The short-range order structure of a water-quenched Ni-12.5 at. pct Si alloy—a synchrotron x-ray diffuse scattering study

A wide-angle X-ray diffuse scattering measurement of a water-quenched Ni-12.5 at. pct Si alloy single crystal was performed using synchrotron radiation. The Cowley-Warren short-range order (SRO) parameters and static displacement terms between atom pairs were obtained. The first seven SRO parameters were fitted in an 8000-atom model, from which it was deduced that no orderedγ′ domains existed in the water-quenched structure, but an enhancement of the C16 and C17 nearest-neighbor configurations did occur as compared to a completely random model. The C16 configuration is the basic structural unit of the L1₂ ordered structure, and the C17 may be thought of as a faulted variant thereof. These results were confirmed by performing equivalent SRO modeling in a 140,608-atom model. Silicon-silicon nearest neighbors show a repulsive strain of approximately 12 pct, while Ni-Ni pairs contract by less than 1 pct.     

High-temperature deformation behavior of the intermetallic Ti-47 At. Pct Al-3 At. Pct Cr alloy

A study of the high-temperature deformation behavior of a binary α ₂+γTi-47 at. pct Al-3 at. pct Cr alloy was undertaken. The alloy was produced by induction melting and exhibited a structure of coarse columnar grains oriented in the radial direction. After a solution treatment at 1653 K for 3600 seconds and aging at 1223 K for 28,800 seconds, a nearly lamellar structure was formed. Deformation behavior was investigated by compression-strain-rate-change tests at strain rates ranging from 10⁻⁶ to 10⁻³ s⁻¹ and temperatures ranging from 1073 to 1373 K. This alloy shows at low temperature/high stress a stress exponent of about 5. The deformation behavior is explained in this regimen by a dislocation climb mechanism, which includes a threshold stress. Finally, at the lowest stress levels and highest temperatures of testing, a stress exponent of about 3 is observed, which suggests that deformation is controlled by the viscous glide of dislocations.     

The role of mass transport in the stress-corrosion cracking mechanism of Cu-25 At. Pct Au single crystals in chloride solutions

Available crack growth rate data obtained during discontinuous and continuous propagation of stresscorrosion cracks in Cu-25 at. pct Au single crystals in chloride solutions have been used to investigate the role of mass transport in the mechanism of transgranular stress-corrosion (TSCC) cracking. The results of calculations suggest that during discontinuous crack growth the stage of rapidly increasing crack extension will lead to the formation of a salt film near the crack tip, ultimately resulting in crack arrest. Also, during continuous cracking, the crack growth rate appears to be controlled by the formation of a salt film at the crack tip.     

Determination of long range order in Ni-Base ternary alloys by X-ray anomalous diffraction using synchrotron radiation

Long range order (LRO) parameters in three ternary Ll₂ alloys [Ni₇₅Al₁₅Ti₁₀, Ni₇₀Al₂₀Cr₁₀ and (Ni₃Fe)_96.4Cr_3.6] have been measured using a new method. This method takes advantage of the variation in atomic scattering factors for X-rays near absorption threshold and opens a new area of research with the development of synchrotron facilities. The results show that Ti substitutes mostly, but not exclusively, for Al in NiAlTi. In NiAlCr, Cr occupies both Ni and Al sites. In NiFeCr, the order is not perfect; the Cr atoms are distributed on both types of sites, with a slight preference for Fe sites.     

Effect of Aging on Microstructure and Shape Memory Properties of a Ni-48Ti-25Pd (At. Pct) Alloy

The microstructure and properties of a precipitation-hardenable Ni-48Ti-25Pd (at. pct) shape memory alloy have been investigated as a function of various aging conditions. Both the hardness and martensitic transformation temperatures increased with increasing aging time up to 100 hours at 673 K (400 °C), while no discernable differences were observed after heat treatment at 823 K (550 °C), except for a slight decrease in hardness. For aging at 673 K (400 °C), these effects were attributed to the formation of nano-scale precipitates, while precipitation was absent in the 823 K (550 °C) heat-treated specimens. The precipitation-strengthened alloy exhibited stable pseudoelastic behavior and load-biased-shape memory response with little or no residual strains. The precipitates had a monoclinic base-centered structure, which is the same structure as the P-phase recently reported in Ni(Pt)-rich NiTiPt alloys. 3D atom probe analysis revealed that the precipitates were slightly enriched in Ni and deficient in Pd and Ti as compared with the bulk alloy. The increase in martensitic transformation temperatures and the superior dimensional stability during shape memory and pseudoelastic testing are attributed to the fine precipitate phase and its effect on matrix chemistry, local stress state because of the coherent interface, and the ability to effectively strengthen the alloy against slip.     

