S. Malinov - Academia.edu (original) (raw)

Papers by S. Malinov

Acta Materialia, 2005

A system of partial differential equations was derived to describe diffusion in the two-phase reg... more A system of partial differential equations was derived to describe diffusion in the two-phase region of a ternary alloy by assuming that the mixture concentration in an infinitesimally small volume can be changed by external fluxes over the boundaries of this volume. A numerical procedure was developed for solving the system of partial differential equation (PDE) and treating the problem with the moving boundaries between various single-phase or two-phase layers. The mathematical model was applied for numerical simulation of the formation and growth of the single-phase and two-phase layers, developed in ternary alloy specimen, through diffusion from the surface to the core.

Electroless Ni-P (EN) and composite Ni-P-SiC (ENC) coatings were developed on cast aluminium allo... more Electroless Ni-P (EN) and composite Ni-P-SiC (ENC) coatings were developed on cast aluminium alloy substrate, LM24. The coating phase composition, microstructure and microhardness were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and microhardness tester, respectively, on as-plated and heattreated specimens. The original microstructure of the Ni-P matrix is not affected by the inclusion of the hard particles SiC. No formation of Ni-Si phase was observed up to 500°C of heat treatment. The microhardness is increased on incorporation of SiC in Ni-P matrix. The hardening mechanism is the formation of intermetallic phase Ni 3 P on annealing at elevated temperature.

Modelling and Simulation in Materials Science and Engineering, 2006

A two-dimensional time dependent model for simultaneous growth of gas pore and solid phase from g... more A two-dimensional time dependent model for simultaneous growth of gas pore and solid phase from gas saturated melt was developed. This model was applied to structure formation of ordered porosity metal materials. Fabrication of copper porosity castings was simulated numerically. A procedure for calculating inter-pore spacing and pore radius for a certain technological regime was discussed. It was proved that the structure of ordered porosity metal materials formed at steady-state conditions could consist of pores with different radii. This is observed in real ingots. This is the main distinction between normal eutectic structures and ordered porosity structure.

Metallurgical and Materials Transactions A, 2001

The relationship between heat-treatment parameters and microstructure in titanium alloys has so f... more The relationship between heat-treatment parameters and microstructure in titanium alloys has so far been mainly studied empirically, using characterization techniques such as microscopy. Calculation and modeling of the kinetics of phase transformation have not yet been widely used for these alloys. Differential scanning calorimetry (DSC) has been widely used for the study of a variety of phase transformations. There has been much work done on the calculation and modeling of the kinetics of phase transformations for different systems based on the results from DSC study. In the present work, the kinetics of the ␤ ⇒ ␣ transformation in a Ti-6Al-4V titanium alloy were studied using DSC, at continuous cooling conditions with constant cooling rates of 5 ЊC, 10 ЊC, 20 ЊC, 30 ЊC, 40 ЊC, and 50 ЊC/min. The results from calorimetry were then used to trace and model the transformation kinetics in continuous cooling conditions. Based on suitably interpreted DSC results, continuous cooling-transformation (CCT) diagrams were calculated with lines of isotransformed fraction. The kinetics of transformation were modeled using the Johnson-Mehl-Avrami (JMA) theory and by applying the "concept of additivity." The JMA kinetic parameters were derived. Good agreement between the calculated and experimental transformed fractions is demonstrated. Using the derived kinetic parameters, the ␤ ⇒ ␣ transformation in a Ti-6Al-4V alloy can be described for any cooling path and condition. An interpretation of the results from the point of view of activation energy for nucleation is also presented.

Surface & Coatings Technology, 2005

This paper studies the phase composition, microstructure, hardness and wear resistance of nickel-... more This paper studies the phase composition, microstructure, hardness and wear resistance of nickel-base plasma sprayed coatings, on two types of substrates, steel and cast iron. The processing method of metal and compound powders for plasma spraying is detailed, together with the characteristics of the powders before and after processing. It has been found that in as-coated condition, the surface layers

Computational Materials Science, 2005

... Z. Guo, S. Malinov and W. Sha Corresponding Author Contact Information , E-mail The Correspon... more ... Z. Guo, S. Malinov and W. Sha Corresponding Author Contact Information , E-mail The Corresponding Author. ... An artificial neural network (ANN) model is developed to simulate the non-linear relationship between the beta transus (β tr ) temperature of titanium alloys and the ...

A study was performed to characterize the microstructure of nickel-based plasma coat- ings obtain... more A study was performed to characterize the microstructure of nickel-based plasma coat- ings obtained at different plasma conditions using light microscopy and X-ray diffraction. A partially amorphous phase was observed in the as-coated condition but then changed to a homogeneous crystalline structure after heat treatment. The results show that the increase of power during spraying has no effect on the ratio of the amounts of amor- phous to crystalline phases as well as the width of the X-ray peaks of the crystalline phase. This study also examines the forma- tion of new phases when the specimens were heated to different temperatures up to 565, 700, 950, 1035, and 1200°C. Microstructural images were taken from the nickel alloy coatings at room temperature after the heating process.

