Zener pinning between a curved Cu grain boundary (GB) and a differently shaped and oriented Ag particle has been simulated via molecular dynamics. The computed magnitudes of the maximum pinning force agreed with theoretical predictions only when the force was small. As the force increased, discrepancy became obvious. Through carefully inspecting structures of the Cu-Ag interfaces, detailed interaction processes and variation of the Cu GB during the interaction, the discrepancy is found to mainly result from GB faceting, which can reduce the maximum pinning force and facilitate boundary passage. GB anisotropy and/or interface natures are also found to slightly contribute to the discrepancy. These findings suggest that the assumption of an isotropic GB with constant energy utilized in previous theoretical works for deriving the maximum pinning force is inappropriate and a correct maximum pinning force could not be predicted without knowing the effects of GB evolution together with detailed properties of both GBs and interfaces.
{"title":"Effects of Grain Boundary Faceting, Grain Boundary Anisotropy and Interface Natures on the Maximum Pinning Force of a Differently Shaped and Oriented Particle","authors":"Jian Zhou, Runjie Li, Qingyu Zhang","doi":"10.2139/ssrn.3683529","DOIUrl":"https://doi.org/10.2139/ssrn.3683529","url":null,"abstract":"Zener pinning between a curved Cu grain boundary (GB) and a differently shaped and oriented Ag particle has been simulated via molecular dynamics. The computed magnitudes of the maximum pinning force agreed with theoretical predictions only when the force was small. As the force increased, discrepancy became obvious. Through carefully inspecting structures of the Cu-Ag interfaces, detailed interaction processes and variation of the Cu GB during the interaction, the discrepancy is found to mainly result from GB faceting, which can reduce the maximum pinning force and facilitate boundary passage. GB anisotropy and/or interface natures are also found to slightly contribute to the discrepancy. These findings suggest that the assumption of an isotropic GB with constant energy utilized in previous theoretical works for deriving the maximum pinning force is inappropriate and a correct maximum pinning force could not be predicted without knowing the effects of GB evolution together with detailed properties of both GBs and interfaces.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"19 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91296798","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Suzuki, H. Kitagawa, A. H. Pham, S. Morito, K. Kikuchi
Sintered polycrystalline Bi0.4Sb1.6Te3 thermoelectric materials with various degrees of crystal alignment and grain sizes were prepared by pulse-current sintering under cyclic uniaxial pressure at sintering temperatures of 350–425 °C for holding times of 0–60 min to clarify the relationship between the microstructure and the thermoelectric properties. The degree of crystal alignment was enhanced with an increase of both the sintering temperature and holding time, and grain growth was also confirmed in the high temperature or long-time sintering process. The thermoelectric properties were measured perpendicular to the pressing direction, which corresponds to the crystal alignment direction. The electrical resistivity decreased and the thermal conductivity slightly increased with increasing sintering temperature and holding time. As a result, the figures of merit of the crystal-aligned samples sintered at high temperatures or for long holding times tended to reach 0.9–1 with large power factors because of the small electrical resistivity. The relationships between the quantified microstructure parameters and thermoelectric properties are discussed. The electrical resistivity decreased with increasing degree of crystal alignment and it saturated at a certain degree of crystal alignment, indicating that perfect crystal alignment is not necessary to obtain the lower limit of the electrical resistivity. Conversely, no significant change of the lattice thermal conductivity was observed in the grain size range 0.6–9.7 μm. This means that the lattice thermal conductivity of crystal aligned Bi0.4Sb1.6Te3 is almost independent of the degree of crystal alignment and grain size in the measured range.