Comparison of the Microstructure, Tensile, and Creep Behavior for Ti-22Al-26Nb (At. Pct) and Ti-22Al-26Nb-5B (At. Pct)

The effect of the addition of 5 at. pct boron on the microstructure and creep behavior of a nominally Ti-22Al-26Nb (at. pct) alloy was investigated. The boron-modified alloy contained boride needles enriched in titanium and niobium, and because to these borides, this material was considered to be a discontinuously reinforced metal matrix composite. These needle-shaped borides made up to 2 pct of the volume and were up to 158-μm long and 22-μm wide. The effect of boron on the mechanical properties was evaluated through in-situ creep testing and tensile testing at room temperature (RT) and 650 °C. Overall, the addition of 5 at. pct boron proved to be detrimental to the tensile and creep behavior. The composite exhibited a brittle failure and lower elongations-to-failure than the monolithic material. The in-situ tensile and creep experiments revealed that the deformation process initiated in the boride needles, which cracked extensively, and significantly greater primary creep strains and creep rates were exhibited by the composite.

---

Formation of the myosin.ADP.gallium fluoride complex and its solution structure by small-angle synchrotron X-ray scattering

The products of the SOS-regulated umuDC operon are required for most UV and chemical mutagenesis in Escherichia coli, a process that results from a translesion synthesis mechanism. The UmuD protein is activated for its role in mutagenesis by a RecA-facilitated autodigestion that removes the N-terminal 24 amino acids. A previous genetic screen for nonmutable umuD mutants had resulted in the isolation of a set of missense mutants that produced UmuD proteins that were deficient in RecA-mediated cleavage (J. R. Battista, T. Ohta, T. Nohmi, W. Sun, and G. C. Walker, Proc. Natl. Acad. Sci. USA 87:7190-7194, 1990). To identify elements of the UmuD' protein necessary for its role in translesion synthesis, we began with umuD', a modified form of the umuD gene that directly encodes the UmuD' protein, and obtained missense umuD' mutants deficient in UV and methyl methanesulfonate mutagenesis. The D39G, L40R, and T51I mutations affect residues located at the UmuD'2 homodimer interface and interfere with homodimer formation in vivo. The D75A mutation affects a highly conserved residue located at one end of the central strand in a three-stranded beta-sheet and appears to interfere with UmuD'2 homodimer formation indirectly by affecting the structure of the UmuD' monomer. When expressed from a multicopy plasmid, the L40R umuD' mutant gene exhibited a dominant negative effect on a chromosomal umuD+ gene with respect to UV mutagenesis, suggesting that the mutation has an effect on UmuD' function that goes beyond its impairment of homodimer formation. The G129D mutation affects a highly conserved residue that lies at the end of the long C-terminal beta-strand and results in a mutant UmuD' protein that exhibits a strongly dominant negative effect on UV mutagenesis in a umuD+ strain. The A30V and E35K mutations alter residues in the N-terminal arms of the UmuD'2 homodimer, which are mobile in solution.     

Study of the hydrogen internal friction peak in Nb-10 At. Pct V in the presence of oxygen

Low concentrations of hydrogen in Nb-10 at. pct V yield a relatively broad internal friction peak at low temperatures, which is interpreted as a Snoek-type relaxation peak. The broadening is attributed to hydrogen atoms occupying a spectrum of energy levels caused by a random distribution of vanadium in niobium, such that at different frequencies, different energy levels are probed. The major aim of the present study was to determine the effects of oxygen on this hydrogen peak. A small decrease in peak height and a small increase of the broadening of the peak were observed, but there was no change in the activation parameters. It is concluded that oxygen and hydrogen interact weakly in this alloy, if at all. This supports earlier work in which it was concluded that there is no convincing evidence for a synergistic effect of oxygen and hydrogen on the mechanical properties of this alloy. Formerly Graduate Student at Ames Laboratory, is living in Indonesia.     

Short range order in a single crystal of Fe-19.5 at.% Al in the ferromagnetic range measured through X-ray diffuse scattering

The local atomic arrangement in FeAl_19.5% has been investigated by X-ray diffuse scattering on a single crystal quenched from 772 K in the ferromagnetic range. We find a very short ranged order, the largest SRO parameters being the first one (repulsive AlAl interaction) and the third one (attractive one). The displacement amplitude also rapidly decreases with the atomic shell radius. SRO pair interaction potentials have been deduced through an inverse cluster variation method.     

Anomalous small-angle X-ray scattering determination of the partial structure factors of an aged Fe-Ni-W alloy: A synchrotron radiation study

The phase transformation at 480°C of a Fe-0.17 Ni-0.027 W (at.%) alloy was studied by anomalous small-angle X-ray scattering (ASAXS). Partial structure factors (PSF) were extracted from ASAXS data obtained in the neighbourhood of K Fe and L_IIIW absorption edges. The PSF were decomposed into two contributions: a pseudobinary one and a complementary one. This latter was shown to be very low ( ∼- 3%). From these PSF, it has then been concluded that the precipitation occurs according to a two-phase system. Such a result agrees well with TEM observations which have revealed two phases having different crystalline structures: precipitates of hexagonal symmetry embedded in a b.c.c. depleted ex-martensitic matrix. The composition of both phases does not change during isothermal ageing, being for the precipitate C_Fe = 0.956, C_W = 0.044, C_Ni∼-0 and for the matrix C_Fe = 0.696, C_Ni = 0.291, C_w = 0.013 with a volume fraction of precipitates of about 45%.     

