Supersaturation and solute enrichment and their role in phase transformations in metal alloys

2011 ◽  
Vol 83 (5) ◽  
pp. 1085-1092 ◽  
Author(s):  
Markus Rettenmayr
Keyword(s):  
Phase Transformation ◽  
Phase Transformations ◽  
Single Phase ◽  
Driving Forces ◽  
Secondary Phase ◽  
Transformation Process ◽  
Primary Phase ◽  
Two Phase ◽  
Phase Mixture ◽  
Phase Out

Supersaturations and depletion or enrichment of solute/solvent are known to be the driving forces for phase transformations. In the present work, a series of different experiments is presented where in a single phase or a two-phase mixture supersaturation or enrichment/depletion of solute occur in at least one of the phases. In all cases the result is a phase transformation, particularly either the precipitation of a secondary phase out of a primary phase, or the migration of the interface in a two-phase mixture. It is demonstrated that solute transport in the phase exhibiting faster kinetics controls the phase transformation process.

scholarly journals Constitutive Modelling and Identification of Parameters of 316L Stainless Steel at Cryogenic Temperatures

2014 ◽  
Vol 8 (3) ◽  
pp. 136-140 ◽  
Author(s):  
Maciej Ryś
Keyword(s):  
Phase Transformation ◽  
Nonlinear Response ◽  
316L Stainless Steel ◽  
Parent Phase ◽  
Secondary Phase ◽  
Material Model ◽  
Transformation Process ◽  
Constitutive Modelling ◽  
Model Parameters ◽  
Two Phase

Abstract In this work, a macroscopic material model for simulation two distinct dissipative phenomena taking place in FCC metals and alloys at low temperatures: plasticity and phase transformation, is presented. Plastic yielding is the main phenomenon occurring when the yield stress is reached, resulting in nonlinear response of the material during loading. The phase transformation process leads to creation of two-phase continuum, where the parent phase coexists with the inclusions of secondary phase. An identification of the model parameters, based on uniaxial tension test at very low temperature, is also proposed.

Studies of phase transformation of Fe1-xS by in Situ TEM

1989 ◽  
Vol 47 ◽  
pp. 648-649
Author(s):  
Thao A. Nguyen ◽  
Linn W. Hobbs
Keyword(s):  
Phase Transformation ◽  
Single Phase ◽  
Nucleation And Growth ◽  
In Situ Tem ◽  
Two Phase ◽  
S Matrix ◽  
In Situ Heating ◽  
Phase Mixture ◽  
Lamellar Type

The transformation from Fe1-xS (IC) phase to a mixture of FeS (2C) and iron poor Fe1-xS (IC) phases has been investigated by a series of in-situ heating experiments. The purpose of this study is to resolve the controversy over the mechanism of phase transformation (spinodal decomposition versus nucleation and growth) and to explain the different microstructures observed in the two phase mixture of FeS and Fe1-xS (Figure 1).In-situ heating experiments were carried out using a JEOL JEM EM-SHTH double tilt heating holder. Synthetic “single” Fe0.97S crystals were cut into 3 mm disks, mechanically and ion thinned to electron transparency. In all cooling experiments, the sample was first held at 390 K, a temperature above the transition temperature in order to generate an initial single phase material; then, the temperature was quickly reduced to the temperature of interest.Figure 2a shows the development of a lamellar type microstructure after the sample's temperature was reduced from 390 K to 363 K and then held at this temperature for ten minutes. At 363 K, the undercooling is 27 K. The troilite FeS (2C) phase heterogeneously nucleates and grows along the edge of the sample. Diffraction analysis shows that the FeS (2C) phase is embedded in the iron-poor Fe1-x,S matrix with a rod-like structure.

scholarly journals Directional Solidification of Sn-Cu6Sn5 In Situ Composites

2019 ◽  
Vol 2019 ◽  
pp. 1-8 ◽  
Author(s):  
Osvaldo Fornaro
Keyword(s):  
Directional Solidification ◽  
Eutectic Reaction ◽  
Secondary Phase ◽  
Phase Region ◽  
Primary Phase ◽  
Point Of View ◽  
System Stability ◽  
Two Phase ◽  
Directional Growth ◽  
Free Solder

