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Article
Publication date: 8 July 2019

Łukasz Łach, Dmytro Svyetlichnyy and Robert Straka

A fundamental principle of materials engineering is that the microstructure of a material controls the properties. The phase transformation is an important phenomenon that…

158

Abstract

Purpose

A fundamental principle of materials engineering is that the microstructure of a material controls the properties. The phase transformation is an important phenomenon that determines the final microstructure. Recently, many analytical and numerical methods were used for modeling of phase transformation, but some limitations can be seen in relation to the choice of the shape of growing grains, introduction of varying grain growth rate and modeling of diffusion phenomena. There are also only few comprehensive studies that combine the final microstructure with the actual conditions of its formation. Therefore, the objective of the work is a development of a new hybrid model based on lattice Boltzmann method (LBM) and cellular automata (CA) for modeling of the diffusional phase transformations. The model has a modular structure and simulates three basic phenomena: carbon diffusion, heat flow and phase transformation. The purpose of this study is to develop a model of heat flow with consideration of enthalpy of transformation as one of the most important parts of the proposed new hybrid model. This is one of the stages in the development of the complex model, and the obtained results will be used in a combined solution of heat flow and carbon diffusion during the modeling of diffusion phase transformations.

Design/methodology/approach

Different values of overheating/overcooling affect different values in the enthalpy of transformation and thus the rate of transformation. CA and LBM are used in the hybrid model in part related to heat flow. LBM is used for modeling of heat flow, while CA is used for modeling of the microstructure evolution during the phase transformation.

Findings

The use of LBM and CA in one numerical solution creates completely new possibilities for modeling of phase transformations. CA and LBM in comparison with commonly used approaches significantly simplify interface and interaction between different parts of the model, which operates in a common domain. The CA can be used practically for all possible processes that consist of nucleation and grains growth. The advantages of the LBM method can be well used for the simulation of heat flow during the transformation, which is confirmed by numerical results.

Practical implications

The developed heat flow model will be combined with the carbon diffusion model at the next stage of work, and the new complex hybrid model at the final stage will provide new solutions in numerical simulation of phase transformations and will allow comprehensive modeling of the diffusional phase transformations in many processes. Heating, annealing and cooling can be considered.

Originality/value

The paper presents the developed model of heat flow (temperature module), which is one of the main parts of the new hybrid model devoted to modeling of phase transformation. The model takes into account the enthalpy of transformation, and the connection with the model of microstructure evolution was obtained.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 27 March 2020

Łukasz Łach and Dmytro Svyetlichnyy

Some functional properties of engineering materials, i.e. physical, mechanical and thermal ones, depend directly on the microstructure, which is a result of processes occurring in…

Abstract

Purpose

Some functional properties of engineering materials, i.e. physical, mechanical and thermal ones, depend directly on the microstructure, which is a result of processes occurring in the material during the forming and thermomechanical processing. The proper microstructure can be obtained in many cases by the phase transformation. This phenomenon is one of the most important processes during hot forming and heat treatment. The purpose of this paper is to develop a new comprehensive hybrid model for modeling diffusion phase transformations. A problem has been divided into several tasks and is carried out on several stages. The purpose of this stage is a development of the structure of a hybrid model, development of an algorithm used in the diffusion module and one-dimensional heat flow and diffusion modeling. Generally, the processes of phase transformations are studied well enough but there are not many tools for their complex simulations. The problems of phase transformation simulation are related to the proper consideration of diffusion, movement of phase boundaries and kinetics of transformation. The proposed new model at the final stage of development will take into account the varying grain growth rate, different shape of growing grains and will allow for proper modeling of heat flow and carbon diffusion during the transformation in many processes, where heating, annealing and cooling can be considered (e.g. homogenizing and normalizing).

