Research Interests:
In this paper, the effects of carbon, Si, Cr and Mn partitioning on ferrite hardening were studied in detail using a medium Si low alloy grade of 35CHGSA steel under ferrite-martensite/ferrite-pearlite dual-phase (DP) condition. The... more
In this paper, the effects of carbon, Si, Cr and Mn partitioning on ferrite hardening were studied in detail using a medium Si low alloy grade of 35CHGSA steel under ferrite-martensite/ferrite-pearlite dual-phase (DP) condition. The experimental results illustrated that an abnormal trend of ferrite hardening had occurred with the progress of ferrite formation. At first, the ferrite microhardness decreased with increasing volume fraction of ferrite, thereby reaching the minimum value for a moderate ferrite formation, and then it surprisingly increased with subsequent increase in ferrite volume fraction. Beside a considerable influence of martensitic phase transformation induced residual compressive stresses within ferrite, these results were further rationalized in respect of the extent of carbon, Si, Cr and Mn partitioning between ferrite and prior austenite (martensite) microphases leading to the solid solution hardening effects of these elements on ferrite.
Research Interests:
Research Interests:
A combination of physical simulation and laboratory rolling experiments, including thermomechanical rolling and low-temperature ausforming, was conducted for designing a suitable processing route to enable phase transformation from... more
A combination of physical simulation and laboratory rolling experiments, including thermomechanical rolling and low-temperature ausforming, was conducted for designing a suitable processing route to enable phase transformation from austenite to ultrafine bainite in a medium-carbon steel. Following low-temperature ausforming at 500-550 °C, two different cooling and holding paths were tried in the study: (1) water cooling close to martensite start temperature (300 °C), followed by isothermal holding (route A), and (2) air cooling to 350 °C followed by isothermal holding (route B). For reference, a third sample was directly water-cooled to 300 °C after hot rolling without ausforming treatment, followed by isothermal holding (route C). Field emission scanning electron microscopy and electron backscatter diffraction, as well as x-ray diffraction, were employed for microstructural analysis and correlations with the mechanical properties evaluated in respect of hardness and tensile propert...
Research Interests:
Research Interests:
FEMS - (Federation of European Materials Societies)Excellent combinations of strength and toughness can be obtained from high-carbon nanobainite, but this requires heat-treating highly alloyed steels for long periods of time. In this... more
FEMS - (Federation of European Materials Societies)Excellent combinations of strength and toughness can be obtained from high-carbon nanobainite, but this requires heat-treating highly alloyed steels for long periods of time. In this project we aim to develop very fine bainitic microstructures in medium carbon steels (0.3-0.5 wt.%) in a more cost–effective way, using shorter processing times via thermomechanical ausforming. Tensile strengths above 1600 MPa are aimed at to give hot rolled steels with enhanced wear resistance combined with good toughness. Suitable compositions and processing parameters have been developed using modelling and physical simulation. We will present the main achievements so far obtained under the auspices of a Research Fund for Coal and Steel (RFCS) project, TIANOBAIN
Research Interests:
A novel concept of direct quenching and partitioning (DQ&P) processing route has been exp lored with the specific aim of producing ultra -high strength structural steels with yield strengths ≈1100 M Pa co mb ined with good uniform and... more
A novel concept of direct quenching and partitioning (DQ&P) processing route has been exp lored with the specific aim of producing ultra -high strength structural steels with yield strengths ≈1100 M Pa co mb ined with good uniform and total elongations and impact toughness. The approach used was to design suitable compositions based on high silicon and/or aluminiu m content, establish the DQ&P parameters with the aid of physical simulation on a Gleeble simu lator and finally, design the DQ&P p rocessing route for trials on a laboratory ro lling mill. Dilatation experiments were made on a Gleeb le simulator to determine the appropriate cooling rates and quench stop temperatures for obtaining martensite fractions in the range 60-90%. Two types of dilatation tests were conducted starting with either strained or unstrained austenite prior to quenching to roughly simulate industrial rolling with low and high fin ish rolling temperatures, respectively. Laboratory rolled samples were direc...
