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Weikuo Tao - One of the best experts on this subject based on the ideXlab platform.
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wrf sbm simulations of melting layer structure in mixed Phase Precipitation events observed during lpvex
Journal of Applied Meteorology and Climatology, 2014Co-Authors: Weikuo Tao, Takamichi Iguchi, Toshihisa Matsui, Alexander Khain, Vaughan T J Phillips, Chris Kidd, Tristan LecuyerAbstract:AbstractTwo mixed-Phase Precipitation events were observed on 21 September and 20 October 2010 over the southern part of Finland during the Light Precipitation Validation Experiment (LPVEx). These events have been simulated using the Weather Research and Forecasting Model coupled with spectral bin microphysics (WRF–SBM). The detailed ice-melting scheme with prognosis of the liquid water fraction during melting enables explicit simulation of microphysical properties in the melting layer. First, the simulations have been compared with C-band 3D radar measurements for the purpose of evaluating the overall profiles of cloud and Precipitation. The simulation has some artificial convective patterns and errors in the forecast displacement of the Precipitation system. The overall overestimation of reflectivity is consistent with a bias toward the range characterized by large-diameter droplets in the surface drop size distribution. Second, the structure of the melting bands has been evaluated against vertically po...
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a melting layer model for passive active microwave remote sensing applications part 2 simulation of trmm observations
2013Co-Authors: William S Olson, Peter Bauer, Christian D Kummerow, Yang Hong, Weikuo TaoAbstract:The one-dimensional, steady-state melting-layer model developed in Part I of this study is used to calculate both the microphysical and radiative properties of melting Precipitation, based upon the computed concentrations of snow and graupel just above the freezing level at applicable horizontal grid points of three-dimensional cloudresolving model simulations. The modified 3D distributions of Precipitation properties serve as input to radiative transfer calculations of upwelling radiances and radar extinction/reflectivities at the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Precipitation radar (PR) frequencies, respectively. At the resolution of the cloud-resolving model grids (;1 km), upwelling radiances generally increase if mixed-Phase Precipitation is included in the model atmosphere. The magnitude of the increase depends upon the optical thickness of the cloud and Precipitation, as well as the scattering characteristics of the mixed-Phase particles and ice-Phase Precipitation aloft. Over the set of cloud-resolving model simulations utilized in this study, maximum radiance increases of 43, 28, 18, and 10 K are simulated at 10.65, 19.35, 37.0, and 85.5 GHz, respectively. The impact of melting on TMI-measured radiances is determined not only by the physics of the melting particles but also by the horizontal extent of the melting Precipitation, given that the lower-frequency channels have footprints that extend over tens of kilometers. At TMI resolution, the maximum radiance increases are 16, 15, 12, and 9Ka t thesame frequencies. Simulated PR extinction and reflectivities in the melting layer can increase dramatically if mixed-Phase Precipitation is included, a result consistent with previous studies. Maximum increases of 0.46 (22 dB) in extinction optical depth and 5 dB in reflectivity are simulated based upon the set of cloud-resolving model simulations.
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a melting layer model for passive active microwave remote sensing applications part i model formulation and comparison with observations
Journal of Applied Meteorology, 2001Co-Authors: William S Olson, Peter Bauer, Nicolas Viltard, Daniel E Johnson, Weikuo Tao, Robert Meneghini, Liang LiaoAbstract:Abstract In this study, a 1D steady-state microphysical model that describes the vertical distribution of melting Precipitation particles is developed. The model is driven by the ice-Phase Precipitation distributions just above the freezing level at applicable grid points of “parent” 3D cloud-resolving model (CRM) simulations. It extends these simulations by providing the number density and meltwater fraction of each particle in finely separated size categories through the melting layer. The depth of the modeled melting layer is primarily determined by the initial material density of the ice-Phase Precipitation. The radiative properties of melting Precipitation at microwave frequencies are calculated based upon different methods for describing the dielectric properties of mixed-Phase particles. Particle absorption and scattering efficiencies at the Tropical Rainfall Measuring Mission Microwave Imager frequencies (10.65–85.5 GHz) are enhanced greatly for relatively small (∼0.1) meltwater fractions. The rel...
Henrik Sieurin - One of the best experts on this subject based on the ideXlab platform.
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sigma Phase Precipitation in duplex stainless steel 2205
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007Co-Authors: Henrik SieurinAbstract:Sigma Phase Precipitation is known to embrittle duplex stainless steel. Accordingly, heat treatment and welding must be performed carefully. Nucleation and diffusional growth of sigma Phase in th ...
Angelo Fernando Padilha - One of the best experts on this subject based on the ideXlab platform.
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chi Phase Precipitation in a duplex stainless steel
Materials Characterization, 2009Co-Authors: D M Escriba, Ronald Lesley Plaut, E Maternamorris, Angelo Fernando PadilhaAbstract:Abstract The aim of this study is to investigate the Precipitation of intermetallic Phases, especially the chi-Phase, in a 45N (type UNS S31803) duplex stainless steel through aging heat-treatments carried out at 700 and 750 °C. Two intermetallic Phases are detected: chi (χ) and sigma (σ). The χ-Phase precipitates at ferrite/ferrite grain boundaries prior to the σ-Phase Precipitation, which occurs preferentially at ferrite/austenite interfaces and at ferrite/ferrite grain boundaries. The σ-Phase Precipitation is a eutectoid type reaction of ferrite leading to σ-Phase Phase and austenite. The χ-Phase is consumed in the σ-Phase Precipitation after becoming completely surrounded by both the σ-Phase and the newly formed austenite.
