J. Dong, N. Gao, Ying Chen, Ling-fei Cao, Hui Song, Hannes Fröck, B. Milkereit, M. Starink
The combined strengthening effects of high pressure torsion (HPT) and age hardening on a recently developed 3rd generation Al-Cu-Li alloy was investigated. Solution treated samples were processed through HPT at room temperature, followed by low temperature artificial ageing (i.e. T4-HPT-AA). A micro-hardness of ~240 Hv was achieved on ageing at 110°C/60h after HPT. A further improvement in the hardness to ~260 Hv was accomplished by a pre-ageing 110°C/24h before HPT in combination with a post-HPT ageing process at 110°C for 180h (i.e. T6-HPT-AA). These novel multi-stage processes give rise to an increase in hardness by a factor of 2 as compared to the T4 condition (~120 Hv). After HPT the grain size was dramatically refined to the ultrafine-grained (UFG) structure, accompanied by a large amount of dislocations. No long-range ordered precipitates were observed after HPT and subsequent ageing treatments. Instead, atom probe tomography (APT) provided clear evidence that Cu-Mg co-clusters were homogeneously distributed in the matrix of T4 and T6 processed samples and they segregate strongly to the grain boundaries (GBs) during HPT. Further ageing treatment after HPT leads to the segregation of clusters to the dislocations. A strengthening model that incorporates dislocation hardening, grain boundary hardening, solid solution strengthening and a new short-range order strengthening mechanisms was used to predict the yield strength of the alloy. This model indicates that the combined effect due to all three types of Cu-Mg clusters (clustering in matrix, clustering at GBs and at dislocations) is dominant for the strength in all conditions.
{"title":"Achieving Ultra-High Strength of Al-Cu-Li Alloys by the Combination of High Pressure Torsion and Age-Hardening","authors":"J. Dong, N. Gao, Ying Chen, Ling-fei Cao, Hui Song, Hannes Fröck, B. Milkereit, M. Starink","doi":"10.2139/ssrn.3802822","DOIUrl":"https://doi.org/10.2139/ssrn.3802822","url":null,"abstract":"The combined strengthening effects of high pressure torsion (HPT) and age hardening on a recently developed 3<sup>rd</sup> generation Al-Cu-Li alloy was investigated. Solution treated samples were processed through HPT at room temperature, followed by low temperature artificial ageing (i.e. T4-HPT-AA). A micro-hardness of ~240 Hv was achieved on ageing at 110°C/60h after HPT. A further improvement in the hardness to ~260 Hv was accomplished by a pre-ageing 110°C/24h before HPT in combination with a post-HPT ageing process at 110°C for 180h (i.e. T6-HPT-AA). These novel multi-stage processes give rise to an increase in hardness by a factor of 2 as compared to the T4 condition (~120 Hv). After HPT the grain size was dramatically refined to the ultrafine-grained (UFG) structure, accompanied by a large amount of dislocations. No long-range ordered precipitates were observed after HPT and subsequent ageing treatments. Instead, atom probe tomography (APT) provided clear evidence that Cu-Mg co-clusters were homogeneously distributed in the matrix of T4 and T6 processed samples and they segregate strongly to the grain boundaries (GBs) during HPT. Further ageing treatment after HPT leads to the segregation of clusters to the dislocations. A strengthening model that incorporates dislocation hardening, grain boundary hardening, solid solution strengthening and a new short-range order strengthening mechanisms was used to predict the yield strength of the alloy. This model indicates that the combined effect due to all three types of Cu-Mg clusters (clustering in matrix, clustering at GBs and at dislocations) is dominant for the strength in all conditions.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"58 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88675164","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}
This paper addresses the damage behaviour of a nickel/yttria-stabilised zirconia (Ni-YSZ) anode, in order to understand microstructural degradation processes of Solid Oxide Fuel Cells (SOFCs) during long-term operation. Numerical investigations are carried out to analyse the failure mechanisms in detail. For this purpose, finite element (FE) models are generated from focused ion beam-scanning electron microscopy 3D image data, representing the anode microstructure with varying phase compositions. A brittle model and a ductile material model were assigned to the YSZ phase and the nickel phase, respectively. The porosity is found to affect the strength of the microstructure significantly, leading to low compressive strength results. A high Ni content generally increases the toughness of the overall structure. However, the orientation and the geometry of the nickel phase is essential. When the Ni phase is aligned parallel to the loading direction, a supporting effect on the microstructure is observed, resulting in a significant high toughness. On the contrary, a rapid failure of the sample occurs when the Ni phase is oriented perpendicular to the loading direction. Two main failure mechanisms are identified: (i) cracking at the Ni/YSZ interface and (ii) cracking of struts at the location of the smallest diameter.
