Hongbiao Dong | University of Leicester (original) (raw)

Papers by Hongbiao Dong

IOP Conference Series: Materials Science and Engineering, 2012

ABSTRACT The project Modelling of Interface evolution in advanced Welding (MIntWeld) is a 4-year ... more ABSTRACT The project Modelling of Interface evolution in advanced Welding (MIntWeld) is a 4-year international research project funded by the European Commission under their FP7 programme. Its main target is to develop a numerical toolbox which can be used to predict the evolution of interfaces during welding. There are various interfaces involving multiple phenomena and different spatial scales, which can be simulated using corresponding numerical modelling methods respectively. The modelling methods include quantum dynamics, molecular dynamics, phase field, phase field crystal, computational fluid dynamics, phase transformation and heat transfer, thermodynamics, continuum mechanics and life and defects prediction. Although each modelling method is based on different physical theories and involves different scales, they are not isolated. Therefore, this project aims to design a common framework which couples each model with the upstream and/or downstream model at the relevant neighbouring length scales. The data exchange framework which underpins the coupling of the models is described, and typical examples addressing the solution to the challenges faced, such as those of data interpolation between one discretisation of the computational domain and another, are discussed. Initial successes from the model-linking efforts of the authors are also presented.

Metallurgical and Materials Transactions A, 2017

Acta Materialia, 2011

Large scatters occur in composition measurements using wavelength-dispersive X-ray spectroscopy (... more Large scatters occur in composition measurements using wavelength-dispersive X-ray spectroscopy (WDS) when only a few precipitates are captured in the X-ray sampling volume, because the measured signal represents an averaged composition of the precipitate and the matrix phase in the sampling volume. The scatters become small when sufficient numbers of precipitates are captured and solidification segregation in the sampling volume is not significant. Monte Carlo simulations were carried out to obtain the X-ray signals from the matrix c and precipitated c 0 phases in as-cast Ni-base superalloys using different beam sizes for given c 0 precipitate sizes. The optimum beam size in relation to the precipitate size can be predicted for accurate composition measurements.

Journal of Alloys and Compounds, 2015

Metallurgical and Materials Transactions A, 2015

Journal of Thermal Analysis and Calorimetry, 2001

... KFP, KPC and KCS are the coeffi-cients between the furnace and the plate, the plate and the c... more ... KFP, KPC and KCS are the coeffi-cients between the furnace and the plate, the plate and the container, the container and the sample. ... The ratio of KFP/KPC is initially set to 1 and KFP is adjusted until the calculated jump in the enthalpy plot is equivalent to the latent heat. ...

Fish & shellfish immunology, Jan 30, 2015

Vibrio parahaemolyticus is a virulent pathogen that affects shrimp aquaculture. Reactive oxygen s... more Vibrio parahaemolyticus is a virulent pathogen that affects shrimp aquaculture. Reactive oxygen species are produced by the immune system that defends the host against foreign microorganisms. In the present study, the oxidative stress response in hepatopancreas and gills of Penaeus monodon to V. parahaemolyticus challenge were studied, such as respiratory burst, ROS production (·O2(-) and ·OH), activities of antioxidant enzymes (CAT, GPx, SOD, POD and GST) and oxidative damage to lipid and protein (indexed by contents of MDA). Compared with the control group, after V. parahaemolyticus challenge, respiratory burst and ROS production were up-regulated significantly. GPx and POD activity increased significantly in hepatopancreas and gills of the shrimps at 12 h, but CAT activity decreased markedly at 12 h and 24 h. SOD and GST activity in hepatopancreas of the shrimps increased significantly at 1.5 h, but decreased markedly at 12 h to 48 h. MDA content increased significantly after 6 h...

Scripta Materialia, 2007

Differential thermal analyses along with microstructural characterization has been used to study ... more Differential thermal analyses along with microstructural characterization has been used to study the solidification path in the Ni-based superalloy CMSX 10 K. It was found that solidification initiates with freezing of primary c dendrites, continues with a peritectic reaction resulting in nucleation and growth of c 0 particles in the interdendritic liquid, and terminates with the precipitation of fine lamellar [c-c 0 ] phases between the coarsened c 0 particles.