{"title":"Effect of the Crystal Alignment and Grain Size on the Thermoelectric Properties of Bi 0.4Sb 1.6Te 3 Sintered Materials","authors":"A. Suzuki, H. Kitagawa, A. H. Pham, S. Morito, K. Kikuchi","doi":"10.2139/ssrn.3673588","DOIUrl":"https://doi.org/10.2139/ssrn.3673588","url":null,"abstract":"Sintered polycrystalline Bi0.4Sb1.6Te3 thermoelectric materials with various degrees of crystal alignment and grain sizes were prepared by pulse-current sintering under cyclic uniaxial pressure at sintering temperatures of 350–425 °C for holding times of 0–60 min to clarify the relationship between the microstructure and the thermoelectric properties. The degree of crystal alignment was enhanced with an increase of both the sintering temperature and holding time, and grain growth was also confirmed in the high temperature or long-time sintering process. The thermoelectric properties were measured perpendicular to the pressing direction, which corresponds to the crystal alignment direction. The electrical resistivity decreased and the thermal conductivity slightly increased with increasing sintering temperature and holding time. As a result, the figures of merit of the crystal-aligned samples sintered at high temperatures or for long holding times tended to reach 0.9–1 with large power factors because of the small electrical resistivity. The relationships between the quantified microstructure parameters and thermoelectric properties are discussed. The electrical resistivity decreased with increasing degree of crystal alignment and it saturated at a certain degree of crystal alignment, indicating that perfect crystal alignment is not necessary to obtain the lower limit of the electrical resistivity. Conversely, no significant change of the lattice thermal conductivity was observed in the grain size range 0.6–9.7 μm. This means that the lattice thermal conductivity of crystal aligned Bi0.4Sb1.6Te3 is almost independent of the degree of crystal alignment and grain size in the measured range.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83491416","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
O. Brazil, Johann P. de Silva, J. Pethica, G. Cross
Confined geometries offer useful and experimentally amenable mechanical testing arrangements in which to study the molecular and micro-structural processes which govern plastic yield in stress environments dominated by hydrostatic pressure over shear. However, the changes to macroscopic stress strain behaviour that result from switching from an unconfined mode such as uniaxial compression to a confined one are often overlooked and display a surprising level of complexity, even for simple elastic plastic constitutive models. Here we report a confinement induced strain hardening effect in polystyrene thin films achieved through repeated plastic loading with a cylindrical flat punch whose diameter is many times the initial film thickness. This high aspect ratio combines with constraint provided by film material surrounding the contact to generate a state of confined uniaxial strain in the indented region, rendering the deformation one dimensional. By repeated loading into the plastic domain, we achieve a 66% increase in the confined yield stress, from 0.3 GPa to 0.5 GPa. Through finite element simulation and analytic modelling of the principal stresses and strains, we show that this effect arises not from intrinsic changes to the structure of the material, but rather residual stresses imparted during plastic loading. We contrast this effect with intrinsic changes to glassy thin films such as physical ageing and thermal cross-linking.
{"title":"Extrinsic and Intrinsic Mechanical Responses of Confined Indented Thin Films","authors":"O. Brazil, Johann P. de Silva, J. Pethica, G. Cross","doi":"10.2139/ssrn.3661923","DOIUrl":"https://doi.org/10.2139/ssrn.3661923","url":null,"abstract":"Confined geometries offer useful and experimentally amenable mechanical testing arrangements in which to study the molecular and micro-structural processes which govern plastic yield in stress environments dominated by hydrostatic pressure over shear. However, the changes to macroscopic stress strain behaviour that result from switching from an unconfined mode such as uniaxial compression to a confined one are often overlooked and display a surprising level of complexity, even for simple elastic plastic constitutive models. Here we report a confinement induced strain hardening effect in polystyrene thin films achieved through repeated plastic loading with a cylindrical flat punch whose diameter is many times the initial film thickness. This high aspect ratio combines with constraint provided by film material surrounding the contact to generate a state of confined uniaxial strain in the indented region, rendering the deformation one dimensional. By repeated loading into the plastic domain, we achieve a 66% increase in the confined yield stress, from 0.3 GPa to 0.5 GPa. Through finite element simulation and analytic modelling of the principal stresses and strains, we show that this effect arises not from intrinsic changes to the structure of the material, but rather residual stresses imparted during plastic loading. We contrast this effect with intrinsic changes to glassy thin films such as physical ageing and thermal cross-linking.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"61 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87149660","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present a detailed study of solid state dewetting choosing epitaxial bismuth films on silicon as a model system. Exploiting both diffraction and imaging methods, we determine atomistic parameters like unit cell coverage, lattice spacings and gradients thereof through the analysis of x-ray diffraction crystal truncation rods. We use a Johnson-Mehl-Avrami-Kolmogorov model to describe the kinetics of the dewetting process on an atomic scale. The role of a vertical strain gradient, that impedes solid state dewetting, is revealed and a detailed model for the atomic jump diffusion during dewetting is presented.