{"title":"Numerical Investigations on the Damage Behaviour of a Reconstructed Anode for Solid Oxide Fuel Cell Application","authors":"Katharina Steier, V. Guski, S. Schmauder","doi":"10.2139/ssrn.3659799","DOIUrl":"https://doi.org/10.2139/ssrn.3659799","url":null,"abstract":"This paper addresses the damage behaviour of a nickel/yttria-stabilised zirconia (Ni-YSZ) anode, in order to understand microstructural degradation processes of Solid Oxide Fuel Cells (SOFCs) during long-term operation. Numerical investigations are carried out to analyse the failure mechanisms in detail. For this purpose, finite element (FE) models are generated from focused ion beam-scanning electron microscopy 3D image data, representing the anode microstructure with varying phase compositions. A brittle model and a ductile material model were assigned to the YSZ phase and the nickel phase, respectively. The porosity is found to affect the strength of the microstructure significantly, leading to low compressive strength results. A high Ni content generally increases the toughness of the overall structure. However, the orientation and the geometry of the nickel phase is essential. When the Ni phase is aligned parallel to the loading direction, a supporting effect on the microstructure is observed, resulting in a significant high toughness. On the contrary, a rapid failure of the sample occurs when the Ni phase is oriented perpendicular to the loading direction. Two main failure mechanisms are identified: (i) cracking at the Ni/YSZ interface and (ii) cracking of struts at the location of the smallest diameter.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"13 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80481391","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}
Distributions showing the frequencies of occurrence of grain boundaries as functions of their 5 macroscopic boundary parameters have been computed for a set of yttria-stabilized zirconia samples sintered at different conditions and thus having different grain sizes. For this purpose, datasets containing both grain misorientation and boundary plane parameters have been collected by the means of the 3D EBSD technique. Then, the 5-parameter distributions have been computed using the approach based on kernel density estimation. A few top peaks are visible in all of the obtained distributions. Their heights exceed the level of the random distribution by at least about 3 multiples of the corresponding statistical errors. The list of favored grain boundaries includes the Σ3/(111) and Σ11/(1‾13) boundaries, as well as the boundaries having both the boundary plane (100) and misorientation by 10° to 37° about the [100] axis.
{"title":"Five Dimensional Grain Boundary Distribution for Yttria Stabilized Zirconia Based on Experimentally Determined Macroscopic Boundary Parameters","authors":"M. Faryna, K. Głowiński","doi":"10.2139/ssrn.3906843","DOIUrl":"https://doi.org/10.2139/ssrn.3906843","url":null,"abstract":"Distributions showing the frequencies of occurrence of grain boundaries as functions of their 5 macroscopic boundary parameters have been computed for a set of yttria-stabilized zirconia samples sintered at different conditions and thus having different grain sizes. For this purpose, datasets containing both grain misorientation and boundary plane parameters have been collected by the means of the 3D EBSD technique. Then, the 5-parameter distributions have been computed using the approach based on kernel density estimation. A few top peaks are visible in all of the obtained distributions. Their heights exceed the level of the random distribution by at least about 3 multiples of the corresponding statistical errors. The list of favored grain boundaries includes the Σ3/(111) and Σ11/(1‾13) boundaries, as well as the boundaries having both the boundary plane (100) and misorientation by 10° to 37° about the [100] axis.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84585070","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 plasmon-mediated process is one of the most common and well-studied methods to synthesize silver nanoplates (AgNPts). In a typical plasmon-mediated process, silver seeds are generated by chemical reduction using NaBH4 (abbreviated as CR seeds) before the plasmon-mediated process. However, a broad localized surface plasmon resonance (LSPR) band of AgNPts (usually broader than 150 nm) synthesized using the typical plasmon-mediated process would possibly limit their further applications. In this study, silver seeds are generated using a photochemical reduction method (abbreviated as PCR seeds). These PCR seeds then convert to AgNPts with irradiation by green LEDs or by a sodium lamp through the plasmon-mediated process. Furthermore, a very narrow LSPR bandwidth (approximately 67 nm) can be obtained when these AgNPts are further irradiated with red LEDs. Due to high refractive index sensitivity and sharp LSPR bandwidth, the as-prepared AgNPts have a high figure of merit (FOM) and can be used for spectroscopic chemical sensing applications. The silver seeds generated by this photochemical method can provide another choice for the plasmon-mediated process to synthesize AgNPts with high optical quality.
