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Rajarshi Banerjee - One of the best experts on this subject based on the ideXlab platform.
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contrasting mechanical behavior in precipitation hardenable alxcocrfeni high entropy alloy microstructures single phase Fcc vs dual phase Fcc bcc
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2019Co-Authors: Sindhura Gangireddy, Bharat Gwalani, Vishal Soni, Rajarshi Banerjee, Rajiv S MishraAbstract:Abstract AlxCoCrFeNi is a prominent high entropy alloy system with varying crystal structure from Fcc to BCC depending on aluminum content. The mechanical behavior of Al0.7CoCrFeNi with dual phase Fcc+BCC microstructure has been compared with that of single phase Fcc Al0.3CoCrFeNi. Both quasi-static and dynamic strain rate regimes were investigated. Hypo-eutectic Al0.7CoCrFeNi showed much higher strength due to fine lamellar microstructure with a large number of Fcc-BCC interphase boundaries. But this also leads to lower strain rate sensitivity due to the long-range nature of these interfaces, overcoming them is indifferent with temperature elevation to assist slip, thus making them athermal barriers. Both these precipitation hardenable alloys were aged to induce precipitation of ordered L12 in the Fcc phase. This coherent nano-scale L12 precipitate caused a significant increase in the yield strength of both single-phase and dual phase structures while reducing the strain rate sensitivity (SRS) only slightly. L12 precipitation in Fcc matrix greatly enhanced twinning during dynamic deformation. Large-scale deformation twins were observed in coarse Al0.3CoCrFeNi Fcc and Fcc + L12 microstructures. The scale of deformation twins was much smaller in the dual phase Al0.7CoCrFeNi whose refined lamellae width retarded twinning. The lamellar structures, nevertheless, had higher work hardening due to their higher dislocation density storage capability.
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Deformation induced intermediate metastable lattice structures facilitate ordered B2 nucleation in a Fcc-based high entropy alloy
Taylor & Francis Group, 2019Co-Authors: Deep Choudhuri, Bharat Gwalani, Rajarshi Banerjee, Shivakant Shukla, Rajiv S MishraAbstract:Ordered B2 precipitates typically nucleate at the grains-boundaries of Fcc-based high entropy alloys. Here, we report a novel mixed-mode coupled displacive-diffusional transformation resulting in homogeneously distributed intra-granular B2 precipitates within the Fcc matrix. Severe plastic deformation forms compositionally invariant, metastable distorted Fcc structures, resembling hexagon-like templates, at the deformation twin-boundaries. These shear-induced hexagon-like templates correspond to the symmetry of the {111}bcc planes, and act as sites for B2 nucleation, establishing the Fcc-bcc Kurdjumov–Sachs (KS) orientation relationship. However, the composition of these B2 precipitates is far-from-equilibrium. Subsequent isothermal annealing causes solute partitioning driving the composition of the B2 precipitates towards equilibrium
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Deformation induced intermediate metastable lattice structures facilitate ordered B2 nucleation in a Fcc-based high entropy alloy
2018Co-Authors: Deep Choudhuri, Bharat Gwalani, Rajarshi Banerjee, Shivakant Shukla, Rajiv S MishraAbstract:Ordered B2 precipitates typically nucleate at the grains-boundaries of Fcc-based high entropy alloys. Here, we report a novel mixed-mode coupled displacive-diffusional transformation resulting in homogeneously distributed intra-granular B2 precipitates within the Fcc matrix. Severe plastic deformation forms compositionally invariant, metastable distorted Fcc structures, resembling hexagon-like templates, at the deformation twin-boundaries. These shear-induced hexagon-like templates correspond to the symmetry of the {111}bcc planes, and act as sites for B2 nucleation, establishing the Fcc-bcc Kurdjumov–Sachs (KS) orientation relationship. However, the composition of these B2 precipitates is far-from-equilibrium. Subsequent isothermal annealing causes solute partitioning driving the composition of the B2 precipitates towards equilibrium. For the first time, a mixed mode displacive-diffusional Fcc-to-bcc-ordered B2 transformation mechanism was revealed in a deformed Fcc-based Al0.3CoCrFeNi complex concentrated or high entropy alloy.