The Sn-Cu system presents an important interest from academic and technological point of view because it is part of the family of alloys proposed as lead-free solder alloys for electronic components and also due to the mechanisms involved during the growth of the different phases. Sn-Cu system has two intermetallic phases, i.e., ε-Cu3Sn and η-Cu6Sn5, and η can be used as the negative (anode) electrode in Li-ion batteries, alone or as part of (Co,Ni)xCu6−xSn5-type composites. Obtaining this η phase from liquid with the appropriate chemical composition is a very difficult task because it has a formation temperature lower than liquidus for such a composition. In this way, the η phase appears as a consequence of a solid-solid transformation from the ε phase However, it is possible to find the η phase as the primary or secondary phase after a eutectic reaction for lower concentrations of Cu. On the other side, the Cu6Sn5 phase shows a hexagonal to monoclinic solid-solid transformation around 187°C, which could affect the mechanical system stability when it is used as solder. In this work, directional solidification at different growth velocities of hypereutectic Sn-Cu samples was performed. The resultant microstructure varies with the growth velocity, but it is formed for a fibber-like primary phase Cu6Sn5 which is projected towards the liquid phase. Behind this region, these fibbers are rounded by a two-phase Sn-Cu6Sn5 structure. In this way, three zones could to be defined in the sample during the directional growth: (i) an entirely solid two-phase region, formed by η rounded by β(Sn) + η eutectic-like structure, (ii) a two-phase solid (η) + liquid, and (iii) the remnant liquid in front of the interface.

Lithium electrochemical deintercalation from O2-LiCoO2: structural study and first principles calculations

2002 ◽  
Vol 756 ◽  
Author(s):  
D. Carlier ◽  
A. Van der Ven ◽  
G. Ceder ◽  
L. Croguennec ◽  
M. Ménétrier ◽  
...  
Keyword(s):  
Phase Transformations ◽  
Density Functional ◽  
Driving Forces ◽  
Charge Ordering ◽  
Ionic Exchange ◽  
Two Phase ◽  
Entropy Maximization ◽  
Vacancy Ordering ◽  
Voltage Curve ◽  
Ordered Phases

ABSTRACTWe present a detailed study of the O2-LiCoO2 phase used as positive electrode in lithium batteries. This phase is a metastable form of LiCoO2 and is prepared by ionic exchange from P2-Na0.70CoO2. The O2-LiCoO2 system presents interesting fundamental problems as it exhibits several phase transformations upon lithium deintercalation that imply either CoO2 sheet gliding or lithium/vacancy ordering. Two unusual structures are observed: T#2 and O6. The T#2 phase was characterized by X-ray, neutron and electron diffraction, whereas the O6 phase was only characterized by XRD.In order to better understand the structures and the driving forces responsible for the phase transformations involved in lithium deintercalation, we combine our experimental study of this system with a theoretical approach. The voltage-composition curve at room temperature is calculated using Density Functional Theory combined with Monte Carlo simulations, and is qualitatively in good agreement with the experimental voltage curve over the complete lithium composition range. Pseudopotential and thermodynamic calculations both show that two tetrahedral sites have to be considered for Li in the T#2 structure. The calculated voltage curve thus exhibits a two-phase O2/T#2 region that indicates that this phase transformation is driven by the entropy maximization and not by a non-metal to metal transition. We also predict two ordered phases for Li1/4CoO2 (O2) and Li1/3CoO2 (O6) and show that the formation of the O6 phase is not related to Li staging or Co3+/Co4+ charge ordering.

scholarly journals Effect of a Symmetric Contraction on the Concentration Profiles of a Particle-Laden Slurry

2011 ◽  
Author(s):  
A. Deshpande ◽  
K. Ramisetty ◽  
F. W. Chambers ◽  
M. E. McNally ◽  
R. M. Hoffman
Keyword(s):  
Single Phase ◽  
Solid Phase ◽  
Fluid Dynamic ◽  
Density Ratio ◽  
Primary Phase ◽  
Solid Particles ◽  
Concentration Profiles ◽  
Two Phase ◽  
Horizontal Pipe ◽  
Slurry Concentration