{"title":"Synthesis of Silver Nanoplates With a Narrow LSPR Band for Chemical Sensing Through a Plasmon-Mediated Process Using Photochemical Seeds","authors":"Chien-Chia Huang, Hong-Jun Chen, Qi Lun Leong, Wai-Kit Lai, C. Hsu, Jui-Chang Chen, Cheng-Liang Huang","doi":"10.2139/ssrn.3910604","DOIUrl":"https://doi.org/10.2139/ssrn.3910604","url":null,"abstract":"The plasmon-mediated process is one of the most common and well-studied methods to synthesize silver nanoplates (AgNPts). In a typical plasmon-mediated process, silver seeds are generated by chemical reduction using NaBH4 (abbreviated as CR seeds) before the plasmon-mediated process. However, a broad localized surface plasmon resonance (LSPR) band of AgNPts (usually broader than 150 nm) synthesized using the typical plasmon-mediated process would possibly limit their further applications. In this study, silver seeds are generated using a photochemical reduction method (abbreviated as PCR seeds). These PCR seeds then convert to AgNPts with irradiation by green LEDs or by a sodium lamp through the plasmon-mediated process. Furthermore, a very narrow LSPR bandwidth (approximately 67 nm) can be obtained when these AgNPts are further irradiated with red LEDs. Due to high refractive index sensitivity and sharp LSPR bandwidth, the as-prepared AgNPts have a high figure of merit (FOM) and can be used for spectroscopic chemical sensing applications. The silver seeds generated by this photochemical method can provide another choice for the plasmon-mediated process to synthesize AgNPts with high optical quality.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"79 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80987460","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}
Hui Zhao, Yuanchao Ji, T. Ma, Minxia Fang, Yanshuang Hao, Tianzi Yang, Chao Zhou, Sen Yang, X. Ren
Magnetostrictive materials with large magnetostriction, low hysteresis and wide working temperature range are desired for applications, but rarely obtained so far. In this work, we report a surprising finding in (1-x)TbFe2-xDyCo2 alloys: the composition of x=0.5 exhibits a low hysteretic magnetostriction, λ//, max ~2066 ppm, which is 159% larger than that of the commercial giant magnetostrictive alloy of Terfenol-D, λ//, max ~1298 ppm. Moreover, its temperature range for λ// >1298 ppm is even larger than 240 K, and another working temperature window for λ// >1000 ppm is from 40 K to 324 K, which can cover a large temperature fluctuation in space environments (e.g. 120-290 K in Mars). The established phase diagram of (1-x)TbFe2-xDyCo2 by systematic studies of magnetic susceptibility, X-ray diffraction and convergent-beam electron diffraction results, shows an emergence of morphotropic phase boundary (MPB) between rhombohedral (R) and orthorhombic (O) ferromagnetic phases, which is different from the MPB between R and T (tetragonal) phases in (1-x)TbFe2-xDyFe2 . We reveal that the exceptional combination of giant magnetostriction, low hysteresis and wide working temperature range is caused by this R-O MPB. The comparison between R-O MPB and R-T MPB further shows the O phase plays a vital role in the property enhancement of R-O MPB composition. Our work indicates the construction of R-O MPB may provide a new way to find high-performance magnetostrictive materials.