Research Interests:
The residual compressive stresses and dimensional changes related to the lattice strains of retained austenite (RA) phase in a high‐Si, medium‐carbon steel (Fe‐0.53C‐1.67Si‐0.72Mn‐0.12Cr) are investigated for samples austenitized and... more
The residual compressive stresses and dimensional changes related to the lattice strains of retained austenite (RA) phase in a high‐Si, medium‐carbon steel (Fe‐0.53C‐1.67Si‐0.72Mn‐0.12Cr) are investigated for samples austenitized and quenched for isothermal bainitic transformation (Q&B) in the range 5 s to 1 h at 350 °C. Also, samples are directly quenched in water (DWQ) from the austenitization temperature for comparison with Q&B samples. Field emission scanning electron microscopy (FE‐SEM) combined with electron backscatter diffraction (EBSD) analyses, and X‐ray diffraction are used to investigate the microstructural evolution, phase distribution, and lattice parameters of RA phase. While the Q&B samples showed formation of bainite and high‐carbon fresh martensite in conjunction with stabilization of various fractions of RA, the DWQ samples displayed nearly complete martensitic microstructure. For short holding durations (≪200 s), there was limited formation of bainite and the ina...
Research Interests:
In this study, a set of thermodynamic, kinetic, and microstructure data is presented to simulate the non-equilibrium solidification of Fe-Al-Mn-Si-C alloys. The data were further validated with the experimental measurements and then used... more
In this study, a set of thermodynamic, kinetic, and microstructure data is presented to simulate the non-equilibrium solidification of Fe-Al-Mn-Si-C alloys. The data were further validated with the experimental measurements and then used in a thermodynamic–kinetic software, IDS, to establish the effect of the alloying and cooling rate on the solidification behavior of high-AlMnSi (Al ≥ 0.5 wt pct, Mn ≥ 2 wt pct, Si ≥ 1 wt pct) steels. The modeling results were additionally validated by conducting electron probe microanalysis (EPMA) measurements. The results reveal that (1) solidification in high-AlMnSi steels occurs at much lower temperatures than in carbon steels; (2) increasing the cooling rate marginally lowers the solidus; (3) the microsegregation of Mn in austenite is much stronger than that of Si and Al due to the tendency of Al and Si to deplete from the liquid phase; (4) the residual delta ferrite content may be influenced by a proper heat treatment but not to the extent tha...
Research Interests:
Research Interests:
Research Interests:
A finite element (FE) simulation model illustrating the stress relaxation test was established with the Abaqus TM software. The microstructural evolution of steel during relaxation includes the complex phenomena of recrystallization.... more
A finite element (FE) simulation model illustrating the stress relaxation test was established with the Abaqus TM software. The microstructural evolution of steel during relaxation includes the complex phenomena of recrystallization. While the compression introduces the planned deformation and stress into the test piece, subsequent softening relieves the stress and at the same time creates microstructural reconstitution and refinement. In this study, a model was developed to simulate the kinetics of static recrystallization taking place during holding, using a technique based on FE-simulation. The simulation results have been compared to the experimental stress relaxation data obtained on a Gleeble TM 3800 thermo-mechanical simulator. The model can be used to estimate the recrystallization kinetics throughout the test piece. In the future, these results can be used for estimating the required rolling forces for multi-pass roughing with reasonable accuracy, for instance. The modellin...
Research Interests:
A model for static recrystallization by Zurob et al. [1] has been fitted to experimental stress relaxation [2] data obtained on a low-alloyed steel using a Gleeble thermomechanical simulator. The model has been implemented as an algorithm... more
A model for static recrystallization by Zurob et al. [1] has been fitted to experimental stress relaxation [2] data obtained on a low-alloyed steel using a Gleeble thermomechanical simulator. The model has been implemented as an algorithm that calculates the stress relaxation as a function of time, including physical descriptions of the recovery and recrystallization processes. The activation energy and volume were used as fitting parameters for recovery, and the activation energy of diffusion and nucleation site density were used as the fitting parameters for recrystallization. The four fitting parameters were determined from the experimental data by applying the Nelder-Mead algorithm within Matlab software. It can be concluded from the preliminary results that Zurob’s model can be successfully fitted to the stress relaxation data in order to illustrate the static restoration characteristics and kinetics in carbon steels using these fitting parameters.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Recent interests in developing novel super-high strength steels have led to extensive research efforts in direct quenching with or without tempering (DQ, DQT) or combined with partitioning (DQP). Both strip and plate products have been... more
Recent interests in developing novel super-high strength steels have led to extensive research efforts in direct quenching with or without tempering (DQ, DQT) or combined with partitioning (DQP). Both strip and plate products have been targeted for different applications. For boron-microalloyed DQ/DQT steels, the ASTM A255 approach for predicting the hardenability was considered inapplicable. Fresh attempts were made to develop new hardenability models through non-linear regression analysis by dynamically varying both the boron factor and multiplying factors of most elements in the alloy factor. Based on the recent concept of quenching and partitioning (Q&P), a novel processing route comprising thermomechanical rolling followed by direct quenching and partitioning (TMR-DQP) has been established for the development of ultra-high strength structural steels with yield strengths ≈1100 MPa combined with good uniform and total elongations and impact toughness. Examples of recent advances ...