Metallurgical and Materials Transactions A, 2009

Differential thermal analyses along with microstructural characterization has been used to study ... more Differential thermal analyses along with microstructural characterization has been used to study the solidification path in the Ni-based superalloy CMSX 10 K. It was found that solidification initiates with freezing of primary c dendrites, continues with a peritectic reaction resulting in nucleation and growth of c 0 particles in the interdendritic liquid, and terminates with the precipitation of fine lamellar [c-c 0 ] phases between the coarsened c 0 particles.

Metallurgical and Materials Transactions A, 2005

A comparison has been made between the amount of microsegregation predicted by a numerical model ... more A comparison has been made between the amount of microsegregation predicted by a numerical model and that found experimentally in Al-Cu alloys varying in composition between 1 and 8 wt pct Cu. A depleted region was predicted and observed experimentally near the Al2Cu. The depleted region was formed below the eutectic temperature and had a significant effect on the ordered composition-fraction plots, particularly for high alloy compositions. Although the fit between experiment and theory was reasonably good, it was concluded that it was necessary to propose that local equilibrium was not maintained between the phases in the solid-state reactions.

Metallurgical and Materials Transactions A, 2003

A single-pan scanning calorimeter has been developed that eliminates the smearing of latent heat ... more A single-pan scanning calorimeter has been developed that eliminates the smearing of latent heat that occurs in a conventional two-pan heat-flux differential scanning calorimeter (DSC). In the new calorimeter, accurate enthalpy/temperature data was obtained in pure Al without smearing, and excellent sensitivity to new phases was obtained in a multicomponent Al alloy (LM25). The calorimeter has been used to investigate microsegregation in an Al-4.45 wt pct Cu alloy. The enthalpy/temperature data fell between that calculated, assuming no mixing in the solid (Scheil) and complete mixing in the solid (equilibrium solidification). The amount of segregation agreed well with that calculated using a diffusion-based model of microsegregation. The difficulty of getting the fraction solid from the enthalpy data is discussed, and it is concluded that it is not possible to do so without using a microsegregation model. In addition, it is concluded that it is wrong to assume that the enthalpy of an alloy can be given by a specific heat term and a constant latent heat term that depend on fraction liquid as is assumed in most casting models.

Metallurgical and Materials Transactions A, 2011

In this article, grain selection in spiral selectors during investment casting of single-crystal ... more In this article, grain selection in spiral selectors during investment casting of single-crystal (SX) components is simulated using a cellular automaton grain structure model (CAFE) within a finite element thermal model (PROCAST). The models were validated against experimental observations and then were applied to model the effect of geometry of the spiral selectors on grain selection through a systematic approach. It was found that the efficiency of the spiral selector is significantly dependent on its geometry; the spiral becomes more efficient in selecting single grain with a smaller wax wire diameter; larger spiral rotation diameter, and smaller takeoff angle. Recommendations for optimizing the spiral geometry are provided.

Journal of Rare Earths, 2012

ABSTRACT The effect of rolling and heat treatment on microstructure and mechanical properties of ... more ABSTRACT The effect of rolling and heat treatment on microstructure and mechanical properties of Mg3.5Y0.8Ca0.4Zr alloy was investigated. With the addition of 0.4Zr, the average grain size of the as-cast alloy was markedly refined to 5–10 μm. After hot rolling process, the grain size of Mg3.5Y0.8Ca0.4Zr alloy was refined further into 3–5 μm and the tensile strength was enhanced while the plasticity was degraded because the accumulation of rolling reduction increased the density of twins, and refined the grain structures. After the solution heat treatment at 743 K, the elongation of alloy was greatly enhanced from 3% to 17%.

Journal of Molecular Modeling, 2008

The geometric and electronic structures of rare earth metallofullerenes Eu@C72 were investigated ... more The geometric and electronic structures of rare earth metallofullerenes Eu@C72 were investigated using density functional theory (DFT) within a generalized gradient approximation (GGA). The geometric optimization revealed that the most favorable endohedral site for Eu is off-center along the C2 axis on the sigma(v) plane pointing to the (5, 5) bond at the fusion of two pentagons. Calculations for electronic structures show that two 6s electrons in Eu transfer to the lowest-unoccupied-molecular orbitals of C72 while 4f electrons remain in Eu.

