Defect Structure of β NiAl Using the BFS Method for Alloys

1995 ◽  
Vol 408 ◽  
Author(s):  
Guillermo Bozzolo ◽  
Carlos Amador ◽  
John Ferrante ◽  
Ronald D Noebe
Keyword(s):  
Point Defects ◽  
Stoichiometric Composition ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
New Approach ◽  
Al Content ◽  
Steep Decrease ◽  
Basic Features ◽  
And Behavior ◽  
Rich Side

AbstractThe semiempirical BFS method for alloys is generalized by replacing experimental input with firstprinciples results thus allowing for the study of complex systems. In order to examine trends and behavior of a system in the vicinity of a given point of the phase diagram a search procedure based on a sampling of selected configurations is employed. This new approach is applied to the study of the/3 phase of the Ni-Al system, which exists over a range of composition from 45–60 at. % Ni. This methodology results in a straightforward and economical way of reproducing and understanding the basic features of this system. At the stoichiometric composition, NiAl should exist in a perfectly ordered B2 structure. Ni-rich alloys are characterized by antisite point defects (with Ni atoms in the Al sites) with a decrease in lattice parameters. On the Al-rich side of stoichiometry there is a steep decrease in lattice parameter and density with increasing Al content. The presence of vacancies in Ni sites would explain such behavior. Recent X-ray diffraction experiments suggest a richer structure: the evidence, while strongly favoring the presence of vacancies in Ni sites, also suggests the possibility of some vacancies in Al sites in a 3:1 ratio. Moreover, local ordering of vacant sites may be preferred over a random distribution of individual point defects.

Pt3Ga: Thermodynamics and Nonstoichiometry

2004 ◽  
Vol 59 (9) ◽  
pp. 999-1005 ◽  
Author(s):  
Agnes Schweitzer ◽  
Yongzhang Huang ◽  
Wenxia Yuan ◽  
Zhiyu Qiao ◽  
Olga Semenova ◽  
...  
Keyword(s):  
Intermetallic Compound ◽  
Point Defects ◽  
Stoichiometric Composition ◽  
Lattice Parameter ◽  
Emf Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
Fitting Procedure ◽  
Activity Measurements ◽  
Disorder Parameter

Thermodynamic activities of gallium were measured between about 1000 and 1300 K in the nonstoichiometric intermetallic compound Pt3Ga using an emf-method based on an oxygen conducting solid electrolyte. The variation of the lattice parameter with composition was determined by powder X-ray diffraction. The results of the activity measurements are interpreted in terms of a statisticalthermodynamic model for L12-phases considering four types of point defects, i. e. anti-structure atoms and vacancies on the platinum and gallium substructures. The energies of formation of the point defects at the stoichiometric composition are estimated from a curve fitting procedure yielding Ef(PtGa) = Ef(GaPt) = 1.25 eV, assuming that Ef(VPt) = Ef(VGa) = 2.0 eV. This results in a disorder parameter α’ = 3 · 10−6 at 1173 K which means that at the stoichiometric composition 0.0012% of the gallium substructure sites are occupied by platinum atoms and 0.0004% of the platinum sites by gallium atoms at this temperature.

Phase selection in precursor-derived yttrium aluminum garnet and related Al2O3–Y2O3 compositions

2005 ◽  
Vol 20 (4) ◽  
pp. 1017-1025 ◽  
Author(s):  
Ashutosh S. Gandhi ◽  
Carlos G. Levi
Keyword(s):  
Heat Treatment ◽  
Yttrium Aluminum Garnet ◽  
Lattice Parameter ◽  
Defect Structures ◽  
X Ray Diffraction ◽  
Phase Selection ◽  
X Ray ◽  
Yttrium Aluminum ◽  
Rich Side ◽  
Nitrate Solutions

Al2O3–Y2O3 powders were synthesized in the range of 25–55% Y2O3 by reverse coprecipitation of nitrate solutions. All starting powders were amorphous and formed primary yttrium aluminum garnet (YAG) upon crystallization. X-ray diffraction detected only garnet in compositions of 30–40% Y2O3 after heat treatment at 1250 °C. Compositions of 45–55% Y2O3 established a metastable YAG + Y4Al2O9 microstructure. The YAG phase field was metastably extended away from its stoichiometry, as indicated by a systematic increase in lattice parameter with Y2O3 content. Although some Al2O3 enrichment was achieved, YAG appears to tolerate greater off-stoichiometry on the Y2O3-rich side. Possible defect structures accommodating the solubility extension were examined. Phase selection results indicate that compositional inhomogeneity is not the only reason behind the appearance of hexagonal YAlO3, which is frequently reported during YAG synthesis.