Research Interests: Materials Science, Metallurgy, Boron, Alloy, Martensite, and 3 moreToughness, Tempering, and Hardenability
Research Interests:
Research Interests:
Recent advances in transmission electron microscopy (TEM) in respect of structural characterization down to atomic scale have enabled confirmation of stabilization of long ignored hexagonal omega (ω) phase in steel. The presence of ω... more
Recent advances in transmission electron microscopy (TEM) in respect of structural characterization down to atomic scale have enabled confirmation of stabilization of long ignored hexagonal omega (ω) phase in steel. The presence of ω phase is suggested to increase the strength of steel, and one of the factors concerning its stabilization is enrichment caused by the presence of certain solute atoms in the nanometer sized areas. Here, we report a density functional theory study conducted on a (3×3×2) ω –Fe supercell by introducing alloying elements in such a way that at a particular instant, either interstitial or substitutional C co-exist with any one of the elements Mn, Cr, Al, Si, and Co in substitutional position. From total energy calculations, we show that the cohesive energy of ω-Fe supercell increases in general, and the most stable combinations in the decreasing order of stability are Csub-Cr > Csub-Co > Csub-Si. Even though the ferromagnetic state is more stable when c...
Research Interests:
Systematic physical simulation of thermo-mechanical processing routes has been applied on a Gleeble 1500 simulator to four copper alloys(mass %)Cu-0.57Co-0.32Si,Cu-0.55Cr-0.065P,Cu-0.22Zr-0.035Si and Cu-1.01Ni-0.43Si aimed at clarifying... more
Systematic physical simulation of thermo-mechanical processing routes has been applied on a Gleeble 1500 simulator to four copper alloys(mass %)Cu-0.57Co-0.32Si,Cu-0.55Cr-0.065P,Cu-0.22Zr-0.035Si and Cu-1.01Ni-0.43Si aimed at clarifying the influences of processing conditions on their final properties,strength and electrical conductivity.Flow curves were determined over wide temperature and strain rate ranges.Hardness was used as a measure of the strength level achieved.High hardness was obtained as using equal amounts(strains 0.5)of cold deformation before and after the precipitation annealing stage.The maximum values achieved for the Cu-Co-Si,Cu-Cr-P,Cu-Zr-Si and Cu-Ni-Si alloys were 190,165,178 and 193 HV5,respectively.A thermo-mechanical schedule involving the hot deformation-ageing-cold deformation stages showed even better results for the Cu-Zr-Si alloy.Consequently,the processing routes were designed based on simulation test results and wires of 5 and 2mm in diameters have be...
Research Interests:
Abstract A new combination of factors enhancing the stabilization of austenite, including pre-existed austenite among quenched martensite, prior deformation, and partitioning at high temperatures is employed to create a multi-component... more
Abstract A new combination of factors enhancing the stabilization of austenite, including pre-existed austenite among quenched martensite, prior deformation, and partitioning at high temperatures is employed to create a multi-component refined microstructure in a medium Mn steel (Fe–4Mn–0.31C–2Ni–0.5Al–0.2Mo, wt.%). The microstructure evolution and phase fraction during the processing are systematically investigated using various characterization methods. The microstructure of the specimen after 0.4 strain deformation of 73% martensite–27% austenite at 250 °C and subsequent partition-annealing at 600 °C for 20 min was composed of several phases including tempered martensite, fresh martensite, pearlite, 10% of retained austenite (RA) and undissolved cementite. By increasing the annealing temperature, the pearlitic transformation was suppressed, whereas recrystallization of the deformed martensite and carbide dissolution occurred following annealing at 650 °C for 20 min resulting in an ultrafine-grained microstructure composed of equiaxed ferrite, 32% RA along with some fresh martensite during final cooling and few carbide precipitates. The results demonstrate that the combinatorial approach accelerated partitioning of alloying elements from martensite and carbides to largely pre-existing austenite is responsible for the improved austenite stabilization during intercritical annealing of the deformed dual-phase specimens. However, competitive processes are also enhanced so that the RA content is not increased by deformation
Research Interests:
... It has been confirmed that fine-grained ferrite can form from the austenite during deformation at high strains and at low deformation temperatures above Ar3 in the process termed as dynamic strain-induced transformation (DSIT) [1-5].... more
... It has been confirmed that fine-grained ferrite can form from the austenite during deformation at high strains and at low deformation temperatures above Ar3 in the process termed as dynamic strain-induced transformation (DSIT) [1-5]. Yada et al. ... Yada et al. ...
