A. P. Miodownik’s research while affiliated with Surrey Place Centre and other places

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Publications (89)


Modelling of the Thermo-Physical and Physical Properties for Solidification of Al-Alloys
  • Chapter

January 2016

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38 Reads

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12 Citations

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X. Li

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A. P. Miodownik

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J.-P. Schillé

The thermo-physical and physical properties of the liquid and solid phases are critical components in casting simulations. Such properties include the fraction solid transformed, enthalpy release, thermal conductivity, volume and density, all as a function of temperature. Due to the difficulty in experimentally determining such properties at solidification temperatures, little information exists for multi-component alloys. As part of the development of a new computer program for modelling of materials properties (JMatPro) extensive work has been carried out on the development of sound, physically based models for these properties. Wide ranging results will presented for Al-based alloys, which will include more detailed information concerning the density change of the liquid that intrinsically occurs during solidification due to its change in composition.


Modelling of the Thermo-Physical and Physical Properties for Solidification of Mg-Alloys

January 2016

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26 Reads

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3 Citations

The thermo-physical and physical properties of the liquid and solid phases are critical components in casting simulations. Such properties include the fraction solid transformed, enthalpy release, thermal conductivity, volume and density all as a function of temperature. Due to the difficulty in experimentally determining such properties at solidification temperatures, little information exists for multi-component alloys. As part of the development of a new computer program for modeling of materials properties (JMatPro) extensive work has been carried out on the development of sound, physically based models for these properties. Wide ranging results will presented for Mg-based alloys including more detailed information concerning the density change of the liquid that intrinsically occurs during solidification due to its change in composition.


Modelling Deformation-Induced Precipitation Kinetics in Microalloyed Steels during Hot Rolling
  • Article
  • Publisher preview available

January 2012

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32 Reads

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5 Citations

This paper reports the framework of a computer model that calculates the precipitation kinetics of MX type carbides or carbonitrides from austenite matrix in microalloyed steels during hot rolling. The kinetic model is based on the classical Johnson-Mehl-Avrami theory adapted to include the saturation of nucleation sites. The effect of deformation on precipitation kinetics is quantitatively described through its effect on flow stress, from which the number of potential nucleation sites can be estimated. The time-temperature precipitation diagram can then be calculated for a given alloy chemistry and deformation conditions. A preliminary study has been carried out to test its performance in both undeformed and deformed conditions.

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Modelling materials properties critical to simulation of thermomechanical processing in titanium alloys

January 2012

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32 Reads

This paper reviews the development of materials models that are able to calculate the material data required in the computer-aided engineering (CAE) simulation of thermomechanical processing in titanium alloys,including: Time-temperature transformation (TTT) and continuous-cooling transformation (CCT) diagrams; Physical and thermophysical properties,e. g. density,thermal conductivity, Young's modulus,and specific heat; Temperature and strain rate dependent mechanical properties,including high temperature strength and flow stress curves. All the materials models developed have been implemented in the computer software JMatPro so that they can be easily used by process modellers. The material data calculated can now be organised in such a format that can be directly read by commercial CAE simulation packages for casting, forging, welding and heat treatment simulation.


Figure 1 Microstructure evolution in a 4140 steel during cooling at (a) 20°C/s and (b) 5°C/s (see online version for colours)
Figure 2 Properties calculated for a 4140 steel at cooling rates from 0.01°C/s to 100°C/s (see online version for colours)
Figure 3 Cooling curves for three positions from quenching end on a Jominy bar (see online version for colours)
Figure 4 Microstructure change along the Jominy quench bar for (a) 4140, and (b) 5140 alloys (see online version for colours)
Figure 5 Jominy hardenability comparison between experimental and calculated curves for (a) 4140, and (b) 5140 alloys (see online version for colours)

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Modeling Phase Transformations and Material Properties Critical to Processing Simulation of Steels

February 2011

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643 Reads

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45 Citations

This article describes the development of JMatPro, a computer software that can provide many of the material properties required by processing simulation. The success of the model is based on accurate description of all major phase transformations taking place, as well as calculation of the properties of different phases formed during the heat treatment process. Predictive phase transformation models in the past mainly concerned carbon and low alloy steels. An advantage of the current model is that it can be applied to many types of steels, including medium to high alloy types. In addition to TTT/CCT diagrams, a wide range of physical, thermophysical, and mechanical properties, including strength and stress-strain curves, can be calculated.