JOM, 2013

Various physical interfacial phenomena occur during the process of welding and influence the fina... more Various physical interfacial phenomena occur during the process of welding and influence the final properties of welded structures. As the features of such interfaces depend on physics that resolve at different spatial scales, a multiscale and multiphysics numerical modeling approach is necessary. In a collaborative research project Modeling of Interface Evolution in Advanced Welding, a novel strategy of model linking is employed in a multiscale, multiphysics computational framework for fusion welding. We only directly link numerical models that are on neighboring spatial scales instead of trying to link all submodels directly together through all available spatial scales. This strategy ensures that the numerical models assist one another via smooth data transfer, avoiding the huge difficulty raised by forcing models to attempt communication over many spatial scales. Experimental activities contribute to the modeling work by providing valuable input parameters and validation data. Representative examples of the results of modeling, linking and characterization are presented.

Journal of Applied Animal Research, 2010

Chen, G., Zhang, M., Zhang, J., Dong, H., Zhou, H., Tang, B., Huang, J., Shi, G., Jiang, L., Wu, ... more Chen, G., Zhang, M., Zhang, J., Dong, H., Zhou, H., Tang, B., Huang, J., Shi, G., Jiang, L., Wu, Z. and Gu, B. 2010. Effects of L-carnitine and dietary protein on body composition and liver lipid content in juvenile new GIFT strain Nile tilapia (Oreochromis niloticus). J. Appl. Anim. Res., 37: 141–144.To assess the effects of different levels of dietary protein and L-carnitine on body composition and liver lipid content in juvenile Nile tilapia, triplicate groups of fish were fed on three levels of dietary protein (22, 25 and 28%) and five levels of L-carnitine (0, 200, 400, 600 and 800 mg kg) for a period of 56 d. The whole body and muscle protein contents increased, but the lipid content decreased with the increases in dietary protein levels. At the same dietary protein levels, protein contents in whole body and muscle tissue increased with the increases in L-carnitine levels. Lipid contents in whole body, muscle tissue and liver in all treatment groups decreased with the increases in L-carnitine levels. This experiment demonstrated that L-carnitine supplementation can help improve utilization of fats from the diets.

Journal of Alloys and Compounds, 2014

The as-solidified microstructure of an Al-Mg-Si-Cu alloy was characterized by scanning electron m... more The as-solidified microstructure of an Al-Mg-Si-Cu alloy was characterized by scanning electron microscopy and transmission electron microscopy. Quaternary Q particles were found to elongate preferentially along the solidification direction of the cylindrical cast ingot, whilst a small number of Si leaf-like particles aggregate mainly along the grain boundaries. The volume fractions of the Q and Si particles are quantitatively measured from electron microscopy images and thermodynamically simulated based on the Scheil-Gulliver solidification model. The results from experimental measurement agree well with those from simulation. The Q particles, which have dendrite-like internal structure and are uniformly distributed within the a-Al grains with a different orientation from that found in the aged alloys, are fast-dissolving and aid the formation of uniform aged microstructures. The aggregation of the Si particles along the grain boundaries in the as-solidified microstructure results in Si-rich boundaries even after a solution treatment, and causes the re-emergence of Si particles in the over-aged microstructure. This phenomenon helps to reduce the width of the precipitate-free zones.

IOP Conference Series: Materials Science and Engineering, 2012

Various physical interfacial phenomena occur during the process of welding and influence the fina... more Various physical interfacial phenomena occur during the process of welding and influence the final properties of welded structures. As the features of such interfaces depend on physics that resolve at different spatial scales, a multiscale and multiphysics numerical modeling approach is necessary. In a collaborative research project Modeling of Interface Evolution in Advanced Welding, a novel strategy of model linking is employed in a multiscale, multiphysics computational framework for fusion welding. We only directly link numerical models that are on neighboring spatial scales instead of trying to link all submodels directly together through all available spatial scales. This strategy ensures that the numerical models assist one another via smooth data transfer, avoiding the huge difficulty raised by forcing models to attempt communication over many spatial scales. Experimental activities contribute to the modeling work by providing valuable input parameters and validation data. Representative examples of the results of modeling, linking and characterization are presented.

