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.

scholarly journals STUDY OF INFLUENCE OF TEMPERATURE-TIME FACTORS ALUMINIUM ALLOY STUCTURE АД31 Al-Mg-Si SYSTEM

2020 ◽  
pp. 64-68
Author(s):  
O. B. Kryuchkov ◽  
A. F. Trudov ◽  
D. A. Mordvintseva ◽  
Yu. Yu. Turapin ◽  
A. A. Bochinskaya
Keyword(s):  
Grain Size ◽  
Aluminium Alloy ◽  
Mechanical Treatment ◽  
Time Factors ◽  
Simultaneous Increase ◽  
High Temperature Annealing ◽  
Influence Of Temperature ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Temperature Time

The results of the study of macro and microstructure, grain sizes and their dispersion, as well as the degree of transformation of α and β iron phases, in cylindrical blanks with diameter of 0.203 m and length of 6.4 m from aluminium alloy АД31 Al-Mg-Si system obtained according to the technology: Melting, semi-continuous casting, mechanical treatment, homogenization annealing at temperatures of 560, 570 and 590 оС with subsequent holding for 0.5 h and cooling together with furnace, fan, sprayer and in water. It has been found that the highest cooling rate and lowest average grain size and dispersion are observed downwards for media: water, sprayer, fan, oven. It has been found that high temperature annealing at a temperature of 590 ° C is more effective than annealing at temperatures of 560 and 570 ° C, which is due to a decrease in the number of iron phases with a simultaneous increase in the proportion of trans-formed inclusions.

Characterization of Defect Nucleation and Propagation in Fe2O3+FCC-Al Nanocomposites During Uniaxial Tensile and Compressive Deformations

2006 ◽  
Author(s):  
Vikas Tomar ◽  
Min Zhou
Keyword(s):  
Molecular Dynamics ◽  
Grain Size ◽  
Defect Formation ◽  
Voronoi Tessellation ◽  
Orientation Distribution ◽  
Uniaxial Tensile ◽  
Grain Sizes ◽  
Classical Molecular Dynamics ◽  
Average Grain Size ◽  
Nanocrystalline Structures

The objective of this research is to analyze uniaxial tensile and compressive mechanical deformations of α-Fe2O3 + fcc Al nanoceramic-metal composites using classical molecular dynamics (MD). Specifically, variations in the nucleation and the propagation of defects (such as dislocations and stacking faults etc.) with variation in the nanocomposite phase morphology and their effect on observed tensile and compressive strengths of the nanocomposites are analyzed. For this purpose, a classical molecular dynamics (MD) potential that includes an embedded atom method (EAM) cluster functional, a Morse type pair function, and a second order electrostatic interaction function is developed, see Tomar and Zhou (2004) and Tomar and Zhou (2006b). The nanocrystalline structures (nanocrystalline Al, nanocrystalline Fe2O3 and the nanocomposites with 40% and 60% Al by volume) with average grain sizes of 3.9 nm, 4.7 nm, and 7.2 nm are generated using a combination of the well established Voronoi tessellation method with the Inverse Monte-Carlo method to conform to prescribed log-normal grain size distributions. For comparison purposes, nanocrystalline structures with a specific average grain size have the same grain morphologies and the same grain orientation distribution. MD simulations are performed at the room temperature (300 K). Calculations show that the deformation mechanism is affected by a combination of factors including the fraction of grain boundary (GB) atoms and the electrostatic forces between atoms. The significance of each factor is dependent on the volume fractions of the Al and Fe2O3 phases. Depending on the relative orientations of the two phases at an interface, the contribution of the interface to the defect formation varies. The interfaces have stronger effect in structures with smaller average grain sizes than in structures with larger average grain sizes.

Nanostructure Evolution of ZnO in Ultra-fast Microwave Sintering

2011 ◽  
Vol 691 ◽  
pp. 65-71 ◽  
Author(s):  
Rodolfo F. K. Gunnewiek ◽  
Ruth Herta Goldsmith Aliaga Kiminami
Keyword(s):  
Grain Size ◽  
Zinc Oxide ◽  
Grain Growth ◽  
Microwave Sintering ◽  
High Heating Rate ◽  
Heating Rates ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Conventional Sintering ◽  
Holding Temperature

Grain growth is inevitable in the sintering of pure nanopowder zinc oxide. Sintering depend on diffusion kinetics, thus this growth could be controlled by ultra-fast sintering techniques, as microwave sintering. The purpose of this work was to investigate the nanostructural evolution of zinc oxide nanopowder compacts (average grain size of 80 nm) subjected to ultra-rapid microwave sintering at a constant holding temperature of 900°C, applying different heating rates and temperature holding times. Fine dense microstructures were obtained, with controlled grain growth (grain size from 200 to 450nm at high heating rate) when compared to those obtained by conventional sintering (grain size around 1.13µm), which leads to excessively large average final grain sizes.

