L. Hou, Siyuan Yang, Xingfu Yu, Y. Fautrelle, Zongbin Li, D. Cong, Z. Ren, Yanyan Zhu, Xi Li
In the present work, the effect of a transverse magnetic field-assisted directional solidification (MFADS) on the microstructures in Ni-Mn-Ga alloys has been investigated. The results show that the magnetic field is capable of inducing transversal macro segregation perpendicular to magnetic field, causing the emergence of martensite clusters in austenite matrix. Moreover, the magnetic field alleviates the micro segregation on a dendritic scale and promotes the preferred growth of austenite dendrites. On the basis of above investigation, several special samples are designed using the MFADS to study the crystallographic evolution and mechanical behavior during thermal/stress induced martensite transformation. The martensite cluster in austenite matrix is used to investigate the martensite transformation and growth under cooling-heating cycles. The crystallographic relationship and phase boundary microstructure between martensite and austenite have been characterized. In addition, the micro segregation on a dendritic scale can significantly influence the martensite variant distribution, corresponding to the performance during compressive circles based on the analysis about deformation gradient tensor. The stress-induced super elasticity is closely dependent on orientation, well explained from the perspective of different resolved shear stress factors and correspondence variant pair formation transformation strain. The crystallographic evolution has been characterized during in-situ stress-induced transformation. The findings not only deepen the understanding of martensite transformation and mechanical behavior under a thermal/stress field in Ni-Mn-Ga alloys, but also propose a promising strategy to obtain microstructure-controllable functional alloys by MFADS.
{"title":"Microstructural and Mechanical Characteristics in Ni-Mn-Ga Alloys Under a Magnetic Field-Assisted Directional Solidification","authors":"L. Hou, Siyuan Yang, Xingfu Yu, Y. Fautrelle, Zongbin Li, D. Cong, Z. Ren, Yanyan Zhu, Xi Li","doi":"10.2139/ssrn.3892169","DOIUrl":"https://doi.org/10.2139/ssrn.3892169","url":null,"abstract":"In the present work, the effect of a transverse magnetic field-assisted directional solidification (MFADS) on the microstructures in Ni-Mn-Ga alloys has been investigated. The results show that the magnetic field is capable of inducing transversal macro segregation perpendicular to magnetic field, causing the emergence of martensite clusters in austenite matrix. Moreover, the magnetic field alleviates the micro segregation on a dendritic scale and promotes the preferred growth of austenite dendrites. On the basis of above investigation, several special samples are designed using the MFADS to study the crystallographic evolution and mechanical behavior during thermal/stress induced martensite transformation. The martensite cluster in austenite matrix is used to investigate the martensite transformation and growth under cooling-heating cycles. The crystallographic relationship and phase boundary microstructure between martensite and austenite have been characterized. In addition, the micro segregation on a dendritic scale can significantly influence the martensite variant distribution, corresponding to the performance during compressive circles based on the analysis about deformation gradient tensor. The stress-induced super elasticity is closely dependent on orientation, well explained from the perspective of different resolved shear stress factors and correspondence variant pair formation transformation strain. The crystallographic evolution has been characterized during in-situ stress-induced transformation. The findings not only deepen the understanding of martensite transformation and mechanical behavior under a thermal/stress field in Ni-Mn-Ga alloys, but also propose a promising strategy to obtain microstructure-controllable functional alloys by MFADS.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"69 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89089398","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}
Yufan Zhao, Huakang Bian, Hao Wang, K. Aoyagi, Yujie Cui, Y. Lei, K. Yamanaka, A. Chiba
For components built by powder bed fusion with electron beam (PBF-EB), the resulting microstructure arising from non-equilibrium solidification–microsegregation and the formation of interdendritic phases significantly affects the mechanical properties and hot cracking resistance. Notably, the powder characteristics influence heat absorption and conduction, thereby altering the molten pool behavior and solidification parameters. However, the effect of powder feedstock on non-equilibrium solidification during PBF has not been widely investigated. In this study, a CoCrMo alloy was built using powders prepared by gas-atomization (GA) and plasma rotating electrode process (PREP). Under the given operating conditions, the samples built with the two powders were experimentally characterized and their compression properties were compared. By performing multi-scale numerical simulations, powder melting and solidification were visualized and analyzed to elucidate the mechanism through which the powder characteristics influence the non-equilibrium solidification behavior during PBF-EB. The study revealed that upon appropriated size control, compared to the GA powder, the PREP powder had a smaller specific surface area and higher sphericity; thus, the generated powder layer exhibited higher heat absorption and dissipation rates. Therefore, a high solidification rate is facilitated, thereby suppressing microsegregation. The findings contribute to PBF knowledge related to feedstock, thus proving to be an essential reference for selecting and optimizing metallic powders applicable to additive manufacturing.
