polycrystalline near-stoichiometric NiAl produced by room temperature plastic deformation under uniaxial compression was investigated by means of optical microscopy, velocity of sound measurements, and acoustic emission monitoring. Results show that strains greater than 2 % are required to produce microcrack populations which can be evaluated by microscopical investigation or velocity of sound measurements. However, acoustic emission monitoring during compression testing indicates that microcracking starts at about 0.7 % compressive plastic strain which is identical with the typical tensile fracture strain for NiAl. Thus it is concluded that there is little or no stable microcracking prior to failure in tension. Acoustic emission results show also that the process of microcracking does not primarily occur during the applied compressive deformation. A considerable fraction of the microcracking takes place during the quasi-elastic unloading following deformation.
An Hrem Investigation of a {121}L10 Boundary in Tial
Authors: Inkson B. J. , Humphreys C. J. 
Published: April 2011

AbstractA consideration of {121}L10 boundaries in their unrelaxed form shows that there are at least three ィ2, six ィ3 and three ィ6 variants possible due to the tetragonal ordering of the L10 lattice. Experimental observations of コ-TiAl, obtained by HREM, show that two コ-grains with a true-twin orientation relationship exhibit a rigid body shift between the {111} planes perpendicular to and either side of a {121}L10 interface, and that the interfacial structure is distinct from those previously observed in f.c.c. metals.
The Temperature Dependence of the Mechanical Properties of Gamma TiAl
Authors: Viguier B. , Bonneville J. , Hemker K. J. , Martin J. L. 
Published: April 2011

AbstractMechanical properties of a polycrystalline single phased γ Ti47Al51Mn2alloy were studied by compression tests in a wide range of temperature (100 K - 1300 K). We report, in this paper, the temperature dependence of both the flow stress and its strain rate sensitivity. These dependencies show the existence of three temperature domains corresponding to different dislocation motion mechanisms. The temperature dependence of the flow stress strain rate sensitivity is compared with values measured in single crystals1.
Dislocations and Charge Density Distributions of γ Phase in Ti47.5Al2.5V Deformed at Room Temperature and 400°C
Authors: Zhu Jing , Gao Ying , Miao Yu 
Published: April 2011

AbstractThe observations on quantity and configuration of dislocations by TEM conventional diffraction contrast method as well as the determinations of the electron charge density distributions by the quantitative electron crystallography method in Ti47. 5A12. 5V deformed at 400°C and room temperature (R. T.) have been carried out. The metallic bonding between Al—Al or Ti—Ti atom pair along <C110] and Ti — Ti along <C112] direction is strengthened; while the metallic bonding between Ti — Al atom pair both along <C101] and <12l] direction is weakened at 400°C. The quantities of a/2<110], a/2<112] and dissociated a <101] (a[101] →a/2[110] + a/3[112] + SISF+a/6[112] ) dislocations are increased at 400°C, compared with that at R. T.. The a/ 2 < 121] superdislocations have not been seen both at 400°C and R. T..
Dislocation Substructures in Shock-Loaded N13AI
Authors: Albert Diane E. , George T. 
Published: April 2011

AbstractThe deformation substructure and mechanical response of the LI2intermetallic, Ni3Al, subjected to shock-wave loading was studied. Following shock prestrains to shock pressures of approximately 14.0 GPa, 23.5 GPa, and 47.2 GPa, the reload yield strength of Ni3Al was measured to be 750 MPa, 1250 MPa and 1500 MPa, respectively. The effective hardening in the shock-loaded Ni3Al exceeds that quasistatically obtained when deformed to roughly the same equivalent strains. Coarse planar slip on {111} type planes, a high density of stacking faults, and deformation twins with a {111} type twinning plane were observed in the shocked material. An increasing propensity for twinning and stacking fault formation was observed with higher shock peak pressures.
Effect of Ternary Additions on the Intrinsic Ductility of Ni3Al Alloys
Authors: Chiba A. , Hanada S. , Watanabe S. 
Published: April 2011