A computer model based on backpropagation multilayer feedforward artificial neural networks (ANN)... more A computer model based on backpropagation multilayer feedforward artificial neural networks (ANN) was designed for the simulation and prediction of crystallization temperatures of the Ni-P based amorphous alloys, as functions of alloy composition and heating rate. The model was trained using data from the published literature as well as own experimental data. The input parameters of the neural network (NN) model are alloy composition, heating rate of the heating processes, and processing parameters of the alloys. The output parameters are crystallization temperatures (onset, peak and end temperatures) of major crystallization reaction of the amorphous alloys. In training and testing, the neural network for the simulation and prediction of crystallization peak temperature shows a comparatively good result. However, the neural networks for the crystallization onset and end temperatures did not show satisfactory performance, due to some unjustified collected data. Some comparisons between NN predictions and own experimental data are given. For easy use of the model a graphical user interface (GUI) was created.

High porosity metallic materials are designed for special properties, which can be used in many i... more High porosity metallic materials are designed for special properties, which can be used in many industrial applications. The development of new porous structures is a challenge for materials scientists. This paper discusses general characteristics, structure, properties and some manufacturing practices of a class of relatively new metallic materials named gasars, ordered porosity materials, or lotus type porous materials. An overview of the metals and alloys used and mechanical properties studied is presented. Some relations between structure characteristics and mechanical properties are discussed. Basic relations between processing parameters and structure characteristics are analysed. Special attention is paid to the complex physical phenomena in ordered porosity structure formation. Conditions for production of high porosity ingot are discussed.

The electroless nickel composite (ENC) with various silicon carbide contents was deposited onto a... more The electroless nickel composite (ENC) with various silicon carbide contents was deposited onto aluminium alloy (LM24) substrate. The wear behaviour and the microhardness of the composite coating samples were investigated and compared with particles free and aluminium substrate samples using micro-scale abrasion tester and microhardness tester respectively. The wear scar marks and wear volume were analysed by optical microscope. The wear tracks were further studied using scanning electron microscopy (SEM). The embedded particles were found to get pressed into the matrix which helps resisting further wearing process for composite samples. However, random orientation of microcuts and microfallow were seen for ENC sample but more uniform wearing was observed for EN sample. The composite coating with low content of SiC was worn minimum. Early penetration into the substrate was seen for samples with higher SiC content. Microhardness was improved after heat treatment for all the samples containing various SiC content. Under dry sliding condition, inclusion of particles in the matrix did not improve the wearing resistance performance in as-deposited state. The wearing worsened as the content of the particles increased generally. However, on heat treatment, the composite coatings exhibited improved wear resistance and the best result was obtained from the one with low particle contents.

Acta Materialia, 2005

A system of partial differential equations was derived to describe diffusion in the two-phase reg... more A system of partial differential equations was derived to describe diffusion in the two-phase region of a ternary alloy by assuming that the mixture concentration in an infinitesimally small volume can be changed by external fluxes over the boundaries of this volume. A numerical procedure was developed for solving the system of partial differential equation (PDE) and treating the problem with the moving boundaries between various single-phase or two-phase layers. The mathematical model was applied for numerical simulation of the formation and growth of the single-phase and two-phase layers, developed in ternary alloy specimen, through diffusion from the surface to the core.

Electroless Ni-P (EN) and composite Ni-P-SiC (ENC) coatings were developed on cast aluminium allo... more Electroless Ni-P (EN) and composite Ni-P-SiC (ENC) coatings were developed on cast aluminium alloy substrate, LM24. The coating phase composition, microstructure and microhardness were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and microhardness tester, respectively, on as-plated and heattreated specimens. The original microstructure of the Ni-P matrix is not affected by the inclusion of the hard particles SiC. No formation of Ni-Si phase was observed up to 500°C of heat treatment. The microhardness is increased on incorporation of SiC in Ni-P matrix. The hardening mechanism is the formation of intermetallic phase Ni 3 P on annealing at elevated temperature.

Modelling and Simulation in Materials Science and Engineering, 2006

A two-dimensional time dependent model for simultaneous growth of gas pore and solid phase from g... more A two-dimensional time dependent model for simultaneous growth of gas pore and solid phase from gas saturated melt was developed. This model was applied to structure formation of ordered porosity metal materials. Fabrication of copper porosity castings was simulated numerically. A procedure for calculating inter-pore spacing and pore radius for a certain technological regime was discussed. It was proved that the structure of ordered porosity metal materials formed at steady-state conditions could consist of pores with different radii. This is observed in real ingots. This is the main distinction between normal eutectic structures and ordered porosity structure.

