scholarly journals Sigma Phase: Nucleation and Growth

Metals ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 34 ◽  
Author(s):  
Gláucio Soares da Fonseca ◽  
Priscila Sousa Nilo Mendes ◽  
Ana Carolina Martins Silva
Keyword(s):  
Stainless Steels ◽  
Sigma Phase ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Interfacial Area ◽  
Intermetallic Phases ◽  
Phase Nucleation ◽  
The Mean ◽  
First Time ◽  
Kinetics Of

Duplex stainless steels (DSS) and superduplex stainless steels (SDSS) are important classes of stainless steels, because they combine the benefits of austenite and ferrite phases. This results in steels with better mechanical properties and higher corrosion resistance. Owing to these characteristics, DSS and SDSS are widely employed in industry. However, the appearance of undesirable intermetallic phases in their microstructure impairs the properties of DSS and SDSS. Among the undesirable intermetallic phases, the main one is the sigma phase (σ), which can be nucleated when the steel is exposed to the temperature range between 650 °C and 900 °C, reducing the steel’s toughness and resistance to corrosion. In a previous work, Fonseca and collaborators used two descriptors of the microstructural path to analyze the formation of sigma phase (σ), the interfacial area per unit volume between sigma phase and austenite (SV), and the mean chord length of sigma (<λ>), both as a function of VV, the volume fraction of sigma, known in the literature as the microstructural partial path (MP). In this work, the contiguity ratio is applied for the first time to describe the microstructural path in the study of sigma phase precipitation in SDSS. The contiguity ratio shows that the distribution of the ferrite/sigma boundaries is homogeneous. Thus, it is reasonable to infer that one has a uniform distribution of sigma phase nuclei within the ferrite. About the kinetics of sigma phase formation, the DSS can be described by the classical Johnson-Mehl, Avrami, and Kolmogorov (JMAK) equation, whereas for the SDSS, the kinetics tend to follow the Cahn model for grain edge nucleation. Finally, we present the three-dimensional (3D) reconstruction of the sigma phase in SDSS. The results demonstrate that the sigma phase nucleates at the edges of the ferrite/austenite interfaces. Moreover, the sigma phase grows and consumes the ferrite, but is not fully interconnected.

scholarly journals Sigma Phase: Nucleation and Growth

2018 ◽  
Author(s):  
Gláucio Fonseca ◽  
Priscila Mendes ◽  
Ana Silva
Keyword(s):  
Stainless Steels ◽  
Sigma Phase ◽  
Volume Fraction ◽  
Interfacial Area ◽  
Nucleation And Growth ◽  
Phase Precipitation ◽  
Phase Nucleation ◽  
First Time ◽  
Kinetics Of ◽  
Partial Path

Duplex Stainless Steels (DSS) and Superduplex Stainless Steels (SDSS) are an important class of stainless steels because they combine the benefits of austenite and ferrite phases, resulting in steels with better mechanical properties and higher corrosion resistance. Due to these characteristics are widely employed in various industries. However, the appearance of deleterious phases in their microstructure impairs the properties of DSS and SDSS. Among the deleterious phases, the main one is the sigma phase (&sigma;), which can be nucleated when the steel is exposed to the temperature range between 650 &deg;C and 900 &deg;C, reducing its toughness and resistance to corrosion. In a previous work, Fonseca and collaborators used two descriptors of the microstructural path to analyze the formation of sigma phase (&sigma;), SV, interfacial area per unit volume between sigma phase and austenite, and &lt;&lambda;&gt;, mean chord length of sigma, both in function of the VV, volume fraction of sigma, known in the literature as microstructural partial path (MP). In this work, the contiguity ratio is applied for the first time to describe the microstructural path in the study of sigma phase precipitation in SDSS. The contiguity ratio showed that the distribution of the ferrite/sigma boundaries is homogeneous. Thus, it is reasonable to infer that one has a uniform distribution of sigma phase nuclei within the ferrite. About the kinetics of sigma phase formation, the DSS can be described by the classical JMAK equation, whereas for the SDSS, the kinetics tends to follow the Cahn model for grain edge nucleation. Finally, we present the 3D reconstruction of the sigma phase in SDSS. The results demonstrate that the sigma phase nucleates at the edges of the ferrite/austenite interfaces. Moreover, the sigma phase grows consuming the ferrite, but it is not fully interconnected.

scholarly journals Study of the Precipitation of Secondary Phases in Duplex and Superduplex Stainless Steel