Design/methodology/approach

One of the most suitable methods for modeling of microstructure evolution during the phase transformation is cellular automata (CA), while lattice Boltzmann method (LBM) suits for modeling of diffusion and heat flow. Then, the proposed new hybrid model is based on CA and LBM methods and uses high performing parallel computations.

Findings

The first simulation results obtained for one-dimensional modeling confirm the correctness of interaction between LBM and CA in common numerical solution and the possibility of using these methods for modeling of phase transformations. The advantages of the LBM method can be used for the simulation of heat flow and diffusion during the transformation taking into account the results obtained from the simulations. LBM creates completely new possibilities for modeling of phase transformations in combination with CA.

Practical implications

The studies are focused on diffusion phase transformations in solid state in condition of low cooling rate (e.g. transformation of austenite into ferrite and pearlite) and during the heating and annealing (e.g. transformation of the ferrite-pearlite structure into austenite, the alignment of carbon concentration in austenite and growth of austenite grains) in carbon steels within a wide range of carbon content. The paper presents the comprehensive modeling system, which can operate with the technological processes with phase transformation during heating, annealing or cooling.

Originality/value

A brief review of the modeling of phase transformations and a description of the structure of a new CA and LBM hybrid model and its modules are presented in the paper. In the first stage of model implementation, the one-dimensional LBM model of diffusion and heat flow was developed. The examples of simulation results for several variants of modeling with different boundary conditions are shown.

Details

Engineering Computations, vol. 37 no. 8
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 1 July 1953

Ing. H. Reichert

EXACT methods for thermodynamic calculations of high temperature combustion processes at equilibrium are very involved and time‐consuming because of the increasing influence of

Abstract

EXACT methods for thermodynamic calculations of high temperature combustion processes at equilibrium are very involved and time‐consuming because of the increasing influence of dissociation with increasing temperatures above 1800dcg. K. Many simplified methods have been proposed, but most of them are still rather complicated or approximate and are cither suitable for a special type of application only or based on assumptions valid within conditional limits. From the research engineer's point of view Mollier‐charts (total heat—entropy diagrams) would be most useful, but for general use too many charts would be required. For every possible reaction as many charts as there are mixture ratios have to be considered. Professor Lutz of Braunschweig proposed in 1947 a new type of enthalpy‐chart, which enables a wide range of applications to be covered by a reasonable number of charts. A number of such charts have been constructed by the Ministry of Supply.

Details

Aircraft Engineering and Aerospace Technology, vol. 25 no. 7
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 1 March 1993

C.R. SWAMINATHAN and V.R. VOLLER

Two common fixed grid enthalpy methods used in the numerical modelling of phase change problems are the apparent heat capacity and the source based methods. In this paper, a…

1510

Abstract

Two common fixed grid enthalpy methods used in the numerical modelling of phase change problems are the apparent heat capacity and the source based methods. In this paper, a general enthalpy method that includes as subsets both apparent heat capacity and source based methods, is derived. Following this, an optimal enthalpy scheme is identified. The superiority of the optimal scheme over the apparent heat capacity and the source based schemes is illustrated by solving sample phase change problems.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 3 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 7 December 2023

Luca Sciacovelli, Aron Cannici, Donatella Passiatore and Paola Cinnella

The purpose of the paper is to analyse the performances of closures and compressibility corrections classically used in turbulence models when applied to highly-compressible…

Abstract

Purpose

The purpose of the paper is to analyse the performances of closures and compressibility corrections classically used in turbulence models when applied to highly-compressible turbulent boundary layers (TBLs) over flat plates.

Design/methodology/approach

A direct numerical simulation (DNS) database of TBLs, covering a wide range of thermodynamic conditions, is presented and exploited to perform a priori analyses of classical and recent closures for turbulent models. The results are systematically compared to the “exact” terms computed from DNS.

Findings

The few compressibility corrections available in the literature are not found to capture DNS data much better than the uncorrected original models, especially at the highest Mach numbers. Turbulent mass and heat fluxes are shown not to follow the classical gradient diffusion model, which was shown instead to provide acceptable results for modelling the vibrational turbulent heat flux.