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change in the primary solidification phase from Fcc to bcc based b2 in high entropy or complex concentrated alloys
Scripta Materialia, 2017Co-Authors: D Choudhuri, Bharat Gwalani, Rajarshi Banerjee, Stephane Gorsse, C V Mikler, R V Ramanujan, Mark A GibsonAbstract:Abstract An examination of a compositionally graded Al x CuCrFeNi 2 high entropy alloy (HEA) or complex concentrated alloy (CCA), revealed that marginally increasing Al content from x = 0.8 to x = 1.0 (+ 6 at.%) changes the primary solidification phase from a simple disordered- Fcc to a bcc -based ordered-B2 phase. Subsequently, a second solidification product forms, a disordered- bcc in case of x = 0.8 and a disordered- Fcc in case of x = 1.0. Solid-state decomposition within these phases results in Fcc + L1 2 and bcc + B2 products, accompanied by compositional partitioning. These results provide new insights into the influence of Al on the primary solidification product, and have been rationalized using a computational thermodynamic approach.
A L Greer - One of the best experts on this subject based on the ideXlab platform.
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novel phase decomposition good soft magnetic and mechanical properties for high entropy fe0 25co0 25ni0 25cr0 125mn0 125 100 b x 9 13 amorphous alloys
Journal of Alloys and Compounds, 2020Co-Authors: C C Zhao, Akihisa Inoue, F L Kong, J Y Zhang, C J Chen, B L Shen, F Almarzouki, A L GreerAbstract:Abstract As-spun (Fe0.25Co0.25Ni0.25Cr0.125Mn0.125)100–xBx (x = 9–13 at%) alloys are fully amorphous with bending plasticity and good soft-magnetic properties. Manganese addition favors amorphous phase formation at lower B content than in comparable alloys. On heating, the alloys transform: [am] → [am’ + bcc + Fcc] → [Fcc] at 9–11% B; and [am] → [am’ + bcc + Fcc] → [bcc + Fcc + borides] → [Fcc + borides] at 12–13% B. Novel observations are the formation of metastable bcc + Fcc phases, and an endotherm due to the [bcc + Fcc] → [Fcc] transition. The Vickers hardness of 9–11% B alloys is ∼650 in the as-spun state, shows a maximum of 1010 for [bcc + Fcc] state and then decreases to 750 upon transition to [Fcc]. As-cast 9–11% B 2-mm-diameter rods, mainly [bcc + Fcc], exhibit compressive strength of 1520–1705 MPa and plastic strain >25%. These high-strength alloys, and the as-spun amorphous alloys with soft-magnetic properties, are encouraging for the further development of structural and functional materials.
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formation stability and ultrahigh strength of novel nanostructured alloys by partial crystallization of high entropy fe0 25co0 25ni0 25cr0 125mo0 125 86 89b11 14 amorphous phase
Acta Materialia, 2019Co-Authors: Fengwu Wang, F L Kong, F Almarzouki, Shengli Zhu, E Shalaan, W J Botta, C S Kiminami, Yu P Ivanov, A L GreerAbstract:Abstract Heating-induced crystallization of high-entropy (HE) (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)86‒89B11‒14 amorphous (am) alloys is examined to develop new structural materials with low B contents. The crystallization of 11B alloy occurs in three stages: first nanoscale bcc precipitates form in the amorphous matrix, second nanoscale Fcc precipitates form, and the residual amorphous phase disappears in the third stage which yields borides in addition to the bcc and Fcc phases. Crystallization of 14B alloy is the same, except that the order of appearance of bcc and Fcc is reversed. The bcc and Fcc particle diameters are 5–15 nm and remain almost unchanged up to ∼960 K. On annealing, ultrahigh hardness of 1500–1550 (unprecedented for boride-free structures) is attained just before the third crystallization stage. This hardening and the thermal stability of the novel [am + bcc + Fcc] structures are remarkable at such low boron content and encouraging for development as ultrahigh-strength alloys. The results are interpreted in terms of the nature and extent of partitioning of elemental components between the bcc/Fcc phases and the amorphous matrix, and the size and defect structures of the bcc and Fcc precipitates. The magnetic flux density at room temperature increases by precipitation of bcc and decreases by appearance of Fcc. Slower quenching of the 11B alloy shows a pseudo-polymorphic crystallization that may be characteristic of multicomponent HE systems.
Levente Vitos - One of the best experts on this subject based on the ideXlab platform.