Fluid Phase Equilibria, 2003

The traditional method of obtaining the fraction liquid from DSC enthalpy data is discussed. It i... more The traditional method of obtaining the fraction liquid from DSC enthalpy data is discussed. It is concluded that accurate values cannot be obtained directly unless an allowance is made for the microsegregation which always occurs during solidification of alloys. A technique is developed, which allows the fraction liquid to be calculated indirectly.

Advanced Engineering Materials, 2013

ABSTRACT The columnar to equiaxed transition (CET) provides a challenging simulation goal for com... more ABSTRACT The columnar to equiaxed transition (CET) provides a challenging simulation goal for computational models of alloy solidification, in addition to being an important technological feature of many casting processes. CET thus provides an industrially relevant test-case for those developing numerical models across a range of scales. Whether or not CET occurs depends on numerous experimental parameters such as cooling rate, speed of columnar growth, thermal gradient in the liquid, and level of grain refiner in the alloy. Information on columnar and equiaxed grain structure, and the transition between the two, is very useful for foundry engineers, at the macroscopic scale of the casting. The detailed microstructure within each grain is determined by typically dendritic growth and local transport of solute and heat. This paper presents a review of recent progress on modeling CET at multiple length scales. It is evident that, whilst micro-models can provide simulations of physical phenomena, such as the evolution of dendrite morphology, at scales 10−3 to 10−5 m, finite computational resources preclude this resolution over the length scale of castings which is in the 10−2–100 m range. Instead, reasonably accurate models of CET formation in castings can be achieved by meso-scale modeling featuring 10−3–10−2 m phenomena. Such meso-scale models make use of analytical expressions to simulate dendrite growth in undercooled melts. Recent progress in modeling of CET, at both macro/meso- and micro-scales is reviewed, and computational challenges yet to be met are summarized.

IOP Conference Series: Materials Science and Engineering, 2012

ABSTRACT The project Modelling of Interface evolution in advanced Welding (MIntWeld) is a 4-year ... more ABSTRACT The project Modelling of Interface evolution in advanced Welding (MIntWeld) is a 4-year international research project funded by the European Commission under their FP7 programme. Its main target is to develop a numerical toolbox which can be used to predict the evolution of interfaces during welding. There are various interfaces involving multiple phenomena and different spatial scales, which can be simulated using corresponding numerical modelling methods respectively. The modelling methods include quantum dynamics, molecular dynamics, phase field, phase field crystal, computational fluid dynamics, phase transformation and heat transfer, thermodynamics, continuum mechanics and life and defects prediction. Although each modelling method is based on different physical theories and involves different scales, they are not isolated. Therefore, this project aims to design a common framework which couples each model with the upstream and/or downstream model at the relevant neighbouring length scales. The data exchange framework which underpins the coupling of the models is described, and typical examples addressing the solution to the challenges faced, such as those of data interpolation between one discretisation of the computational domain and another, are discussed. Initial successes from the model-linking efforts of the authors are also presented.

Metallurgical and Materials Transactions A, 2017

Acta Materialia, 2011

Large scatters occur in composition measurements using wavelength-dispersive X-ray spectroscopy (... more Large scatters occur in composition measurements using wavelength-dispersive X-ray spectroscopy (WDS) when only a few precipitates are captured in the X-ray sampling volume, because the measured signal represents an averaged composition of the precipitate and the matrix phase in the sampling volume. The scatters become small when sufficient numbers of precipitates are captured and solidification segregation in the sampling volume is not significant. Monte Carlo simulations were carried out to obtain the X-ray signals from the matrix c and precipitated c 0 phases in as-cast Ni-base superalloys using different beam sizes for given c 0 precipitate sizes. The optimum beam size in relation to the precipitate size can be predicted for accurate composition measurements.