{"title":"Exceptional Combination of Large Magnetostriction, Low Hysteresis and Wide Working Temperature Range in (1-x)TbFe2-xDyCo2 Alloys","authors":"Hui Zhao, Yuanchao Ji, T. Ma, Minxia Fang, Yanshuang Hao, Tianzi Yang, Chao Zhou, Sen Yang, X. Ren","doi":"10.2139/ssrn.3890355","DOIUrl":"https://doi.org/10.2139/ssrn.3890355","url":null,"abstract":"Magnetostrictive materials with large magnetostriction, low hysteresis and wide working temperature range are desired for applications, but rarely obtained so far. In this work, we report a surprising finding in (1-x)TbFe2-xDyCo2 alloys: the composition of x=0.5 exhibits a low hysteretic magnetostriction, λ//, max ~2066 ppm, which is 159% larger than that of the commercial giant magnetostrictive alloy of Terfenol-D, λ//, max ~1298 ppm. Moreover, its temperature range for λ// >1298 ppm is even larger than 240 K, and another working temperature window for λ// >1000 ppm is from 40 K to 324 K, which can cover a large temperature fluctuation in space environments (e.g. 120-290 K in Mars). The established phase diagram of (1-x)TbFe2-xDyCo2 by systematic studies of magnetic susceptibility, X-ray diffraction and convergent-beam electron diffraction results, shows an emergence of morphotropic phase boundary (MPB) between rhombohedral (R) and orthorhombic (O) ferromagnetic phases, which is different from the MPB between R and T (tetragonal) phases in (1-x)TbFe2-xDyFe2 . We reveal that the exceptional combination of giant magnetostriction, low hysteresis and wide working temperature range is caused by this R-O MPB. The comparison between R-O MPB and R-T MPB further shows the O phase plays a vital role in the property enhancement of R-O MPB composition. Our work indicates the construction of R-O MPB may provide a new way to find high-performance magnetostrictive materials.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"36 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80397456","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}
This paper considers the open challenge of identifying complete, concise, and explainable quantitative microstructure representations for disordered heterogeneous material systems. Completeness and conciseness have been achieved through existing data-driven methods, e.g., deep generative models, which, however, do not provide mathematically explainable latent representations. This study investigates representations composed of three-point correlation functions, which are a special type of spatial convolutions. We show that a variety of microstructures can be characterized by a concise subset of three-point correlations, and the identification of such subsets can be achieved by Bayesian optimization. Lastly, we show that the proposed representation can directly be used to compute material properties based on the effective medium theory.
{"title":"Data-Driven Learning of 3-Point Correlation Functions as Microstructure Representations","authors":"Sheng Cheng, Yang Jiao, Max Yi Ren","doi":"10.2139/ssrn.3931596","DOIUrl":"https://doi.org/10.2139/ssrn.3931596","url":null,"abstract":"This paper considers the open challenge of identifying complete, concise, and explainable quantitative microstructure representations for disordered heterogeneous material systems. Completeness and conciseness have been achieved through existing data-driven methods, e.g., deep generative models, which, however, do not provide mathematically explainable latent representations. This study investigates representations composed of three-point correlation functions, which are a special type of spatial convolutions. We show that a variety of microstructures can be characterized by a concise subset of three-point correlations, and the identification of such subsets can be achieved by Bayesian optimization. Lastly, we show that the proposed representation can directly be used to compute material properties based on the effective medium theory.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"34 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88457217","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}
R. Sarochawikasit, Congying Wang, P. Kumam, H. Beladi, T. Okita, G. Rohrer, S. Ratanaphan
Abstract Polycrystalline α iron has been used in various applications, yet its microstructure design via grain boundary engineering (GBE) is not well established. One limiting factor is that while there are many different grain boundaries in the five-dimensional space of grain boundary types, relatively few of the energies have been determined. In this study, a piece-wise continuous grain boundary energy function for α iron is constructed to fill the entire five-dimensional space of grain boundary types using scaffolding subsets with lower dimensionality. Because the energies interpolated from the grain boundary energy function are consistent with the 408 boundaries that have been calculated using atomistic simulations, the energy function is then employed to generate a larger set of grain boundary energies. Comparisons between the interpolated energies and the measured grain boundary population indicate that they are inversely correlated for the high-energy anisotropy misorientations (those for which the difference between the maximum and minimum grain boundary energies is greater than 0.4 J/m2). The results suggest that GBE in the α iron should consider the high-energy anisotropy misorientations, rather than the twinning-related grain boundaries (Σ3, Σ9, Σ27a, and Σ27b) as in the case of fcc metals.