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phase selection rule for al doped crmnfeconi high entropy alloys from first principles
Acta Materialia, 2017Co-Authors: Xun Sun, Levente Vitos, Hualei Zhang, Xiangdong Ding, Yunzhi WangAbstract:Abstract Using ab initio alloy theory, we investigate the lattice stability of paramagnetic Al x CrMnFeCoNi (0 ≤ x ≤ 5) high-entropy alloys considering the competing body-centered cubic (bcc) and face-centered cubic (Fcc) crystal structures. The theoretical lattice constants increase with increasing x , in good agreement with experimental data. Upon Al addition, the crystal structure changes from Fcc to bcc with a broad two-phase field region, in line with observations. The magnetic transition temperature for the bcc structure strongly decreases with x , whereas that for the Fcc structure shows weak composition dependence. Within their own stability fields, both structures are predicted to be paramagnetic at ambient conditions. Bain path calculations support that within the duplex region both phases are dynamically stable. As compared to Al x CrFeCoNi, equiatomic Mn addition is found to shrink the stability range of the Fcc phase and delay the appearance of the bcc phase in terms of Al content, thus favoring the duplex region in 3 d -metals based high-entropy alloys.
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thermal spin fluctuation effect on the elastic constants of paramagnetic fe from first principles
Physical Review B, 2015Co-Authors: Zhihua Dong, Stephan Schonecker, Dengfu Chen, Levente VitosAbstract:We investigate the impact of longitudinal thermal spin fluctuations on the temperature dependence of the elastic constants of paramagnetic body-centered-cubic (bcc) and face-centered-cubic (Fcc) Fe. Based on a series of constrained local magnetic moment calculations, the spin fluctuation distribution is established using Boltzmann statistics and involving the Jacobian weight, and a temperature-dependent quadratic mean moment is introduced that accurately represents the spin fluctuation state as a function of temperature. We show that with increasing temperature, c' and c(44) for the Fcc phase and c(44) for the bcc phase decrease at different rates due to different magnetoelastic coupling strengths. In contrast, c' in the bcc phase exhibits relatively high thermal stability. Longitudinal thermal spin fluctuations diminish the softening of both elastic constants in either phase and have comparatively large contributions in the Fcc phase. In both bcc and Fcc Fe, c(44) has a larger temperature factor than c'. On the other hand, c' is more sensitive to the longitudinal thermal spin fluctuations, which balance the volume-induced softening by 21.6% in Fcc Fe.
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influence of manganese on the bulk properties of fe cr mn alloys a first principles study
Physica Scripta, 2014Co-Authors: Noura Alzoubi, Levente Vitos, Stephan Schonecker, Borje JohanssonAbstract:We investigate the effect of manganese on lattice stability and magnetic moments of paramagnetic Fe-Cr-Mn steel alloys along the Bain path connecting the body-centered cubic (bcc) and face-centered cubic (Fcc) structures. The calculations are carried out using the ab initio exact muffin-tin orbital method, in combination with the coherent potential approximation, and the paramagnetic phase is modeled by the disordered local magnetic moment scheme. For all Fe-Cr-Mn alloys considered here, the local magnetic moments on Fe atoms have the minimum values for the Fcc structure and the maximum values for the bcc structure, whereas the local magnetic moments on Mn have almost the same value along the constant-volume Bain path. Our results show that Mn addition to paramagnetic Fe-Cr solid solution stabilizes the bcc structure. However, when considering the paramagnetic Fcc phase relative to the ferromagnetic bcc ground state, then Mn turns out to be a clear Fcc stabilizer, in line with observations.
Th J M De Hosson - One of the best experts on this subject based on the ideXlab platform.
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the Fcc bcc crystallographic orientation relationship in alxcocrfeni high entropy alloys
Materials Letters, 2016Co-Authors: Jiancun Rao, Vaclav Ocelik, D Vainchtein, Z Tang, Peter K Liaw, Th J M De HossonAbstract:Abstract This paper concentrates on the crystallographic-orientation relationship between the various phases in the Al-Co-Cr-Fe-Ni high-entropy alloys. Two types of orientation relationships of bcc phases (some with ordered B2 structures) and Fcc matrix were observed in Al0.5CoCrFeNi and Al0.7CoCrFeNi alloys at room temperature: (1 −1 0)bcc//(200)Fcc, [001]bcc//[001]Fcc, (b) (1 −1 1)B2//(2−2 0)Fcc, [011]B2//[11 2 ]Fcc.
