Constants Of Alloys Research Articles

Elastic Properties of B2-NiAl with W addition: A first-principles study

The effect of tungsten alloying on the elastic properties of B2-NiAl at low-temperature and high-temperature distribution of W atoms on sublattices. By means of the exact muffin-tin orbitals method in conjunction with the coherent potential approximation, the constants C11,C12,C44, Young's modulus E, shear modulus G, Cauchy pressure values, G/B ratios are calculated. Using phenomenological criteria of the correlation between ductility and elastic properties of solution phases, it has been shown that the addition of tungsten could yield improved ductility for B2-NiAl in both types of alloys. It is established that with the high-temperature distribution of W atoms on the Al sublattice, there is a loss of mechanical stability and a decrease in mechanical properties with increasing W concentration. In alloys with a low-temperature distribution of tungsten atoms between Al and Ni sites a unique combination of properties occurs: in addition to the ductility enhancement, a simultaneous increase of the elastic constants C44 and C11 and C11, shear modulus G, Young's modulus E with increasing W content is observed. The differences in the behavior of elastic constants in alloys with different types of tungsten distribution on NiAl sublattices are analyzed by calculating the density of electronic states. Keywords: NiAl, alloying elements, tungsten, elastic properties, ductility, first-principles calculations.

Упругие свойства B2-NiAl с добавлением W: исследование из первых принципов

The effect of tungsten alloying on the elastic properties of B2 NiAl at low-temperature and high-temperature distribution of W atoms on sublattices. By means of the exact muffin-tin orbitals method in conjunction with the coherent potential approximation, the constants C11, C12, C44, Young's modulus E, shear modulus G, Cauchy pressure values, G/B ratios are calculated. Using phenomenological criteria of the correlation between ductility and elastic properties of solution phases, it has been shown that the addition of tungsten could yield improved ductility for B2 NiAl in both types of alloys. It is established that with the high-temperature distribution of W atoms on the Al sublattice, there is a loss of mechanical stability and a decrease in mechanical properties with increasing W concentration. In alloys with a low–temperature distribution of tungsten atoms between Al and Ni sites a unique combination of properties occurs: in addition to the ductility enhancement, a simultaneous increase of the elastic constants C44 and C11, shear modulus G, Young modulus E with increasing W content is observed. The differences in the behavior of elastic constants in alloys with different types of tungsten distribution on NiAl sublattices are analyzed by calculating the density of electronic states.

Interplay of force constants in the lattice dynamics of disordered alloys: Anab initiostudy

A reliable prediction of interatomic force constants in disordered alloys is an outstanding problem. This is due to the need for a proper treatment of multisite (atleast pair) correlation within a random environment. The situation becomes even more challenging for systems with large difference in atomic size and mass. We propose a systematic density functional theory (DFT) based study to predict the ab-initio force constants in random alloys. The method is based on a marriage between special quasirandom structures (SQS) and the augmented space recursion (ASR) to calculate phonon spectra, density of states (DOS) etc. bcc TaW and fcc NiPt alloys are considered as the two distinct test cases. Ta-Ta (W-W) bond distance in the alloy is predicted to be smaller (larger) than those in pure Ta (W), which, in turn, yields stiffer (softer) force constants for Ta (W). Pt-Pt force constants in the alloy, however, are predicted to be softer compared to Ni-Ni, due to a large bond distance of the former. Our calculated force constants, phonon spectra and DOS are compared with experiments and other theoretical results, wherever available. Correct trend of present results for the two alloys pave a path for further future studies in more complex alloy systems.