Investigation of the kinetics of short range order formation and quenched-in vacancy annihilation in Au-15at.%Ag by resistivity measurements

The short range order (SRO)-induced resistivity contribution ρ_s was measured during isothermal annealing at temperatures T_a after quenching from T_q and evaluated by the Schulze-Lücke method. Downquenching (T_qs>T_a) resulted in a complicated kinetics for the resistivity changes whereas up-quenching (T_q < T_a) led to a strict first order kinetics. It could be concluded that the SRO-induced resistivity is proportional to a SRO parameter which changes according to a first order kinetics and that the deviations from first order after down-quenching are here caused by the annealing-out of quenched-in surplus vacancies. From the rate of resistivity change, the jump frequency and the concentration of the vacancies could be determined (the latter down to the extremely low value of 10⁻¹¹ per atom) and thus the activation energies for vacancy migration and formation and for self-diffusion as well as the annealing-out kinetics of vacancies could be derived. At low quenching temperature first order and at higher temperatures second order annealing-out kinetics has been found. Additionally some atomic parameters not discussed before could be evaluated.     

The effect of ternary trace additions on the nucleation and growth of γ′ precipitates in an Al-4.2 At. Pct Ag alloy

The role of trace elements on the nucleation and growth kinetics of γ′ precipitates in an aged Al-4.2 at. pct Ag alloy was determined. Comparing the characteristic properties of different trace elements on the precipitate dimensions and density after aging showed that a combination of high solute/vacancy binding energy and diffusivity was required to significantly affect the length, thickness, and density of γ′ precipitates. The elements which had the most pronounced effect were In and Sn, and the high solute/vacancy binding energy of In and Sn appears to be largely electronic in origin. The mechanism by which these trace elements affect the micro-structure is to reduce the number of quenched-in dislocation loops for heterogeneous nucleation of γ′ precipitates. The decreased number of nucleation sites leads to a prolonged matrix super-saturation, which causes an increase in the length, thickness, and ledge density of γ′ precipitates. Formerly with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University Formerly with the Department of Metallurgical Engineering and Materials Science, Carnegie Mellon University, Pittsburgh, PA     

Orthogonal higher order structure of the Wechsler Intelligence Scale for Children--Fourth edition.

According to J. B. Carroll's (1993) 3-stratum theory, performance on any subtest reflects a mixture of both 2nd-order and 1st-order factors. To disentangle these influences, variance explained by the general factor should be extracted first. The 1st-order factors are then residualized, leaving them orthogonal to the general factor and each other. When these methods were applied to the WISC-IV standardization sample, the general factor accounted for the greatest amount of common (71.3%) and total (38.3%) variance. The largest contribution by a first-order factor was 6.5% of total variance. It was recommended that interpretation of the WISC-IV not discount the strong general factor. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Morpheme order and syllable structure in the learning of miniature linguistic systems.

"Two experiments were conducted to test the effects of several variables confounded or uncontrolled in Esper's 1925 study of the learning of Miniature Linguistic Systems… . Of the possible causes of Esper's results, phonetic symbolism, particular grouping of nonsense syllables, particular referent dimensions, and morpheme order produced no effects in these experiments. The only variable causing a significant difference was whether or not the Miniature Linguistic System learned contained syllables of non-English structure." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Determination of the shortest interatomic distance in a liquid metal using its structure factor

The structure factor (SF) and atomic radial distribution function (RDF) of liquid lead simulated at a temperature of 613 K are compared. The shortest interatomic distance obtained from SF is found to be smaller than that determined as the abscissa of the first RDF coordination peak. It is shown that a satisfactory agreement between the experimental and calculated curves in the high-angle portion of SF can only be obtained when at least two most probable shortest interatomic distances r ₁ and r ₂, which indicate a complex structure of the first coordination shell of the liquid metal, are taken into account.     

Orthogonal higher order factor structure of the Stanford-Binet Intelligence Scales--fifth edition for children and adolescents.

Orthogonal higher-order factor structure of the Stanford-Binet Intelligence Scales-Fifth Edition (SB-5; Roid, 2003a) for child and adolescent samples is reported. Multiple criteria for factor extraction unanimously supported extraction of only one dimension and a unidimensional model. However, following results from DiStefano and Dombrowski (2006) and theoretical consideration, two factors were extracted and obliquely rotated and further subjected to the Schmid and Leiman (1957) procedure using MacOrtho (Watkins, 2004). Results showed that the largest portions of total and common variance were accounted for by the second-order, global ('g') factor and interpretation of the SB-5 should focus primarily, if not exclusively, on the general, Full Scale IQ. No evidence for a five-factor solution was found. (PsycINFO Database Record (c) 2010 APA, all rights reserved)