The early stages of phase formation during mechanical alloying of Ti–Al

1994 ◽  
Vol 9 (1) ◽  
pp. 47-52 ◽  
Author(s):  
T. Klassen ◽  
M. Oehring ◽  
R. Bormann
Keyword(s):  
Mechanical Alloying ◽  
Phase Formation ◽  
X Ray Diffraction ◽  
Annealing Behavior ◽  
Early Stages ◽  
Transmission Electron ◽  
Fcc Phase ◽  
Multilayered Thin Films ◽  
Kinetics Of ◽  
Structural Disordering

The early stages of phase formation during mechanical alloying of Ti/Al powder blends were investigated using x-ray diffraction and transmission electron microscopy. After the initial formation of an hep solid solution by the diffusion of Al into Ti, the first phase nucleated at the Ti/Al interface is a (partially) Ll2-ordered fcc phase with a crystallite size of about 10–30 nm. This observation is ascribed to the kinetics of phase formation and the energetic destabilization of the equilibrium intermetallic compounds during milling due to chemical and structural disordering. A mechanism of phase formation during mechanical alloying is proposed, and comparisons are made with the thermal annealing behavior of Ti/Al multilayered thin films.

Evolution of the two-phase microstructure L12 + DO22 in near-eutectoid Ni3(Al,V) alloy

1994 ◽  
Vol 9 (12) ◽  
pp. 3068-3082 ◽  
Author(s):  
L.A. Bendersky ◽  
F.S. Biancaniello ◽  
M.E. Williams
Keyword(s):  
Stage Iv ◽  
High Angle ◽  
X Ray Diffraction ◽  
Two Phase ◽  
Fast Kinetics ◽  
X Ray ◽  
Transmission Electron ◽  
Discontinuous Coarsening ◽  
Fcc Phase ◽  
Kinetics Of

Transmission electron microscopy and powder x-ray diffraction methods have been used to investigate the evolution of two-phase (L12 + DO22) microstructures from the quenched fcc phase of the Ni-5Al-20V (at. %) alloy. The microstructure after annealing in a temperature range from 650 to 900 °C differs from the eutectoid structure which might be expected for the alloy according to the eutectoid-type phase diagram of the Ni3Al-Ni3V section. This structure results from fast kinetics of ordering in the fcc → L12 and fcc → DO22 phase transitions. Four main stages in the microstructural evolution were observed. Stage I is the formation of spheroidal coherent L12 clusters in a disordered fcc matrix. During stage II the L12 clusters transform into cuboidal precipitates, and the fcc matrix orders into three DO22 variants (which may have interfaces that are wetted by thin fcc layers). In stage III accommodation of misfit (elastic energy) between different phases and variants occurs by formation of (110) twins or a single variant of the DO22 phase and tetragonally strained lamellae of the L12 phase. Stage IV is a discontinuous coarsening process in which a coarse incoherent two-phase structure replaces the fine coherent one. Grains of the coarse structure are nucleated on high-angle boundaries of primary fcc or other surfaces. Many of the grains are found twinned.

Icosahedral Phase Formation Domain in Al–Cu–Fe System by Mechanical Alloying

2002 ◽  
Vol 17 (3) ◽  
pp. 653-659 ◽  
Author(s):  
P. Barua ◽  
B. S. Murty ◽  
B. K. Mathur ◽  
V. Srinivas
Keyword(s):  
Mechanical Alloying ◽  
Phase Formation ◽  
Volume Fraction ◽  
Structural Evolution ◽  
Icosahedral Phase ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Metal Ratio ◽  
First Time ◽  
Systematic Composition

A systematic composition dependence study on icosahedral phase (i-phase) formation in the Al–Cu–Fe system has been carried out. Structural evolution during mechanical alloying and on subsequent heat treatment has been investigated by x-ray diffraction and transmission electron microscopy. The i-phase is observed to evolve from the reaction between the Al2Cu and b phases. The influence of the Cu to Fe ratio (RCuFe), Al to transition metal ratio (RAlTM), and the electron to atom ratio (e/a) on the volume fraction of the i-phase has been studied. The analysis of the present results and those published earlier indicates that quasicrystal-forming ability correlates better with the RAlTM and e/a ratios. The volume fraction of the i-phase is maximum when the RAlTM ˜ 2.3 and e/a ratio ˜ 2.0. Formation of the i-phase in Al65Cu25Fe10 by mechanical alloying is reported for the first time.