{"title":"Non-Equilibrium Solidification Behavior With Solute Trapping Associated With Powder Characteristics During Electron Beam Additive Manufacturing","authors":"Yufan Zhao, Huakang Bian, Hao Wang, K. Aoyagi, Yujie Cui, Y. Lei, K. Yamanaka, A. Chiba","doi":"10.2139/ssrn.3866407","DOIUrl":"https://doi.org/10.2139/ssrn.3866407","url":null,"abstract":"For components built by powder bed fusion with electron beam (PBF-EB), the resulting microstructure arising from non-equilibrium solidification–microsegregation and the formation of interdendritic phases significantly affects the mechanical properties and hot cracking resistance. Notably, the powder characteristics influence heat absorption and conduction, thereby altering the molten pool behavior and solidification parameters. However, the effect of powder feedstock on non-equilibrium solidification during PBF has not been widely investigated. In this study, a CoCrMo alloy was built using powders prepared by gas-atomization (GA) and plasma rotating electrode process (PREP). Under the given operating conditions, the samples built with the two powders were experimentally characterized and their compression properties were compared. By performing multi-scale numerical simulations, powder melting and solidification were visualized and analyzed to elucidate the mechanism through which the powder characteristics influence the non-equilibrium solidification behavior during PBF-EB. The study revealed that upon appropriated size control, compared to the GA powder, the PREP powder had a smaller specific surface area and higher sphericity; thus, the generated powder layer exhibited higher heat absorption and dissipation rates. Therefore, a high solidification rate is facilitated, thereby suppressing microsegregation. The findings contribute to PBF knowledge related to feedstock, thus proving to be an essential reference for selecting and optimizing metallic powders applicable to additive manufacturing.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"10 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86452706","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}
Traditional plasticity theories, either time-dependent phenomenological plasticity or crystal plasticity, have been discovered to have some inconsistency problems under dynamic loadings. Such discrepancy is essentially arisen from the fundamental postulation that only internal states of the material determine the additive plastic strain rate tensor. However, in logical, except for internal states, the external loading conditions are also close-relevant factors. In this article, we modified the fundamental postulation, and proposed a set of general disciplines for the determination of material plastic flow, which is based on the view that the plastic flow is determined by both internal states and external loading conditions, and is satisfied with the principle of maximal increment of entropy. Then, we proposed a crystal plasticity model and a phenomenological model based on the new disciplines. A few shock experiments on single-crystal zirconium were conducted to validate the new disciplines and models, including two shots of poly-crystal OFHC copper impacting and one shot of high-energy laser ablation. It was demonstrated that our disciplines and models are well-matched and applicable even up to the strain rate at the order of 109s-1.