AbstractDuctility of binary and ternary Ni3Al alloys with conventional purity, fabricated by isothermal hot-forging, was examined by tensile tests in dry oxygen to eliminate environmental embrittlement. Re crystallized Ni-23A1 doped with approximately 0.4 mol% X(X=Hf, Nb, and Zr) alloys exhibits pronounced ductility, whereas recrystallized Ni-23A1–2X alloys exhibits elongation of less than 3%. Ductility of a highly purified binary Ni-23A1 alloy was also examined and showed remarkable ductility, resulting in trans granular fracture. This indicates that a Ni-rich Ni3Al alloy inherently exhibits marked ductility without intergranular fracture if impurity atoms and other extrinsic factors(e.g., environmental effect and internal microcracks) are eliminated in the alloy. Thus it is found that Hf, Nb and Zr in the significant ductilization of Ni-23A1 can act as a scavenger of harmful impurities when added in a small amount. With further increasing amount of additions of Hf, Nb and Zr, elongation decreases rapidly and reaches almost no ductility at 2 mol% additions, indicating that Hf, Nb and Zr lower the intrinsic ductility of Ni3Al alloy.
Reaction Synthesis of Intermetallics
Authors: Deevi Seetharama C. , Sikka Vinod K. 
Published: April 2011

AbstractExothermicity associated with the synthesis of aluminides was utilized to obtain nickel, iron, and cobalt aluminides. Combustion synthesis, extrusion, and hot pressing were utilized to obtain intermetallics and their composites. Extrusion conditions, reduction ratios, and hot-pressing conditions of the intermetallics and their composites are discussed.
Microstructures and Properties of Ds in-Situ Composites of Nb-Ti-Si Alloys
Authors: Bewlay B. P. , Jackson M. R. , Reeder W. J. , Lipsitt H. A. 
Published: April 2011

AbstractIn-situ composites based on binary Nb-Si alloys and consisting of a Nb solid solution with Nb3Si or Nb5Si3 have shown a promising combination of low temperature and high temperature mechanical properties. The environmental resistance and room temperature fracture toughness of these composites can be further enhanced by additions such as Ti, Hf, Cr, and Al. In the present study, ternary Nb-Ti-Si alloys were prepared by directional solidification to generate aligned two and three phase composites containing a Nb solid solution with Nb3Si and/or Nb5Si3. The present paper will describe microstructures, phase equilibria and fracture toughness of these composites. The improvement in the room temperature fracture toughness over binary Nb-Nb5Si3 composites is discussed.
High Temperature Corrosion Behavior of Ni3A1-Based Alloys
Authors: Li H. , Guo J. T. , Lai W. H. , Wang S. H. , Tan M. H. 
Published: April 2011

AbstractThe corrosion behavior of a Ni3A1–1 5at%Fe alloy has been studied in air and melted salts, and also that of Ni3Al alloys contained series boron in melted salts. The first alloy has two oxidation rate constants. Its initial oxidation activity energy is 319 kJ / mol. There was much FeAl2O4 formed at 950°C, which possessed better oxidation resistance than NiFe2O4, therefore the alloy had the best oxidation resistance at 950°C. It also had better sulfidation resistance than 00Cr19NillTi stainless steel at 850°C, but the alloy was sulfidized seriously at 950°C. The sulfides were FeS2 at 850°C and A12S3, Ni2S3 at 950°C. There were different initial oxides formed, which were Fe3O4 at 850°C, and mixture oxides of NiO, NiMoO4, A12O3 and NiAl2O4 at 950°C , respectively. The Ni3Al alloys with boron contents from 0 to 3.7at% had better sulfidation resistance than the stainless steel at 850°C, and the alloy with 1.37at%B was the best. The sulfides were the same in the boron containing Ni3Al alloys which were Al2S3 and Ni7S6.
Oxidation Behaviour of Intermetallic Compounds Based on Ti-Al System
Authors: Tomasi A. , Gialanella S. , Orsini P. G. , Nazmy M. 
Published: April 2011

