scholarly journals Temperature Dependence of the γ/γ′ Interfacial Energy in Binary Ni–Al Alloys

2021 ◽  
Author(s):  
Alan J. Ardell
Keyword(s):  
Temperature Dependence ◽  
Comprehensive Evaluation ◽  
Chemical Diffusion ◽  
Interfacial Free Energy ◽  
Al Alloys ◽  
Published Data ◽  
Liquid Region ◽  
Theoretical Predictions ◽  
Coarsening Kinetics ◽  
Increasing Temperature

AbstractPublished data on the coarsening kinetics of γ′ (Ni3Al) precipitates in binary Ni–Al alloys aged at 12 temperatures ranging from 773 K to 1073 K are analyzed to provide a comprehensive evaluation of the temperature dependence of the γ/γ′ interfacial free energy, σ. The data are analyzed using equations of the trans-interface-diffusion-controlled (TIDC) theory of coarsening, with temporal exponent n = 2.4. The results show that σ decreases with increasing temperature, T. A linear empirical equation is fitted to the data on σvsT; it extrapolates to σ = 0 in the liquid region of the Ni–Al phase diagram, as it should do. A quantitative temperature-dependent transition radius, rtrans, is calculated; it depends on the product of the interface width and the ratio of the chemical diffusion coefficients in the γ phase and interface regions. Applying the TIDC coarsening equations to calculate σ is justified when the average radius, 〈r〉, satisfies the condition 〈r〉 < rtrans, which is valid for all the data used in the fit. The data on σvsT are compared with theoretical predictions. The results are discussed in the context of previous work, as well as with values of σ obtained through analyses using the equations of traditional LSW coarsening kinetics, n = 3.

scholarly journals Roles of the semisolid heating on the microstructure of a hypereutectic Al–Fe–Cu alloy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Wei Wang ◽  
Bo Liu
Keyword(s):  
Volume Fraction ◽  
High Volume ◽  
Holding Time ◽  
Second Phase ◽  
Liquid Region ◽  
Cu Alloy ◽  
Initial Stage ◽  
Coarsening Kinetics ◽  
Increasing Temperature ◽  
Solid Liquid

AbstractA hypereutectic Al–Fe–Cu alloy with a high-volume fraction ferro-aluminum second phase (AlFe phases for short) was reheated in the solid–liquid region and the microstructure evolution was investigated. During semisolid heating, the high-melting AlFe phases in the Al–Fe–Cu alloy were demonstrated to stunt the grain growth and to block the liquid coalescing and the solid moving. Consequently, the grain sizes in the alloy increased rapidly and then slowly with increasing holding time, and the grains increased gradually with increasing temperature. Smaller grain grew into the large grain but it did not continually grow into the larger grain with increasing temperature or holding time. The shape factor (SF) of the alloy increased gradually and then decreased quickly with increasing temperature or holding time. The major alloying elements in addition to magnesium in the hypereutectic Al–Fe–Cu alloy were finally enriched at the grain boundaries or around the AlFe phases. Besides dissolving in the grains or AlFe phases, copper also diffused between the grains or around AlFe phases, resulting in the formation of diverse Cu-enriched zones. Cu constituents in the inter-grains are outnumbered in the intra-grains. The coarsening kinetics of the alloy was controlled by grain boundary diffusion. The coarsening rate constants K in the initial stage of heating (5–20 min) were several times larger than that in the later stage of heating (20–60 min), indicating the blocking effect of AlFe phases on coarsened grain being obvious.

Polydomain Structure of Epitaxial PbTiO3 films on MgO

1997 ◽  
Vol 493 ◽  
Author(s):  
S. P. Alpay ◽  
A. S. Prakash ◽  
S. Aggarwal ◽  
R. Ramesh ◽  
A. L. Roytburd ◽  
...  
Keyword(s):  
Domain Structure ◽  
Pulsed Laser ◽  
Laser Deposition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Theoretical Predictions ◽  
The Stability ◽  
Increasing Temperature ◽  
Stable Domains ◽  
Domain Stability

ABSTRACTA PbTiO3(001) film grown on MgO(001) by pulsed laser deposition is examined as an example to demonstrate the applications of the domain stability map for epitaxial perovskite films which shows regions of stable domains and fractions of domains in a polydomain structure. X-ray diffraction studies indicate that the film has a …c/a/c/a… domain structure in a temperature range of °C to 400°C with the fraction of c-domains decreasing with increasing temperature. These experimental results are in excellent agreement with theoretical predictions based on the stability map.