Damage and Lattice Strain in Ion-Irradiated AlxGai-xAs

1994 ◽  
Vol 354 ◽  
Author(s):  
P. Partyka ◽  
R.S. Averback ◽  
D.V. Forbes ◽  
J.J. Coleman ◽  
P. Ehrhart ◽  
...  
Keyword(s):  
Rutherford Backscattering Spectrometry ◽  
Lattice Parameter ◽  
Large Strains ◽  
X Ray Diffraction ◽  
Al Content ◽  
Plane Lattice ◽  
Transmission Electron ◽  
Out Of Plane ◽  
Radiation Induced ◽  
High Al Content

AbstractRadiation-induced damage and strain in AlxGai-xAs (x=5 to 1) were investigated by measurements of the lattice parameter using x-ray diffraction. Irradiations employed MeV C, Ar and Au ion beams with a substrate temperature of 80 K. For samples with high Al content, the out-of-plane lattice parameter increased with fluence at low doses, saturated, and then decreased to nearly its original value. The in-plane lattice parameter did not change, throughout. These results were independent of the irradiation particle when scaled by damage energy. For the Al.5Ga.5As samples, however, the out-of-plane lattice parameter increased monotonically with dose to large strains until the layer amorpnized. Selected samples were examined by high resolution and conventional transmission electron microscopy (TEM). Channeling Rutherford backscattering spectrometry (CRBS) was also employed to monitor the buildup of damage in many samples. Recovery of the lattice parameter during subsequent thermal annealing was also investigated.

In situX-ray diffraction study of point defects in neptunium dioxide at elevated temperature

2014 ◽  
Vol 47 (3) ◽  
pp. 1008-1015 ◽  
Author(s):  
M. Chollet ◽  
J. Léchelle ◽  
R. C. Belin ◽  
J.-C. Richaud
Keyword(s):  
Elevated Temperature ◽  
Point Defects ◽  
Chemical Reduction ◽  
Atomic Displacement ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
Neptunium Dioxide ◽  
Atomic Displacement Parameters ◽  
First Time ◽  
Energy Of Formation

High-temperature X-ray diffraction measurements have been performed on neptunium dioxide up to 2000 K for the first time under He, He/5%H2and air atmospheres. Up to 1643 K, NpO2remains stoichiometric under all the considered atmospheres, and the coefficients of thermal expansion have been evaluated. Above 1643 K, the lattice parameter departs from linearity towards higher values. The atomic displacement parameters of the O and Np atoms were determined from Rietveld refinement and the Debye temperature subsequently obtained. This was used to study the contribution of point defects to the evolution of the lattice parameter at elevated temperature by estimating the energy of formation of vacancies. It is shown that only the chemical reduction of NpO2to NpO2−xis responsible for the departure from linearity below 1750 K. Above this temperature, the evolution is due to the simultaneous effect of reduction and the formation of oxygen Frenkel pairs.

Microstructure and Mechanical Properties of Cr1-xAlxN Coating

2012 ◽  
Vol 531 ◽  
pp. 3-6
Author(s):  
C.L. Zhong ◽  
L.E. Luo
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
Magnetron Sputtering ◽  
Lattice Parameter ◽  
Reactive Magnetron ◽  
X Ray Diffraction ◽  
X Ray ◽  
Al Content ◽  
Compound Coating ◽  
Cubic Structure

A series of Cr1-xAlxN coatings were deposited by reactive magnetron sputtering. The content, microstructure and the hardness of the thin films were characterized respectively with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and nanoindentor. The effect of Al content on the microstructure and hardness was studied. It was found that Cr1-xAlxN compound coating exhibits a cubic structure with (1 1 1) preferred orientations and that the lattice parameter of Cr1-xAlxN coatings decrease with the increase of Al content. The hardness of Cr1-xAlxN compound coating is higher than that of CrN and increases with the increase of Al content.

Structural Transformations During the Mechanical Alloying of Nickel and Ruthenium Elemental Powders

1990 ◽  
Vol 205 ◽  
Author(s):  
A. Van Neste ◽  
S. Kaliaguine ◽  
M. Trudeau ◽  
R. Schulz
Keyword(s):  
Structural Evolution ◽  
High Energy ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Fcc Lattice ◽  
Hcp Structure ◽  
The One ◽  
Rich Side ◽  
Fcc Structure

AbstractThe structural evolution of a mixture of elemental Ni and Ru powders during high energy ball milling has been studied as a function of milling time using X-ray diffraction and transmission electron microscopy. On the Ni-rich side of the phase diagram (Ni70Ru30) we observe, during the milling, the diffusion of Ru in the Ni and an expansion of the Ni fcc lattice. After about 20 hours of milling, all the Ru has diffused into the Ni and we are left with an oversaturated Ni(Ru) fcc structure with a lattice parameter about 3.6% larger than the one of pure Ni. The Ni does not seem to diffuse into Ru during the process. On the Ru-rich side (Ni43Ru57) we observe initially the same diffusion process taking place but more rapidly. After about 8 hours of milling, the incorporation of Ru in the Ni has driven the fcc Ni lattice to its limit of stability (about 3.9% expansion) and the fcc structure transforms, upon further milling, into a new hcp structure. In the later stage of the process the remaining Ru diffuses into this new phase.