2016 ◽  
Vol 879 ◽  
pp. 2537-2542 ◽  
Author(s):  
Núria Llorca-Isern ◽  
Isabel López-Jiménez ◽  
Héctor López-Luque ◽  
Maria Victoria Biezma ◽  
Antoni Roca
Keyword(s):  
Sigma Phase ◽  
Intermetallic Phases ◽  
Isothermal Treatment ◽  
Secondary Phases ◽  
Chromium Nitrides ◽  
Superduplex Stainless Steel ◽  
Backscattered Electron ◽  
Phase Nucleation ◽  
Suitable Technique ◽  
Kinetics Of

The aim of this work is to study the precipitation mechanism of the intermetallic phases present in duplex stainless steels (UNS S32205 and UNS S32750), as well as to find out the most suitable method for detecting and analyzing accurately these secondary phases, particularly Sigma-phase, Chi-phase, nitrides and carbides. The samples were characterized after a solution annealing at 1080oC followed by an isothermal treatment at 830oC from 1 min to 9 h, with the purpose of figuring out the mechanism of chi-phase nucleation and nitrides formation in relation with the sigma-phase. The study has two main objectives: 1) to find out the most suitable technique for the detection, identification and quantification of the secondary phases, obtaining the best results with the combination of field emission scanning electron microscopy (FESEM) and backscattered electron detector (BSE) in comparison with the optical microscopy (MO); 2) to study the influence of the chemical composition on the nucleation mechanism of the intermetallic phases. It has been concluded that molybdenum balance content in chi-phase related to sigma phase is close to two, consequently the kinetics of nucleation and growth of these phases is remarkably faster when this alloying element content in the steel is higher. Chromium nitrides and carbides were also observed to precipitate as a result of the heat treatments carried out to the specimen wherein chromium nitrides role is a favorable site for the nucleation of sigma and chi phases.

Manufacture of Specialty Stainless Steels through Triplex Route at Mukand

2013 ◽  
Vol 794 ◽  
pp. 90-102
Author(s):  
Sunil Nair ◽  
Dominic Savio ◽  
Y. M. Srinivas ◽  
K.R. Srinivasan
Keyword(s):  
Stainless Steels ◽  
Sigma Phase ◽  
Intermetallic Phases ◽  
Low Carbon ◽  
Hot Workability ◽  
Corrosion Properties ◽  
Process Route ◽  
Phase Intermetallic ◽  
Phase Balance ◽  
Superior Corrosion Resistance

Specialty stainless steels designed with higher levels of Chromium, Nickel and Molybdenum than the general austenitic grades AISI 304 and AISI 316 have distinctly superior corrosion resistance properties. The commercial production of such high alloyed stainless steels came with advent of improved steel melting, refining and casting technologies. These technological improvements made it possible to produce such steels with low carbon levels and close control of chemical composition necessary to achieve the desired phase balance and avoid formation of undesirable intermetallic phases. Further, ability to achieve low sulphur levels combined with freedom from undesirable level of tramp elements improved the hot workability characteristics. Thermodynamic aspects of steelmaking and refining in Vacuum Oxygen Decarburization ( VOD) process for manufacture of specialty grades 904L (24% Ni, 20% Cr, 4% Mo, 1.2%Cu) , 317LM ( 19% Cr, 14.5% Ni, 4% Mo,) , 2205 ( 22.5% Cr, 5% Ni, 3% Mo) at Mukand through the Triplex process route ( Ultra High Power Furnace Oxygen Top and Bottom Blown Convertor VOD) are outlined. The effects of undesirable intermetallic phases, particularly sigma phase, on mechanical and corrosion properties are discussed. Application areas for such specialty grades are reviewed. Keywords: High alloyed Stainless steels, triplex process, sigma phase, intermetallic phases, tramp elements, hot workability, corrosion properties, vacuum oxygen decarburization.

The Effect of Surface on the Kinetics of Crystallization of Pd-Si Glassy Metals

1986 ◽  
Vol 80 ◽  
Author(s):  
A. Calka ◽  
A. P. Radliński
Keyword(s):  
Nucleation Rate ◽  
Metallic Glasses ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Growth Morphology ◽  
Thermally Activated ◽  
Glassy Metals ◽  
Dimensional Growth ◽  
Kinetics Of ◽  
Effect Of Surface