Research Interests:
New continuous cooling transformation (CCT) equations have been optimized to calculate the start temperatures and critical cooling rates of phase formations during austenite decomposition in low-alloyed steels. Experimental CCT data from... more
New continuous cooling transformation (CCT) equations have been optimized to calculate the start temperatures and critical cooling rates of phase formations during austenite decomposition in low-alloyed steels. Experimental CCT data from the literature were used for applying the recently developed method of calculating the grain boundary soluble compositions of the steels for optimization. These compositions, which are influenced by solute microsegregation and precipitation depending on the heating/cooling/holding process, are expected to control the start of the austenite decomposition, if initiated at the grain boundaries. The current optimization was carried out rigorously for an extended set of steels than used previously, besides including three new solute elements, Al, Cu and B, in the CCT-equations. The validity of the equations was, therefore, boosted not only due to the inclusion of new elements, but also due to the addition of more low-alloyed steels in the optimization. T...
Research Interests:
The aim of the current study is to design multiaxial forging (MAF) schedules in order to achieve submicron-grained (<1μm) structure in a microalloyed (MA) steel as well as an interstitial-free (IF) steel, which could impart a good... more
The aim of the current study is to design multiaxial forging (MAF) schedules in order to achieve submicron-grained (<1μm) structure in a microalloyed (MA) steel as well as an interstitial-free (IF) steel, which could impart a good combination of yield strength and tensile ductility. At the same time, an effort has been made to evaluate the fracture toughness characteristics by conducting 3-point bend tests and computing the KQ, Kee and J-integral values of ultrafine grained (UFG) samples and correlating them with the microstructure, besides evaluating the other mechanical properties. Fatigue strength in the high cycle fatigue (HCF) regime were also investigated and fracture mechanisms analyzed and comparison established between differently processed samples. The microstructural analysis was performed using transmission electron microscopy (TEM) and Electron backscatter diffraction (EBSD) and results corroborated with the mechanical properties. Superior combinations of yield stren...
Research Interests:
This work deals with the kinetic aspects of bainite formation during isothermal holding above and below the martensite start (Ms~275 °C) temperature using a low-alloy, high-silicon DIN 1.5025 steel in a range suitable for achieving... more
This work deals with the kinetic aspects of bainite formation during isothermal holding above and below the martensite start (Ms~275 °C) temperature using a low-alloy, high-silicon DIN 1.5025 steel in a range suitable for achieving ultrafine/nanostructured bainite. Dilatation measurements were conducted to study transformation behaviour and kinetics, while the microstructural features were examined using laser scanning confocal microscopy and electron backscatter diffraction (EBSD) techniques combined with hardness measurements. The results showed that for isothermal holding above the Ms temperature, the maximum bainitic transformation rate decreased with the decrease in isothermal holding temperature between 450 and 300 °C. On the other hand, for isothermal holding below the Ms temperature at 250 and 200 °C, the maximum rate of transformation was achieved corresponding to region I due to the partitioning of carbon and also possibly because of the ledged growth of isothermal martens...
