Xin Li, Jingzhi Han, Xiongzuo Zhang, R. Wu, Yinfeng Zhang, Haidong Tian, M. Xue, X. Wen, Zhichao Li, Shunquan Liu, Wenyun Yang, Changsheng Wang, H. Du, Xiaodong Zhang, Yingchang Yang, Jinbo Yang
Magnetic properties of single perovskite-structure epitaxial film are reported to have layered distribution recently. However, the different responses of spin configurations in individual layers to the variation of temperature and strain state, especially the subtle response of layered film due to structural phase transformation of SrTiO3 (STO) substrate around 105 K, have not been revealed completely. Drastic drop and concomitant abnormal increase of remnant magnetic moments (REM) and coercivity of low-doped La1-xSrxMnO3 (x=0.175) /SrTiO3 film were observed for the first time around 105 K only in the in-plane direction, and layered magnetic structures were further inferred based on investigation of microstructure, strain distribution and chemical inhomogeneity. Abnormal change of magnetic properties around 105 K was discussed by a three-layer model, in which softer ferromagnetic layer was supposed to form in the middle layer of strain induced layered structure, and the spin configuration of middle layer underwent non-synchronous transformation relative to other parts of the film, which may be attributed to the change of in-plane strain inside the film around 105 K. Our work reveals the variation of individual magnetic layers with the increase of temperature through utilizing the remnant magnetic field in measuring system, and the abrupt reversal of spin configuration at the intermediate layer can also serve the design of novel spintronics devices in the future.
{"title":"Non-Synchronized Rotation of Layered Spin Configurations in La 0.825Sr 0.175MnO 3/SrTiO 3 Film","authors":"Xin Li, Jingzhi Han, Xiongzuo Zhang, R. Wu, Yinfeng Zhang, Haidong Tian, M. Xue, X. Wen, Zhichao Li, Shunquan Liu, Wenyun Yang, Changsheng Wang, H. Du, Xiaodong Zhang, Yingchang Yang, Jinbo Yang","doi":"10.2139/ssrn.3370282","DOIUrl":"https://doi.org/10.2139/ssrn.3370282","url":null,"abstract":"Magnetic properties of single perovskite-structure epitaxial film are reported to have layered distribution recently. However, the different responses of spin configurations in individual layers to the variation of temperature and strain state, especially the subtle response of layered film due to structural phase transformation of SrTiO<sub>3</sub> (STO) substrate around 105 K, have not been revealed completely. Drastic drop and concomitant abnormal increase of remnant magnetic moments (REM) and coercivity of low-doped La<sub>1-x</sub>Sr<sub>x</sub>MnO<sub>3</sub> (x=0.175) /SrTiO<sub>3</sub> film were observed for the first time around 105 K only in the in-plane direction, and layered magnetic structures were further inferred based on investigation of microstructure, strain distribution and chemical inhomogeneity. Abnormal change of magnetic properties around 105 K was discussed by a three-layer model, in which softer ferromagnetic layer was supposed to form in the middle layer of strain induced layered structure, and the spin configuration of middle layer underwent non-synchronous transformation relative to other parts of the film, which may be attributed to the change of in-plane strain inside the film around 105 K. Our work reveals the variation of individual magnetic layers with the increase of temperature through utilizing the remnant magnetic field in measuring system, and the abrupt reversal of spin configuration at the intermediate layer can also serve the design of novel spintronics devices in the future.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85347851","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}
In the present study, a micromechanics-based strength criterion for frozen soils is proposed to estimate the macroscopic nonlinear strength properties of the matrix-inclusion systems. In the representative frozen soil element, the strength behaviors of soil particles and ice-crystals are assumed to be respectively characterized by two different elliptical strength criteria. With consideration of Mori-Tanaka scheme in continuum micromechanics, the interactions between soil particles and ice-crystals could well be taken into account by means of homogenization techniques, and moreover the φ-breakage function is introduced to describe the cracked effect of ice-crystals regardless of the influence of unfrozen water. In the framework of support function and plastic dissipative energy, the strength criterion is formulated with the equivalent principle from the microscopic and macroscopic viewpoint. The parameters of ice-crystals are decided in the reported literature with different temperatures, and meanwhile those of soil particles are determined by various soil types such as silty soils, loess and sands. In addition, the parameters in the proposed strength criterion have clear physical meanings by comparisons with macroscopic strength criterion. Compared with the existing experimental data, the predictions in the proposed strength criterion can qualitatively and quantitatively simulate the macroscopic strength responses of frozen soils.