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the Fcc bcc crystallographic orientation relationship in alxcocrfeni high entropy alloys
Materials Letters, 2016Co-Authors: Jiancun Rao, Vaclav Ocelik, D Vainchtein, Z Tang, Peter K Liaw, Th J M De HossonAbstract:This paper concentrates on the crystallographic-orientation relationship between the various phases in the Al-Co-Cr-Fe-Ni high-entropy alloys. Two types of orientation relationships of bcc phases (some with ordered B2 structures) and Fcc matrix were observed in Al0.5CoCrFeNi and Al0.7CoCrFeNi alloys at room temperature: (1 -1 0)(bcc)//(200)(Fcc), [CM](bcc)//[001](Fcc), (b) (1 -1 1)B2//(2 - 2 0)(Fcc), [011]B2//[11 root 2](Fcc). (C) 2016 Elsevier B.V. All rights reserved.
Weiping Chen - One of the best experts on this subject based on the ideXlab platform.
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effects of co and ti on microstructure and mechanical behavior of al0 75fenicrco high entropy alloy prepared by mechanical alloying and spark plasma sintering
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Zhen Chen, Weiping Chen, Xueyang Cao, Lusheng LiuAbstract:Abstract The effects of Co removal and Ti addition on the microstructure and mechanical behavior of a high-entropy alloy (HEA), Al0.75FeNiCrCo, were studied systematically. Al0.75FeNiCrCo, Al0.75FeNiCr and Al0.75FeNiCrCoTi0.25 were successfully prepared by the combination of mechanical alloying (MA) and spark plasma sintering (SPS). During the MA process, a primary body-centered cubic (BCC) supersaturated solid-solution phase and a face-centered cubic (Fcc) supersaturated solid-solution phase were formed in each of the three investigated alloys. Removing Co from the Al0.75FeNiCrCo HEA or adding Ti into the Al0.75FeNiCrCo HEA could facilitate increasing the content of BCC phase both during the MA process and after the SPS process. Following SPS, bulk Al0.75FeNiCrCo was composed of a major Fcc phase (∼79 vol%) and a minor BCC phase (∼21 vol%). However, with Co removal, bulk Al0.75FeNiCr alloy exhibited a main BCC phase (∼60 vol%) and an Fcc phase (∼40 vol%). With Ti addition, bulk Al0.75FeNiCrCoTi0.25 alloy consisted of a major Fcc phase (∼77 vol%) and a minor BCC phase (∼23 vol%). The EDS/TEM results of the bulk Al0.75FeNiCrCo alloy revealed that the BCC phase was enriched in Al–Ni, while the Fcc phase was enriched in Fe–Cr–Co. Meanwhile, a small fraction of nanoscale twins were present in the bulk Al0.75FeNiCrCo alloy. The bulk Al0.75FeNiCrCo alloy exhibited high strength and high hardness, mainly attributed to solid-solution strengthening, twin-boundary strengthening and grain-boundary strengthening. With Co removal, the bulk Al0.75FeNiCr alloy showed lower strength, hardness and ductility in comparison with the Al0.75FeNiCrCo alloy. With Ti addition, compared to the Al0.75FeNiCrCo alloy, the bulk Al0.75FeNiCrCoTi0.25 alloy exhibited higher strength and hardness with a slightly lower ductility.
