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.

A phase transformation study in the BaO · Al2O3 · 2SiO2 (BAS)–Si3N4 system

1995 ◽  
Vol 10 (12) ◽  
pp. 3143-3148 ◽  
Author(s):  
A. Bandyopadhyay ◽  
P.B. Aswath
Keyword(s):  
Phase Transformation ◽  
Phase Transformations ◽  
Metastable Phase ◽  
Heat Treating ◽  
Intermediate Step ◽  
Hexagonal Form ◽  
Heat Treated ◽  
Different Temperatures ◽  
Barium Aluminosilicate ◽  
Transformation Study

A phase transformation study was carried out with barium aluminosilicate (BAS) forming powders (BaCO3, Al2O3, and SiO2) in a BAS-Si3N4 system. Powders were heat-treated in air at 1 atm pressure at different temperatures from 600 to 1150 °C at an interval of 50 °C to study the phase transformations during the formation of BAS. The phase transformations of α to β-Si3N4 is studied by heat-treating the powders at 1600 °C for different sintering times in a nitrogen environment at 1 atm pressure. Formation of different phases was identified by using powder x-ray diffraction. Formation of different forms of barium silicates occurs as an intermediate step between 650 and 950 °C and hexagonal BAS forms between 900 and 950 °C. The hexagonal form of BAS always forms first and persists as a metastable phase in the composites with no evidence of the monoclinic phase. An attempt made to fully transform hexagonal BAS to monoclinic BAS by using LiF as a mineralizer proved to be successful. The hexagonal form of BAS forms first when heat-treated at 1000 °C and is fully transformed to monoclinic BAS when heat-treated at 1100 °C.

Metastable Phase Transformations in Ti-40Al-10V Alloy

1994 ◽  
Vol 364 ◽  
Author(s):  
G. Shao ◽  
P. Tsakiropoulos ◽  
A. P. Miodownik
Keyword(s):  
Phase Transformation ◽  
Phase Transformations ◽  
Volume Fraction ◽  
Metastable Phase ◽  
Equilibrium Phase ◽  
Rapid Quenching ◽  
Β Phase ◽  
Transformation Sequence ◽  
Melt Spun ◽  
Melt Spun Ribbons

AbstractThe microstructures in arc melted ingots and melt spun ribbons have been investigated by electron microscopy and thermodynamic modelling has been used to study the phase transformations. In the ingot, solidification starts with the bcc β phase and at room temperature the structure consists of B2, ωordered, γ and α2 phases. The calculated equilibrium phase transformation sequence during cooling is L → L+ β→β→β + α→β2+α → α+β2+γ → α2+γ + B2. The phase transformation sequence is dramatically changed by rapid quenching from the melt. Athermal ordered w phase is formed in metastable B2 and the α→α2 ordering process is completely suppressed in the melt spun ribbons. The volume fraction of the α precipitates is also dependent on cooling rates.

Evolution of order in amorphous-to-crystalline phase transformation of MgF2

2013 ◽  
Vol 46 (4) ◽  
pp. 1105-1116 ◽  
Author(s):  
Xiaoke Mu ◽  
Sridhar Neelamraju ◽  
Wilfried Sigle ◽  
Christoph T. Koch ◽  
Nico Totò ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Electron Diffraction ◽  
Short Range ◽  
Volume Fraction ◽  
Metastable Phase ◽  
Dynamics Simulation ◽  
Structure Evolution ◽  
Stable Phase ◽  
Type Phase ◽  
Short Range Ordering

