Effect of Electron Irradiation on Nanocrystallization of Fe-Nd-B Amorphous Alloys

2006 ◽  
Vol 512 ◽  
pp. 107-110 ◽  
Author(s):  
Akihiro Nino ◽  
Takeshi Nagase ◽  
Yukichi Umakoshi
Keyword(s):  
Grain Size ◽  
Amorphous Phase ◽  
Electron Irradiation ◽  
Amorphous Alloys ◽  
Single Phase ◽  
Nanocrystalline Structure ◽  
Rapid Quenching ◽  
Thermal Crystallization ◽  
Average Grain Size ◽  
Induced Crystallization

Formation of a nanocrystalline structure through rapid solidification, thermal crystallization and electron irradiation induced crystallization was investigated in Fe-Nd-B alloys. A nanocrystalline structure was obtained by rapid quenching of the melt in a Fe86Nd9B5 alloy, while an amorphous single phase was formed in a Fe77Nd4.5B18.5 alloy. In the latter alloy, a nanocrystalline structure was obtained by thermal crystallization and electron irradiation induced crystallization of the amorphous phase. The average grain size of the precipitate obtained by irradiation at 298 K was about 8 nm, which is much smaller than that obtained during thermal crystallization. Results indicate that electron irradiation is effective for obtaining a novel nanocrystalline structure in Fe-Nd-B alloys.

Effect of Annealing on Nanocrystalline Structure of Nb3Sn Diffusion Layers in Composites with Internal Tin Sources

2010 ◽  
Vol 297-301 ◽  
pp. 126-131 ◽  
Author(s):  
E.N. Popova ◽  
Vladimir V. Popov ◽  
E.P. Romanov ◽  
S.V. Sudareva ◽  
L.V. Elohina ◽  
...  
Keyword(s):  
Grain Size ◽  
Carrying Capacity ◽  
Nanocrystalline Structure ◽  
Diffusion Annealing ◽  
External Diameter ◽  
High Temperature Annealing ◽  
Grain Sizes ◽  
Diffusion Layers ◽  
Average Grain Size ◽  
Complete Transformation

Multifilamentary Nb3Sn-based superconducting composites manufactured by an internal-tin method have been studied by transmission (TEM) and scanning (SEM) electron microscopy. The main goal of this study is to reveal the effect of diffusion annealing regimes as well as the external diameter of the wires on the structure of nanocrystalline Nb3Sn layers (average grain size, grain size distribution, layer thickness, amount of Sn, etc.). It is demonstrated that multistep diffusion annealing results in quite a complete transformation of Nb filaments into Nb3Sn though some amount of the residual Nb remains in the filaments center. With an external diameter decrease the superconducting layers structure has been found to refine and get somewhat more uniform. An additional high-temperature annealing results in marked growth of Nb3Sn grain sizes and their scattering in sizes, which may negatively affect the current-carrying capacity of a wire.

MICROSTRUCTURE EVALUATION OF Fe-BASED AMORPHOUS ALLOYS INVESTIGATED BY DOPPLER BROADENING POSITRON ANNIHILATION TECHNIQUE

2013 ◽  
Vol 27 (19) ◽  
pp. 1341014
Author(s):  
WEI LU ◽  
PING HUANG ◽  
YUXIN WANG ◽  
BIAO YAN
Keyword(s):  
Grain Size ◽  
Positron Annihilation ◽  
Amorphous Alloys ◽  
Annealing Temperature ◽  
Amorphous Matrix ◽  
Nanocrystalline Phase ◽  
Magnetic Alloy ◽  
Type I ◽  
Doppler Broadening ◽  
Average Grain Size

Microstructure of Fe -based amorphous and nanocrystalline soft magnetic alloy has been investigated by X-ray diffraction (XRD), transmission electronic microscopy (TEM) and Doppler broadening positron annihilation technique (PAT). Doppler broadening measurement reveals that amorphous alloys (Finemet, Type I) which can form a nanocrystalline phase have more defects (free volume) than alloys (Metglas, Type II) which cannot form this microstructure. XRD and TEM characterization indicates that the nanocrystallization of amorphous Finemet alloy occurs at 460°C, where nanocrystallites of α- Fe with an average grain size of a few nanometers are formed in an amorphous matrix. With increasing annealing temperature up to 500°C, the average grain size increases up to around 12 nm. During the annealing of Finemet alloy, it has been demonstrated that positron annihilates in quenched-in defect, crystalline nanophase and amorphous-nanocrystalline interfaces. The change of line shape parameter S with annealing temperature in Finemet alloy is mainly due to the structural relaxation, the pre-nucleation of Cu nucleus and the nanocrystallization of α- Fe ( Si ) phase during annealing. This study throws new insights into positron behavior in the nanocrystallization of metallic glasses, especially in the presence of single or multiple nanophases embedded in the amorphous matrix.

scholarly journals Effect of Milling Time on Microstructure, Crystallite Size and Dielectric Properties of Srtio3 Ceramic Synthesized via Mechanical Alloying Method

