Generation of 4H and 6H Structures During the Hexagonal-Rhombohedral Transformation in Dy2Co17

1975 ◽  
Vol 33 ◽  
pp. 38-39
Author(s):  
C. W. Allen ◽  
D. L. Kuruzar
Keyword(s):  
Elevated Temperatures ◽  
Layer Structure ◽  
Transition Element ◽  
Temperature Structure ◽  
Allotropic Transformation ◽  
Layer Plane ◽  
Planar Defects ◽  
Topologically Close Packed ◽  
Transformation Mechanisms ◽  
Shear Transformation

The rare earth/transition element intermetallics R2T17 are essentially topologically close packed phases for which layer structure models have already been presented. Many of these compounds are known to undergo allotropic transformation of the type at elevated temperatures. It is not unexpected that shear transformation mechanisms are involved in view of the layering character of the structures. The transformations are evidently quite sluggish, illustrated in furnace cooled Dy2Co17 by the fact that only rarely has the low temperature rhombohedral form been seen. The more usual structures observed so far in furnace cooled alloys include 4H and 6H in Dy2Co17 (Figs. 1 and 2) . In any event it is quite clear that the general microstructure is very complicated as a consequence of the allotropy, illustrated in Fig. 3. Numerous planar defects in the layer plane orientation are evident as are non-layer plane defects inherited from a high temperature structure.

INTERMETALLIC COMPOUND AlxTi – ARE PROMISING MATERIAL FOR HIGH ELEVATED TEMPERATURES (review) Part 1. The crystaline structure and properties of the intermetallic compound Al2Ti

2021 ◽  
pp. 28-43
Author(s):  
N.A. Nochovnaya ◽  
◽  
V.I. Ivanov ◽  
L.Yu. Avilochev ◽  
◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Intermetallic Compound ◽  
Lamellar Structure ◽  
Power Plants ◽  
Elevated Temperatures ◽  
Texture Formation ◽  
Structure And Properties ◽  
High Temperature Alloys ◽  
Transformation Mechanisms ◽  
Increased Strength

The Al2Ti intermetallic compound is the most promising base for high-temperature alloys designed for advanced power plants. This work provides an overview of the structures of binary alloys concerning to the Ti–Al system, as well as the phase transformation mechanisms and the peculiarities of plastic deformation of alloys. The alloys which phase composition is represented by a mixture of r-Al2Ti+γ-TiAl with a lamellar structure show anomalous mechanical properties depending on texture formation and grain size. These alloys possess increased strength and decreased plasticity at elevated temperatures.

scholarly journals Структура и термоэлектрические свойства пленочных композитов на основе CoSi

2019 ◽  
Vol 53 (6) ◽  
pp. 784
Author(s):  
В.С. Кузнецова ◽  
С.В. Новиков ◽  
Ч.К. Ниченаметла ◽  
И. Кальво ◽  
М. Вагнер-Ритц
Keyword(s):  
Thin Films ◽  
Chemical Vapor Deposition ◽  
Thermal Treatment ◽  
Vapor Deposition ◽  
Multilayer Structure ◽  
Elevated Temperatures ◽  
Layer Structure ◽  
Chemical Vapor ◽  
Structural Data ◽  
Temperature Dependences

Properties of Co-Si thin films produced by thermal treatment of Co and Si layers are studied in this article. Co/Si layers were produced by chemical vapor deposition. The two-layer structure was annealed at elevated temperatures for the formation of cobalt silicide. Thermoelectric properties of the film structures were investigated in the temperature range 300-800 K. Temperature dependences of thermopower and resistivity as well as structural data indicate the formation a multilayer structure with Si-rich and Co-rich layers.

scholarly journals Estimation of Turbulence Parameters in the Lower Troposphere from ShUREX (2016–2017) UAV Data

Atmosphere ◽  
2019 ◽  
Vol 10 (7) ◽  
pp. 384 ◽  
Author(s):  
Hubert Luce ◽  
Lakshmi Kantha ◽  
Hiroyuki Hashiguchi ◽  
Dale Lawrence
Keyword(s):  
Richardson Number ◽  
Layer Structure ◽  
Lower Troposphere ◽  
Energy Dissipation Rate ◽  
Function Parameter ◽  
Mixing Efficiency ◽  
Temperature Structure ◽  
Frequency Spectra ◽  
Kolmogorov Turbulence ◽  
Turbulence Parameters