Structural disorder and distortion play a significant role in phase transformations. Experimentally, electron diffraction in the transmission electron microscope offers the ability to characterize disorderviathe pair distribution function (PDF) at high spatial resolution. In this work, energy-filteredin situelectron diffraction is applied to measure PDFs of different phases of MgF2from the amorphous deposit through metastable modifications to the thermodynamically stable phase. Despite the restriction of thick specimens resulting in multiple electron scattering, elaborate data analysis enabled experimental and molecular dynamics simulation data to be matched, thus allowing analysis of the evolution of short-range ordering. In particular, it is possible to explain the theoretically not predicted existence of a metastable phase by the presence of atomic disorder and distortion. The short-range ordering in the amorphous and crystalline phases is elucidated as three steps: (i) an initial amorphous phase exhibiting CaCl2-type short-range order which acts as a crystallization nucleus to guide the phase transformation to the metastable CaCl2-type phase and thus suppresses the direct appearance of the rutile-type phase; (ii) a metastable CaCl2-type phase containing short-range structural features of the stable rutile type; and (iii) the formation of a large volume fraction of disordered intergranular regions which stabilize the CaCl2-type phase. The structure evolution is described within the energy landscape concept.

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 Nucleation of {1012} Twins in Magnesium through Reversible Martensitic Phase Transformation

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1030
Author(s):  
Jamie Ombogo ◽  
Amir Hassan Zahiri ◽  
Tengfei Ma ◽  
Lei Cao
Keyword(s):  
Phase Transformation ◽  
Phase Transformations ◽  
Tetragonal Phase ◽  
Metastable Phase ◽  
Critical Role ◽  
Martensitic Phase ◽  
Growth Speed ◽  
Orientation Relations ◽  
Martensitic Phase Transformations ◽  
Dynamics Simulations

We report the discovery of a rigorous nucleation mechanism for {101¯2} twins in hexagonal close-packed (hcp) magnesium through reversible hcp-tetragonal-hcp martensitic phase transformations with a metastable tetragonal phase as the intermediate state. Specifically, the parent hcp phase first transforms to a metastable tetragonal phase, which subsequently transforms to a twinned hcp phase. The evanescent nature of the tetragonal phase severely hinders its direct observation, while our carefully designed molecular dynamics simulations rigorously reveal the critical role of this metastable phase in the nucleation of {101¯2} twins in magnesium. Moreover, we prove that the reversible hcp-tetragonal-hcp phase transformations involved in the twinning process follow strict orientation relations between the parent hcp, intermediate tetragonal, and twin hcp phases. This phase transformation-mediated twinning mechanism is naturally compatible with the ultrafast twin growth speed. This work will be important for a better understanding of the twinning mechanism and thus the development of novel strategies for enhancing the ductility of magnesium alloys.

Heat capacities and enthalpies of fusion and transformation for solvates of some salts with dimethyl sulfoxide and dimethylformamide

1988 ◽  
Vol 53 (12) ◽  
pp. 3072-3079
Author(s):  
Mojmír Skokánek ◽  
Ivo Sláma
Keyword(s):  
Heat Capacity ◽  
Phase Transformation ◽  
Phase Transformations ◽  
Dimethyl Sulfoxide ◽  
Liquidus Temperature ◽  
Molar Heat Capacity ◽  
Solid Phase ◽  
Zinc Nitrate ◽  
Heat Capacities ◽  
Liquid Phases

Molar heat capacities and molar enthalpies of fusion of the solvates Zn(NO3)2 . 2·24 DMSO, Zn(NO3)2 . 8·11 DMSO, Zn(NO3)2 . 6 DMSO, NaNO3 . 2·85 DMSO, and AgNO3 . DMF, where DMSO is dimethyl sulfoxide and DMF is dimethylformamide, have been determined over the temperature range 240 to 400 K. Endothermic peaks found for the zinc nitrate solvates below the liquidus temperature have been ascribed to solid phase transformations. The molar enthalpies of the solid phase transformations are close to 5 kJ mol-1 for all zinc nitrate solvates investigated. The dependence of the molar heat capacity on the temperature outside the phase transformation region can be described by a linear equation for both the solid and liquid phases.

scholarly journals Stable and Metastable Phase Equilibria Involving the Cu6Sn5 Intermetallic

2021 ◽  
Author(s):  
A. Leineweber ◽  
M. Löffler ◽  
S. Martin
Keyword(s):  
Phase Equilibria ◽  
Electron Backscatter Diffraction ◽  
Metastable Phase ◽  
Stable Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Heat Treated ◽  
Ordered Phases ◽  
Backscatter Diffraction ◽  
Kinetics Of