Dielectric Properties of Nanograined BaTiO3 Ceramics Fabricated by Aerosol Deposition Method

2011 ◽  
Vol 485 ◽  
pp. 183-186 ◽  
Author(s):  
Tsutomu Furuta ◽  
Saki Hatta ◽  
Yoichi Kigoshi ◽  
Takuya Hoshina ◽  
Hiroaki Takeda ◽  
...  
Keyword(s):  
Grain Size ◽  
Room Temperature ◽  
Annealing Treatment ◽  
Aerosol Deposition ◽  
Dielectric Measurement ◽  
Deposition Method ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Aerosol Deposition Method ◽  
Polarization Electric Field

Freestanding BaTiO3 ceramics films were fabricated using the aerosol deposition (AD) method and the size effect of nanograined BaTiO3 ceramics was demonstrated. Dense BaTiO3 thick film fabricated by the AD method was crystallized and detached from substrate by an annealing treatment at 600 °C, and then the grain size was controlled by a reannealing treatment at various temperatures. As a result, freestanding BaTiO3 thick films with various grain sizes from 24 to 170 nm were successfully obtained. Polarization–electric field (P–E) measurement revealed that BaTiO3 ceramics with grain sizes of more than 58 nm showed ferroelectricity, whereas BaTiO3 ceramics with an average grain size of 24 nm showed paraelectricity at room temperature. Dielectric measurement indicated that the permittivity decreased with decreasing grain size in the range of 170 to 24 nm.

Microstructure Prediction by Finite Element Analysis during Hot Rolling of Magnesium Alloy Sheets

2015 ◽  
Vol 661 ◽  
pp. 105-112
Author(s):  
Yeong Maw Hwang ◽  
Tso Lun Yeh
Keyword(s):  
Grain Size ◽  
Magnesium Alloy ◽  
Optimal Conditions ◽  
Compression Tests ◽  
Element Analysis ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Microstructure Prediction ◽  
Alloy Microstructure ◽  
The Relationship

Material’s plastic deformation by hot forming processes can be used to make the materials generate dynamic recrystallization (DRX) and fine grains and accordingly products with more excellent mechanical properties, such as higher strength and larger elongation can be obtained. In this study, compression tests and water quenching are conducted to obtain the flow stress of the materials and the grain size after DRX. Through the regression analysis, prediction equations for the magnesium alloy microstructure were established. Simulations with different rolling parameters are conducted to find out the relationship between the DRX fractions or grain sizes of the rolled products and the rolling parameters. The simulation results show that rolling temperature of 400°C and thickness reduction of 50% are the optimal conditions. An average grain size of 0.204μm-0.206μm in the microstructure is obtained and the strength and formability of ZK60 magnesium alloys can be improved.

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.

Microstructural Evolution of AZ31 Mg Wrought Alloy during Partial Remelting for Thixoextrusion

2006 ◽  
Vol 116-117 ◽  
pp. 251-254
Author(s):  
Young Ok Yoon ◽  
Shae K. Kim
Keyword(s):  
Grain Size ◽  
Microstructural Evolution ◽  
Liquid Fraction ◽  
Isothermal Holding ◽  
Holding Time ◽  
Interesting Point ◽  
Grain Sizes ◽  
Partial Remelting ◽  
Average Grain Size ◽  
Holding Temperature

An attempt has been made to investigate feasibility of thixoextrusion for AZ31 Mg wrought alloy through simple partial remelting. Microstructural evolution of AZ31 Mg wrought alloy for thixoextrusion was investigated as functions of isothermal holding temperature and time in the partially remelted semisolid state. The interesting point of this study was that the thixotropic structures of AZ31 Mg wrought alloy without additional pretreatment could be obtained through simple partial remelting. The uniform average grain size and liquid fraction according to the isothermal holding time were very important for the thixoextrusion. Because, it is must be considered on actual extrusion time. The liquid fraction was increased with increasing isothermal holding temperature and time. But, the liquid fraction was almost uniform after 10 min. The average grain size was decreased with increasing isothermal holding temperature. On the other hand, as the holding time increased, the average grain sizes were uniform at 615 and 622. This phenomenon is very useful for thixoextrusion in terms of process control such as actual extrusion time.