Originality/value

The main originality of the present paper resides in the DNS database on which the a priori tests are conducted. The database contains some high-enthalpy simulations at large Mach numbers, allowing to test the performances of the turbulence models in the presence of both chemical dissociation and vibrational relaxation processes.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 14 September 2011

Shenghai Wang and Chuncheng Yang

The microstructure difference and enthalpy changes have been investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) during the as-cast…

Abstract

The microstructure difference and enthalpy changes have been investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) during the as-cast ageing process. After the as-cast ageing process, the eutectic silicon and α-Al is in the ideal state for the alloy with 0.08 wt% mischmetal (MM) addition. The energy of the phase transformations is 5.8 J/g during the isothermal process, when Al-11%Si-0.27%Mg alloy is aged at 150°C. When the additive contents of MM are 0.03, 0.06, 0.08 and 0.1 wt%, respectively, the energies of phase transformations are 4.98, 1.39, 1.07 and 1.25 J/g correspondingly. It is shown that the energies of phase transformations decrease gradually as the MM content increases from 0 wt% to 0.08 wt%; the energies then increase upon further addition of the MM concentration from 0.08 wt% to 0.1 wt% in the as-cast ageing process. Furthermore, the beginning time of phase transformations is delayed with the MM addition.

Details

World Journal of Engineering, vol. 8 no. 3
Type: Research Article
ISSN: 1708-5284

Keywords

Article
Publication date: 16 September 2013

Anirban Bhattacharya and Pradip Dutta

In the present work, a numerical method, based on the well established enthalpy technique, is developed to simulate the growth of binary alloy equiaxed dendrites in presence of

Abstract

Purpose

In the present work, a numerical method, based on the well established enthalpy technique, is developed to simulate the growth of binary alloy equiaxed dendrites in presence of melt convection. The paper aims to discuss these issues.

Design/methodology/approach

The principle of volume-averaging is used to formulate the governing equations (mass, momentum, energy and species conservation) which are solved using a coupled explicit-implicit method. The velocity and pressure fields are obtained using a fully implicit finite volume approach whereas the energy and species conservation equations are solved explicitly to obtain the enthalpy and solute concentration fields. As a model problem, simulation of the growth of a single crystal in a two-dimensional cavity filled with an undercooled melt is performed.

Findings

Comparison of the simulation results with available solutions obtained using level set method and the phase field method shows good agreement. The effects of melt flow on dendrite growth rate and solute distribution along the solid-liquid interface are studied. A faster growth rate of the upstream dendrite arm in case of binary alloys is observed, which can be attributed to the enhanced heat transfer due to convection as well as lower solute pile-up at the solid-liquid interface. Subsequently, the influence of thermal and solutal Peclet number and undercooling on the dendrite tip velocity is investigated.

Originality/value

As the present enthalpy based microscopic solidification model with melt convection is based on a framework similar to popularly used enthalpy models at the macroscopic scale, it lays the foundation to develop effective multiscale solidification.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 23 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 29 October 2021

Rasiha Nefise Mutlu, Ayşe Nur Acar and Ahmet Murat Gizir

Lightweight, durable and economical materials production has gained considerable importance according to the needs of developing technology. The purpose of this paper is to…

Abstract

Purpose

Lightweight, durable and economical materials production has gained considerable importance according to the needs of developing technology. The purpose of this paper is to develop an new aluminum alloy by powder metalurgy.

Design/methodology/approach

Powder metallurgy, which provides controllably on desired end product, method was applied. Aluminum alloy was created with Al, Zn, Mg, Cu powders and 1.5% Na2[B4O5(OH)4].8H2O added. It was pressed under high pressure and sintered at 600 °C under N2 gas atmosphere. Density, hardness behaviors and thermal properties were determined. Surfaces and crystal structures of samples were characterized.