{"title":"A New Approach to Predict the Strength Criterion of Frozen Soils Based on Micromechanical Framework","authors":"De Zhang, E. Liu","doi":"10.2139/ssrn.3313263","DOIUrl":"https://doi.org/10.2139/ssrn.3313263","url":null,"abstract":"In the present study, a micromechanics-based strength criterion for frozen soils is proposed to estimate the macroscopic nonlinear strength properties of the matrix-inclusion systems. In the representative frozen soil element, the strength behaviors of soil particles and ice-crystals are assumed to be respectively characterized by two different elliptical strength criteria. With consideration of Mori-Tanaka scheme in continuum micromechanics, the interactions between soil particles and ice-crystals could well be taken into account by means of homogenization techniques, and moreover the φ-breakage function is introduced to describe the cracked effect of ice-crystals regardless of the influence of unfrozen water. In the framework of support function and plastic dissipative energy, the strength criterion is formulated with the equivalent principle from the microscopic and macroscopic viewpoint. The parameters of ice-crystals are decided in the reported literature with different temperatures, and meanwhile those of soil particles are determined by various soil types such as silty soils, loess and sands. In addition, the parameters in the proposed strength criterion have clear physical meanings by comparisons with macroscopic strength criterion. Compared with the existing experimental data, the predictions in the proposed strength criterion can qualitatively and quantitatively simulate the macroscopic strength responses of frozen soils.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"60 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86044272","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}
Yong Tao, Wenqin Zhang, Neng Lia, W. Ching, Fazhou Wang, Shu-guang Hu
In this work, multiple theoretical methods including Fukui functions, effective charges, localization index, and density of states are employed to clarify the influence of Zn impurity on hydration reactivity of clinker phases at atomic level. Zn ions are found to decrease the number of reactive sites and effective charges of tricalcium silicate and tricalcium aluminate dramatically, which could account for the significant retarding effect in these two phases. For tetracalcium aluminoferrite, Zn doping causes no influence on the number of reactive sites but an increase of effective charges and total localization index, which implies somewhat reactivity promotion. PDOS analysis suggests this particular effect of tetracalcium aluminoferrite is due to the strong localization capacity of Fe-3d states. Our calculated results is in good agreement with previous experimental observations.
{"title":"Atomistic Insights into Hydration Reactivity of Clinker Crystals with Chemical Impurity","authors":"Yong Tao, Wenqin Zhang, Neng Lia, W. Ching, Fazhou Wang, Shu-guang Hu","doi":"10.2139/ssrn.3313265","DOIUrl":"https://doi.org/10.2139/ssrn.3313265","url":null,"abstract":"In this work, multiple theoretical methods including Fukui functions, effective charges, localization index, and density of states are employed to clarify the influence of Zn impurity on hydration reactivity of clinker phases at atomic level. Zn ions are found to decrease the number of reactive sites and effective charges of tricalcium silicate and tricalcium aluminate dramatically, which could account for the significant retarding effect in these two phases. For tetracalcium aluminoferrite, Zn doping causes no influence on the number of reactive sites but an increase of effective charges and total localization index, which implies somewhat reactivity promotion. PDOS analysis suggests this particular effect of tetracalcium aluminoferrite is due to the strong localization capacity of Fe-3d states. Our calculated results is in good agreement with previous experimental observations.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"53 47 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80404381","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 thermodynamic model of equilibrium grain boundary segregation in real binary systems is proposed which is based on the prediction of all the necessary parameters. These parameters are (i) the standard enthalpy, (ii) the standard entropy of grain boundary segregation, both related to ideal behavior, as well as (iii) the Fowler binary interaction coefficient describing real contribution. Application of the model is shown in detail for the example of iron-based binary systems and the prediction is compared to data published in the literature.