The Inverse Hall-Petch Effect—Fact or Artifact?

2000 ◽  
Vol 634 ◽  
Author(s):  
Carl C. Koch ◽  
J. Narayan
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Computer Simulations ◽  
Nanocrystalline Materials ◽  
Grain Sizes ◽  
Average Grain Size

ABSTRACTThis paper critically reviews the data in the literature which gives softening—the inverse Hall-Petch effect—at the finest nanoscale grain sizes. The difficulties with obtaining artifactfree samples of nanocrystalline materials will be discussed along with the problems of measurement of the average grain size distribution. Computer simulations which predict the inverse Hall-Petch effect are also noted as well as the models which have been proposed for the effect. It is concluded that while only a few of the experiments which have reported the inverse Hall-Petch effect are free from obvious or possible artifacts, these few along with the predictions of computer simulations suggest it is real. However, it seems that it should only be observed for grain sizes less than about 10 nm.

Fracture Resistant and Wear Corrosion Performance of CrN/ZrN Bilayers Deposited onto AISI 420 Stainless Steel

2008 ◽  
Vol 38 ◽  
pp. 63-75 ◽  
Author(s):  
N.A. de Sánchez ◽  
Héctor Enrique Jaramillo Suárez (1) ◽  
Z. Vivas ◽  
W. Aperador ◽  
C. Amaya ◽  
...  
Keyword(s):  
Grain Size ◽  
Stainless Steel ◽  
Impact Resistance ◽  
Grain Sizes ◽  
Aisi 420 ◽  
Average Grain Size ◽  
Afm Analysis ◽  
Corrosive Environments ◽  
Steel Substrates ◽  
Gas Ratio

CrN/ZrN (1, 8, 15, and 30) bilayers were deposited onto AISI 420 steel substrates at 250 °C and 6.6x10-3 mbar with gas ratio Ar/N2 50:3.0 as gas mixture and bias -60V were applied. AFM analysis presented different morphologies, showing that the coatings with 15 bilayers had an average grain size of 49 nm; while the 30-bilayer coating exhibited grain sizes of 99 nm. Coating thicknesses were 3 μm, approximately. The Vickers Test revealed that coatings with 8, 15, and 30 bilayers bore better impact resistance than coatings with 1 bilayer. This result is considered, bearing in mind that in many bilayers propagation of fissures is slower, because the presence of layer inter-phases leads to fissures straying in other directions. Slight corrosion specks are present, but mass loss was around 40 mg. in one bilayer, a higher value than for the coatings with 15 bilayers that was near 18 mg. Homogeneity, grain size, fracture resistance, and corrosion resistance of the coatings with 15 and 30 bilayers are suitable for mechanical applications of these types of coatings, as shown in mechanical measurements. These results indicate that for engineering applications under corrosive environments, the use of these types of bilayer coatings on AISI 420 stainless steel is highly recommended.

scholarly journals Snow depths and grain-size relationships with relevance for passive microwave studies

1993 ◽  
Vol 17 ◽  
pp. 171-176 ◽  
Author(s):  
Richard L. Armstrong ◽  
Alfred Chang ◽  
Albert Rango ◽  
Edward Josberger
Keyword(s):  
Grain Size ◽  
Snow Cover ◽  
Regional Scale ◽  
Passive Microwave ◽  
Microwave Radiometry ◽  
Grain Sizes ◽  
Snow Properties ◽  
Average Grain Size ◽  
Retrieval Algorithms ◽  
Passive Microwave Radiometry

The application of passive microwave radiometry to the remote sensing of snow properties is based on the ratio of emitted to scattered portions of the upwelling radiation. Increased scattering is indicative of increased snow amount, i.e. the number of snow grains present. However, scattering is also directly proportional to snow grain-size for a given snow amount. Current snow cover retrieval algorithms produce inaccurate results when snow grain-sizes are unusually large. Therefore, it is necessary to characterize snow grain-size on a regional scale (and perhaps local scale in extreme situations) in order to adjust passive microwave algorithms. Preliminary analysis indicates that: (1) algorithms are not as sensitive to the presence of large grain-sizes as the initial theory had indicated; (2) standard deviation of grain-size diameters throughout the total snow cover may often be less than 0.5 mm, thus average grain-size data may often serve to characterize the detailed stratigraphy of the total snow cover; (3) conditions in subfreezing snow which produce grain-sizes that greatly exceed a mean diameter value of 1–2 mm result from snow cover/climate relationships which can be modelled/monitored on a regional scale. A preliminary method is investigated for selecting snow retrieval algorithms according to prevailing regional-scale grain-size.

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