Temporal Evolution of Bimodal Distribution of γ’ Precipitates in Ni-Al-Mo Alloys under the Influence of Coherency Strains

1995 ◽  
Vol 398 ◽  
Author(s):  
A.D. Sequeira ◽  
H.A. Calderon ◽  
G. Kostorz
Keyword(s):  
Lattice Mismatch ◽  
Bimodal Distribution ◽  
X Ray Diffraction ◽  
Double Step ◽  
Bimodal Size Distribution ◽  
Elastic Fields ◽  
Transmission Electron ◽  
The Matrix ◽  
Kinetics Of ◽  
Coherency Strains

ABSTRACTThe influence of coherency strains produced by the γ-γ’ lattice mismatch, δ, on the decomposition process of Ni-Al-Mo alloys with a bimodal size distribution is presented. Samples with δ ranging from positive to negative, were investigated in a double-step aging procedure. The evolution of the microstructure and the kinetics of coarsening were studied using transmission electron microscopy (TEM). The lattice mismatch between the matrix and the different classes of precipitates was determined by high-resolution high-temperature x-ray diffraction. It is shown that the strain fields produced by the lattice mismatch can influence dramatically the decomposition of metallic alloys. It is suggested that the reduction of the coarsening rate of the large precipitates, the fast coarsening rate of the small precipitates and the distortions detected in the matrix are all direct consequences of the elastic fields produced by the γ-γ’ lattice mismatch.

A Powder Diffractometry Study of γ'-Phase Formation

1991 ◽  
Vol 6 (2) ◽  
pp. 66-69
Author(s):  
S. Ariely ◽  
G. Kimmel ◽  
S. F. Dirnfeld ◽  
M. Bamberger ◽  
B. Prinz
Keyword(s):  
Phase Formation ◽  
Early Stage ◽  
Pure Nickel ◽  
X Ray Diffraction ◽  
Type Alloy ◽  
Optimal Program ◽  
X Ray ◽  
Nickel Base ◽  
Kinetics Of ◽  
Base Superalloy

AbstractThe kinetics of γ'-phase formation in a Ni-base superalloy were studied. The data (pairs of cps and 2θ) were processed by the deconvolution program (Wiedemann, Unnam and Clark, 1987), which was rewritten in FORTRAN and installed on an IBM/VM and a VAX/VMS host computer. Optimal program parameters were found. Pure nickel was used as a standard. The only evidence obtained from the raw data is that the early stage of the aging process is accompanied by broadening. Deconvolution resolved the peaks into three kinds of diffraction lines: Ni(γ), precipitate (γ'), and undefined lines which have been interpreted as satellites. The results show that our X-ray diffraction lines are composed of the main diffraction lines of nickel-base A1 type alloy and additive satellites. In an advanced stage of aging the satellites assume the typical diffraction pattern of γ' phase.

A Model for Formation and Consumption of Transient Phase

2011 ◽  
Vol 172-174 ◽  
pp. 646-651 ◽  
Author(s):  
Gamra Tellouche ◽  
Khalid Hoummada ◽  
Dominique Mangelinck ◽  
Ivan Blum
Keyword(s):  
Differential Scanning Calorimetry ◽  
Phase Formation ◽  
Transient Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Proposed Model ◽  
Transient Phases ◽  
Kinetics Of

The phase formation sequence of Ni silicide for different thicknesses is studied by in situ X ray diffraction and differential scanning calorimetry measurements. The formation of a transient phase is observed during the formation of δ-Ni2Si; transient phases grow and disappear during the growth of another phase. A possible mechanism is proposed for the transient phase formation and consumption. It is applied to the growth and consumption of θ-Ni2Si. A good accordance is found between the proposed model and in situ measurement of the kinetics of phase formation obtained by x-ray diffraction and differential scanning calorimetry for higher thickness.

Reactive phase formation in sputter-deposited Ni/Al multilayer thin films

1997 ◽  
Vol 12 (1) ◽  
pp. 133-146 ◽  
Author(s):  
K. Barmak ◽  
C. Michaelsen ◽  
G. Lucadamo
Keyword(s):  
Phase Formation ◽  
Molar Ratio ◽  
X Ray Diffraction ◽  
Nucleation Kinetics ◽  
Scanning Calorimetry ◽  
Calorimetric Analysis ◽  
Transmission Electron ◽  
Nial Phase ◽  
Magnetron Sputter ◽  
Sputter Deposited

We have investigated reactive phase formation in magnetron sputter-deposited NiyAl multilayer films with a 1 : 3 molar ratio and various periodicities, L, ranging from 320 nm down to a codeposited film with zero effective periodicity. The films were studied by x-ray diffraction, differential scanning calorimetry, electrical resistance measurements, and transmission electron microscopy. We find that Ni and Al have reacted during deposition to form the B2 NiAl phase and an amorphous phase. The formation of these phases substantially reduces the driving force for subsequent reactions and explains why nucleation kinetics become important for these reactions. Depending on the periodicity, these reactions result in the formation of NiAl3 or Ni2Al9 followed by NiAl3. Detailed calorimetric analysis reveals differences in the nucleation and growth behavior of NiAl3 compared with other studies.