Homogenisation of Cast Microstructures: Thermodynamic Calculation and Kinetic Simulation

This paper uses a combination of thermodynamic calculation and kinetic simulation to model the homogenisation process of cast microstructure for multi-component alloys. The approach assumes that the solute segregation profile across the half dendrite arm spacing can be scaled to the solute concentration profile during solidification as generated by a Scheil type calculation. When secondary phases dissolve during homogenisation, they are treated as an additional fraction of pseudo-eutectic to the initial solute concentration profile of the primary solution phase. The methodology is compared with the assumptions made by other authors, highlighting the significant advantages in the present treatment. Examples are drawn from a cast nickel-based superalloy.


Material properties for process simulation

January 2009

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434 Reads

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114 Citations

Materials Science and Engineering A

This paper reviews the recent developments in material property modelling and its applications in processing simulation. Many material properties needed by process simulation can now be readily provided, such as the solidification properties and high temperature stress–strain curves. The solidification properties are affected by changes in composition within the specification range of an alloy; such changes in properties then affect casting simulation results. The mechanical properties are calculated by considering two competing deformation mechanisms (dominated by either dislocation glide or dislocation climb), with automatic selection of the dominant mechanism. Sample calculations are given for a variety of engineering alloys, including steels, aluminum, titanium, and nickel-based superalloys. The material properties data calculated can now be passed directly into commercial computer-aided engineering packages for casting and deformation simulation.


Overview: Modeling material properties critical for process simulation

January 2008

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34 Reads

Process simulation requires reliable data for a wide variety of material properties, ranging from thermal conductivity to flow stress curves. This paper reviews the development of computer models that can provide in situ calculations of many material properties, such as solidification properties and high temperature stress-strain curves. How changes in composition within the specification range of an alloy may affect its properties during solidification and how casting simulation results are consequently influenced by such changes in properties are examined. The mechanical properties are calculated by considering two competing deformation mechanisms, dominated by either dislocation glide or dislocation climb, with automatic selection of the operating mechanism. These models have been integrated into the computer software package JMatPro, which can be used to export data files directly to computer-aided engineering (CAE) packages used for casting, forging and heat treatment simulation.


Fig. 3. Comparison between calculated and experimental yield strength for a series of commercial nickel-based superalloys with precipitation hardening
Quantification of High Temperature Strength of Nickel-Based Superalloys

May 2007

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1,611 Reads

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29 Citations

The strength of nickel-based superalloys usually consists of solid solution strengthening from the gamma matrix and precipitation hardening due to the gamma' and/or gamma" precipitates. In the present work, a model was developed to calculate the high temperature strength of nickel-based superalloys, where the temperature dependence of each strengthening contribution was accounted for separately. The high temperature strength of these alloys is not only a function of microstructural changes in the material, but the result of a competition between two deformation modes, i.e. the normal low to mid temperature tensile deformation and deformation via a creep mode. Extensive validation had been carried out during the model development. Good agreement between calculated and experimental results has been achieved for a wide range of nickel-based superalloys, including solid solution alloys and precipitation-hardened alloys with different type/amount of precipitates. This model has been applied to two newly developed superalloys and is proved to be able to make predictions to within useful accuracy.


Metastable Phase Formation in MultiComponent Aluminium Alloys

March 2007

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52 Reads

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1 Citation

Many Aluminium alloys use the precipitation of metastable phases to generate optimum properties. The effect of including additional structures such as θ' and GP zones is described in the context of a hierarchy of metastable structures. Extending a Thermodynamic data base that has been designed solely to deal with equilibrium conditions is a vital prerequisite to handling the heat-treatment of aluminium alloys. It is then possible to generate TTT and CCT diagrams, using the Johnson-Mehl-Avrami treatment previously applied in to other materials providing provision is made for the presence of supersaturated quenched-in vacancies. Calculations using JMatPro are given for the expected behavior of commercial aluminium alloys of increasing complexity, including AA319, AA6061 and AA7075.


Citations (68)


... However, some authors note that their accuracy is constrained by the quality of the thermodynamic databases they rely on [23][24][25]. These software packages use the Scheil-Gulliver (SG) model to consider non-equilibrium solidification, assuming negligible solute diffusion in the solid state and complete diffusion in the liquid state [26]. This model is highly accurate for aluminum alloys and matches experimental results well [27]. ...