AbstractIn this study we present some results regarding phase and surface stability, with particular reference to the oxidation, of Ti alloys based on the γ-TiAl phase.We investigated the stability of the metallic phases with TG and DSC methods, according to the temperature range over which the relevant transformations do occur. These tests were particularly useful to select times and temperatures for precipitation hardening treatments and also to evaluate the oxidation resistance.The isothermal oxidation kinetics were followed with a thermobalance (TG) for time up to 25 hours and, for longer treatments, we put the samples in a furnace and measured their weight changes at fixed time intervals. The microstructure of the oxide scale was investigated with scanning electron microscopy and energy dispersion X-ray analysis and mapping. The identification of the crystalline phases was carried out with X-ray diffraction analysis.The obtained results afford clear information on the predominant phenomena assisting the observed oxidation kinetics and give indications on the operating conditions suitable for these materials.
TEM Characterization of Al/Al2O3 Composite Fabricated by Reactive Metal Infiltration
Authors: Gao Y. , Jia J. , Loehman R. E. , Ewsuk K. G. 
Published: April 2011

ABSTRACTThe microstructure of Al/α-Al2O3 composites made by infiltrating into dense mullite preforms has been characterized using transmission electron microscopy. Observations revealed that the formation of the Al/Al2O3 composites involves three stages. Initially, infiltrates into a dense mullite preform through grain boundary diffusion, and reacts with mullite at grain boundaries to form a partial reaction zone. Then, a complete reaction takes place in the reaction region between the partial reaction zone and the full reaction zone to convert the dense mullite preform to a composite of α-Al2O3 (matrix) and an Al-Si phase (thin channels). Finally, the reduced Si from the reaction diffuses out of the Al/A2O3 composite through the metal channels, whereas from the molten pool is continuously drawn to the reaction region until the mullite preform is consumed or the sample is removed from the molten pool. Based on the observed microstructure, infiltration mechanisms have been discussed, and a growth model of the composites is proposed in which the process involves repeated nucleation of Al2O3 grains and grain growth.
Polymer-Derived Silicon Carbide Fibers with Near-Stoichiometric Composition and Low Oxygen Content
Authors: Sacks Michael D. , Scheiffele Gary W. , Saleem Mohamed , Staab Gregory A. , Morrone Augusto A. , Williams Thomas J. 
Published: April 2011

ABSTRACTFine-diameter (∼ 10–15 µm), polymer-derived SiC fibers were characterized. The average tensile strength of the fibers was ∼ 2.8 GPa, although some lots had average strengths exceeding 3.5 GPa. Microstructure observations showed that fibers had fine grain sizes (mostly ∼0.05–0.2 µm), high densities (∼3.1–3.2 g'cm3), and small residual pore sizes (≤0.1 µm). Elemental analysis showed that fibers had near-stoichiometric composition. Electron and X-ray diffraction analyses indicated that fibers were primarily beta silicon carbide, with a minor amount of the alpha phase. A small amount of graphitic carbon was detected in some samples using high resolution transmission electron microscopy. The residual oxygen content in the fibers was ≤0.1 wt%. Fibers exhibited good thermomechanical stability, as heat treatment at 1800°C for 4h in argon resulted in only an ∼ 8% decrease in strength.
Characterization of BN Rich Layer on Ammonia Treated Nextel™312 Fibers
Authors: Khasgiwale N.R. , Butler E.P. , Tsakalakos L. , Hensley D.A. , Cannon W.R. , Danforth S.C. , Gonczy S.T. 
Published: April 2011

ABSTRACTA BN rich layer grown on Nextel™312 fibers by appropriate ammonia treatments was evaluated using various complimentary techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM)/ Parallel Electron Energy Loss Spectroscopy (PEELS in TEM). Three different ammonia treatments were studied. Ammonia treatment resulted in crystallization of the Nextel™312 fiber. The BN rich surface layer formed due to ammonia treatment was clearly detected in XPS and PEELS both before and after oxidation. The layer thickness was estimated to be between 5–10 nm. The layer was stable after oxidation treatment at 600°C for 100 hours. High resolution TEM observations of the fiber surface revealed a variable BN rich layer thickness. Patches of turbostratic BN were observed under certain conditions, however mostly the layer appeared to be amorphous.