A structural analysis of the Pd/GaN ohmic contact annealing behavior

2002 ◽  
Vol 743 ◽  
Author(s):  
C. C. Kim ◽  
P. Ruterana ◽  
J. H. Je
Keyword(s):  
Ohmic Contact ◽  
Ohmic Contacts ◽  
Structural Evolution ◽  
Electron Beam Evaporation ◽  
Intermetallic Phases ◽  
X Ray Diffraction ◽  
Annealing Behavior ◽  
X Ray ◽  
Transmission Electron ◽  
The Relationship

AbstractFor ohmic contact on p GaN, palladium is one of the best candidates showing ohmic characteristics already without annealing. To be realized in devices, it is necessary to know the behavior of the ohmic contacts at accelerated conditions, especially for high temperatures and power. We report on the structural evolution of palladium layers (30 nm) deposited on GaN (0001) by electron beam evaporation without intentional annealing. They were next cut into various pieces which were individually submitted to rapid thermal annealing at 400, 500, 600, 700 and 800°C for 10 sec. We investigate the differences in the microstructure and the location of interfacial phases and their relationships as determined by X-ray diffraction and transmission electron microscopy, we then suggest the formation mechanism based on the relationship. It is shown that the interface is disrupted at annealing above 600°C and by 800°C only very small patches of Pd are still present, however they area completely imbedded in a matrix of intermetallic phases (gallides) formed by the reaction with GaN.

Effect of Rb+ -Doping on the Crystallization, Phase Transition and Photocatalytic Activity of Nanosized TiO2 Catalyst

2012 ◽  
Vol 476-478 ◽  
pp. 954-957 ◽  
Author(s):  
Zhao Hui Ni ◽  
Xiao Li Kou ◽  
Xin Yu Ding ◽  
Cun Wang Ge ◽  
Xiao Hui Jing
Keyword(s):  
Photocatalytic Activity ◽  
Methyl Orange ◽  
Surface Area ◽  
Sol Gel ◽  
Rutile Phase ◽  
Bet Surface Area ◽  
X Rays ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Kinetics Of

In order to study the ion effect on titania phase structure, crystallite size, and photocatalytic activity, Rb+-doped TiO2 nanoparticles were prepared via a modified sol-gel method and characterized by means of X-ray diffraction, Energy Dispersive X-rays spectroscopy and transmission electron microscopy. The photocatalytic activity of the elaborated powders was studied following the degradation of methyl orange. The results indicate that doping Rb+ increases the BET surface area of TiO2 crystals, decreases the crystal size, reduces the diminishing rates of surface area with increasing calcinations temperature, raises the temperature at which anatase changes into rutile phase, and so significantly increases the photocatalytic activity of TiO2. The kinetics of the methyl orange degradation fits Langmuir-Hinshelwood kinetics model well.

Transformation kinetics for mullite in kaolin–Al2O3 ceramics

2003 ◽  
Vol 18 (6) ◽  
pp. 1355-1362 ◽  
Author(s):  
Yung-Feng Chen ◽  
Moo-Chin Wang ◽  
Min-Hsiung Hon
Keyword(s):  
Glassy Phase ◽  
Avrami Equation ◽  
Mullite Formation ◽  
Transformation Kinetics ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Energy Dispersion Spectrometry ◽  
Two Stages ◽  
Kinetics Of

Transformation kinetics of mullite formation in kaolin–Al2O3 ceramics was studied by x-ray diffraction, transmission electron microscopy, and energy dispersion spectrometry. The mullitization process of kaolin–Al2O3 ceramics is described by two stages; one is the primary mullite transformation at 1273 to 1573 K, and the other is the secondary mullite formation at 1573 to 1873 K. The activation energy of 1164.6 kJ mol-1 obtained for the secondary mullite formation is lower than 1356.9 kJ mol-1 for the primary mullite transformation by the general form of the Johnson–Mehl–Avrami equation. The lower value of growth morphology parameter strongly supports that in the secondary mullite formation the added alumina is dissolved into glassy phase and the mullite is then precipitated.

Characterization of Nanocrystalline γ–Fe2O3Prepared by Wet Chemical Method

1999 ◽  
Vol 14 (4) ◽  
pp. 1570-1575 ◽  
Author(s):  
G. Ennas ◽  
G. Marongiu ◽  
A. Musinu ◽  
A. Falqui ◽  
P. Ballirano ◽  
...  
Keyword(s):  
Isothermal Treatment ◽  
X Ray Diffraction ◽  
Ferrous Chloride ◽  
Scanning Calorimetry ◽  
Direct Transformation ◽  
X Ray ◽  
Transmission Electron ◽  
Xrd Techniques ◽  
Kinetics Of

Homogeneous maghemite (γ–Fe2O3) nanoparticles with an average crystal size around 5 nm were synthesized by successive hydrolysis, oxidation, and dehydration of tetrapyridino-ferrous chloride. Morphological, thermal, and structural properties were investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and x-ray diffraction (XRD) techniques. Rietveld refinement indicated a cubic cell. The superstructure reflections, related to the ordering of cation lattice vacancies, were not detected in the diffraction pattern. Kinetics of the solid-state phase transition of nanocrystalline maghemite to hematite (α–Fe2O3), investigated by energy dispersive x-ray diffraction (EDXRD), indicates that direct transformation from nanocrystalline maghemite to microcrystalline hematite takes place during isothermal treatment at 385 °C. This temperature is lower than that observed both for microcrystalline maghemite and for nanocrystalline maghemite supported on silica.

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