Journal of Alloys and Compounds, 2015

Metallurgical and Materials Transactions A, 2015

Journal of Thermal Analysis and Calorimetry, 2001

... KFP, KPC and KCS are the coeffi-cients between the furnace and the plate, the plate and the c... more ... KFP, KPC and KCS are the coeffi-cients between the furnace and the plate, the plate and the container, the container and the sample. ... The ratio of KFP/KPC is initially set to 1 and KFP is adjusted until the calculated jump in the enthalpy plot is equivalent to the latent heat. ...

Fish & shellfish immunology, Jan 30, 2015

Vibrio parahaemolyticus is a virulent pathogen that affects shrimp aquaculture. Reactive oxygen s... more Vibrio parahaemolyticus is a virulent pathogen that affects shrimp aquaculture. Reactive oxygen species are produced by the immune system that defends the host against foreign microorganisms. In the present study, the oxidative stress response in hepatopancreas and gills of Penaeus monodon to V. parahaemolyticus challenge were studied, such as respiratory burst, ROS production (·O2(-) and ·OH), activities of antioxidant enzymes (CAT, GPx, SOD, POD and GST) and oxidative damage to lipid and protein (indexed by contents of MDA). Compared with the control group, after V. parahaemolyticus challenge, respiratory burst and ROS production were up-regulated significantly. GPx and POD activity increased significantly in hepatopancreas and gills of the shrimps at 12 h, but CAT activity decreased markedly at 12 h and 24 h. SOD and GST activity in hepatopancreas of the shrimps increased significantly at 1.5 h, but decreased markedly at 12 h to 48 h. MDA content increased significantly after 6 h...

Scripta Materialia, 2007

Differential thermal analyses along with microstructural characterization has been used to study ... more Differential thermal analyses along with microstructural characterization has been used to study the solidification path in the Ni-based superalloy CMSX 10 K. It was found that solidification initiates with freezing of primary c dendrites, continues with a peritectic reaction resulting in nucleation and growth of c 0 particles in the interdendritic liquid, and terminates with the precipitation of fine lamellar [c-c 0 ] phases between the coarsened c 0 particles.

Metallurgical and Materials Transactions A, 2009

Differential thermal analyses along with microstructural characterization has been used to study ... more Differential thermal analyses along with microstructural characterization has been used to study the solidification path in the Ni-based superalloy CMSX 10 K. It was found that solidification initiates with freezing of primary c dendrites, continues with a peritectic reaction resulting in nucleation and growth of c 0 particles in the interdendritic liquid, and terminates with the precipitation of fine lamellar [c-c 0 ] phases between the coarsened c 0 particles.

Metallurgical and Materials Transactions A, 2005

A comparison has been made between the amount of microsegregation predicted by a numerical model ... more A comparison has been made between the amount of microsegregation predicted by a numerical model and that found experimentally in Al-Cu alloys varying in composition between 1 and 8 wt pct Cu. A depleted region was predicted and observed experimentally near the Al2Cu. The depleted region was formed below the eutectic temperature and had a significant effect on the ordered composition-fraction plots, particularly for high alloy compositions. Although the fit between experiment and theory was reasonably good, it was concluded that it was necessary to propose that local equilibrium was not maintained between the phases in the solid-state reactions.

Metallurgical and Materials Transactions A, 2003

A single-pan scanning calorimeter has been developed that eliminates the smearing of latent heat ... more A single-pan scanning calorimeter has been developed that eliminates the smearing of latent heat that occurs in a conventional two-pan heat-flux differential scanning calorimeter (DSC). In the new calorimeter, accurate enthalpy/temperature data was obtained in pure Al without smearing, and excellent sensitivity to new phases was obtained in a multicomponent Al alloy (LM25). The calorimeter has been used to investigate microsegregation in an Al-4.45 wt pct Cu alloy. The enthalpy/temperature data fell between that calculated, assuming no mixing in the solid (Scheil) and complete mixing in the solid (equilibrium solidification). The amount of segregation agreed well with that calculated using a diffusion-based model of microsegregation. The difficulty of getting the fraction solid from the enthalpy data is discussed, and it is concluded that it is not possible to do so without using a microsegregation model. In addition, it is concluded that it is wrong to assume that the enthalpy of an alloy can be given by a specific heat term and a constant latent heat term that depend on fraction liquid as is assumed in most casting models.