{"title":"Modeling Grain Boundary Segregation by Prediction of All Necessary Parameters","authors":"P. Lejček, S. Hofmann","doi":"10.2139/ssrn.3310277","DOIUrl":"https://doi.org/10.2139/ssrn.3310277","url":null,"abstract":"A thermodynamic model of equilibrium grain boundary segregation in real binary systems is proposed which is based on the prediction of all the necessary parameters. These parameters are (i) the standard enthalpy, (ii) the standard entropy of grain boundary segregation, both related to ideal behavior, as well as (iii) the Fowler binary interaction coefficient describing real contribution. Application of the model is shown in detail for the example of iron-based binary systems and the prediction is compared to data published in the literature.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"98 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80554117","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 bulk properties of uranium dioxide (UO2) have been investigated using Hubbard corrected density functional theory (DFT+U) calculations. Monitoring of the occupation matrix for 5f electrons of the uranium atoms is found to be crucial to avoid metastable state solutions and consequently to obtain the true ground state properties of bulk UO2. The lattice contribution to the thermal conductivity was obtained by the solution of the Boltzmann transport equation for phonons based on the interatomic force constants obtained from DFT+U calculations. Furthermore, the relative stabilities of noble gases (He, Ne, Ar, Kr, and Xe) in the octahedral interstitial site of bulk UO2 and their migration are revisited. The effect of the supercell approach for point defects is taken into account by considering the long-range elastic interactions. The computed incorporation energy and energy barriers indicate a size-dependent mechanism for the interstitial migration of noble gases.
{"title":"DFT+ U Study of the Thermal Conductivity and Noble Gas Impurities in Uranium Dioxide","authors":"E. Torres, T. Kaloni","doi":"10.2139/ssrn.3310275","DOIUrl":"https://doi.org/10.2139/ssrn.3310275","url":null,"abstract":"The bulk properties of uranium dioxide (UO<sub>2</sub>) have been investigated using Hubbard corrected density functional theory (DFT+<i>U</i>) calculations. Monitoring of the occupation matrix for 5f electrons of the uranium atoms is found to be crucial to avoid metastable state solutions and consequently to obtain the true ground state properties of bulk UO<sub>2</sub>. The lattice contribution to the thermal conductivity was obtained by the solution of the Boltzmann transport equation for phonons based on the interatomic force constants obtained from DFT+<i>U</i> calculations. Furthermore, the relative stabilities of noble gases (He, Ne, Ar, Kr, and Xe) in the octahedral interstitial site of bulk UO<sub>2</sub> and their migration are revisited. The effect of the supercell approach for point defects is taken into account by considering the long-range elastic interactions. The computed incorporation energy and energy barriers indicate a size-dependent mechanism for the interstitial migration of noble gases.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"21 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80346343","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}
Tao Yang, PhD, Yilu Zhao, PhD, Lei Fan, PhD, Jie Wei, PhD, Junhua Luan, PhD, Weihong Liu, PhD, Cheng Wang, PhD, Zengbao Jiao, PhD, Ji-jung Kai, PhD, C.T. Liu, Phd
Thermally stable high-entropy alloys (HEAs) consisting of a high density of coherent precipitates show a great potential for high-temperature applications. In this work, we systematically investigated the phase stability and coarsening kinetics of L12-type coherent precipitates in a Ni-Co-Fe-Cr-Al-Ti-based HEA isothermally aged at 800, 900 and 1000 °C. Aged microstructures in the grain interiors under this temperature range were essentially dominated by the uniform precipitation of multicomponent L12 (Ni, Co, Fe, Cr)3(Ti, Al)-type precipitates. The coarsening kinetics of these intragranular L12 precipitates were quantitatively determined, which were adequately characterized by the classical Lifshitz-Slyozov-Wagner model. The activation energy for coarsening was determined to be 378 kJ/mol, which is relatively higher than that of conventional Ni or Co-based superalloys, suggesting a slow elemental diffusion in the HEA matrix. More importantly, the heterogeneous precipitation and the associated metastable phase transformation mechanism along grain boundaries (GBs) were carefully analyzed. Localized chemical heterogeneity was identified within the discontinuous L12 phase at the GBs, which thermodynamically destabilizes the L12 structure and encourages the formation of brittle Heusler phase. Finally, we establish a unique duplex-aging strategy that can be efficiently utilized for GB stabilization, by which these detrimental intergranular heterostructures can be greatly eliminated, leading to an exceptional resistance to intermediate-temperature embrittlement, along with enhanced tensile strengths. These findings will not only shed light on the precipitation mechanisms in compositionally complex HEAs but also generate new opportunities to the interfacial design of HEAs for advanced high-temperature applications with superior properties.