{"title":"Grain Boundary Energy Function for α Iron","authors":"R. Sarochawikasit, Congying Wang, P. Kumam, H. Beladi, T. Okita, G. Rohrer, S. Ratanaphan","doi":"10.2139/ssrn.3854492","DOIUrl":"https://doi.org/10.2139/ssrn.3854492","url":null,"abstract":"Abstract Polycrystalline α iron has been used in various applications, yet its microstructure design via grain boundary engineering (GBE) is not well established. One limiting factor is that while there are many different grain boundaries in the five-dimensional space of grain boundary types, relatively few of the energies have been determined. In this study, a piece-wise continuous grain boundary energy function for α iron is constructed to fill the entire five-dimensional space of grain boundary types using scaffolding subsets with lower dimensionality. Because the energies interpolated from the grain boundary energy function are consistent with the 408 boundaries that have been calculated using atomistic simulations, the energy function is then employed to generate a larger set of grain boundary energies. Comparisons between the interpolated energies and the measured grain boundary population indicate that they are inversely correlated for the high-energy anisotropy misorientations (those for which the difference between the maximum and minimum grain boundary energies is greater than 0.4 J/m2). The results suggest that GBE in the α iron should consider the high-energy anisotropy misorientations, rather than the twinning-related grain boundaries (Σ3, Σ9, Σ27a, and Σ27b) as in the case of fcc metals.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"31 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84551470","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}
C. Jamin, Apurv Dash, Nachiketa Mishra, R. Bordia, O. Guillon
Abstract The sintering behavior of ring-shaped alumina films on different types of substrates (polished sapphire and platinum coated sapphire) has been investigated. Variation of substrate material, layer thickness and heating schedule led to different interface properties which were quantified using the interfacial friction parameter as a measure of the slip distance of the free edge. This interfacial friction implies the compliance of the film-substrate interface, thus allowing the quantification of the ability of the free edges to slide along the substrate. Ring structures were made with outer radii of 100 –500 µm and the ratios of inner to outer radii were 0.1 (broad ring segment with small inner hole) and 0.4 (narrow ring segment with big inner hole). During sintering, the outer film edge was found to recede in all systems, whereas the behavior of the free edge located at the inner hole was strongly dependent on the interfacial friction. When sintering of alumina micro-rings were carried out on sapphire substrate, a high interfacial friction resulted in the positive displacement of the inner edge, causing the inner hole to open. Sapphire substrates coated with platinum offered a lower interfacial friction resulting in the opening of the hole in a more distinct manner as compared to the uncoated sapphire substrates. As the thickness of the film also affects the interfacial friction, a thicker film (27 µm) on platinum coated substrate had very low friction. This resulted in a negative displacement of the inner ring leading to closing of the hole. These effects are in qualitative agreement with the predicted analytical model for constrained sintering of annular ceramic films. A combination of film thickness, substrate material and aspect ratio of the ring either leading to constriction or dilation of the annular alumina film were carefully investigated.
{"title":"Constrained Sintering of Alumina Micro-Ring Films on Stiff and Compliant Substrates: Constriction or Dilation?","authors":"C. Jamin, Apurv Dash, Nachiketa Mishra, R. Bordia, O. Guillon","doi":"10.2139/ssrn.3828265","DOIUrl":"https://doi.org/10.2139/ssrn.3828265","url":null,"abstract":"Abstract The sintering behavior of ring-shaped alumina films on different types of substrates (polished sapphire and platinum coated sapphire) has been investigated. Variation of substrate material, layer thickness and heating schedule led to different interface properties which were quantified using the interfacial friction parameter as a measure of the slip distance of the free edge. This interfacial friction implies the compliance of the film-substrate interface, thus allowing the quantification of the ability of the free edges to slide along the substrate. Ring structures were made with outer radii of 100 –500 µm and the ratios of inner to outer radii were 0.1 (broad ring segment with small inner hole) and 0.4 (narrow ring segment with big inner hole). During sintering, the outer film edge was found to recede in all systems, whereas the behavior of the free edge located at the inner hole was strongly dependent on the interfacial friction. When sintering of alumina micro-rings were carried out on sapphire substrate, a high interfacial friction resulted in the positive displacement of the inner edge, causing the inner hole to open. Sapphire substrates coated with platinum offered a lower interfacial friction resulting in the opening of the hole in a more distinct manner as compared to the uncoated sapphire substrates. As the thickness of the film also affects the interfacial friction, a thicker film (27 µm) on platinum coated substrate had very low friction. This resulted in a negative displacement of the inner ring leading to closing of the hole. These effects are in qualitative agreement with the predicted analytical model for constrained sintering of annular ceramic films. A combination of film thickness, substrate material and aspect ratio of the ring either leading to constriction or dilation of the annular alumina film were carefully investigated.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87833003","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 According to the principles of diffusional creep, the normal and tangent components of the velocity jumps between adjacent grains arise from, respectively, the climbing and sliding of disconnections along grain boundaries. Stationary deformation thus implies a balance between nucleation and recovery of moving disconnections. The model considers a periodic lattice of hexagonal grains with nucleation of disconnection multipoles at triple junctions. The strain energy coupled to the population of climbing disconnections is calculated by inferring that the internal strain field associated to disconnection pile-ups brings a distribution of tractions along GBs that is consistent with the field of diffusion potential gradient that drives disconnection climb. It follows that the distribution of the density of climbing disconnections is parabolic and that the dissipation due to the nucleation and recovery of climbing disconnections is equal to 50% of the dissipation arising from diffusion fluxes. These results hold for both Nabarro-Herring creep and Coble creep. The analysis of the disconnection nucleation process highlights the sources of non-Newtonian behaviour and the existence of a threshold stress as an intrinsic feature of diffusional creep.