In-line measurements and sample stream withdrawals for on-line and/or at-line measurements of slurries flowing in horizontal pipes can be complicated by nonuniform slurry profiles. More uniform profiles would improve measurements. Area contractions are a common means used to produce more uniform velocity fields for single phase flows. For example, contractions are used to condition the flow entering wind tunnel test sections and make velocity profiles more uniform at venturi throats. It was desired to determine whether area contractions could be used to make slurry concentration profiles more uniform in horizontal pipe flows. An ASME flow nozzle with a contraction diameter ratio of 0.5 was chosen as a well defined geometry to consider in a Computational Fluid Dynamic (CFD) study of the effects of a contraction on slurry concentration profiles. The pipe was 2.8 m long with a 50.8 mm diameter. The entrance of the contraction was placed at 35 pipe diameters from the inlet in fully developed flow. A length of 20 diameters followed the contraction. The slurry had a xylene liquid phase and an ADP solid phase with a density ratio of 1.7. The simulations were performed at primary phase velocities of 2 m/s and 4 m/s, corresponding to Reynolds numbers of 1.4E05 and 2.8E05. Spherical particle diameters of 38, 75, and 150 μm were used at concentrations of 0.05, 0.2, and 0.3. ANSYS FLUENT 12 software was used with the standard k-ε turbulence model and standard wall function. The mixture multi-phase model was used for the two-phase flow. An unstructured tetrahedral meshing scheme was used with 1.4 million elements. The grid was adjusted until the condition 30 < y+ <60 for the mesh point nearest the wall was satisfied. A grid refinement study was performed to insure grid independence. The computational scheme first was validated by comparing pipe flow velocity and concentration profiles to results in the literature. The computations performed with the contraction showed that in all cases the concentration profiles of the solid particles displayed greater uniformity than the profiles in the pipe upstream of the contraction. The effect of the contraction was more pronounced for the larger particles. As in the case of single phase flows, the contraction caused the axial turbulence intensity to decrease. The greater uniformity of the concentration profiles at the exit plane of the nozzle, suggest that the contraction can provide better conditions for performing measurements of a particle-laden slurry.

Peritectoid carbide transformation based on ε-carbide Fe2C in Fe-C-system alloys. Part 1. Basics of theory

2020 ◽  
pp. 15-21
Author(s):  
S. V. Davydov ◽  
Keyword(s):  
Phase Transformation ◽  
Phase Transformations ◽  
Metastable Phase ◽  
State Diagram ◽  
Stable Phase ◽  
Cement Slurry ◽  
Two Phase ◽  
Peritectoid Transformation ◽  
Decomposition Phase ◽  
Carbon System

In the present work low-temperature carbide phase transformations in the system of Fe-C alloys based on ε-сarbide Fe2C with consideration of identification of θ-Fe3C cement as a solid solution were studied. It has been proved that the θ-Fe3C cement slurry is colourfastonide, and the ε-Fe2C carbide slurry is bertollide. When tempering hardened steels, ε-сarbide Fe2C is emitted in the structure of hardened martensite, which is absent in the phase diagram of iron-carbon system alloys. It is believed that ε-сarbide Fe2C is not a stable phase, and since it is metastable, it is formed only in quenched steels under non-equilibrium conditions. The isolation and dissolution of ε-сarbide Fe2C is a classic phase transformation and the absence of this transformation on the diagram is not caused by the metastable phase of ε-сarbide Fe2C, but by the incomplete iron-carbon diagram. The martensite decomposition phase transformation is based on the formation of carbon enriched zones. The processes of carbon segregation on dislocation structures and grid planes of martensite create zones with excess energy. Beginning approximately with temperature 100 °С in structure of martensite begins to allocate ε-сarbide Fe2C, finishing a stage of two-phase segregational disintegration of martensite. At rather small concentrations of carbon in cluster zones the fastest and most effective way of relaxation of redundant energy in these zones, as well as in the tetragonal lattice of martensite is the formation of phases with low value of work of nucleation, first of all ε-сarbide Fe2C and α-Fe(C) or ferrite. The main stages of phase transformations in the peritectoid reaction of martensite decomposition are considered. It is proposed to introduce the peritectoid transformation horizontal at 382 °C and the peritectic transformation horizontal of cement at 1650 °C into the Fe-C alloy state diagram.

Phase Stability in the Al(6−x)CuxZr2 System for 0 < × < 1.