由高密度共相组成的热稳定高熵合金(HEAs)具有很大的高温应用潜力。在这项工作中，我们系统地研究了ni - co - fe - cr - al - ti基HEA在800、900和1000℃等温时效过程中l12型共晶相的相稳定性和粗化动力学。在此温度范围内，晶粒内部的时效组织主要以均匀析出的多组分L12 (Ni, Co, Fe, Cr)3(Ti, Al)型相为主。定量测定了这些L12晶内相的粗化动力学，并用经典的Lifshitz-Slyozov-Wagner模型对其进行了充分表征。粗化活化能为378 kJ/mol，高于传统镍基或钴基高温合金，表明元素在HEA基体中的扩散较慢。更重要的是，仔细分析了非均相析出及其沿晶界亚稳相变机制。在GBs的不连续L12相中发现了局部化学非均质性，这使得L12结构在热力学上不稳定，并促进了脆性Heusler相的形成。最后，我们建立了一种独特的双时效策略，可以有效地用于GB稳定化，通过这种策略，可以极大地消除这些有害的晶间异质结构，从而具有优异的耐中温脆化能力，同时提高了拉伸强度。这些发现不仅揭示了组成复杂的HEAs中的沉淀机制，而且为具有优越性能的高级高温应用的HEAs界面设计提供了新的机会。
{"title":"Control of Nanoscale Precipitation and Elimination of Intermediate-Temperature Embrittlement in Multicomponent High-Entropy Alloys","authors":"Tao Yang, PhD, Yilu Zhao, PhD, Lei Fan, PhD, Jie Wei, PhD, Junhua Luan, PhD, Weihong Liu, PhD, Cheng Wang, PhD, Zengbao Jiao, PhD, Ji-jung Kai, PhD, C.T. Liu, Phd","doi":"10.2139/ssrn.3477998","DOIUrl":"https://doi.org/10.2139/ssrn.3477998","url":null,"abstract":"Thermally stable high-entropy alloys (HEAs) consisting of a high density of coherent precipitates show a great potential for high-temperature applications. In this work, we systematically investigated the phase stability and coarsening kinetics of L1<sub>2</sub>-type coherent precipitates in a Ni-Co-Fe-Cr-Al-Ti-based HEA isothermally aged at 800, 900 and 1000 °C. Aged microstructures in the grain interiors under this temperature range were essentially dominated by the uniform precipitation of multicomponent L1<sub>2</sub> (Ni, Co, Fe, Cr)<sub>3</sub>(Ti, Al)-type precipitates. The coarsening kinetics of these intragranular L1<sub>2</sub> precipitates were quantitatively determined, which were adequately characterized by the classical Lifshitz-Slyozov-Wagner model. The activation energy for coarsening was determined to be 378 kJ/mol, which is relatively higher than that of conventional Ni or Co-based superalloys, suggesting a slow elemental diffusion in the HEA matrix. More importantly, the heterogeneous precipitation and the associated metastable phase transformation mechanism along grain boundaries (GBs) were carefully analyzed. Localized chemical heterogeneity was identified within the discontinuous L1<sub>2</sub> phase at the GBs, which thermodynamically destabilizes the L1<sub>2</sub> structure and encourages the formation of brittle Heusler phase. Finally, we establish a unique duplex-aging strategy that can be efficiently utilized for GB stabilization, by which these detrimental intergranular heterostructures can be greatly eliminated, leading to an exceptional resistance to intermediate-temperature embrittlement, along with enhanced tensile strengths. These findings will not only shed light on the precipitation mechanisms in compositionally complex HEAs but also generate new opportunities to the interfacial design of HEAs for advanced high-temperature applications with superior properties.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"21 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90856429","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}
P. Lynch, W. Stevenson, D. Fox, A. Ghaderi, L. Xie, M. R. Barnett
A fully automated laboratory Micro X-ray Laue diffraction system capable of illuminating individual grains in polycrystalline sample is described. A high brightness tungsten micro-focus X-ray source coupled with a capillary focussing optic is used to define a variable spot, ranging in size from 20micron to 200 micron, on the sample. Extension of the Laue technique for micro-texture mapping is then achieved by raster scanning the sample in the focal plane of the focussing optic. The attributes of this new methodology is highlighted by a series of 3 case studies. The first case study demonstrates the high-angular resolution capabilities based on orientation mapping in large grain Si steel electrical transformer plates. An angular resolution better than 0.01degree was readily achieved. Further, the orientation and grain morphology