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microstructure and mechanical behavior of a novel co20ni20fe20al20ti20 alloy fabricated by mechanical alloying and spark plasma sintering
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Weiping Chen, Haiming Wen, Enrique J. Lavernia, Sam Morgan, Fei Chen, Baolong Zheng, Yizhang Zhou, Lianmeng ZhangAbstract:Abstract A novel equiatomic Co20Ni20Fe20Al20Ti20 (at%) alloy was designed and synthesized to study the effect of high atomic concentrations of Al and Ti elements on the microstructure, phase composition and mechanical behavior of high-entropy alloys (HEAs) fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). Following the MA process, the Co20Ni20Fe20Al20Ti20 alloy was composed of a primary body-centered cubic (BCC) supersaturated solid solution and a face-centered cubic (Fcc) supersaturated solid solution. However, following SPS, a primary Fcc solid-solution phase, a BCC solid-solution phase and a trace amount of Al3Ti intermetallics were observed. Transmission electron microscopy (TEM) results confirmed the presence of the Fcc solid-solution phase, the BCC (B2-type) solid-solution phase and Al3Ti intermetallics in the bulk alloy. The Fcc and B2-type phases are ultrafine-grained, and Al3Ti intermetallics is nano/ultrafine-grained. Our results suggest that consideration of a single existing empirical design criterion is inadequate to explain phase formation in the Co20Ni20Fe20Al20Ti20 alloy. Solid-solution strengthening, grain-boundary strengthening, twin-boundary strengthening, the presence of the strong B2-type BCC phase, and precipitate strengthening due to the presence of a trace amount of Al3Ti are responsible for the ultra-high compressive strength of ~2988 MPa and hardness of ~704 Hv. The strain-to-failure of ~5.8% with visible ductility is dominated by the Fcc solid-solution phase.
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microstructure and mechanical properties of twinned al0 5crfenico0 3c0 2 high entropy alloy processed by mechanical alloying and spark plasma sintering
Materials & Design, 2014Co-Authors: Sicong Fang, Weiping Chen, Zhiqiang FuAbstract:Abstract Most of multi-component high entropy alloys (HEAs) only consist of metallic elements. In the present paper, by introducing nonmetallic carbon element, non-equiatomic Al 0.5 CrFeNiCo 0.3 C 0.2 HEA has been successfully prepared by mechanical alloying (MA) and spark plasma sintering (SPS) process. Alloying behavior, microstructure, phase evolution and mechanical properties of the alloy were investigated systematically. During the MA process, a supersaturated solid solution with both face-center cubic (Fcc) and body-center cubic (BCC) structures was formed within 38 h of milling. However, a major Fcc phase, a BCC phase, Cr 23 C 6 carbide and an ordered BCC phase were observed after SPS. The Fcc phase is enriched in Fe–Ni, the BCC phase is enriched in Ni–Al and the ordered BCC phase is especially enriched in Al, respectively. In addition, nanoscale deformation twins obviously presented only in partial Fcc phase after SPS. The compressive strength and Vickers hardness of Al 0.5 CrFeNiCo 0.3 C 0.2 high entropy alloy are 2131 MPa and 617 ± 25 HV, respectively.
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Influence of Ti addition and sintering method on microstructure and mechanical behavior of a medium-entropy Al 0.6 CoNiFe alloy
Materials Science and Engineering: A, 2014Co-Authors: Weiping Chen, Zhen Chen, Haiming Wen, Enrique J. LaverniaAbstract:Abstract The influence of Ti addition and sintering method on the microstructure and mechanical behavior of a medium-entropy alloy, Al0.6CoNiFe alloy, was studied in detail. Alloying behavior, microstructure, phase evolution and mechanical properties of Al0.6CoNiFe and Ti0.4Al0.6CoNiFe alloys were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), as well as by mechanical testing. During the mechanical alloying (MA) process, a supersaturated solid solution consisting of both BCC and Fcc phases was formed in the Al0.6CoNiFe alloy. With Ti addition, the Ti0.4Al0.6CoNiFe alloy exhibited a supersaturated solid solution with a single Fcc phase. Following hot pressing (HP), the HP sintered (HP’ed) Al0.6CoNiFe bulk alloy was composed of a major BCC phase and a minor Fcc phase. The HP’ed Ti0.4Al0.6CoNiFe alloy exhibited a Fcc phase, two BCC phases and a trace unidentified phase. Nanoscale twins were present in the HP’ed Ti0.4Al0.6CoNiFe alloy, where deformation twins were observed in the Fcc phase. Our results suggest that the addition of Ti facilitated the formation of nanoscale twins. The compressive strength and Vickers hardness of HP’ed Ti0.4Al0.6CoNiFe alloy were slightly lower than the corresponding values of the HP’ed Al0.6CoNiFe alloy. In contrast with HP’ed Al0.6CoNiFe alloy, spark plasma sintered (SPS’ed) Al0.6CoNiFe alloy exhibited a major Fcc phase and a minor BCC phase. Moreover, the SPS’ed Al0.6CoNiFe alloy exhibited a lower compressive strength and Vickers hardness, but singificantly higher plasticity, as compared to those of the HP’ed counterpart material.