Article

1998 ◽  
Vol 76 (4) ◽  
pp. 411-413
Author(s):  
Yixing Zhao ◽  
Gordon R Freeman
Keyword(s):  
Absorption Spectrum ◽  
Optical Absorption ◽  
Temperature Dependence ◽  
Optical Absorption Spectrum ◽  
Infrared Light ◽  
Solvated Electron ◽  
Solvated Electrons ◽  
Tert Butanol ◽  
Solvent Dependence ◽  
Increasing Temperature

The energy and asymmetry of the optical absorption spectrum of solvated electrons, es- , change in a nonlinear fashion on changing the solvent through the series HOH, CH3OH, CH3CH3OH, (CH3)2CHOH, (CH3)3COH. The ultimate, quantum-statistical mechanical, interpretation of solvated electron spectra is needed to describe the solvent dependence. The previously reported optical spectrum of es- in tert-butanol was somewhat inaccurate, due to a small amount of water in the alcohol and to limitations of the infrared light detector. The present note records the remeasured spectrum and its temperature dependence. The value of the energy at the absorption maximum (EAmax) is 155 zJ (0.97 eV) at 299 K and 112 zJ (0.70 eV) at 338 K; the corresponding values of G epsilon max (10-22 m2 aJ-1) are 1.06 and 0.74. These unusually large changes are attributed to the abnormally rapid decrease of dielectric permittivity of tert-butanol with increasing temperature. The band asymmetry at 299 K is Wb/Wr = 1.8.Key words: optical absorption spectrum, solvated electron, solvent effects, tert-butanol, temperature dependence.

Temperature Dependence of the Diffusivity–Mobility Ratio in Degenerate Semiconductors in the Presence of a Large Magnetic Field

1973 ◽  
Vol 51 (4) ◽  
pp. 491-492 ◽  
Author(s):  
A. N. Chakravarti ◽  
D. P. Parui
Keyword(s):  
Magnetic Field ◽  
Temperature Dependence ◽  
Low Temperatures ◽  
Mobility Ratio ◽  
Degenerate Semiconductors ◽  
Large Magnetic Field ◽  
Increasing Temperature

The diffusivity–mobility ratio in degenerate semiconductors in the presence of a large magnetic field is found to increase with increasing temperature at a rate which is dependent on temperature at relatively low temperatures. It is also found that, at any given temperature, the ratio is increased by the application of the field.

scholarly journals Temperature dependence of the specific heat and thermodynamic functions AК1М2 alloy, doped strontium

2019 ◽  
Vol 21 (1) ◽  
pp. 35-42 ◽  
Author(s):  
I. N. Ganiev ◽  
S. E. Otajonov ◽  
N. F. Ibrohimov ◽  
M. Mahmudov
Keyword(s):  
Heat Capacity ◽  
Gibbs Energy ◽  
Specific Heat ◽  
Temperature Dependence ◽  
Specific Heat Capacity ◽  
Thermodynamic Functions ◽  
Inverse Relationship ◽  
Alloying Element ◽  
Enthalpy And Entropy ◽  
Increasing Temperature

In the heat «cooling» investigated the temperature dependence of the specific heat capacity and thermodynamic functions doped strontium alloy AK1М2 in the range 298,15—900 K. Mathematical models are obtained that describe the change in these properties of alloys in the temperature range 298.15—900 K, as well as on the concentration of the doping component. It was found that with increasing temperature, specific heat capacity, enthalpy and entropy alloys increase, and the concentration up to 0.5 wt.% of the alloying element decreases. Gibbs energy values have an inverse relationship, i.e., temperature — decreases the content of alloying component — is up to 0.5 wt.% growing.

What Determines the Peak-Temperature in Binary Ni3Al?