2011 ◽  
Vol 364 ◽  
pp. 388-392
Author(s):  
Yick Jeng Wong ◽  
Hassan Jumiah ◽  
Mansor Hashim ◽  
Swee Yin Wong ◽  
Leow Chun Yan
Keyword(s):  
Dielectric Constant ◽  
Grain Size ◽  
Dielectric Properties ◽  
Mechanical Alloying ◽  
Crystallite Size ◽  
Single Phase ◽  
Milling Time ◽  
Average Grain Size ◽  
Average Lattice ◽  
Milled Powders

SrTiO3 sample has been successfully prepared by mechanical alloying (MA) method. The effect of milling time on microstructure, crystallite size and dielectric properties of SrTiO3 were studied. The results revealed that the mean crystallite size of milled powders decreased from 84.56 to 12.87 nm with increasing milling time. However, the average lattice strain of milled powders increased from 0.2 to 0.93% with increasing milling time. A single phase SrTiO3 could not be formed with milling alone and required annealing process. A transformation of anatase-TiO2 to rutile-TiO2 was observed at 16 h of milling. After the milled powders were subjected to sintering process at 1200°C, formation of single-phase SrTiO3-type cubic (Pm-3m) perovskite structure was observed. The peak intensities of the sintered SrTiO3 samples decreased as the milling time was increased. For microstructural observations, the average grain size of the sintered SrTiO3 sample milled for 8 h showed the largest. For dielectric measurements, the dielectric constant of the sintered SrTiO3 sample milled for 8 h showed the highest among others. This could be due to the largest grain size obtained for sintered SrTiO3 sample milled for 8 h. The decrease in the grain size with increasing milling time resulted to the decrease in dielectric constant.

Self-Diffusion as A Limiting Factor of a-SiGe Crystallization

1997 ◽  
Vol 469 ◽  
Author(s):  
F. Edelman ◽  
T. Raz ◽  
Y. Komem ◽  
P. Werner ◽  
W. Beyer ◽  
...  
Keyword(s):  
Grain Size ◽  
Nanocrystalline Structure ◽  
Limiting Factor ◽  
In Situ Tem ◽  
Large Area ◽  
Self Diffusion ◽  
Glass Substrates ◽  
Vacancy Generation ◽  
Nonequilibrium Vacancy ◽  
Average Grain Size

ABSTRACTHighly doped (∼1018 to 1021cm−3) polycrystalline Si1-xGex films, crystallized from amorphous (a) state at relative low temperatures, are prospective materials in a variety of applications, such as liquid-crystal displays, solar cells and integrated thermoelectric sensors on large-area glass substrates. Since the nature of the grains in the crystallized film defines properties such as carrier mobility, the nucleation and growth process of the a-SiGe films is of fundamental interest. We have studied the crystallization of undoped and highly doped (B or Ga) amorphous SiGe films. The films were deposited by RFCVD or molecular beam on oxidized (001)Si and for TEM study on cleaved NaCl. The incubation time and grain growth rate were studied by means of in situ TEM using a heating stage. The crystallization process in undoped SiGe followed Avrami relationship. An average grain size between 0.1 and 2μm was observed. However, the highly p-doped (with B or Ga) SiGe films crystallized to a stable nanocrystalline structure (grain size <10nm). The process of the a-SiGe crystallization is explained on the basis of self-diffusion. During the first stage, the nucleation of crystals is accompanied with nonequilibrium vacancy generation at the amorphous/crystalline interface. During the second stage, the growth of crystals takes place by vacancy outdiffusion which is hindered by B and Ga interaction with vacancies.

Influence of Annealing Time on Microstructure of Ni-W Alloys

2013 ◽  
Vol 747-748 ◽  
pp. 613-618
Author(s):  
Qiao Zhang ◽  
Shu Hua Liang ◽  
Chen Zhang ◽  
Jun Tao Zou
Keyword(s):  
Electron Microscopy ◽  
Solid Solution ◽  
Grain Size ◽  
Grain Boundaries ◽  
Annealing Time ◽  
Single Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Average Grain Size ◽  
Scanning Electron

The as-cast Ni-W alloys with 15wt%W, 25wt%W and 30wt%W were annealed in hydrogen at 1100. The effect of the annealing time on the microstructure of Ni-W alloys was studied, and the phase constituents and microstructure of annealed Ni-W alloys were characterized by the X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that no any phase changed for Ni-15%W, Ni-25%W and Ni-30%W alloys annealed for 60 min, 90 min and 150 min, which were still consisted of single-phase Ni (W) solid solution. However, microstructure had a significant change after annealing. With increase of annealing time, the microstructure of Ni-15%W alloy became more uniform after annealing for 90 min, and the average grain size was 95μm, whereas the grain size of Ni-15%W alloy increased significantly after annealing for 150 min. For Ni-25%W and Ni-30%W, there was no obvious change on the grain size with increase of annealing time, and the amount of oxides at grain boundaries gradually reduced. After annealing for 150 min, the impurities at grain boundaries almost disappeared. Subsequently, the annealing at 1100 for 150 min was beneficial for the desired microstructure of Ni-25%W and Ni-30%W alloys.