was verified based on synchrotron Laue maps acquired from the same region of interest. Case study 2 addresses the minimum grain size/resolution that can be practically measured. By use of the 20micron probe size orientation maps were acquired for an additive manufactured Ti-5553 wall. A bimodal grain size could be identified. These results were in good agreement with EBSD measurements performed on a sample prepared under the same conditions. Finally, demonstration of large scale grain orientation mapping was performed on an as-received Ti-5553 billet. An orientation map of 65 x 35mm at a step resolution of 0.2mm was used to map the orientation and change in grain morphology across the billet.
描述了一种全自动实验室微x射线劳厄衍射系统，该系统能够照亮多晶样品中的单个颗粒。高亮度钨微聚焦x射线源与毛细管聚焦光学元件相结合，用于在样品上定义大小从20微米到200微米不等的可变光斑。然后通过在聚焦光学的焦平面上对样品进行光栅扫描，扩展了用于微纹理映射的Laue技术。这一新方法的特性通过一系列的3个案例研究得到了突出体现。第一个案例研究展示了基于取向映射的大晶粒硅钢变压器板的高角分辨率能力。很容易获得优于0.01度的角分辨率。此外，基于从同一感兴趣区域获得的同步加速器劳厄图，验证了取向和晶粒形态。案例研究2解决了可以实际测量的最小晶粒尺寸/分辨率。通过使用20微米探针尺寸获得了添加剂制造的Ti-5553壁的取向图。可以识别出双峰粒度。这些结果与在相同条件下制备的样品上进行的EBSD测量结果非常一致。最后，在Ti-5553坯料上进行了大规模晶粒取向映射演示。采用步进分辨率为0.2mm的65 x 35mm的取向图来绘制整个坯料的取向和晶粒形态变化。
{"title":"Application of Laboratory Based Laue Micro-XRD for Generalised Grain Orientation Mapping","authors":"P. Lynch, W. Stevenson, D. Fox, A. Ghaderi, L. Xie, M. R. Barnett","doi":"10.2139/ssrn.3446901","DOIUrl":"https://doi.org/10.2139/ssrn.3446901","url":null,"abstract":"A fully automated laboratory Micro X-ray Laue diffraction system capable of illuminating individual grains in polycrystalline sample is described. A high brightness tungsten micro-focus X-ray source coupled with a capillary focussing optic is used to define a variable spot, ranging in size from 20micron to 200 micron, on the sample. Extension of the Laue technique for micro-texture mapping is then achieved by raster scanning the sample in the focal plane of the focussing optic. The attributes of this new methodology is highlighted by a series of 3 case studies. The first case study demonstrates the high-angular resolution capabilities based on orientation mapping in large grain Si steel electrical transformer plates. An angular resolution better than 0.01degree was readily achieved. Further, the orientation and grain morphology was verified based on synchrotron Laue maps acquired from the same region of interest. Case study 2 addresses the minimum grain size/resolution that can be practically measured. By use of the 20micron probe size orientation maps were acquired for an additive manufactured Ti-5553 wall. A bimodal grain size could be identified. These results were in good agreement with EBSD measurements performed on a sample prepared under the same conditions. Finally, demonstration of large scale grain orientation mapping was performed on an as-received Ti-5553 billet. An orientation map of 65 x 35mm at a step resolution of 0.2mm was used to map the orientation and change in grain morphology across the billet.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89921704","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 environmental degradation of four different types of grain boundaries were investigated on alloy 690 following slow strain rate tensile tests in 360 oC hydrogenated water. Random high angle boundaries (RHABs) support fast Cr diffusion that promotes the formation of a compact surface oxide film and grain boundary migration. Surprisingly, coherent twin boundaries (CTBs) are susceptible to intergranular oxidation and do not exhibit Cr diffusion or grain boundary migration. When CTBs are changed to transformed twin boundaries (TTBs) by cold work, they behave like RHABs. Finally, incoherent twin boundaries (ITBs) undergo intergranular oxidation with limited Cr depletion but no boundary migration beyond the oxide. The Cr diffusivity along grain boundary in this alloy is directly related to the density of coincident site in the grain boundary plane and determines the morphology of oxide formed near the grain boundary. CTBs are still highly resistant to stress corrosion cracking (SCC) due to the semi-coherent interface between the intergranular chromia and grain matrix. In contrast, the intergranular oxides formed along RHABs inherit highly-disordered boundary structure from the original grain boundaries and show much higher SCC susceptibility. The grain boundary structure dependence of SCC resistance should be understood from its effects on solute diffusivity, structure of intergranular oxide and the local stress-strain state.