Metallurgical and Materials Transactions A, 2011

In this article, grain selection in spiral selectors during investment casting of single-crystal ... more In this article, grain selection in spiral selectors during investment casting of single-crystal (SX) components is simulated using a cellular automaton grain structure model (CAFE) within a finite element thermal model (PROCAST). The models were validated against experimental observations and then were applied to model the effect of geometry of the spiral selectors on grain selection through a systematic approach. It was found that the efficiency of the spiral selector is significantly dependent on its geometry; the spiral becomes more efficient in selecting single grain with a smaller wax wire diameter; larger spiral rotation diameter, and smaller takeoff angle. Recommendations for optimizing the spiral geometry are provided.

Journal of Rare Earths, 2012

ABSTRACT The effect of rolling and heat treatment on microstructure and mechanical properties of ... more ABSTRACT The effect of rolling and heat treatment on microstructure and mechanical properties of Mg3.5Y0.8Ca0.4Zr alloy was investigated. With the addition of 0.4Zr, the average grain size of the as-cast alloy was markedly refined to 5–10 μm. After hot rolling process, the grain size of Mg3.5Y0.8Ca0.4Zr alloy was refined further into 3–5 μm and the tensile strength was enhanced while the plasticity was degraded because the accumulation of rolling reduction increased the density of twins, and refined the grain structures. After the solution heat treatment at 743 K, the elongation of alloy was greatly enhanced from 3% to 17%.

Journal of Molecular Modeling, 2008

The geometric and electronic structures of rare earth metallofullerenes Eu@C72 were investigated ... more The geometric and electronic structures of rare earth metallofullerenes Eu@C72 were investigated using density functional theory (DFT) within a generalized gradient approximation (GGA). The geometric optimization revealed that the most favorable endohedral site for Eu is off-center along the C2 axis on the sigma(v) plane pointing to the (5, 5) bond at the fusion of two pentagons. Calculations for electronic structures show that two 6s electrons in Eu transfer to the lowest-unoccupied-molecular orbitals of C72 while 4f electrons remain in Eu.

JOM, 2013

Various physical interfacial phenomena occur during the process of welding and influence the fina... more Various physical interfacial phenomena occur during the process of welding and influence the final properties of welded structures. As the features of such interfaces depend on physics that resolve at different spatial scales, a multiscale and multiphysics numerical modeling approach is necessary. In a collaborative research project Modeling of Interface Evolution in Advanced Welding, a novel strategy of model linking is employed in a multiscale, multiphysics computational framework for fusion welding. We only directly link numerical models that are on neighboring spatial scales instead of trying to link all submodels directly together through all available spatial scales. This strategy ensures that the numerical models assist one another via smooth data transfer, avoiding the huge difficulty raised by forcing models to attempt communication over many spatial scales. Experimental activities contribute to the modeling work by providing valuable input parameters and validation data. Representative examples of the results of modeling, linking and characterization are presented.

Journal of Applied Animal Research, 2010

Chen, G., Zhang, M., Zhang, J., Dong, H., Zhou, H., Tang, B., Huang, J., Shi, G., Jiang, L., Wu, ... more Chen, G., Zhang, M., Zhang, J., Dong, H., Zhou, H., Tang, B., Huang, J., Shi, G., Jiang, L., Wu, Z. and Gu, B. 2010. Effects of L-carnitine and dietary protein on body composition and liver lipid content in juvenile new GIFT strain Nile tilapia (Oreochromis niloticus). J. Appl. Anim. Res., 37: 141–144.To assess the effects of different levels of dietary protein and L-carnitine on body composition and liver lipid content in juvenile Nile tilapia, triplicate groups of fish were fed on three levels of dietary protein (22, 25 and 28%) and five levels of L-carnitine (0, 200, 400, 600 and 800 mg kg) for a period of 56 d. The whole body and muscle protein contents increased, but the lipid content decreased with the increases in dietary protein levels. At the same dietary protein levels, protein contents in whole body and muscle tissue increased with the increases in L-carnitine levels. Lipid contents in whole body, muscle tissue and liver in all treatment groups decreased with the increases in L-carnitine levels. This experiment demonstrated that L-carnitine supplementation can help improve utilization of fats from the diets.