{"title":"Atomistic View Onto Solid State Dewetting: The Role of a Strain Gradient","authors":"Constantin Wansorra, E. Bruder, W. Donner","doi":"10.2139/ssrn.3610484","DOIUrl":"https://doi.org/10.2139/ssrn.3610484","url":null,"abstract":"We present a detailed study of solid state dewetting choosing epitaxial bismuth films on silicon as a model system. Exploiting both diffraction and imaging methods, we determine atomistic parameters like unit cell coverage, lattice spacings and gradients thereof through the analysis of x-ray diffraction crystal truncation rods. We use a Johnson-Mehl-Avrami-Kolmogorov model to describe the kinetics of the dewetting process on an atomic scale. The role of a vertical strain gradient, that impedes solid state dewetting, is revealed and a detailed model for the atomic jump diffusion during dewetting is presented.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"74 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82069178","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
H. Masuda, K. Morita, M. Watanabe, T. Hara, H. Yoshida, T. Ohmura
Abstract The orientation-dependent micromechanical properties of nontransformable tetragonal (t’) zirconia, which underwent a diffusionless transformation from the fluorite cubic phase and does not exhibit a stress-induced phase transformation, were characterized via pseudo-single crystal micropillar compression and electron microscopy. The t’ zirconia sample was obtained via atmospheric plasma spraying of 4.5 mol% yttria-stabilized zirconia (YSZ) powders into liquid nitrogen and consolidated into a bulk state via hot pressing at 1100°C. Dense and cylindrical micropillars were fabricated using a focused ion beam from pseudo-single crystalline regions, which exhibited a nanodomain microstructure of three t’ variants partitioned by {1 0 1}c twin boundaries with 90° symmetry. These micropillars were compressed using a flat-end diamond indenter. Near- c compressions were attributed to ferroelastic domain switching and subsequent {1 0 1}c and/or {1 1 1}c hard slips. In ferroelastic deformation, a certain t’ variant diminished, and a binary domain microstructure developed with c axes perpendicular to the compressive direction. Near- c compressions were governed by {0 0 1}c soft slips accompanied by strain hardening with negligible ferroelasticity, which resulted in buckling deformation with rotational kinking. In both the hard- and soft-slip orientations, ferroelastic toughening was observed with certain t’ variants awaken around the crack tips. Contrarily, cleavage fractures subsequent to yielding were observed in near- c compressions. In the cubic counterpart with a domain-free microstructure (8.0 mol% YSZ), ferroelastic toughening was not observed. Hence, it is viewed as the origin of enhanced toughness in t’ zirconia.
{"title":"Ferroelastic and Plastic Behaviors in Pseudo-Single Crystal Micropillars of Nontransformable Tetragonal Zirconia","authors":"H. Masuda, K. Morita, M. Watanabe, T. Hara, H. Yoshida, T. Ohmura","doi":"10.2139/ssrn.3604625","DOIUrl":"https://doi.org/10.2139/ssrn.3604625","url":null,"abstract":"Abstract The orientation-dependent micromechanical properties of nontransformable tetragonal (t’) zirconia, which underwent a diffusionless transformation from the fluorite cubic phase and does not exhibit a stress-induced phase transformation, were characterized via pseudo-single crystal micropillar compression and electron microscopy. The t’ zirconia sample was obtained via atmospheric plasma spraying of 4.5 mol% yttria-stabilized zirconia (YSZ) powders into liquid nitrogen and consolidated into a bulk state via hot pressing at 1100°C. Dense and cylindrical micropillars were fabricated using a focused ion beam from pseudo-single crystalline regions, which exhibited a nanodomain microstructure of three t’ variants partitioned by {1 0 1}c twin boundaries with 90° symmetry. These micropillars were compressed using a flat-end diamond indenter. Near- c compressions were attributed to ferroelastic domain switching and subsequent {1 0 1}c and/or {1 1 1}c hard slips. In ferroelastic deformation, a certain t’ variant diminished, and a binary domain microstructure developed with c axes perpendicular to the compressive direction. Near- c compressions were governed by {0 0 1}c soft slips accompanied by strain hardening with negligible ferroelasticity, which resulted in buckling deformation with rotational kinking. In both the hard- and soft-slip orientations, ferroelastic toughening was observed with certain t’ variants awaken around the crack tips. Contrarily, cleavage fractures subsequent to yielding were observed in near- c compressions. In the cubic counterpart with a domain-free microstructure (8.0 mol% YSZ), ferroelastic toughening was not observed. Hence, it is viewed as the origin of enhanced toughness in t’ zirconia.