{"title":"Alternative General Disciplines for Plastic Flow, New Phenomenological and Crystal-Plasticity Models Applicable from Quasi-Static to Extreme High Strain Rate Loadings","authors":"Yinghua Li, Yan-Qin Gu, Lingcang Cai, Lin Zhang","doi":"10.2139/ssrn.3931607","DOIUrl":"https://doi.org/10.2139/ssrn.3931607","url":null,"abstract":"Traditional plasticity theories, either time-dependent phenomenological plasticity or crystal plasticity, have been discovered to have some inconsistency problems under dynamic loadings. Such discrepancy is essentially arisen from the fundamental postulation that only internal states of the material determine the additive plastic strain rate tensor. However, in logical, except for internal states, the external loading conditions are also close-relevant factors. In this article, we modified the fundamental postulation, and proposed a set of general disciplines for the determination of material plastic flow, which is based on the view that the plastic flow is determined by both internal states and external loading conditions, and is satisfied with the principle of maximal increment of entropy. Then, we proposed a crystal plasticity model and a phenomenological model based on the new disciplines. A few shock experiments on single-crystal zirconium were conducted to validate the new disciplines and models, including two shots of poly-crystal OFHC copper impacting and one shot of high-energy laser ablation. It was demonstrated that our disciplines and models are well-matched and applicable even up to the strain rate at the order of 109s-1.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"39 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80044144","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}
To develop novel Invar alloys in the practically infinite compositional space of multicomponent alloys, rapid alloy prototyping is used to investigate five multicomponent Invar alloys with 5 at.% addition of Al, Cr, Cu, Mn and Si to a super Invar alloy (Fe 63 Ni 32 Co 5 ; at.%), respectively. All alloys show abnormally low thermal expansion coefficients below the Curie temperature and saturation magnetization deviating from the Slater-Pauling curve, revealing their Invar-behavior. The relationships among valence electron concentration, magnetic properties, and Invar behavior of the various multicomponent alloys are discussed. The Invar alloy with Cu addition is particularly promising, as it shows a 40 K larger temperature range (above room temperature) of low thermal expansion coefficient (<5.87×10 -6 K) and 2.8% higher hardness compared to the conventional super Invar alloy. The work thus also successfully demonstrates the capability of using rapid alloy prototyping for developing multicomponent multi-functional alloys.
为了在多组分合金几乎无限的组成空间中开发新型Invar合金，采用快速成形技术对5种含5 at的多组分Invar合金进行了研究。Al、Cr、Cu、Mn和Si在超级Invar合金(Fe 63 Ni 32 Co 5)中的添加量分别为。%)。所有合金均表现出低于居里温度的异常低的热膨胀系数和偏离Slater-Pauling曲线的饱和磁化，显示出其invar行为。讨论了各种多组分合金的价电子浓度、磁性能和因瓦尔行为之间的关系。添加Cu的Invar合金尤其有前景，与传统的超级Invar合金相比，其热膨胀系数(<5.87×10 -6 K)的温度范围(高于室温)增加了40 K，硬度提高了2.8%。因此，这项工作也成功地证明了使用快速合金原型技术开发多组分多功能合金的能力。
{"title":"Combinatorial Development of Multicomponent Invar Alloys Via Rapid Alloy Prototyping","authors":"Z. Rao, H. Springer, D. Ponge, Zhiming Li","doi":"10.2139/ssrn.3920957","DOIUrl":"https://doi.org/10.2139/ssrn.3920957","url":null,"abstract":"To develop novel Invar alloys in the practically infinite compositional space of multicomponent alloys, rapid alloy prototyping is used to investigate five multicomponent Invar alloys with 5 at.% addition of Al, Cr, Cu, Mn and Si to a super Invar alloy (Fe 63 Ni 32 Co 5 ; at.%), respectively. All alloys show abnormally low thermal expansion coefficients below the Curie temperature and saturation magnetization deviating from the Slater-Pauling curve, revealing their Invar-behavior. The relationships among valence electron concentration, magnetic properties, and Invar behavior of the various multicomponent alloys are discussed. The Invar alloy with Cu addition is particularly promising, as it shows a 40 K larger temperature range (above room temperature) of low thermal expansion coefficient (<5.87×10 -6 K) and 2.8% higher hardness compared to the conventional super Invar alloy. The work thus also successfully demonstrates the capability of using rapid alloy prototyping for developing multicomponent multi-functional alloys.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"48 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81404649","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. Bosio, A. Parisini, A. Lamperti, C. Borelli, Laura Fornasini, M. Bosi, I. Cora, Z. Fogarassy, B. Pécz, Z. Zolnai, A. Németh, S. Vantaggio, R. Fornari
The good control of the n-type doping is a key issue for the fabrication of efficient devices based on e-Ga2O3 epilayers. In this work we studied the possibility of doping the e-Ga2O3 thin films, epitaxially grown on c-oriented sapphire by metal-organic chemical vapor deposition, by means of a post-deposition treatment. For the first time, the n-type doping was achieved by depositing a tin-rich SnO2 film on top of the e-Ga2O3 layer and keeping this bi-layer system for 4 hours at a temperature of 600 °C in an evacuated furnace. The diffusion of Sn atoms into thee-Ga2O3 film is evidenced by time-of-flight secondary-ion mass spectrometry depth profiles. Room-temperature resistivity of the order of 1 Ω cm is obtained and the electrical characterization revealed a conduction mechanism based on variable range hopping, according to the Mott’s model.