IntroductionThe isothermal devitrification by nucleation and growth of metallic glasses is usually analysed using the Johnson-Mehl-Avrami (JMA) equation: where x is the volume fraction crystallized after time t, K is a thermally activated rate constant, τ is the nucleation lag time, and n is the so-called Avrami exponent. If the nucleation conditions and growth morphology remain unchanged during the crystallization then n is a constant. There is ample experimental evidence that for the Pd-Si system the growth process is either eutectic or interface-controlled. Therefore, one expects n=3 for crystallization on pre-existing nuclei (zero nucleation rate) and n=4 for crystallization at constant nucleation rate, both for three-dimensional growth. When the growth dimensionality is decreased by one these values decrease stepwise by one as well.

scholarly journals Spatial Distribution of Bacterial Colonies in a Model Cheese

2010 ◽  
Vol 77 (4) ◽  
pp. 1493-1500 ◽  
Author(s):  
S. Jeanson ◽  
J. Chadœuf ◽  
M. N. Madec ◽  
S. Aly ◽  
J. Floury ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Fluorescent Protein ◽  
Three Dimensional ◽  
Interfacial Area ◽  
Food Type ◽  
Ripening Process ◽  
Cheese Ripening ◽  
Cell Biomass ◽  
The Mean ◽  
Green Fluorescent

ABSTRACTIn most ripened cheeses, bacteria are responsible for the ripening process. Immobilized in the cheese matrix, they grow as colonies. Therefore, their distribution as well as the distance between them are of major importance for ripening steps since metabolites diffuse within the cheese matrix. No data are available to date about the spatial distribution of bacterial colonies in cheese. This is the first study to model the distribution of bacterial colonies in a food-type matrix using nondestructive techniques. We compared (i) the mean theoretical three-dimensional (3D) distances between colonies calculated on the basis of inoculation levels and considering colony distribution to be random and (ii) experimental measurements using confocal microscopy photographs of fluorescent colonies of aLactococcus lactisstrain producing green fluorescent protein (GFP) inoculated, at different levels, into a model cheese made by ultrafiltration (UF). Enumerations showed that the final numbers of cells were identical whatever the inoculation level (104to 107CFU/g). Bacterial colonies were shown to be randomly distributed, fitting Poisson's model. The initial inoculation level strongly influenced the mean distances between colonies (from 25 μm to 250 μm) and also their mean diameters. The lower the inoculation level, the larger the colonies were and the further away from each other. Multiplying the inoculation level by 50 multiplied the interfacial area of exchange with the cheese matrix by 7 for the same cell biomass. We finally suggested that final cell numbers should be discussed together with inoculation levels to take into account the distribution and, consequently, the interfacial area of colonies, which can have a significant influence on the cheese-ripening process on a microscopic scale.

Random sequential packing simulations in three dimensions for aligned cubes

1989 ◽  
Vol 26 (3) ◽  
pp. 664-670 ◽  
Author(s):  
Douglas W. Cooper
Keyword(s):  
Volume Fraction ◽  
Three Dimensional ◽  
Random Packing ◽  
Limit Problem ◽  
Three Dimensions ◽  
Standard Errors ◽  
Cube Root ◽  
Random Errors ◽  
Infinite Region ◽  
The Mean

This particular three-dimensional random packing limit problem is to determine the mean fraction of a cubic space that would be occupied by aligned, fixed, equalsize cubes, placed at random locations sequentially until no more can be added. No analytical solution has yet been found for this problem. Simulation results for a finite region and finite number of attempts were extrapolated to an infinite number of attempts (N →∞) in an infinite region by multiple linear regression, using volume fraction occupied (F) as a linear combination of the ratio of the length of the small cube sides (S) to the length of the cubic region side (L) and the cube root of the ratio of the region volume to the total volume of cubes tried, (L3/NS3)⅓. These results for random packing in a volume with penetrable walls can be adjusted with a multiplicative correction factor to give the results for impenetrable walls. A total of N = 107 attempts at placement were made for L/S = 20/1 and N = 14 × 106 attempts were made for L/S = 10/1. The results for volume fraction packed are correlated by F = 0.430(±0.008) + 0.966(±0.072)(S/L) – 0.236(±0.029)(L3/NS)⅓. The numbers in parentheses are twice the standard errors of estimate of the coefficients, indicating the 95% confidence intervals due to random errors. This value for the packing density limit, 0.430 ± 0.008, is slightly larger than that given by a conjecture by Palásti [10], 0.4178. Our value is consistent with that obtained by rather different simulation methods by Jodrey and Tory [8], 0.4227 ± 0.0006, and by Blaisdell and Solomon [2], 0.4262.