Turbulence parameters in the lower troposphere (up to ~4.5 km) are estimated from measurements of high-resolution and fast-response cold-wire temperature and Pitot tube velocity from sensors onboard DataHawk Unmanned Aerial Vehicles (UAVs) operated at the Shigaraki Middle and Upper atmosphere (MU) Observatory during two ShUREX (Shigaraki UAV Radar Experiment) campaigns in 2016 and 2017. The practical processing methods used for estimating turbulence kinetic energy dissipation rate ε and temperature structure function parameter C T 2 from one-dimensional wind and temperature frequency spectra are first described in detail. Both are based on the identification of inertial (−5/3) subranges in respective spectra. Using a formulation relating ε and C T 2 valid for Kolmogorov turbulence in steady state, the flux Richardson number R f and the mixing efficiency χ m are then estimated. The statistical analysis confirms the variability of R f and χ m around ~ 0.13 − 0.14 and ~ 0.16 − 0.17 , respectively, values close to the canonical values found from some earlier experimental and theoretical studies of both the atmosphere and the oceans. The relevance of the interpretation of the inertial subranges in terms of Kolmogorov turbulence is confirmed by assessing the consistency of additional parameters, the Ozmidov length scale L O , the buoyancy Reynolds number R e b , and the gradient Richardson number Ri. Finally, a case study is presented showing altitude differences between the peaks of N 2 , C T 2 and ε , suggesting turbulent stirring at the margin of a stable temperature gradient sheet. The possible contribution of this sheet and layer structure on clear air radar backscattering mechanisms is examined.

Low Cycle Fatigue Behavior of 429EM Ferritic Stainless Steel at Elevated Temperatures

2004 ◽  
Vol 261-263 ◽  
pp. 1135-1140 ◽  
Author(s):  
Keum Oh Lee ◽  
Sam Son Yoon ◽  
Soon Bok Lee ◽  
Bum Shin Kim
Keyword(s):  
Stainless Steel ◽  
Elastic Modulus ◽  
Fatigue Life ◽  
Elevated Temperatures ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Cyclic Hardening ◽  
Dynamic Strain ◽  
Temperature Structure ◽  
Cycle Fatigue

In recent, ferritic stainless steels are widely used in high temperature structure because of their high resistance in thermal fatigue and low prices. Tensile and low cycle fatigue(LCF) tests on 429EM stainless steel were performed at several temperatures from room temperature to 600°C. Elastic modulus, yield stress and ultimate tensile strength(UTS) decreased with increasing temperature. Considerable cyclic hardening occurred at 200°C and 400°C. 475°C embrittlement observed could not explain this phenomenon but dynamic strain aging(DSA) observed from 200°C to 500°C could explain the hardening mechanism at 200°C and 400°C. And it was observed that plastic strain energy density(PSED) was useful to predict fatigue life when large cyclic hardening occurred. Fatigue life using PSED over elastic modulus could be well predicted within 2X scatter band at various temperatures.

Pulsed Laser Deposition of Hafnium Oxide on Silicon

2005 ◽  
Vol 108-109 ◽  
pp. 723-728 ◽  
Author(s):  
Mathias Kappa ◽  
Markus Ratzke ◽  
Jürgen Reif
Keyword(s):  
Substrate Temperature ◽  
Pulsed Laser Deposition ◽  
Hafnium Oxide ◽  
Chemical Structure ◽  
Elevated Temperatures ◽  
Layer Structure ◽  
Critical Role ◽  
Pulsed Laser ◽  
Laser Wavelength ◽  
Laser Deposition

Hafnium oxide films were prepared by Pulsed Laser Deposition (PLD). The influence of laser wavelength (fundamental, second and third harmonic of a Nd:YAG laser), used for evaporation, and substrate temperature on the film morphology, chemical structure and interfacial quality were investigated yielding the following results: While the laser wavelength exhibits minor influence on layer structure, the substrate temperature plays a critical role regarding morphological and chemical structure of the produced hafnium oxide / silicon stacks. Atomic Force Microscopy (AFM) images show a clear transition from smooth layers consisting of small area crystallites to very rough surfaces characterized by large craters and regular, plane features when the growth temperature was increased. These facts suggest a chemical instability which is confirmed by X-ray Photoelectron Spectroscopy (XPS). Investigations of the hafnium and silicon core level spectra indicate the occurrence of silicon dioxide and hafnium silicide in the case the samples were produced at elevated temperatures.

The variability of mixing at the continental slope

1990 ◽  
Vol 331 (1616) ◽  
pp. 183-194 ◽  
Keyword(s):  
Boundary Layer ◽  
Continental Slope ◽  
Tidal Cycle ◽  
Layer Structure ◽  
Internal Gravity Waves ◽  
Benthic Boundary Layer ◽  
Temperature Structure ◽  
Sea Bed ◽  
Stable Conditions ◽  
Mixed Layers