Reference:

The Specificity of Determining the Latent Heat of Solidification of Cast Hypoeutectic AlSiCu Alloys Using the DSC Method
Modelling of the Thermo-Physical and Physical Properties for Solidification of Al-Alloys
  • Citing Chapter
  • January 2016

... Solution treatment of the alloys was carried out at 490 °C for 4 hr. The single -phase region was predicted by CALPHAD modelling method using aluminium thermodynamic databases [11]. All solute atoms and phases are supposedly get dissolved to form a singlephase solution. ...

Modelling of the Thermo-Physical and Physical Properties for Solidification of Mg-Alloys
  • Citing Chapter
  • January 2016

... Thermodynamic calculations based on the Gibbs energy minimisation can be used to confirm the conclusions drawn from EDX analyses. The calculation program used was Thermocalc [25] and the superalloy database (Nidata) was developed by Nigel Saunders [26,27]. Table 2 contains the data used for the thermodynamic calculations. ...

Phase Diagrams, Calculation of
  • Citing Chapter
  • December 2001

... In the CALPHAD approach [14][15][16][17][18], the Gibbs energy of each individual phase is defined, and the model parameters are collected in a thermodynamic database. It is the modeling of the Gibbs energy of individual phases and the coupling of phase diagram and thermochemistry that make the CALPHAD method a powerful technique in the computational thermodynamics of multicomponent materials. ...

Phenomenological Calculations of Phase-Equilibria: the Calphad Approach
  • Citing Chapter
  • January 1994

... Rapidly solidified Al-Fe-Ni alloys derive their attractive ambient and elevated temperature properties from this monoclinic τ-Al 9 FeNi which is isomorphous with Al 9 Co 2 [2,3]. The τ phase is thermally stable, shear resistant and forms a defined orientation relationship with α-Al [4]. In the Al areas the grains were revealed by tilting the specimen in the microscope to obtain the image of grain boundaries. ...

Microstructure of rapidly solifidied Al-8Fe-4Ni-1Mo alloy powders
  • Citing Article
  • January 1993

International Journal of Rapid Solidification

... The precipitation phases considered in the model include M 3 C, M(C,N), M 2 (C,N), M 7 C 3 , M 23 C 6 , M 6 C, Z-phase, Laves, and Cu phase. The precipitation kinetics model is based on the classical Johnson-Mehl-Avrami (JMA) theory [3,4] with an adaption that allows the morphology of the precipitate to be considered as well as specifics associated with potential nucleant sites [5,6]. Critical model inputs such as driving force, amount and composition of the precipitating phases are obtained from thermodynamic calculations via the CALculation of PHAse Diagram (CALPHAD) approach [7]. ...

Modelling Deformation-Induced Precipitation Kinetics in Microalloyed Steels during Hot Rolling

... As seen from the figure, in the pattern of the as-homogenized sample, some peaks overlap with each other forming a broad peak where splitting occurs. These splits are critical for Cu-based shape memory alloys and can be sued in the qualitative analysis of the regularity in the martensite phase [26][27][28]. In this study, it is considered that this broad peak has such a splitted appearance as a result of the shear stresses developed during cutting of the sample. ...

The Role of Ordering in the Loss of Shape Memory in some Copper-base Alloys

... En effet, les essais doivent être réalisés pour chaque composition chimique représentant les différentes sous-couches, et ceci à haute température. Néanmoins, plusieurs auteurs[SAU04],[LI001],[GUO06],[GUO07],[GUO05], et [KIK84] travail conséquent pour estimer les propriétés mécaniques et métallurgiques des matériaux, implantées notamment dans le logiciel JMatPro (Java-based Materials Property simulation software). Ce logiciel peut fournir, pour une composition chimique et une taille de grain données, plusieurs propriétés du matériau en fonction, par exemple, de la température et des constituants micrographiques Nous travaillons toujours sur l'acier 29MnCr5 carbonitruré à 860°C et trempée dans de l'huile à 160°C. ...

Modelling of High Temperature Mechanical Properties and Density Change of Steels during Solidification
  • Citing Article

... The thermodynamic materials properties database JMatPro (version 10.1) was consulted to generate predictions of the bulk thermomechanical properties of the Ti-6Al-4V alloy in the different weld regions, with the different heat treatment operations [21,22]. These bulk materials properties, as calculated in the JMat-Pro software for the composition and mean grain size measured, are presented in the results. ...

MODELLING HIGH TEMPERATURE FLOW STRESS CURVES OF TITANIUM ALLOYS
  • Citing Article