{"title":"The Effect of Grain Boundary Structure on the Intergranular Degradation Behavior of Solution Annealed Alloy 690 in Simulated Pressurized Water Reactor Primary Environment","authors":"Wenjun Kuang, G. Was","doi":"10.2139/ssrn.3427530","DOIUrl":"https://doi.org/10.2139/ssrn.3427530","url":null,"abstract":"The environmental degradation of four different types of grain boundaries were investigated on alloy 690 following slow strain rate tensile tests in 360 oC hydrogenated water. Random high angle boundaries (RHABs) support fast Cr diffusion that promotes the formation of a compact surface oxide film and grain boundary migration. Surprisingly, coherent twin boundaries (CTBs) are susceptible to intergranular oxidation and do not exhibit Cr diffusion or grain boundary migration. When CTBs are changed to transformed twin boundaries (TTBs) by cold work, they behave like RHABs. Finally, incoherent twin boundaries (ITBs) undergo intergranular oxidation with limited Cr depletion but no boundary migration beyond the oxide. The Cr diffusivity along grain boundary in this alloy is directly related to the density of coincident site in the grain boundary plane and determines the morphology of oxide formed near the grain boundary. CTBs are still highly resistant to stress corrosion cracking (SCC) due to the semi-coherent interface between the intergranular chromia and grain matrix. In contrast, the intergranular oxides formed along RHABs inherit highly-disordered boundary structure from the original grain boundaries and show much higher SCC susceptibility. The grain boundary structure dependence of SCC resistance should be understood from its effects on solute diffusivity, structure of intergranular oxide and the local stress-strain state.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"85 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77320945","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 interplay between antiphase boundaries (APBs), magnetic domain structure and functional properties was investigated in the martensitic state of Ni-Mn-Ga single crystals which showed magnetically induced martensite reorientation (MIR) with 6% strain. The APB density was controlled by different heat treatments and the APBs and magnetic domains were observed by Lorentz transmission electron microscopy (LTEM). Slow cooling at ~1 K/min resulted in a low density (<1/μm), air quenching in a medium density (≈8/μm), and water quenching in a high density (≈15/μm) of APBs. Abundant pinning of domain walls on APBs was observed, which resulted in one-to-one correspondence between the magnetic domain walls and antiphase boundaries (APBs), magnetic domain memory, and finer domain patterns for the high APB density. For low APB density, a labyrinth domain structure was established between domain walls pinned on APBs. For low and medium density of APBs the magnetization was oriented mostly parallel to the out-of-plane easy magnetization axis. For high APB density the magnetization switched to the in-plane orientation, indicating that the effective magnetic anisotropy became lower than the stray field energy, and magnetic vortices additionally appeared. The novel functionalities based on a combination of MIR and interactions of the magnetic structure with APBs are feasible since the MIR was observed even for the highest density of APBs.