The benthic boundary layer on the continental slope is a region in which isopycnal surfaces intersect topography. It is, in consequence, particularly subject to variability caused by reflecting internal gravity waves, as well as by trapped baroclinic slope waves. Observations made using an array of moorings off the west slope of the Porcupine Bank reveal the presence there of a northerly along-slope current at depths of 3000-4000 m, which extends to some 20 km off-slope, and of waves of periods 2-9 days trapped within about 10 km ( ca. 1 Rossby radius) of the slope. Lower-frequency variations are dominant at greater distances. The tide has a significant spectral peak, with a first subharmonic apparent near the slope. Measurements of the temperature structure in the boundary layer have been made at 1705 m on the Hebrides slope and at 3447 m off the Porcupine Bank. In both areas the boundary layer structure is dominated by asymmetrical M 2 variations in the isopycnal surfaces, with displacements of50-100 m. Uniform near-bed ‘mixed’ layers appear during the tidal cycle, reaching to some 50 m off the sea bed, but are transient, lasting for only a fraction of the tidal cycle following sharp rises in isotherm levels, later to be replaced by statically stable conditions extending to within a few metres of the sea bed. The slope-trapped waves also modify the mean temperature gradients and are responsible for variations in the locations at which reflecting internal waves of given frequency are critical or resonant.

scholarly journals Lidar Observation of Mesospheric Clouds Above Beijing: A Case Study

2020 ◽  
Vol 237 ◽  
pp. 04003
Author(s):  
Shaohua Gong ◽  
Guotao Yang ◽  
Jihong Wang ◽  
Yuchang Xun ◽  
Foju Wu ◽  
...  
Keyword(s):  
Double Layer ◽  
Layer Structure ◽  
Atmospheric Temperature ◽  
Cloud Layer ◽  
Small Scale ◽  
Temperature Structure ◽  
Altitude Range ◽  
Backscatter Coefficient ◽  
Double Layer Structure ◽  
Mesospheric Clouds

We report on the first observation of mesospheric cloud (MC) at the altitude range of 50-65 km with lidars at Yanqing (40.5°N, 116°E) and Pingquan (41°N, 118.7°E) on 30 October 2018. The MC occurred at the 51-56 km altitude range during the hours of dawn. It had an obvious double-layer structure, but the cloud layer was sparse. The MC was re-observed at the 56-62 km altitude range in the twilight, and the double-layer structure was still obvious. However, the cloud layer became thicker with a maximum volume backscatter coefficient (BSC) 3.1×10−10m−1sr−1. Atmospheric temperature structure was derived according to the lidar observations, and it was found that, several hours before the MC occurrence, a temperature anomaly with coldest temperature ~185 K was propagating downward at the altitudes of 50-65 km. This MC layer was simultaneously observed with lidar at Pingquan in the twilight. It could be a regional MC event and possibly formed locally by a transient cooling due to small-scale disturbances in the mesosphere.

Layer Structured Calcium Bismuth Titanate by Mechanical Activation

2005 ◽  
Vol 23 ◽  
pp. 47-50 ◽  
Author(s):  
M.H. Sim ◽  
J.M. Xue ◽  
J. Wang
Keyword(s):  
Dielectric Constant ◽  
Curie Temperature ◽  
Mechanical Activation ◽  
Room Temperature ◽  
Bismuth Titanate ◽  
Elevated Temperatures ◽  
Layer Structure ◽  
Ferroelectric Properties ◽  
Nitrogen Atmosphere ◽  
Theoretical Density

Nanocrystalline calcium bismuth titanate (CaBi4Ti4O15), which exhibits a layer structure, has been successfully synthesized by mechanical activation of constituent oxides of CaO, Bi2O3 and TiO2 in a nitrogen atmosphere at room temperature. The phase-forming calcination at elevated temperatures that is always required is skipped. CaBi4Ti4O15 derived from mechanical activation consists of nanocrystallites, which occur as aggregates of ~50 nm in sizes. It demonstrates an improved sinterability and was sintered to a density of 93.4% theoretical density at 1175oC for 2 hours. Ferroelectric properties of sintered CaBi4Ti4O15 derived from mechanical activation have been studied. A peak dielectric constant of 1049 at the Curie temperature of 774oC was measured at 1MHz for CaBi4Ti4O15 sintered at 1175oC.

MoS2 deposited by ion beam assisted deposition: 2H or random layer structure?

1998 ◽  
Vol 13 (10) ◽  
pp. 3001-3007 ◽  
Author(s):  
D. N. Dunn ◽  
L. E. Seitzman ◽  
I. L. Singer
Keyword(s):  
Layer Structure ◽  
Ion Beam ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Planar Defects ◽  
Selected Area Electron Diffraction ◽  
Ion Beam Assisted Deposition ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
Dimensional Crystal

The structure of MoS2 films grown by ion beam assisted deposition is investigated using transmission electron microscopy. Films consist of stacks of S–Mo–S planes with a [001] texture; however, three-dimensional crystal symmetry is disrupted by a high density of planar defects. Selected area electron diffraction patterns show (hk0) and (00l) reflections, features similar to a random layer structure, as well as diffuse (103) reflections. It is suggested that these films do not have a true random layer structure, but rather a two-dimensional structure formed by nonrandom in-plane translations.

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