{"title":"n-Type Doping of ε-Ga 2O 3n Epilayers by High-Temperature Tin Diffusion","authors":"A. Bosio, A. Parisini, A. Lamperti, C. Borelli, Laura Fornasini, M. Bosi, I. Cora, Z. Fogarassy, B. Pécz, Z. Zolnai, A. Németh, S. Vantaggio, R. Fornari","doi":"10.2139/ssrn.3757760","DOIUrl":"https://doi.org/10.2139/ssrn.3757760","url":null,"abstract":"The good control of the n-type doping is a key issue for the fabrication of efficient devices based on e-Ga2O3 epilayers. In this work we studied the possibility of doping the e-Ga2O3 thin films, epitaxially grown on c-oriented sapphire by metal-organic chemical vapor deposition, by means of a post-deposition treatment. For the first time, the n-type doping was achieved by depositing a tin-rich SnO2 film on top of the e-Ga2O3 layer and keeping this bi-layer system for 4 hours at a temperature of 600 °C in an evacuated furnace. The diffusion of Sn atoms into thee-Ga2O3 film is evidenced by time-of-flight secondary-ion mass spectrometry depth profiles. Room-temperature resistivity of the order of 1 Ω cm is obtained and the electrical characterization revealed a conduction mechanism based on variable range hopping, according to the Mott’s model.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"9 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87391660","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}
Since the discovery of the M7C3-type carbide in 1935, it has been the subject of many experimental and theoretical studies. Initially, the structure was thought of as being either trigonal or hexagonal, while later publications indicated that the structure was more likely to be orthorhombic. Even today, 8 decades after its discovery, many publications claim that M7C3 carbides are either hexagonal or orthorombic “beyond doubt”, while others, acknowledge the lack of agreement in the literature and try to resolve it using first principles calculations which rely on the atomic positions in the previously suggested structures. To date, no hard evidence was presented to support either claim in an indisputable manner. Using EBSD (electron backscattered diffraction), TEM (transmission electron microscopy) diffractions and high-resolution STEM (scanning transmission electron microscopy) imaging gathered from 8 zone-axis of the (Cr,Fe)7C3 phase formed in the as-cast AlCrFe2Ni2 high entropy alloy, we were able to determine that only the hexagonal structure is a viable option. Furthermore, we demonstrate the co-existence of two variants of the newly revealed atomic structure which we believe were mistakenly identified as stacking faults in previous studies.