Metallurgical and Materials Transactions A, 2001

The relationship between heat-treatment parameters and microstructure in titanium alloys has so f... more The relationship between heat-treatment parameters and microstructure in titanium alloys has so far been mainly studied empirically, using characterization techniques such as microscopy. Calculation and modeling of the kinetics of phase transformation have not yet been widely used for these alloys. Differential scanning calorimetry (DSC) has been widely used for the study of a variety of phase transformations. There has been much work done on the calculation and modeling of the kinetics of phase transformations for different systems based on the results from DSC study. In the present work, the kinetics of the ␤ ⇒ ␣ transformation in a Ti-6Al-4V titanium alloy were studied using DSC, at continuous cooling conditions with constant cooling rates of 5 ЊC, 10 ЊC, 20 ЊC, 30 ЊC, 40 ЊC, and 50 ЊC/min. The results from calorimetry were then used to trace and model the transformation kinetics in continuous cooling conditions. Based on suitably interpreted DSC results, continuous cooling-transformation (CCT) diagrams were calculated with lines of isotransformed fraction. The kinetics of transformation were modeled using the Johnson-Mehl-Avrami (JMA) theory and by applying the "concept of additivity." The JMA kinetic parameters were derived. Good agreement between the calculated and experimental transformed fractions is demonstrated. Using the derived kinetic parameters, the ␤ ⇒ ␣ transformation in a Ti-6Al-4V alloy can be described for any cooling path and condition. An interpretation of the results from the point of view of activation energy for nucleation is also presented.

Surface & Coatings Technology, 2005

This paper studies the phase composition, microstructure, hardness and wear resistance of nickel-... more This paper studies the phase composition, microstructure, hardness and wear resistance of nickel-base plasma sprayed coatings, on two types of substrates, steel and cast iron. The processing method of metal and compound powders for plasma spraying is detailed, together with the characteristics of the powders before and after processing. It has been found that in as-coated condition, the surface layers

Computational Materials Science, 2005

... Z. Guo, S. Malinov and W. Sha Corresponding Author Contact Information , E-mail The Correspon... more ... Z. Guo, S. Malinov and W. Sha Corresponding Author Contact Information , E-mail The Corresponding Author. ... An artificial neural network (ANN) model is developed to simulate the non-linear relationship between the beta transus (β tr ) temperature of titanium alloys and the ...

A study was performed to characterize the microstructure of nickel-based plasma coat- ings obtain... more A study was performed to characterize the microstructure of nickel-based plasma coat- ings obtained at different plasma conditions using light microscopy and X-ray diffraction. A partially amorphous phase was observed in the as-coated condition but then changed to a homogeneous crystalline structure after heat treatment. The results show that the increase of power during spraying has no effect on the ratio of the amounts of amor- phous to crystalline phases as well as the width of the X-ray peaks of the crystalline phase. This study also examines the forma- tion of new phases when the specimens were heated to different temperatures up to 565, 700, 950, 1035, and 1200°C. Microstructural images were taken from the nickel alloy coatings at room temperature after the heating process.

A computer model based on backpropagation multilayer feedforward artificial neural networks (ANN)... more A computer model based on backpropagation multilayer feedforward artificial neural networks (ANN) was designed for the simulation and prediction of crystallization temperatures of the Ni-P based amorphous alloys, as functions of alloy composition and heating rate. The model was trained using data from the published literature as well as own experimental data. The input parameters of the neural network (NN) model are alloy composition, heating rate of the heating processes, and processing parameters of the alloys. The output parameters are crystallization temperatures (onset, peak and end temperatures) of major crystallization reaction of the amorphous alloys. In training and testing, the neural network for the simulation and prediction of crystallization peak temperature shows a comparatively good result. However, the neural networks for the crystallization onset and end temperatures did not show satisfactory performance, due to some unjustified collected data. Some comparisons between NN predictions and own experimental data are given. For easy use of the model a graphical user interface (GUI) was created.

High porosity metallic materials are designed for special properties, which can be used in many i... more High porosity metallic materials are designed for special properties, which can be used in many industrial applications. The development of new porous structures is a challenge for materials scientists. This paper discusses general characteristics, structure, properties and some manufacturing practices of a class of relatively new metallic materials named gasars, ordered porosity materials, or lotus type porous materials. An overview of the metals and alloys used and mechanical properties studied is presented. Some relations between structure characteristics and mechanical properties are discussed. Basic relations between processing parameters and structure characteristics are analysed. Special attention is paid to the complex physical phenomena in ordered porosity structure formation. Conditions for production of high porosity ingot are discussed.

The electroless nickel composite (ENC) with various silicon carbide contents was deposited onto a... more The electroless nickel composite (ENC) with various silicon carbide contents was deposited onto aluminium alloy (LM24) substrate. The wear behaviour and the microhardness of the composite coating samples were investigated and compared with particles free and aluminium substrate samples using micro-scale abrasion tester and microhardness tester respectively. The wear scar marks and wear volume were analysed by optical microscope. The wear tracks were further studied using scanning electron microscopy (SEM). The embedded particles were found to get pressed into the matrix which helps resisting further wearing process for composite samples. However, random orientation of microcuts and microfallow were seen for ENC sample but more uniform wearing was observed for EN sample. The composite coating with low content of SiC was worn minimum. Early penetration into the substrate was seen for samples with higher SiC content. Microhardness was improved after heat treatment for all the samples containing various SiC content. Under dry sliding condition, inclusion of particles in the matrix did not improve the wearing resistance performance in as-deposited state. The wearing worsened as the content of the particles increased generally. However, on heat treatment, the composite coatings exhibited improved wear resistance and the best result was obtained from the one with low particle contents.