1994 ◽  
Vol 364 ◽  
Author(s):  
C. Rentenberger Karnthaler ◽  
H.P. Karnthaler
Keyword(s):  
Maximum Stress ◽  
Dynamic Recovery ◽  
Al Alloys ◽  
Shear Stresses ◽  
Compression Axis ◽  
Pronounced Change ◽  
Diffusion Controlled ◽  
Ordered Alloys ◽  
Multiple Cross ◽  
Increasing Temperature

AbstractIn Ni3Al alloys the yield stress increases with increasing temperature up to a maximum stress, reached at the temperature TP. Below TP glide occurs on primary octahedral planes whereas above TP glide on primary cube planes is dominating. Therefore this change of glide planes was considered to determine TP.TEM investigations were carried out to study the mechanisms that control TP in Ni3Al specimens with [001] compression axis. In this case no shear stresses are acting on any of the cube glide systems. The TEM results show a pronounced change of the dislocation structure on the {111} glide planes below and above the peak. The breakdown of the barriers (locked screw dipoles) starts when the diffusion is high enough to facilitate their annihilation. The dynamic recovery of the locked screws occurs by multiple cross-slip via octahedral planes. It is proposed that, in this and other ordered alloys, the value of TP is diffusion controlled.

Thermoelectric Transport Properties of Individual Bismuth Nanowires

2001 ◽  
Vol 691 ◽  
Author(s):  
Stephen B. Cronin ◽  
Yu-Ming Lin ◽  
Oded Rabin ◽  
Marcie R. Black ◽  
Gene Dresselhaus ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Point Contacts ◽  
Large Spread ◽  
Thermoelectric Transport Properties ◽  
Bismuth Nanowires ◽  
Increasing Temperature ◽  
Magneto Resistance

ABSTRACTWe developed a method for making 4-point contacts to Bi nanowires with a thick oxide coat using a combination of lithographic and focused ion beam (FIB) techniques. The resistivity of Bi nanowires with diameters in the range 70-200nm is found to increase with decreasing wire diameter. In contrast to bulk Bi, the temperature dependence of the resistivity is found to decrease monotonically with increasing temperature. The results are explained on the basis of increased scattering in the nanowire and the known temperature dependence of the electronic properties of bulk Bi. A large magneto-resistance was also measured, indicating a high crystalline quality of the nanowires. A large spread in the measured values of the resistivity indicates significant systematic error in the measurement technique. Possible sources for error are discussed.

Temperature Dependence of Impurity Induced EFG's in Extremely Diluted CuB

1994 ◽  
Vol 49 (1-2) ◽  
pp. 354-360 ◽  
Author(s):  
G. Sulzer ◽  
B. Ittermann ◽  
E. Diehl ◽  
B. Fischer ◽  
H.-P. Frank ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Temperature Behaviour ◽  
Nmr Method ◽  
Increasing Temperature ◽  
Lattice Locations

Abstract The temperature dependence of impurity induced EFG 's around implanted 12B ions in Cu was measured for two lattice locations using the β-NMR method. The induced EFG at the nearest neighbouring host atoms decreases with increasing temperature for the case of 12B stopped on interstitial sites, whereas the opposite temperature behaviour was found if 12B is situated in substi­tutional sites.

scholarly journals Protein aggregation in C-phycocyanin. Studies at very low concentrations with the photoelectric scanner of the ultracentrifuge

1971 ◽  
Vol 122 (4) ◽  
pp. 421-426 ◽  
Author(s):  
R. MacColl ◽  
J. J. Lee ◽  
D. S. Berns
Keyword(s):  
Protein Aggregation ◽  
Temperature Dependence ◽  
Equilibrium Constant ◽  
Ph Dependence ◽  
Sedimentation Velocity ◽  
Scanning System ◽  
High Concentration ◽  
Low Concentrations ◽  
Increasing Temperature ◽  
Schlieren Optics

Solutions of C-phycocyanin of very low concentrations were examined by sedimentation-velocity studies in the Spinco model E ultracentrifuge equipped with a photoelectric scanning system and a monochromator. At sufficiently low concentrations complete disaggregation from the hexamer to the monomer was observed. The equilibrium constant of monomer to hexamer was estimated to be approx. 1030. For studies of aggregation over the complete range of concentration, C-phycocyanins from Phormidium luridum and Lyngbya sp. were used. Sedimentation-velocity studies at high concentration with schlieren optics are reported for C-phycocyanins from Anabaena variabilis and Lyngbya sp. The pH-dependence of aggregation and the temperature-dependence of trimer–hexamer equilibrium for phycocyanins from these algae were found to be similar to those of other C-phycocyanins. The principal feature of the pH-dependence is the dominance of hexamers at the isoelectric point. Increasing temperature increased the amount of hexamer and decreased the amount of trimer.

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