Material Constants of TC18 Titanium Alloy Deformated in α+β Region

The hot deformation behavior of TC18 titanium alloy was studied in alpha-beta phase region. The temperature range was 1023-1123K and strain rate range 1-0.001-1s-1. The material constants of the alloy, including deformation activation energy ΔH as 364.823kJ / mol, stress-level coefficient α as 0.0086mm2/ N, stress exponential n as 3.8442 and structural factor A as 1.2601×1015s–1 were derived by Zener-Hollomon method from the interdependencies of flow stress, strain rate and temperature

Extrapolative procedures in modelling and simulations: the role of instabilities

In modelling and simulations there is a risk that one extrapolates into a region where the model is not valid. In this context instabilities are of particular interest, since they can arise without any precursors. This paper discusses instabilities encountered in the field of materials science, with emphasis on effects related to the vibrations of atoms. Examples deal with, i.a., common lattice structures being either metastable or mechanically unstable, negative elastic constants that imply an instability, unexpected variations in the composition dependence of elastic constants in alloys, and mechanisms governing the ultimate strength of perfect crystals.

Phonons in disordered alloys: Comparison between augmented-space-based approximations for configuration averaging to integration from first principles

A first principles density functional based linear response theory (the so called Density Functional Perturbation theory \cite{dfpt}) has been combined separately with two recently developed formalism for a systematic study of the lattice dynamics in disordered binary alloys. The two formalisms are the Augmented space recursion (ASR) and the Itinerant coherent potential approximation (ICPA). The two different theories (DFPT-ASR and DFPT-ICPA) systematically provides a hierarchy of improvements upon the earlier single site based theories (like CPA etc.) and includes non-local correlations in the disorder configurations. The formalisms explicitly take into account fluctuations in masses, force constants and scattering lengths. The combination of DFPT with these formulation helps in understanding the actual interplay of force constants in alloys. We illustrate the methods by applying to a fcc Fe$_{50}$Pd$_{50}$ alloy.

Condensed state physics elastic constants of alkali metal alloys

The second-and third-order Brogger elastic constants of the disordered Cs-K, Cs-Rb, and Rb-K alloys with different concentrations of the second component are calculated for the pseudopotential model with the use of the Krasko-Gurskii model potential. Results of calculations are in good qualitative agreement with the available experimental data on the elastic constants of alloys.

Elastic Constants of Alloys Measured with Neutron Diffraction

AbstractElastic constants as a function of crystallographic direction have been measured in polycrystalline alloy samples of 17-4PH stainless steel, Ni-Cr-Fe, and Ti-6%AI-4%V using a neutron diffraction technique. The results compare best with the constant stress model of Reuss. It is demonstrated that measurements of stress can be made sampling the bulk of the material using neutrons with an accuracy comparable to more conventional x-ray methods.

The effect of self-irradiation on the lattice constants of alloys of plutonium in alpha-uranium

The effect of self-irradiation on the lattice constants of alloys of plutonium in alpha-uranium

XIX. The hall effect and some other physical constants of alloys

XIX. The hall effect and some other physical constants of alloys

The theoretical interpretation of the optical constants of copper-zinc alloys

The results of the experiments of Lowery, Wilkinson and Smare on the optical constants of alloys of copper and zinc (α, β and γ brass) are discussed from the point of view of the electric theory of metals.

XXXIII.The hall effect and some other physical constants of alloys.—Part V.The antimony-silver series

XXXIII.<i>The hall effect and some other physical constants of alloys</i>.—Part V.<i>The antimony-silver series</i>

LXI.The hall effect and some other physical constants of alloys.—Part IV. The bismuth-cadmium series of alloys

(1935). LXI. The hall effect and some other physical constants of alloys.—Part IV. The bismuth-cadmium series of alloys. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 19, No. 128, pp. 773-787.

V.The hall effect and some other physical constants of alloys. Part II.—The tin-bismuth series of alloys

V.<i>The hall effect and some other physical constants of alloys</i>. Part II.—<i>The tin-bismuth series of alloys</i>

XXVII.The Hall effect and some other physical constants of alloys.—Part I.The lead-bismuth series of alloys

XXVII.<i>The Hall effect and some other physical constants of alloys</i>.—Part I.<i>The lead-bismuth series of alloys</i>