Journal of Alloys and Compounds, 2014

The as-solidified microstructure of an Al-Mg-Si-Cu alloy was characterized by scanning electron m... more The as-solidified microstructure of an Al-Mg-Si-Cu alloy was characterized by scanning electron microscopy and transmission electron microscopy. Quaternary Q particles were found to elongate preferentially along the solidification direction of the cylindrical cast ingot, whilst a small number of Si leaf-like particles aggregate mainly along the grain boundaries. The volume fractions of the Q and Si particles are quantitatively measured from electron microscopy images and thermodynamically simulated based on the Scheil-Gulliver solidification model. The results from experimental measurement agree well with those from simulation. The Q particles, which have dendrite-like internal structure and are uniformly distributed within the a-Al grains with a different orientation from that found in the aged alloys, are fast-dissolving and aid the formation of uniform aged microstructures. The aggregation of the Si particles along the grain boundaries in the as-solidified microstructure results in Si-rich boundaries even after a solution treatment, and causes the re-emergence of Si particles in the over-aged microstructure. This phenomenon helps to reduce the width of the precipitate-free zones.

IOP Conference Series: Materials Science and Engineering, 2012

Various physical interfacial phenomena occur during the process of welding and influence the fina... more Various physical interfacial phenomena occur during the process of welding and influence the final properties of welded structures. As the features of such interfaces depend on physics that resolve at different spatial scales, a multiscale and multiphysics numerical modeling approach is necessary. In a collaborative research project Modeling of Interface Evolution in Advanced Welding, a novel strategy of model linking is employed in a multiscale, multiphysics computational framework for fusion welding. We only directly link numerical models that are on neighboring spatial scales instead of trying to link all submodels directly together through all available spatial scales. This strategy ensures that the numerical models assist one another via smooth data transfer, avoiding the huge difficulty raised by forcing models to attempt communication over many spatial scales. Experimental activities contribute to the modeling work by providing valuable input parameters and validation data. Representative examples of the results of modeling, linking and characterization are presented.

Fluid Phase Equilibria, 2003

The traditional method of obtaining the fraction liquid from DSC enthalpy data is discussed. It i... more The traditional method of obtaining the fraction liquid from DSC enthalpy data is discussed. It is concluded that accurate values cannot be obtained directly unless an allowance is made for the microsegregation which always occurs during solidification of alloys. A technique is developed, which allows the fraction liquid to be calculated indirectly.

Advanced Engineering Materials, 2013

ABSTRACT The columnar to equiaxed transition (CET) provides a challenging simulation goal for com... more ABSTRACT The columnar to equiaxed transition (CET) provides a challenging simulation goal for computational models of alloy solidification, in addition to being an important technological feature of many casting processes. CET thus provides an industrially relevant test-case for those developing numerical models across a range of scales. Whether or not CET occurs depends on numerous experimental parameters such as cooling rate, speed of columnar growth, thermal gradient in the liquid, and level of grain refiner in the alloy. Information on columnar and equiaxed grain structure, and the transition between the two, is very useful for foundry engineers, at the macroscopic scale of the casting. The detailed microstructure within each grain is determined by typically dendritic growth and local transport of solute and heat. This paper presents a review of recent progress on modeling CET at multiple length scales. It is evident that, whilst micro-models can provide simulations of physical phenomena, such as the evolution of dendrite morphology, at scales 10−3 to 10−5 m, finite computational resources preclude this resolution over the length scale of castings which is in the 10−2–100 m range. Instead, reasonably accurate models of CET formation in castings can be achieved by meso-scale modeling featuring 10−3–10−2 m phenomena. Such meso-scale models make use of analytical expressions to simulate dendrite growth in undercooled melts. Recent progress in modeling of CET, at both macro/meso- and micro-scales is reviewed, and computational challenges yet to be met are summarized.