{"title":"Contribution of the Nucleation and Recovery of Disconnections to Shear Viscosity in Diffusional Creep","authors":"F. Delannay","doi":"10.2139/ssrn.3878349","DOIUrl":"https://doi.org/10.2139/ssrn.3878349","url":null,"abstract":"Abstract According to the principles of diffusional creep, the normal and tangent components of the velocity jumps between adjacent grains arise from, respectively, the climbing and sliding of disconnections along grain boundaries. Stationary deformation thus implies a balance between nucleation and recovery of moving disconnections. The model considers a periodic lattice of hexagonal grains with nucleation of disconnection multipoles at triple junctions. The strain energy coupled to the population of climbing disconnections is calculated by inferring that the internal strain field associated to disconnection pile-ups brings a distribution of tractions along GBs that is consistent with the field of diffusion potential gradient that drives disconnection climb. It follows that the distribution of the density of climbing disconnections is parabolic and that the dissipation due to the nucleation and recovery of climbing disconnections is equal to 50% of the dissipation arising from diffusion fluxes. These results hold for both Nabarro-Herring creep and Coble creep. The analysis of the disconnection nucleation process highlights the sources of non-Newtonian behaviour and the existence of a threshold stress as an intrinsic feature of diffusional creep.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"189 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76809104","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}
Abdalrhaman Koko, E. Elmukashfi, K. Dragnevski, A. Wilkinson, T. Marrow
Abstract The strain fields of deformation twins in the ferrite matrix of an age-hardened duplex stainless-steel (Zeron 100: 25%Cr, 7%Ni) have been studied in situ under load, and ex situ (unloaded), using high-resolution electron backscatter diffraction (HR-EBSD). The local two-dimensional (2D) elastic strain field acting on the twin tip was parameterised for the first time using the strain energy release rate (J-integral) and then decomposed into the mode I and mode II stress intensity factors (KI and KII). An improved method to select the strain reference was used, based on the relationship between the HR-EBSD cross-correlation peak height and mean angular error. The elastic field described by KI increased with twin thickness. The in-plane shear field, described by KII, relaxed when the load was removed. Some current limitations of the 2D analysis are discussed, which aims to provide an experimental methodology to quantify the fields that describe the local boundary conditions for twin thickening and propagation.
{"title":"J-Integral Analysis of the Elastic Strain Fields of Ferrite Deformation Twins Using Electron Backscatter Diffraction","authors":"Abdalrhaman Koko, E. Elmukashfi, K. Dragnevski, A. Wilkinson, T. Marrow","doi":"10.2139/ssrn.3860378","DOIUrl":"https://doi.org/10.2139/ssrn.3860378","url":null,"abstract":"Abstract The strain fields of deformation twins in the ferrite matrix of an age-hardened duplex stainless-steel (Zeron 100: 25%Cr, 7%Ni) have been studied in situ under load, and ex situ (unloaded), using high-resolution electron backscatter diffraction (HR-EBSD). The local two-dimensional (2D) elastic strain field acting on the twin tip was parameterised for the first time using the strain energy release rate (J-integral) and then decomposed into the mode I and mode II stress intensity factors (KI and KII). An improved method to select the strain reference was used, based on the relationship between the HR-EBSD cross-correlation peak height and mean angular error. The elastic field described by KI increased with twin thickness. The in-plane shear field, described by KII, relaxed when the load was removed. Some current limitations of the 2D analysis are discussed, which aims to provide an experimental methodology to quantify the fields that describe the local boundary conditions for twin thickening and propagation.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89890020","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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