{"title":"M 7C 3: The Story of a Misunderstood Carbide","authors":"E. Eshed, D. Choudhuri, Shmuel Osovski","doi":"10.2139/ssrn.3751558","DOIUrl":"https://doi.org/10.2139/ssrn.3751558","url":null,"abstract":"Since the discovery of the M7C3-type carbide in 1935, it has been the subject of many experimental and theoretical studies. Initially, the structure was thought of as being either trigonal or hexagonal, while later publications indicated that the structure was more likely to be orthorhombic. Even today, 8 decades after its discovery, many publications claim that M7C3 carbides are either hexagonal or orthorombic “beyond doubt”, while others, acknowledge the lack of agreement in the literature and try to resolve it using first principles calculations which rely on the atomic positions in the previously suggested structures. To date, no hard evidence was presented to support either claim in an indisputable manner. Using EBSD (electron backscattered diffraction), TEM (transmission electron microscopy) diffractions and high-resolution STEM (scanning transmission electron microscopy) imaging gathered from 8 zone-axis of the (Cr,Fe)7C3 phase formed in the as-cast AlCrFe2Ni2 high entropy alloy, we were able to determine that only the hexagonal structure is a viable option. Furthermore, we demonstrate the co-existence of two variants of the newly revealed atomic structure which we believe were mistakenly identified as stacking faults in previous studies.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"122 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87745470","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}
T. Sawaguchi, I. Nikulin, K. Ogawa, S. Takamori, Fumiyoshi Yoshinaka, Yuya Chiba, H. Otsuka, Yasuhiko Inoue, A. Kushibe
A recently developed Fe−15Mn−10Cr−8Ni−4Si (FMS) seismic damping alloy has a superior fatigue life at room temperature due to reversible dislocation motion associated with the γ → e martensitic transformation. The effect of temperature on the low-cycle fatigue life (N f) and the associated plasticity mechanisms of the FMS alloy were evaluated between 253 and 393 K. The longest (N f of 15,644 was obtained at 313 K. The (N f was dependent on the plasticity mechanisms, which were subdivided into three temperature regions with respect to the upper temperature limits for stress-assisted and strain-induced martensitic transformation (Msσ and Mdσ, respectively). At temperatures below Msσ, the Nf exceeded 5,000 cycles, where e-martensite was dominant and a long period stacking ordered structure was formed. The longest Nf values of over 10,000 cycles were obtained in the dual γ/e-phase formed between Mdσ and Mdσ, while Nf decreased rapidly as the deformation temperature increased beyond Mdσ. The effect of temperature on the N f of the FMS alloy was comparable to that of Fe–28Mn–6Si–5Cr shape memory alloy, and to the chemical composition dependence of N f of Fe–30Mn–(6 – x)Si–x Al (x= 0-6) transformation- and twinning-induced plasticity (TRIP/TWIP) steels. A new set of thermodynamic parameters was established to calculate the Gibbs free energy difference between the phases (ΔGγ→e) and the stacking fault energy of austenite (ΓSFE). The superior N f was associated with the cyclic strain-induced martensitic transformation when ΔGγ→e was between –50 and 100 Jmol-1, while reversible martensitic transformation relied on a ΔGγ→e of ~0 Jmol-1.
{"title":"Low-Cycle Fatigue Life and Plasticity Mechanisms of a Fe−15Mn−10Cr−8Ni−4Si Seismic Damping Alloy Under Cyclic Loading at Various Temperatures","authors":"T. Sawaguchi, I. Nikulin, K. Ogawa, S. Takamori, Fumiyoshi Yoshinaka, Yuya Chiba, H. Otsuka, Yasuhiko Inoue, A. Kushibe","doi":"10.2139/ssrn.3746794","DOIUrl":"https://doi.org/10.2139/ssrn.3746794","url":null,"abstract":"A recently developed Fe−15Mn−10Cr−8Ni−4Si (FMS) seismic damping alloy has a superior fatigue life at room temperature due to reversible dislocation motion associated with the γ → e martensitic transformation. The effect of temperature on the low-cycle fatigue life (N f) and the associated plasticity mechanisms of the FMS alloy were evaluated between 253 and 393 K. The longest (N f of 15,644 was obtained at 313 K. The (N f was dependent on the plasticity mechanisms, which were subdivided into three temperature regions with respect to the upper temperature limits for stress-assisted and strain-induced martensitic transformation (Msσ and Mdσ, respectively). At temperatures below Msσ, the Nf exceeded 5,000 cycles, where e-martensite was dominant and a long period stacking ordered structure was formed. The longest Nf values of over 10,000 cycles were obtained in the dual γ/e-phase formed between Mdσ and Mdσ, while Nf decreased rapidly as the deformation temperature increased beyond Mdσ. The effect of temperature on the N f of the FMS alloy was comparable to that of Fe–28Mn–6Si–5Cr shape memory alloy, and to the chemical composition dependence of N f of Fe–30Mn–(6 – x)Si–x Al (x= 0-6) transformation- and twinning-induced plasticity (TRIP/TWIP) steels. A new set of thermodynamic parameters was established to calculate the Gibbs free energy difference between the phases (ΔGγ→e) and the stacking fault energy of austenite (ΓSFE). The superior N f was associated with the cyclic strain-induced martensitic transformation when ΔGγ→e was between –50 and 100 Jmol-1, while reversible martensitic transformation relied on a ΔGγ→e of ~0 Jmol-1.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79979811","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}