Abstract Cu6Sn5 intermetallic occurs in the form of differently ordered phases η, η′ and η′′. In solder joints, this intermetallic can undergo changes in composition and the state of order without or while interacting with excess Cu and excess Sn in the system, potentially giving rise to detrimental changes in the mechanical properties of the solder. In order to study such processes in fundamental detail and to get more detailed information about the metastable and stable phase equilibria, model alloys consisting of Cu3Sn + Cu6Sn5 as well as Cu6Sn5 + Sn-rich melt were heat treated. Powder x-ray diffraction and scanning electron microscopy supplemented by electron backscatter diffraction were used to investigate the structural and microstructural changes. It was shown that Sn-poor η can increase its Sn content by Cu3Sn precipitation at grain boundaries or by uptake of Sn from the Sn-rich melt. From the kinetics of the former process at 513 K and the grain size of the η phase, we obtained an interdiffusion coefficient in η of (3 ± 1) × 10−16 m2 s−1. Comparison of this value with literature data implies that this value reflects pure volume (inter)diffusion, while Cu6Sn5 growth at low temperature is typically strongly influenced by grain-boundary diffusion. These investigations also confirm that η′′ forming below a composition-dependent transus temperature gradually enriches in Sn content, confirming that Sn-poor η′′ is metastable against decomposition into Cu3Sn and more Sn-rich η or (at lower temperatures) η′. Graphic Abstract

Effect of copper incorporation on phase transformation behavior of electroless nickel–phosphorous coating and its effect on the tribological behavior

2020 ◽  
pp. 146442072098160
Author(s):  
Abhijit Biswas ◽  
Suman Kalyan Das ◽  
Prasanta Sahoo
Keyword(s):  
Heat Treatment ◽  
Phase Transformation ◽  
Tribological Behavior ◽  
Electroless Nickel ◽  
Two Phase ◽  
Microstructural Changes ◽  
Treatment Conditions ◽  
Heat Treated ◽  
Higher Temperature ◽  
Effect Of Copper

The microstructural changes of electroless Ni–P–Cu coating at various heat-treatment conditions are investigated to understand its implications on the tribological behavior of the coating. Coatings are heat-treated at temperatures ranging between 200°C and 800 °C and for 1–4 h duration. Ni–P–Cu coatings exhibit two-phase transformations in the temperature range of 350–450 °C and the resulting microstructural changes are found to significantly affect their thermal stability and tribological attributes. Hardness of the coating doubles when heat-treated at 452 °C, due to the formation of harder Ni3P phase and crystalline NiCu. Better friction and wear performance are also noted upon heat treatment of the coating at the phase transformation regime, particularly at 400 °C. Wear mechanism is characterized by a mixed adhesive cum abrasive wear phenomena. Heat treatment at higher temperature (600 °C and above) and longer duration (4 h) results in grain coarsening phenomenon, which negatively influences the hardness and tribological characteristics of the coating. Besides, diffusion of iron from the ferrous substrate as well as greater oxide formation are noticed when the coating is heat-treated at higher temperatures and for longer durations (4 h).

Calculations of Phase Transformations in Welding Simulations

2014 ◽  
Vol 611 ◽  
pp. 46-53 ◽  
Author(s):  
Ladislav Novotný ◽  
Vladimír Ivančo
Keyword(s):  
Heat Flux ◽  
Phase Transformation ◽  
Boundary Conditions ◽  
Phase Transformations ◽  
Diffusion Processes ◽  
Transient Solution ◽  
Welding Simulation

In the paper the principle of welding simulation is presented and the methods of solution of phase transformation are described. The first part characterizes elementary equations of heat transient solution, boundary conditions during welding simulation (prescribing moving heat flux, convection, radiation). The methods of phase transformations’ solution are described for diffusion processes as well as diffusionless processes.

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