Statistical analysis of the parameters and grain size distribution functions of single-phase polycrystalline materials

2020 ◽  
Vol 86 (4) ◽  
pp. 39-45
Author(s):  
S. I. Arkhangelskiy ◽  
D. M. Levin
Keyword(s):  
Grain Size ◽  
Distribution Function ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Single Phase ◽  
Distribution Functions ◽  
Grain Structure ◽  
Polycrystalline Materials ◽  
Grain Sizes ◽  
Average Grain Size

A statistical analysis of the grain size distribution is important both for developing theories of the grain growth and microstructure formation, and for describing the size dependences of various characteristics of the physical and mechanical properties of polycrystalline materials. The grain size distribution is also an important characteristic of the structure uniformity and, therefore, stability of the properties of the products during operation. Statistical Monte Carlo modeling of single-phase and equiaxed polycrystalline microstructures was carried out to determine the type of statistically valid distribution function and reliable estimates of the average grain size. Statistical parameters (mean values, variances, variation coefficient) and distribution functions of the characteristics of the grain microstructure were obtained. It is shown that the distribution function of the effective grain sizes for the studied polycrystal model is most adequately described by γ-distribution, which is recommended to be used in analysis of the experimental distribution functions of grain sizes of single-phase polycrystalline materials with equiaxed grains. The general average (mathematical expectation) of the effective grain size (projection diameter) with γ-distribution function (parameters of the distribution function are to be previously determined in analysis of the grain structure of polycrystalline materials) should be taken as a statistically valid and reliable estimate of the average grain size. The results of statistical modeling are proved by the experimental data of metallographic study of the microstructures of single-phase model and industrial materials with different degree of the grain structure heterogeneity.

Low-Temperature Synthesis of MgAl2O4 by Capsule HIP Using Hydroxides as Starting Materials

2014 ◽  
Vol 617 ◽  
pp. 217-220 ◽  
Author(s):  
Kensuke Yanagida ◽  
Yuki Yamaguchi ◽  
Kenjiro Fujimoto ◽  
Shigeru Ito
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Single Phase ◽  
Intermediate Compound ◽  
High Reactivity ◽  
Low Temperature Synthesis ◽  
Temperature Synthesis ◽  
High Crystallinity ◽  
Average Grain Size ◽  
Active Intermediate

Low-temperature synthesis of spinel (MgAl2O4) was investigated by capsule hot isostatic press (HIP) using hydroxides as starting materials; Mg(OH)2, MgO, Al(OH)3, g-AlOOH, g-Al2O3. MgAl2O4 has been conventionally prepared above 1400 °C, whereas the mixtures containing the hydroxides reacted at 400-500 °C for 1 h under 200 MPa of isostatic pressure to form MgAl2O4. The hydroxides showed high reactivity to form MgAl2O4 with high crystallinity. However, the products more or less contained Mg(OH)2. The single phase of MgAl2O4 was obtained by adding 20 mass% of water to the starting mixtures of Mg(OH)2 - Al(OH)3, Mg(OH)2 - g-Al2O3 and MgO - Al(OH)3. The average grain size of the MgAl2O4 was 70 – 100 nm. It was concluded that the transformation of AlOOH or g-Al2O3 was promoted by a small amount of water and that Mg(OH)2 rapidly reacted with the active intermediate compound between AlOOH or g-Al2O3 and a-Al2O3.

Microstructure and Thermoelectric Properties of CoSb3 Synthesized by MA-SPS Method

2007 ◽  
Vol 336-338 ◽  
pp. 834-837 ◽  
Author(s):  
Wei Shu Liu ◽  
Bo Ping Zhang ◽  
Jing Feng Li ◽  
Heng Wang
Keyword(s):  
Grain Size ◽  
Thermoelectric Properties ◽  
Room Temperature ◽  
Single Phase ◽  
New Combination ◽  
Plasma Sintering ◽  
Average Grain Size ◽  
Spark Plasma ◽  
Xrd Patterns ◽  
Type Conduction

Single-phase polycrystalline CoSb3 skutterudite was prepared through a new combination of mechanical alloying (MA) and spark plasma sintering (SPS). In order to investigate the influence of MA conditions on the microstructure and thermoelectric properties, MA synthesis were carried out under various conditions with different milling times. The powder sample MAed for 6h still consisted of metal Sb, and then transformed to CoSb3 with a little amount of metal Sb and CoSb2 phases after MA for 15h. Further prolonging the MA time resulted in the decomposition of CoSb3 to CoSb2 phase. The average grain size of the SPSed samples decreased from 650nm to 250nm as MA-time was prolonged from 6 to 24h. Lattice parameters estimated form XRD patterns increase with the increasing MA time. All samples SPSed at 600°C for holding 5 min show an n-type conduction. The electrical resistivity was 1030, 895, 410, 260 μm for the samples from the MA-derived powders with MA-time of 6, 15, 24 and 33h at room temperature, respectively, then reduced to 60 μm at 400°C for all samples. An optimum MA time is 24 h in which the sample shows the highest power factor 612μW/m*K2 at 150°C.

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