Vanillin-based thiol-ene systems as photoresins for optical 3D printing

2019 ◽  
Vol 26 (2) ◽  
pp. 402-408 ◽  
Author(s):  
Aukse Navaruckiene ◽  
Sigita Kasetaite ◽  
Jolita Ostrauskaite
Keyword(s):  
Mechanical Properties ◽  
Real Time ◽  
Design Methodology ◽  
Three Dimensional ◽  
Insoluble Fraction ◽  
Content Type ◽  
Three Dimensional Printing ◽  
First Time ◽  
Dimensional Printing ◽  
Kinetics Of

Purpose This study aims to present a design and investigation of novel vanillin-based thiol-ene photocurable systems as candidate materials for optical three-dimensional printing. Design/methodology/approach Two vanillin acrylates, vanillin dimethacrylate and vanillin diacrylate, were tested in thiol-ene photocurable systems with 1,3-benzenedithiol. The kinetics of photocross-linking was investigated by real-time photorheometry using two photoinitiators, diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide or ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate in different quantities. The dependencies of rheological properties of resins on the used vanillin derivative, photoinitiator, and the presence of a solvent, as well as structure, thermal and mechanical properties of the selected polymers were investigated. Findings The most rigid polymers were obtained from vanillin diacrylate-based resins without any solvent. The vanillin diacrylate-based polymer possessed higher values of cross-linking density, the yield of insoluble fraction, thermal stability and better mechanical properties in comparison to the vanillin dimethacrylate-based polymer. Originality/value The kinetics of photocross-linking of vanillin-based thiol-ene systems was investigated by real-time photorheometry for the first time. The designed novel photocurable systems based on vanillin acrylates and 1,3-benzenedithiol are promising renewable photoresins for optical three-dimensional printing on demand.

A Numerical Study of Solid Suspension Layers in a Swirl Fluidised Bed Reactor

2009 ◽  
Vol 7 (1) ◽  
Author(s):  
Wei Zhang
Keyword(s):  
Volume Fraction ◽  
Numerical Study ◽  
Three Dimensional ◽  
Decay Process ◽  
Fluidised Bed ◽  
Swirl Intensity ◽  
Group A ◽  
Quantitative Manner ◽  
Fluidised Bed Reactor ◽  
First Time

Three–dimensional numerical simulations of an isothermal swirl fluidised bed (SFB) system with no chemical reactions were performed to study the swirl decay process and its effects on bed performance, i.e. particle concentration in the freeboard. The commercial CFD code package ANSYS 11.0 was chosen to carry out our simulation. We used 200?m glass beads with property similar to Geldart group A particles as the particulate phase with assumption that they are cohesionless and mono-dispersed, and air at 25°C as the gas phase in our simulation. Different initial swirl intensities were controlled by varying the secondary gas velocities. The solids volume fraction of solids suspension layers in the freeboard agreed generally well with literature description, which showed an annular shape with high values near the wall side. For the first time, swirl intensity and its decay process were predicted numerically by incorporating a swirl number function into ANSYS 11.0 and its effects on the bed fluid dynamics were also discussed in a qualitative or semi-quantitative manner.

Effect of prior cold ring rolling on carbide dissolution during the austenitizing process of an M50 bearing steel

2020 ◽  
Vol 10 (7) ◽  
pp. 1010-1019
Author(s):  
Jiao Su ◽  
Dongsheng Qian ◽  
Feng Wang
Keyword(s):  
Volume Fraction ◽  
Bearing Steel ◽  
Ring Rolling ◽  
Dissolution Behavior ◽  
Scanning Calorimetry ◽  
Cold Ring Rolling ◽  
The Matrix ◽  
Carbide Dissolution ◽  
The Mean ◽  
Kinetics Of

The influence of prior cold ring rolling (PCRR) on carbide dissolution during the austenitizing process of an M50 bearing steel was investigated by combining microstructural observations with kinetics analysis. The microstructural results show that the PCRR leads to a reduction in the volume fraction and the mean diameter of the undissolved carbides. The matrix of the as-quenched specimens after PCRR is enriched with more carbon and alloying elements than those without PCRR, which further confirms that the dissolution behavior of the alloy carbides is enhanced by PCRR during the austenitizing process. The kinetics of the transformation from ferrite to austenite (α → γ) without and with PCRR are determined by differential scanning calorimetry (DSC) upon heating. The austenite onset (Ac1) and end (Ac3) temperatures both decrease with as the thickness reduction from the PCRR increases. The activation energy for the α → γ transformation is calculated and shows a significant decline when the PCRR process is applied. In addition, the PCRR process results in a slight increase in the hardness regardless of the austenitizing temperature.

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