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comparative study on sigma Phase Precipitation of three types of stainless steels austenitic superferritic and duplex
Materials Science and Technology, 2006Co-Authors: D M E Villanueva, F C P, Ronald Lesley Plaut, Angelo Fernando PadilhaAbstract:AbstractThe present work studies, in a comparative manner, the sigma Phase Precipitation of three stainless steels: austenitic type 316L (17Cr–12Ni–2·5Mo, wt-%), superferritic type DIN W. Nr. 1·4575 (Nb–28Cr–4Ni–2Mo, wt-%) and duplex type DIN W. Nr. 1·4462 or UNS S31803 (22Cr–5·5Ni–3Mo–0·14N, wt-%). In austenitic stainless steel, the formation of sigma Phase occurred both at austenite grain boundaries and inside delta ferrite islands. In superferritic stainless steel, sigma Phase occurred both at grain boundaries and in the grain interior. In the ferrites, both in the duplex and in the austenitic steel, sigma Phase formation occurred by eutectoid reaction ferrite→sigma + austenite. The tendency towards Precipitation of the sigma Phase in the three types of steel investigated can be placed in the following sequence: duplex>superferritic>austenitic.
Nabil Kherrouba - One of the best experts on this subject based on the ideXlab platform.
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effect of solution treatment temperature on the Precipitation kinetic of σ Phase in 2205 duplex stainless steel welds
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Riad Badji, M Bouabdallah, B Bacroix, C Kahloun, Khireddine Bettahar, Nabil KherroubaAbstract:Abstract The effect of the prior solution treatment temperature on the δ-ferrite transformation in 2205 duplex stainless welds after aging at 850 °C has been studied. Microstructural examination showed that the σ-Phase and M23C6 chromium carbides precipitate at the δ/γ interfaces and within the δ-ferrite grains. Increasing the solution treatment temperature from 1050 to 1250 °C delays the σ-Phase formation and favours the Precipitation of intragranular secondary austenite γ2. The simulation of the σ-Phase Precipitation kinetic in the base metal, HAZ and weld metal, indicates a good agreement between the experimental fitted data and the modified Johnson–Mehl–Avrami model. The results indicate a marked sensitivity of the σ-Phase Precipitation kinetic to the solution treatment temperature. A high Precipitation rate corresponds to a fine grained structure with ferrite enriched in σ forming elements (Cr, Mo).
G Texier - One of the best experts on this subject based on the ideXlab platform.
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understanding sigma Phase Precipitation in a stabilized austenitic stainless steel 316nb through complementary calphad based and experimental investigations
Acta Materialia, 2014Co-Authors: Aurelien Perron, Caroline Toffolonmasclet, X Ledoux, Francois Buy, T Guilbert, Stephane Urvoy, S Bosonnet, Bernard Marini, Francois Cortial, G TexierAbstract:Abstract Sigma-Phase Precipitation in a 316Nb “stabilized” austenitic stainless steel was studied through complementary CALPHAD-based and dedicated experimental investigations. Thermokinetic calculations performed using Thermo-Calc (with the DICTRA module) and MatCalc software showed that the sigma Phase (σ) precipitated directly at γ-austenite grain boundaries (GB) via a common solid-state reaction when carbon and nitrogen contents fell below a critical threshold. Residual δ ferrite was found to be more susceptible to σ-Phase Precipitation; this type of Precipitation occurred via two mechanisms that depended on the concentration profiles of δ-ferrite stabilizing elements induced by previous thermomechanical processing: direct σ Precipitation (δ → σ) along the periphery of δ islands followed by a eutectoid decomposition (δ → σ + γ2) within these islands. Both simulations and experiments revealed that the σ Phase at γ GB contained higher amounts of Mo and Ni, while σ within δ ferrite possessed higher contents of Fe and Cr. Finally, the simulated time–temperature–Precipitation diagrams for the σ Phase in residual δ ferrite were found to be in very good agreement with the experimental ones and comparable to those observed in duplex stainless steels.
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kinetics of sigma Phase Precipitation in niobium stabilized austenitic stainless steel and effect on the mechanical properties
Materials Science Forum, 2014Co-Authors: X Ledoux, Aurelien Perron, Francois Buy, T Guilbert, Bernard Marini, G Texier, Eric Suzon, Jose Farre, Pierre Wident, V VignalAbstract:Stabilized austenitic stainless steels are widely used in nuclear and oil industries. The 316 Nb steel grade presented in this study holds a small amount of delta ferrite in the austenitic matrix which tends to transform into sigma Phase during prolonged exposures in the temperature range of 600-1000°C. Sigma Phase is promoted by ferritic elements such as chromium, molybdenum, niobium and silicon. Time-Temperature-Transformation (TTT) diagram of the δ-ferrite evolution is established thanks to DSC experiments and quantitative metallographic analysis. It is observed that the highest sigma Phase formation rate occurs between 800 and 900°C, and that the transformation of ferrite begins after a few minutes of exposure in this temperature range. The microstructure of transformed δ-ferrite is mostly dominated by the eutectoid mixture σ + γ2. Tensile tests were performed for three different cooling conditions: a significant embrittlement attributed to the δ-ferrite transformation is measured by a ductility loss for the lowest cooling rate.