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"46 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88512480","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Haoran Sun, Z. Ding, Haoran Sun, Shuang Li, E. Lavernia, Wei Liu
Abstract The formation of twins in face-centered cubic (FCC) crystals is influenced by both the energy barriers and associated shear directions. In this study, we formulate and implement a theoretical framework to study 15 pure FCC metals in an effort to propose a twinning propensity descriptor to predict the tendency for twin formation in FCC metals under different shear directions. Our calculations demonstrate that deformation twins form readily in: Al, Ir, Ni, Rh, Co, Au, Cu, Yb, Ag, Sr, and Ca, but have difficulty forming in: Ce, Pt, Pb, and Pd, and this trend is consistent with available experiment results. Using this descriptor, we further predict that in the case of Cu-Al alloys the highest twinning propensity is achieved at ~6 at. % Al concentration, which is also consistent with experimental observations. These results provide insight into the nature of deformation twins, and furthermore help establish the framework necessary to design FCC metals and alloys with a high tendency for twin formation.
{"title":"The Synergistic Effects of Energy Barriers and Shear Directions on Twinning in Face Centered Cubic Metals","authors":"Haoran Sun, Z. Ding, Haoran Sun, Shuang Li, E. Lavernia, Wei Liu","doi":"10.2139/ssrn.3427531","DOIUrl":"https://doi.org/10.2139/ssrn.3427531","url":null,"abstract":"Abstract The formation of twins in face-centered cubic (FCC) crystals is influenced by both the energy barriers and associated shear directions. In this study, we formulate and implement a theoretical framework to study 15 pure FCC metals in an effort to propose a twinning propensity descriptor to predict the tendency for twin formation in FCC metals under different shear directions. Our calculations demonstrate that deformation twins form readily in: Al, Ir, Ni, Rh, Co, Au, Cu, Yb, Ag, Sr, and Ca, but have difficulty forming in: Ce, Pt, Pb, and Pd, and this trend is consistent with available experiment results. Using this descriptor, we further predict that in the case of Cu-Al alloys the highest twinning propensity is achieved at ~6 at. % Al concentration, which is also consistent with experimental observations. These results provide insight into the nature of deformation twins, and furthermore help establish the framework necessary to design FCC metals and alloys with a high tendency for twin formation.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"54 6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77218784","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
X. Liang, G. Zhao, M. Dodge, T.L. Lee, H. Dong, P. Rivera-Diaz-Del-Castillo
Abstract In super duplex stainless steels (SDSSs), both austenite and ferrite are susceptible to hydrogen embrittlement, however there is a lack of understanding into the effect of hydrogen in each phase. In this study, in neutron diffraction was applied on hydrogen-charged (H-charged) samples to investigate the hydrogen embrittlement behaviour in super duplex stainless steels. The result reveals that austenite maintains good plasticity during tensile testing, whilst a loss of it is realised in ferrite. Fractography analysis reveals the diffusion of hydrogen induced a brittle-to-ductile transition from the sample surface towards the centre; hydrogen embrittlement vanishes as the specimen’s centre is approached, while it is demonstrated to disappear first in austenite but not in ferrite. This transition can be predicted by applying a physics-based hydrogen embrittlement model which incorporates the effects of hydrogen concentration, hydrogen diffusivity, residual stress, loading state and temperature. The present work demonstrates the dissimilar susceptibility of austenite and ferrite to hydrogen embrittlement, providing a tool to describe it.