An investigation into the recovery and recrystallization of the two major texture fibres during annealing, namely α and γ, yielded subtle differences between the two. It is reported that with thermal activation static recovery occurs, where dislocation free sub-grains are formed and tend to grow, coalesce, or bulge out. This can form new strain-free recrystallisation nuclei, with the coalesce or bulging phenomenon depending on stored energy and geometrically dislocation density (GND). Due to low lattice curvature or otherwise, it was found α-fiber has low stored energy and GND values which favours bulging into neighbouring deformed grains as opposed to subgrain coalescement. In contrast, γ-fiber tends to undergo rapid subgrain coalescement due to high lattice curvature, i.e., GND and stored energy. The newly formed grains from both texture fibers were also found to typically differ in size, as γ-fiber has a much higher nucleation rate with rapid subgrain coalescence. Furthermore, it was discovered that Cube texture component though nucleating in higher rates within α-fiber, nucleates in all regions of high dislocation densities but will only survive in regions with a low recovery and nucleation rates, typically as in α-fiber state condition. Moreover, Goss texture component was found to preferentially nucleate from γ-fiber.
{"title":"Disparity in Recrystallization of α- & γ-Fibers and its Impact on Cube Texture Formation in Non-Oriented Electrical Steel","authors":"D. Hawezy, S. Birosca","doi":"10.2139/ssrn.3742922","DOIUrl":"https://doi.org/10.2139/ssrn.3742922","url":null,"abstract":"An investigation into the recovery and recrystallization of the two major texture fibres during annealing, namely α and γ, yielded subtle differences between the two. It is reported that with thermal activation static recovery occurs, where dislocation free sub-grains are formed and tend to grow, coalesce, or bulge out. This can form new strain-free recrystallisation nuclei, with the coalesce or bulging phenomenon depending on stored energy and geometrically dislocation density (GND). Due to low lattice curvature or otherwise, it was found α-fiber has low stored energy and GND values which favours bulging into neighbouring deformed grains as opposed to subgrain coalescement. In contrast, γ-fiber tends to undergo rapid subgrain coalescement due to high lattice curvature, i.e., GND and stored energy. The newly formed grains from both texture fibers were also found to typically differ in size, as γ-fiber has a much higher nucleation rate with rapid subgrain coalescence. Furthermore, it was discovered that Cube texture component though nucleating in higher rates within α-fiber, nucleates in all regions of high dislocation densities but will only survive in regions with a low recovery and nucleation rates, typically as in α-fiber state condition. Moreover, Goss texture component was found to preferentially nucleate from γ-fiber.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"19 10","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91421037","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}
Wanshun Xia, Xinbao Zhao, Quanzhao Yue, L. Yue, Jiangwei Wang, Qingqing Ding, H. Bei, Ze Zhang
The local region of dislocation networks in a nickel-based single crystal superalloy crept under 1373K and 137MPa is spatially divided to two parts: gridlines which compose the arrangements of dislocation networks and mesh regions as intervals between gridlines. The formative and controlled mechanisms of nano-sized γ′ precipitates (γ′ n ) in mesh region are revealed. The enhanced segregation of Cr, Co and Re along gridlines with transformation of dislocation networks from transitional to equilibrium arrangements left the higher contents of γ′-rich elements such as Al in mesh region that facilitates the local phase transition and precipitation of γ′ n . However, the growth of γ′ n precipitates in mesh region, which requires great amounts of solutes diffusion of γ′-rich elements, is restricted by chemical barrier formed along gridlines of dislocation networks. Complete coherent interfaces between ordering mesh region and disordered gridlines could form γ/γ′ substructures to stabilize dislocation networks. In dendrite core, higher contents of Re, W and Mo effectively increase the lattice misfit to form denser dislocation networks. It can expect further subdivided γ/γ′ substructures in dendrite core increase the creep resistance to retard degradation of dislocation networks and topological inversion of rafted structures.