Research Interests:
Research Interests:
The interaction of different alloying elements has a significant impact on the mechanical and microstructural properties of steel products due to the thermodynamic and kinetic effect. This article presents a statistically developed and... more
The interaction of different alloying elements has a significant impact on the mechanical and microstructural properties of steel products due to the thermodynamic and kinetic effect. This article presents a statistically developed and validated model for austenite decomposition during cooling, based on a set of experimental continuous cooling transformation diagrams available in literature. In the model, two-way interactions of the alloying elements are included as add-on terms, and the procedure for the analysis ensures there is no overfitting. The model can be used to predict phase transformation temperatures and critical cooling rates for the formation of polygonal ferrite, bainite or martensite for the production of steel.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Abstract In the current study, the hot deformation characteristics and workability of a CoCrFeMnNi high entropy alloy was characterized using processing maps developed on the basis of dynamic materials model in the temperature range... more
Abstract In the current study, the hot deformation characteristics and workability of a CoCrFeMnNi high entropy alloy was characterized using processing maps developed on the basis of dynamic materials model in the temperature range 1023–1423 K and strain rate range 10−3 – 10s−1. The processing map delineated various deterministic domains including those of cracking processes and unstable flow, thus enabling identification of a ‘safe’ processing window for the hot working of the alloy. Accordingly, a deterministic domain in the temperature and strain rate ranges of 1223–1373 K and 10−2 – 5 × 10−1s−1, respectively, was identified to be the domain of dynamic recrystallization (DRX) with a peak efficiency of the order of ~34% at 1293 K and 3 × 10−2s−1 and these were considered to be the optimum parameters for hot deformation. The DRX grain size was dependent on the deformation temperature and strain rate, increasing with the increase in temperature and decrease in strain rate, whereas DRX volume increased with the strain rate. At still higher temperatures (1403–1423 K) and lower strain rates (10−3 – 3 × 10−3s−1), there was a sharp decrease in efficiency values from 27% to 5% thus forming a trough and the microstructure was characterized with coarse grains. In the instability regime, grain boundary cracking/sliding and localized shear bands manifested at temperatures 1398 K, microstructural reconstitution occurred in the shear bands leading to the formation of fine grains, presumably as a consequence of continuous recrystallization.
Research Interests:
Research Interests:
Microalloying of an eutectoid steel with V may facilitate formation of dispersed nano-scaled VC particles in the microstructure during thermomechanical processing or subsequent heat treatment. In this research, the constitutive flow... more
Microalloying of an eutectoid steel with V may facilitate formation of dispersed nano-scaled VC particles in the microstructure during thermomechanical processing or subsequent heat treatment. In this research, the constitutive flow behavior of vanadium microalloyed eutectoid steel has been investigated in the temperature range 620–770 °C at strain rates in the range 0.01–10 s−1. Microstructural characterization of the deformed specimens was conducted using SEM and EBSD techniques. In this context, various deformation mechanisms occurring during warm deformation have been characterized and delineated through construction of a processing map by establishing a power dissipation map and an instability map for the steel and superimposing them. The results show that the pearlitic microstructure exhibits several deformation mechanisms within these warm working conditions. Dynamic spheroidization of cementite lamella takes place in the range 660–720 °C and 0.01–0.1 s−1 with a power dissipation efficiency of 27–33%, characterizing a safe window of processing this steel. The presence of vanadium carbides at grain boundaries strengthened the pearlitic microstructure and retarded the occurrence of some deformation defects during low temperature, high speed deformation in the range 620–720 °C and 1–10 s−1.
Research Interests:
ABSTRACT Recent trends in the production of high strength steel plate call for increasingly sophisticated thermo-mechanical treatment schedules, including the use of high rate accelerated cooling after finish rolling in order to achieve... more
ABSTRACT Recent trends in the production of high strength steel plate call for increasingly sophisticated thermo-mechanical treatment schedules, including the use of high rate accelerated cooling after finish rolling in order to achieve the desired microstructure and mechanical properties. Achieving the necessary cooling process control accuracy in such cases requires a sound understanding and description of the interactions between external heat transfer processes and changes in internal energy due to phenomena such as solid-state phase transformations The thermal physical properties of the evolving microstructures of complex phase and martensitic steels vary greatly, and are strongly dependent on temperature and constituent phases. As a result, critical parameters such as thermal diffusivity cannot be accurately estimated without appropriate linkage to both phase transformation kinetics and temperature In the present study, a numerical simulation has been developed to investigate the unsteady heat transfer and phase