{"title":"Hydrogen Embrittlement in Super Duplex Stainless Steels","authors":"X. Liang, G. Zhao, M. Dodge, T.L. Lee, H. Dong, P. Rivera-Diaz-Del-Castillo","doi":"10.2139/ssrn.3446899","DOIUrl":"https://doi.org/10.2139/ssrn.3446899","url":null,"abstract":"Abstract In super duplex stainless steels (SDSSs), both austenite and ferrite are susceptible to hydrogen embrittlement, however there is a lack of understanding into the effect of hydrogen in each phase. In this study, in neutron diffraction was applied on hydrogen-charged (H-charged) samples to investigate the hydrogen embrittlement behaviour in super duplex stainless steels. The result reveals that austenite maintains good plasticity during tensile testing, whilst a loss of it is realised in ferrite. Fractography analysis reveals the diffusion of hydrogen induced a brittle-to-ductile transition from the sample surface towards the centre; hydrogen embrittlement vanishes as the specimen’s centre is approached, while it is demonstrated to disappear first in austenite but not in ferrite. This transition can be predicted by applying a physics-based hydrogen embrittlement model which incorporates the effects of hydrogen concentration, hydrogen diffusivity, residual stress, loading state and temperature. The present work demonstrates the dissimilar susceptibility of austenite and ferrite to hydrogen embrittlement, providing a tool to describe it.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"70 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83995438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Understanding on the reaction kinetics associated with the formation of intermetallic compounds and the mechanisms involved in evolution of the reaction product at different temperatures due to solid state reaction in Friction Stir Welding (FSW) of dissimilar materials is very important in selecting optimum operating condition to control intermetallic compounds for safety-critical applications. In this study, the evolution sequence of intermetallic compounds and reaction kinetics during the solid state reaction between Ti and Al has been investigated. It was found that the mechanical mixing of Al and Ti affects evolution of reaction layers (RL) and intermetallic compounds. The thickness of the RL increases with reaction temperature and titanium trialuminide (Al3Ti) was found to be the only ordered phase that is formed at a higher temperature (650 °C). The activation energy for the growth of the reaction layer was found to be significantly lower when compared to conventional welding. The sequence of formation of these intermetallic compounds is proposed based on kinetics and thermodynamic principles such as inter-diffusion and free energy of formation. The variation in stoichiometry at the Al/Ti interfaces due to mechanical mixing as occurred during FSW and difference in diffusivity of Al and Ti through reaction layers are considered responsible for the phase evolution and growth of these layers. The mechanism of the reaction with the reduced activation energy was attributed to fragmentation, mechanical mixing, development of dislocation and twinning in materials, activation of atoms due to severe deformation and grain boundary diffusion.
{"title":"Formation Sequence of Intermetallics and Kinetics of Reaction Layer Growth During Solid State Reaction between Titanium and Aluminum","authors":"A. Kar, S. Kailas, S. Suwas","doi":"10.2139/ssrn.3531305","DOIUrl":"https://doi.org/10.2139/ssrn.3531305","url":null,"abstract":"Abstract Understanding on the reaction kinetics associated with the formation of intermetallic compounds and the mechanisms involved in evolution of the reaction product at different temperatures due to solid state reaction in Friction Stir Welding (FSW) of dissimilar materials is very important in selecting optimum operating condition to control intermetallic compounds for safety-critical applications. In this study, the evolution sequence of intermetallic compounds and reaction kinetics during the solid state reaction between Ti and Al has been investigated. It was found that the mechanical mixing of Al and Ti affects evolution of reaction layers (RL) and intermetallic compounds. The thickness of the RL increases with reaction temperature and titanium trialuminide (Al3Ti) was found to be the only ordered phase that is formed at a higher temperature (650 °C). The activation energy for the growth of the reaction layer was found to be significantly lower when compared to conventional welding. The sequence of formation of these intermetallic compounds is proposed based on kinetics and thermodynamic principles such as inter-diffusion and free energy of formation. The variation in stoichiometry at the Al/Ti interfaces due to mechanical mixing as occurred during FSW and difference in diffusivity of Al and Ti through reaction layers are considered responsible for the phase evolution and growth of these layers. The mechanism of the reaction with the reduced activation energy was attributed to fragmentation, mechanical mixing, development of dislocation and twinning in materials, activation of atoms due to severe deformation and grain boundary diffusion.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91537072","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yanxu Wang, Y. Tomota, T. Ohmura, S. Morooka, W. Gong, S. Harjo
Abstract A high-intensity and high-resolution neutron diffractometer with a thermomechanically controlled processing simulator was employed in-situ to investigate martensite transformation behavior with and without ausforming for a medium-carbon low-alloy steel. Serial neutron diffraction profiles have revealed that the transformation behavior could be successfully monitored during quenching with and without the ausforming process. The fresh martensite exhibits a body-centered tetragonal structure when it forms immediately below the martensite start (Ms) temperature, and its c/a ratio decreases rapidly as time elapses. The lattice parameter and the full width at half maximum of austenite peaks significantly decreases and increases upon martensite transformation, respectively. After ausforming, the data reveal that lattice parameters are larger in austenite whereas smaller in martensite compared with those in the non-ausformed case, which is ascribed to the introduced dislocations. Thus, the lattice defects affect the lattice parameter during martensite transformation. Ausforming also slightly raises the Ms temperature and increases the amount of retained austenite at room temperature as a result of different dislocation densities. The cutting-edge operant quantitative measurements with neutron diffraction for steel production is demonstrated.