{"title":"Antiphase Boundaries, Magnetic Domains, and Magnetic Vortices in Ni-Mn-Ga Single Crystals","authors":"M. Vronka, L. Straka, M. Graef, O. Heczko","doi":"10.2139/ssrn.3465853","DOIUrl":"https://doi.org/10.2139/ssrn.3465853","url":null,"abstract":"The interplay between antiphase boundaries (APBs), magnetic domain structure and functional properties was investigated in the martensitic state of Ni-Mn-Ga single crystals which showed magnetically induced martensite reorientation (MIR) with 6% strain. The APB density was controlled by different heat treatments and the APBs and magnetic domains were observed by Lorentz transmission electron microscopy (LTEM). Slow cooling at ~1 K/min resulted in a low density (<1/μm), air quenching in a medium density (≈8/μm), and water quenching in a high density (≈15/μm) of APBs. Abundant pinning of domain walls on APBs was observed, which resulted in one-to-one correspondence between the magnetic domain walls and antiphase boundaries (APBs), magnetic domain memory, and finer domain patterns for the high APB density. For low APB density, a labyrinth domain structure was established between domain walls pinned on APBs. For low and medium density of APBs the magnetization was oriented mostly parallel to the out-of-plane easy magnetization axis. For high APB density the magnetization switched to the in-plane orientation, indicating that the effective magnetic anisotropy became lower than the stray field energy, and magnetic vortices additionally appeared. The novel functionalities based on a combination of MIR and interactions of the magnetic structure with APBs are feasible since the MIR was observed even for the highest density of APBs.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"62 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85198389","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}
Y. Zhang, Guoqi Tan, D. Jiao, Jian Zhang, Shaogang Wang, Feng Liu, Zengqian Liu, L. Zhuo, Zhefeng Zhang, S. Deville, R. Ritchie
The structures of tungsten and tungsten carbide scaffolds play a key role in determining the properties of their infiltrated composites for multifunctional applications. However, the architectural construction of W/WC systems is challenging because of the difficulty of assembly due to their large densities. Here we present the generation of unidirectionally porous architectures, with high porosities exceeding 65%, for W and WC scaffolds using direct ice-templating techniques, which in many respects reproduce the design motif of wood. This was achieved by adjusting the viscosities of suspensions to retard sedimentation during freezing. The processing, structural characteristics and mechanical properties of the resulting scaffolds were investigated and the correlations between them explored. Quantitative relationships were established to describe their strengths based on a simple model taking into account both inter- and intra-lamellar pores. The fracture mechanisms were also identified, especially in light of the porosity. This study extends the effectiveness of ice-templating techniques for systems with large densities or particle sizes. It further provides preforms for developing new nature-inspired multifunctional materials, as represented by W/WC-Cu composites.
{"title":"Ice-Templated Porous Tungsten and Tungsten Carbide","authors":"Y. Zhang, Guoqi Tan, D. Jiao, Jian Zhang, Shaogang Wang, Feng Liu, Zengqian Liu, L. Zhuo, Zhefeng Zhang, S. Deville, R. Ritchie","doi":"10.2139/ssrn.3427539","DOIUrl":"https://doi.org/10.2139/ssrn.3427539","url":null,"abstract":"The structures of tungsten and tungsten carbide scaffolds play a key role in determining the properties of their infiltrated composites for multifunctional applications. However, the architectural construction of W/WC systems is challenging because of the difficulty of assembly due to their large densities. Here we present the generation of unidirectionally porous architectures, with high porosities exceeding 65%, for W and WC scaffolds using direct ice-templating techniques, which in many respects reproduce the design motif of wood. This was achieved by adjusting the viscosities of suspensions to retard sedimentation during freezing. The processing, structural characteristics and mechanical properties of the resulting scaffolds were investigated and the correlations between them explored. Quantitative relationships were established to describe their strengths based on a simple model taking into account both inter- and intra-lamellar pores. The fracture mechanisms were also identified, especially in light of the porosity. This study extends the effectiveness of ice-templating techniques for systems with large densities or particle sizes. It further provides preforms for developing new nature-inspired multifunctional materials, as represented by W/WC-Cu composites.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"373 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76620436","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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