transformation behaviour of a moving steel plate during accelerated cooling The simulation includes semi-empirical microstructure evolution sub-models, fitted to measured CCT data using non-linear regression These are coupled to thermal-physical properties sub-models and thermal conduction calculations. A comprehensive suite of thermal boundary condition models which account for direct water cooling, forced convection film boiling, air cooling, radiation and heat transfer between plate and transport rollers are also included. The required equations for the plate temperature and microstructure evolution are solved numerically using a cell centred finite volume method, and the model has been validated by comparing simulated cooling stop temperatures with measurements obtained on the plate cooling section of an industrial plate mill. The predicted cooling stop temperatures of steel plates for different thicknesses, velocities and water flow rates are in good agreement with plant operational data
Research Interests:
ABSTRACT We describe here the attributes of a promising ‘phase reversion’ approach that results in nanograined/ultrafine grained (NG/UFG) structure in austenitic stainless steels with high strength– high ductility combination. The... more
ABSTRACT We describe here the attributes of a promising ‘phase reversion’ approach that results in nanograined/ultrafine grained (NG/UFG) structure in austenitic stainless steels with high strength– high ductility combination. The approach involves severe cold deformation (about 45–75%) of metastable austenite to martensite, which, on annealing for short durations, reverts to austenite via diffusional or shear mechanism, depending on the chemical composition of steel. There was, however, a need to optimise the severity of cold deformation and temperature–time annealing sequence to obtain NG/UFG structure. The fundamental criteria to obtain NG/UFG structure via ‘phase reversion’ approach were to obtain dislocation cell type martensite. In high strength NG/ UFG steel, mechanical twinning contributed to the excellent ductility, while in low strength coarse grained (CG) steel, ductility was also good, but due to nucleation of strain induced martensite at shear bands. The difference in deformation mechanism between NG/UFG and CG steels was attributed to increase in the stability of austenite with decrease in austenite grain size.
Research Interests:
Research Interests:
Research Interests:
... R. Devesh K. Misra 1,* ,; Bhupendra Girase 1 ,; Pavan KC Venkata Surya 1 ,; Mahesh C. Somani 2 ,; L. Pentti Karjalainen 2. Article first published online: 20 JUN 2011. DOI: 10.1002/adem. 201180009. ... A. Thapa, TJ Webster, KM... more
... R. Devesh K. Misra 1,* ,; Bhupendra Girase 1 ,; Pavan KC Venkata Surya 1 ,; Mahesh C. Somani 2 ,; L. Pentti Karjalainen 2. Article first published online: 20 JUN 2011. DOI: 10.1002/adem. 201180009. ... A. Thapa, TJ Webster, KM Haberstroth, J. Biomed. Mater. Res. A 2003, 67, 1374 ...
Research Interests:
ABSTRACT Materials science, engineering, and biological sciences have been combined to improve the tissue compatibility of medical devices. In this regard, nano/ultrafine structuring of austenitic stainless steel obtained using an... more
ABSTRACT Materials science, engineering, and biological sciences have been combined to improve the tissue compatibility of medical devices. In this regard, nano/ultrafine structuring of austenitic stainless steel obtained using an innovative approach of “phase-reversion” has been evaluated for modulation of cellular activity. The biochemical and morphology study with fibroblasts point toward the improvement of tissue compatibility on comparison with coarse-grained structures, strengthening the foundation of nanostructured materials for bio-medical applications.
Research Interests:
Metallic biomedical devices with nanometer-sized grains (NGs) provide surfaces that are different from their coarse-grained (CG) (tens of micrometer) counterparts in terms of increased fraction of grain boundaries (NG&amp;amp;gt;50%;... more
Metallic biomedical devices with nanometer-sized grains (NGs) provide surfaces that are different from their coarse-grained (CG) (tens of micrometer) counterparts in terms of increased fraction of grain boundaries (NG&amp;amp;gt;50%; CG&amp;amp;lt;2-3%). The novel concept of &amp;amp;#39;phase-reversion&amp;amp;#39; involving a controlled deformation-annealing sequence is used to obtain a wide range of grain structures, starting from the NG regime to the CG regime, to demonstrate that the grain structure significantly impacts cellular interactions and osteoblast functions. The uniqueness of this concept is the ability to address the critical aspect of cellular activity in nanostructured materials, because a range of grain sizes from NG to CG are obtained in a single material using an identical set of parameters. This is in addition to a high strength/weight ratio and superior wear and corrosion resistance. These multiple attributes are important for the long-term stability of biomedical devices. Experiments on the interplay between grain structure from the NG regime to CG in austenitic stainless steel on osteoblast functions indicated that cell attachment, proliferation, viability, morphology and spread varied with grain size and were favorably modulated on the NG and ultrafine-grain structure. Furthermore, immunofluorescence studies demonstrated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on the NG surface. The differences in the cellular response with change in grain structure are attributed to grain structure and degree of hydrophilicity. The study lays the foundation for a new branch of nanostructured materials for biomedical applications.