1990 ◽  
Vol 186 ◽  
Author(s):  
P. B. Desch ◽  
R. B. Schwarz ◽  
P. Nash
Keyword(s):  
Thermal Stability ◽  
Phase Stability ◽  
Single Phase ◽  
Lattice Parameter ◽  
Elemental Powder ◽  
Mechanically Alloyed ◽  
Two Phase ◽  
Powder Mixtures ◽  
Phase Mixture ◽  
Thermal Stability Of

AbstractWe have determined the structures and thermal stability of AI(6-x) CuxZr2 (0≤ × ≤ 1) powders prepared by mechanically alloying elemental powder mixtures. In the as mechanically alloyed condition the structure is L12 for all ×. After heating to 750°C the alloy is single phase D023 for 0 < × < 0.2, is a two-phase mixture of D023 and L12 for 0.2 < × < 0.6, and remains in the Ll2 phase for 0.6 < × < 1. Al5CuZr2 is stable in the Ll2 structure up to 1300°C. The lattice parameter of the annealed L12 phase is Independent of ×.

Design of a novel single‐phase in two‐phase out matrix converter driving an induction motor

2016 ◽  
Vol 9 (7) ◽  
pp. 1391-1397 ◽  
Author(s):  
Gullu Boztas ◽  
Sedat Sünter ◽  
Omur Aydogmus
Keyword(s):  
Induction Motor ◽  
Single Phase ◽  
Matrix Converter ◽  
Two Phase ◽  
Phase Out

COMPONENT MINIMIZED TOPOLOGY OF DC TO THREE-PHASE INVERTER

2004 ◽  
Vol 13 (04) ◽  
pp. 863-875 ◽  
Author(s):  
MIRO MILANOVIC ◽  
FRANC MIHALIC ◽  
DRAGO DOLINAR
Keyword(s):  
Phase Transformation ◽  
Theoretical Analysis ◽  
Single Phase ◽  
Main Element ◽  
Two Phase ◽  
Phase Inverter ◽  
Three Phase ◽  
Phase Converter ◽  
Inverter Topology ◽  
Three Phase Inverter

A DC to three-phase converter based on using a two-phase to three-phase transformation has been developed. To provide a better understanding of the operation principle, the transformer, which is the main element of the system, has been supplied by two single-phase inverters. According to this, the theoretical analysis of the proposed system is shown. This analysis is based on two-phase to three-phase transformation. The theoretical analysis and the experimental verification of the proposed principle are presented. In this paper the component minimized inverter topology is also proposed.

scholarly journals Establishing regularities in the propagation of phase transformation front during timber thermal modification

2021 ◽  
Vol 1 (10 (109)) ◽  
pp. 30-36
Author(s):  
Yuriy Tsapko ◽  
Oleksandra Horbachova ◽  
Аleksii Tsapko ◽  
Serhii Mazurchuk ◽  
Denys Zavialov ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Phase Transformations ◽  
Moisture Absorption ◽  
Chemical Properties ◽  
Water Repellency ◽  
Temperature Treatment ◽  
Transformation Process ◽  
Thermal Modification ◽  
Building Structures ◽  
Hardness Increase

The creation of environmentally friendly protective materials for building structures made of wood could make it possible to influence the processes of stability and the physical-chemical properties at the thermal modification of hornbeam wood over a certain time. That necessitates studying the conditions for investigating phase transformations when the timber is exposed to high temperature, as well as establishing the mechanism of hornbeam wood thermal modification. Given this, a mathematical model of the phase transformation process during the transfer of heat flux to a sample was built. Based on the derived dependences, it was established that when hornbeam wood is exposed to temperature treatment, it undergoes endothermic phase transformations characterized by the heat absorption and change in the color of hornbeam wood. In particular, at a temperature of 200 °C, the temperature in the wood decreases by 5 % due to the chemical changes in the structure of cell wall components (lignin, cellulose, and hemicellulose). It was found that the process of thermal modification is accompanied by the decomposition of hemicellulose and the amorphous part of cellulose, a decrease in moisture absorption, as well as a decrease in the volume of substances that are a medium for the development of fungi. In addition, lignin and the resulting pseudo lignin undergo a process of polymerization and redistribution throughout the cell volume. At the same time, they give the cell walls higher density, hardness, increase hydrophobicity (water repellency), thereby reducing the ability to absorb moisture and swell. It was established that the most effective parameter of phase transformations is the temperature and aging duration. The results of moisture absorption have been given; it has been found that over 6 hours of modified timber exposure, its moisture absorption decreases by more than 10 times, which allows its application at facilities with high humidity

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