{"title":"Formative and Controlled Mechanisms of Nano-Sized γ' Precipitates with Local Phase-Transition within Dislocation Networks of Nickel-Based Single Crystal Superalloys","authors":"Wanshun Xia, Xinbao Zhao, Quanzhao Yue, L. Yue, Jiangwei Wang, Qingqing Ding, H. Bei, Ze Zhang","doi":"10.2139/ssrn.3734070","DOIUrl":"https://doi.org/10.2139/ssrn.3734070","url":null,"abstract":"The local region of dislocation networks in a nickel-based single crystal superalloy crept under 1373K and 137MPa is spatially divided to two parts: gridlines which compose the arrangements of dislocation networks and mesh regions as intervals between gridlines. The formative and controlled mechanisms of nano-sized γ′ precipitates (γ′ n ) in mesh region are revealed. The enhanced segregation of Cr, Co and Re along gridlines with transformation of dislocation networks from transitional to equilibrium arrangements left the higher contents of γ′-rich elements such as Al in mesh region that facilitates the local phase transition and precipitation of γ′ n . However, the growth of γ′ n precipitates in mesh region, which requires great amounts of solutes diffusion of γ′-rich elements, is restricted by chemical barrier formed along gridlines of dislocation networks. Complete coherent interfaces between ordering mesh region and disordered gridlines could form γ/γ′ substructures to stabilize dislocation networks. In dendrite core, higher contents of Re, W and Mo effectively increase the lattice misfit to form denser dislocation networks. It can expect further subdivided γ/γ′ substructures in dendrite core increase the creep resistance to retard degradation of dislocation networks and topological inversion of rafted structures.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"24 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75891027","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. Scales, David J Armstrong, A. Wilkinson, Bobo Li
The fracture properties of as-cast TiVNbTa, a refractory high-entropy alloy (RHEA), were investigated using four-point bending tests from -139C to 20C under a strain-rate of 10-3 s-1. From those tests and fractography, the conditional fracture toughness values and the brittle-to-ductile transition temperature were obtained. The brittle-to-ductile transition temperature was between -47C to -27C, which gives an estimated activation energy value of 0.52+-0.09 eV for the alloy. This study provides a preliminary understanding of the nature of dislocation motion in a relatively ductile RHEA.
{"title":"On the Brittle-to-Ductile Transition of the As-Cast TiVNbTa Refractory High-Entropy Alloy","authors":"R. Scales, David J Armstrong, A. Wilkinson, Bobo Li","doi":"10.2139/ssrn.3708719","DOIUrl":"https://doi.org/10.2139/ssrn.3708719","url":null,"abstract":"The fracture properties of as-cast TiVNbTa, a refractory high-entropy alloy (RHEA), were investigated using four-point bending tests from -139C to 20C under a strain-rate of 10-3 s-1. From those tests and fractography, the conditional fracture toughness values and the brittle-to-ductile transition temperature were obtained. The brittle-to-ductile transition temperature was between -47C to -27C, which gives an estimated activation energy value of 0.52+-0.09 eV for the alloy. This study provides a preliminary understanding of the nature of dislocation motion in a relatively ductile RHEA.","PeriodicalId":7755,"journal":{"name":"AMI: Acta Materialia","volume":"10 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78290321","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：