Martensitic Transformation of TiAu Shape Memory Alloys

2007 ◽  
Vol 561-565 ◽  
pp. 1541-1544 ◽  
Author(s):  
Hideki Hosoda ◽  
Ryosuke Tachi ◽  
Tomonari Inamura ◽  
Kenji Wakashima ◽  
Shuichi Miyazaki
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory ◽  
Parent Phase ◽  
Stoichiometric Composition ◽  
Transformation Strain ◽  
Martensite Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Rich Side

Martensitic transformation temperatures were measured and transformation strains were evaluated in a promising high temperature shape memory alloy TiAu with a compositional range from 46 to 53mol%Au. It was found by differential scanning calorimetry that martensitic transformation start temperature (Ms) is kept almost constant value of 880K in the Au-rich side of the stoichiometric composition. On the other hand, Ms decreases monotonically with decreasing Au content in the Au-poor side. X-ray diffraction analysis revealed that apparent phase of all the alloys at room temperature is B19 martensite phase. Under an assumption that the atomic volume is constant during martensitic transformation, the lattice parameters of B2 parent phase and maximum transformation strain were calculated. It was found that the maximum transformation strain depends on chemical composition and that it reaches 10.75% for Ti-53mol%Au alloy. The value is comparable to that of Ti-Ni.

Powder x-ray diffraction study of a cryptomelane-type manganic acid and its alkali cation exchanged forms

1993 ◽  
Vol 8 (12) ◽  
pp. 3145-3150 ◽  
Author(s):  
Masamichi Tsuji ◽  
Sridhar Komarneni
Keyword(s):  
Cation Exchange ◽  
Cation Exchange Capacity ◽  
Lattice Parameter ◽  
Exchange Capacity ◽  
Alkali Cation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Steep Decrease ◽  
Exchange Properties ◽  
Good Agreement

Cryptomelane-type manganic acid (CMA), H2Mn8O16 · 2.4H2O, with a theoretical cation exchange capacity of 2.70 meq/g, was prepared and its cation exchange properties were studied as a function of XM which is defined by the ratio of uptake in meq/g to the theoretical capacity. Plots of the corrected selectivity coefficients log KHM vs the fractional exchange M for alkali metal ions on a 2 × 2 type tunnel-structured manganic acid showed a gradual decrease in small XMM regions and a steep decrease in large XMM) were 0.92 for Li+, 0.74 for Na+ and K+, 0.67 for Rb+, and 0.44 for Cs+. These maximums have been attributed to steric limitation as well as a limit on the expansion of the crystal lattice. Some x-ray diffraction (XRD) data of alkali cation exchanged forms were in good agreement with the XRD data of synthetic alkali CMA phases as given in the cards by the Joint Committee on Powder Diffraction Standards (JCPDS). The lattice parameter a0 has been found to depend on the exchanged amounts and the nature of the cations involved, while the c0 value remained almost the same irrespective of the amount of exchange or the nature of the cations.

X-ray diffraction study of the effect of boron on lattice properties of Ni76Al24

1993 ◽  
Vol 8 (4) ◽  
pp. 741-744 ◽  
Author(s):  
Mohan P.V. Rao ◽  
Murthy K. Satyanarayana ◽  
S.V. Suryanarayana ◽  
Naidu S.V. Nagender
Keyword(s):  
Diffraction Study ◽  
Single Phase ◽  
Lattice Parameter ◽  
Small Addition ◽  
X Ray Diffraction ◽  
Fault Probability ◽  
Two Phase ◽  
X Ray ◽  
Al Content ◽  
Stacking Fault Probability

A small addition of boron is suggested to increase the ductility of the polycrystalline Ni3Al when the Al content is less than 25 at.%. Both metallographic and x-ray investigation have shown the alloys of Ni3Al (24 at.% Al) containing 0.20, 0.42, 0.79, 0.98, and 1.22 at.% B to be of single phase and that of 1.76 at.% B to be of two phase. With the addition of boron, the lattice parameter of the Ni3Al phase is found to increase. Microhardness measurements indicate that initially the hardness decreases for the alloy of 0.20 at.% B, while for the rest of the single phase alloys the hardness is found to increase with further addition of boron. The addition of boron increases the deformation stacking fault probability value except for the alloy with 0.20 at.% B.

Microstructure and Mechanical Properties of Ti1-xAlxN Thin Films

2012 ◽  
Vol 534 ◽  
pp. 93-96
Author(s):  
C.L. Zhong ◽  
P.A. Wei ◽  
L.E. Luo
Keyword(s):  
Thin Films ◽  
Lattice Parameter ◽  
Reactive Magnetron ◽  
X Ray Diffraction ◽  
X Ray ◽  
Al Content ◽  
Heat Treated ◽  
High Microhardness ◽  
Cubic Structure ◽  
Heat Treated Temperature

A series of Ti1-xAlxN thin films were deposited by reactive magnetron sputtering. The content, microstructure and the hardness of the thin films were characterized respectively with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and nanoindentor. The effect of Al content on the microstructure and hardness was studied. It was found that Ti1-xAlxN compound thin films exhibits a cubic structure with (1 1 1) preferred orientations and that the lattice parameter of Ti1-xAlxN thin films decrease with the increase of Al content. The hardness of Ti1-x AlxN compound thin films is higher than that of TiN and increases with the increase of Al content. At the heat-treated temperature T = 600 °C, the Ti1-xAlxN thin films is still of high microhardness.

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