Findings

The addition of borax made easier grains coming to together, acting as binders and the AlB2 crystal phase was formed. It was also observed that MgZn2, Al2CuMg phases were formed. In this way, the pores between the particles of the material were reduced from 35% to 5% total porosity and the hardness of the material was increased 29 N/mm2 to 45 N/mm2 (Brinell Hardness, HB). The surface properties improved and the hydrophobicity of the surface (from 63° to 102° contact angle with borax) increased. Thus, the heat transfer among atoms get easier and the borax addition decreased specific heat capacity and enthalpy of aluminum–borax samples. This situation was also simulated with the heat transfer module of COMSOL. As result, the energy required reduced. In the other word, sintering process occurred at low temperature and more efficient.

Originality/value

New aluminum alloy has been created from different amounts of Zn, Mg, Cu elemental powders. In addition to literature, relationship of borax and aluminum and other alloying elements on the mechanical, thermophysical and surface properties of new obtained aluminum alloy has been investigated.

Details

Anti-Corrosion Methods and Materials, vol. 69 no. 1
Type: Research Article
ISSN: 0003-5599

Keywords

Article
Publication date: 1 August 1998

G. Batis, N. Kouloumbi and E. Soulis

The aim of the present work was to compare the performance of two coating systems applied on steel specimens. The first of them demands sandblasting pretreatment of the metal…

432

Abstract

The aim of the present work was to compare the performance of two coating systems applied on steel specimens. The first of them demands sandblasting pretreatment of the metal surface while the second one, which does not need it, leads to rust transformation. These systems were examined in three corrosive environments i.e. a geothermal fluid of low enthalpy, a 3.5 wt per cent NaCl solution and a 5wt per cent NaCl in a salt spray cabinet. The anticorrosive capability of the two coating systems was evaluated at predetermined exposure times by mass loss measurements of the steel substrate, by potentiodynamic polarization curves and by the half‐cell potential time evolution. Visual examination of the degree of rusting and blistering was also carried out. The results indicate that both coating systems exhibit almost similar protective behavior under the same conditions of pretreatment. In all cases, the corrosion rate increases with the increase of the surface roughness.

Details

Anti-Corrosion Methods and Materials, vol. 45 no. 4
Type: Research Article
ISSN: 0003-5599

Keywords

Article
Publication date: 1 May 1993

MICHAEL J. NUSCA

An aerothermodynamic design code for axisymmetric projectiles has been developed using a viscous‐inviscid interaction scheme. Separate solution procedures for the inviscid and the…

Abstract

An aerothermodynamic design code for axisymmetric projectiles has been developed using a viscous‐inviscid interaction scheme. Separate solution procedures for the inviscid and the viscous (boundary layer) fluid dynamic equations are coupled by an iterative solution procedure. Non‐equilibrium, equilibrium and perfect gas boundary layer equations are included. The non‐equilibrium gas boundary layer equations assume a binary mixture (two species; atoms and molecules) of chemically reacting perfect gases. Conservation equations for each species include finite reaction rates applicable to high temperature air. The equilibrium gas boundary layer equations assume infinite rate reactions, while the perfect gas equations assume no chemical reactions. Projectile near‐wall and surface flow profiles (velocity, pressure, density, temperature and heat transfer) representing converged solutions to both the inviscid and viscous equations can be obtained in less than two minutes on minicomputers. A technique for computing local reverse flow regions is included. Computations for yawed projectiles are accomplished using a coordinate system transformation technique that is valid for small angle‐of‐attack. Computed surface pressure, heat transfer rates and aerodynamic forces and moments for 1.25 &le Mach No. &le 10.5 are compared to wind tunnel and free flight measurements on flat plate, blunt‐cone, and projectile geometries such as a cone‐cylinder‐flare.

Details

Engineering Computations, vol. 10 no. 5
Type: Research Article
ISSN: 0264-4401

Keywords

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