Research Interests:
Research Interests:
Metallic materials with submicron- to nanometer-sized grains provide surfaces that are different from conventional polycrystalline materials because of the large proportion of grain boundaries with high free energy. In the study described... more
Metallic materials with submicron- to nanometer-sized grains provide surfaces that are different from conventional polycrystalline materials because of the large proportion of grain boundaries with high free energy. In the study described here, the combination of cellular and molecular biology, materials science and engineering advances our understanding of cell-substrate interactions, especially the cellular activity between preosteoblasts and nanostructured metallic surfaces. Experiments on the effect of nano-/ultrafine grains have shown that cell attachment, proliferation, viability, morphology and spread are favorably modulated and significantly different from conventional coarse-grained structures. Additionally, immunofluorescence studies demonstrated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on nanograined/ultrafine-grained substrate. These observations suggest enhanced cell-substrate interaction and activity. The differences in the cellular response on nanograined/ultrafine-grained and coarse-grained substrates are attributed to grain size and degree of hydrophilicity. The outcomes of the study are expected to reduce challenges to engineer bulk nanostructured materials with specific physical and surface properties for medical devices with improved cellular attachment and response. The data lay the foundation for a new branch of nanostructured materials for biomedical applications.
Research Interests: Molecular Biology, Fluorescence Microscopy, Cell Adhesion, Materials Science and Engineering, Atomic Force Microscopy, and 15 moreMultidisciplinary, Mice, Animals, Medical Device, Grain size, Free Energy, Grain Boundary, Materials Testing, Elsevier, Coarse Grained Soil, Biomedical Application, Molecular Interactions, Biomechanical Phenomena, Metallic Materials, and Metallic Surface
Given the need to develop high strength/weight ratio bioimplants with enhanced cellular response, we describe here a study focused on the processing-structure-functional property relationship in austenitic stainless steel that was... more
Given the need to develop high strength/weight ratio bioimplants with enhanced cellular response, we describe here a study focused on the processing-structure-functional property relationship in austenitic stainless steel that was processed using an ingenious phase reversion approach to obtain an nanograined/ultrafine-grained (NG/UFG) structure. The cellular activity between fibroblast and NG/UFG substrate is compared with the coarse-grained (CG) substrate. A comparative investigation of NG/UFG and CG structures illustrated that cell attachment, proliferation, viability, morphology and spread are favorably modulated and significantly different from the conventional CG structure. These observations were further confirmed by expression levels of vinculin and associated actin cytoskeleton. Immunofluorescence studies demonstrated increased vinculin concentrations associated with actin stress fibers in the outer regions of the cells and cellular extensions on NG/UFG substrate. These observations suggest enhanced cell-substrate interaction and activity. The cellular attachment response on NG/UFG substrate is attributed to grain size and hydrophilicity and is related to more open lattice in the positions of high-angle grain boundaries.
Research Interests: Fluorescence Microscopy, Cell Adhesion, Immunohistochemistry, Confocal Microscopy, Multidisciplinary, and 15 moreCell line, Mice, Animals, Nanostructures, Stainless Steel, Grain size, Actin Cytoskeleton, Grain Boundary, Particle Size, Cell Shape, Austenitic stainless steel, Nanostructured Material, Human Fibroblasts, Coarse Grained Soil, and fibroblasts
Research Interests:
The influence of boron as well as boron with niobium additions on the phase transformation behaviour, resultant microstructures, and mechanical properties of thermomechanically controlled hot-rolled and direct-quenched low-carbon bainitic... more
The influence of boron as well as boron with niobium additions on the phase transformation behaviour, resultant microstructures, and mechanical properties of thermomechanically controlled hot-rolled and direct-quenched low-carbon bainitic steel plates was investigated. Also, the probable factors that could inhibit their specific merits on hardenability, phase transformation behaviour and mechanical properties, were studied. Continuous cooling transformation diagrams of both deformed and non-deformed austenite were constructed for the investigated steels. Laser scanning confocal microscopy (LSCM) and field emission scanning electron microscopy (FESEM) were employed to examine the microstructures, besides detailed analyses of the non-metallic inclusions using FESEM combined with INCA software. Moreover, the precipitates were investigated qualitatively using both FESEM as well as transmission electron microscopy (TEM). The results showed that the addition of boron or boron with niobium...