{"title":"Real Time Observation of Martensite Transformation for a 0.4C Low Alloyed Steel by Neutron Diffraction","authors":"Yanxu Wang, Y. Tomota, T. Ohmura, S. Morooka, W. Gong, S. Harjo","doi":"10.2139/ssrn.3458134","DOIUrl":"https://doi.org/10.2139/ssrn.3458134","url":null,"abstract":"Abstract A high-intensity and high-resolution neutron diffractometer with a thermomechanically controlled processing simulator was employed in-situ to investigate martensite transformation behavior with and without ausforming for a medium-carbon low-alloy steel. Serial neutron diffraction profiles have revealed that the transformation behavior could be successfully monitored during quenching with and without the ausforming process. The fresh martensite exhibits a body-centered tetragonal structure when it forms immediately below the martensite start (Ms) temperature, and its c/a ratio decreases rapidly as time elapses. The lattice parameter and the full width at half maximum of austenite peaks significantly decreases and increases upon martensite transformation, respectively. After ausforming, the data reveal that lattice parameters are larger in austenite whereas smaller in martensite compared with those in the non-ausformed case, which is ascribed to the introduced dislocations. Thus, the lattice defects affect the lattice parameter during martensite transformation. Ausforming also slightly raises the Ms temperature and increases the amount of retained austenite at room temperature as a result of different dislocation densities. The cutting-edge operant quantitative measurements with neutron diffraction for steel production is demonstrated.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"117 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79383481","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The natural pyrite is studied using the method of nuclear gamma resonance (NGR), X-ray diffraction and the method of mineral structure’s microprobe analysis (EPMA). Pyrite is almost never of a stoichiometric structure and, therefore, has cationic and anionic vacant positions. An algorithm of calculating the density of cationic and anionic vacant positions in pyrite-type cubic crystal structures is designed. Analytical expressions for calculating densities of both vacant positions and impurity atoms in pyrite’s structure are given. The calculation is performed for ones of the natural pyrite with different S/Fe ratios. The densities of cationic and anionic vacancies, as well as of all kinds of impurity atoms have been calculated for pyrite.
{"title":"The Iron Substitution Ions in Pyrite Structure","authors":"V. Onufrienok","doi":"10.2139/ssrn.3678766","DOIUrl":"https://doi.org/10.2139/ssrn.3678766","url":null,"abstract":"The natural pyrite is studied using the method of nuclear gamma resonance (NGR), X-ray diffraction and the method of mineral structure’s microprobe analysis (EPMA). Pyrite is almost never of a stoichiometric structure and, therefore, has cationic and anionic vacant positions. An algorithm of calculating the density of cationic and anionic vacant positions in pyrite-type cubic crystal structures is designed. Analytical expressions for calculating densities of both vacant positions and impurity atoms in pyrite’s structure are given. The calculation is performed for ones of the natural pyrite with different S/Fe ratios. The densities of cationic and anionic vacancies, as well as of all kinds of impurity atoms have been calculated for pyrite.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"9 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78603522","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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