| 1. |
- Jaladurgam, Nitesh Raj, 1993, et al.
(författare)
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Load redistribution in eutectic high entropy alloy AlCoCrFeNi 2.1 during high temperature deformation
- 2022
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Ingår i: Materialia. - : Elsevier BV. - 2589-1529. ; 22
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Tidskriftsartikel (refereegranskat)abstract
- The load redistribution between and within phases in eutectic high entropy alloy AlCoCrFeNi2.1 was measured using in-situ neutron diffraction during tensile deformation at 973 K. The load partitioning between phases is reversed compared to lower temperatures, with L12 becoming the stronger phase. The evolution of the orientation-specific stresses and strains in the L12 phase suggests that cube slip dominates the response. The low strength, internal load transfer and ideally plastic response of the B2 phase indicate a change in deformation mechanism compared to lower temperatures.
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| 2. |
- Jaladurgam, Nitesh Raj, 1993, et al.
(författare)
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Temperature dependent load partitioning and slip mode transition in a eutectic AlCoCrFeNi 2.1 high entropy alloy
- 2021
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Ingår i: Materialia. - : Elsevier BV. - 2589-1529. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- Eutectic high entropy alloys are gaining increasing attention due to their excellent castability and combination of strength and ductility in the as-cast state. However, the detailed behavior of the nano-scale lamellar microstructure during deformation, and in particular the interaction between the phases, is not well understood. Here we use in-situ neutron diffraction during tensile testing over a wide temperature range (77–673 K) to obtain new insights into the temperature dependent mechanical interactions between and within phases during initial plastic deformation of an AlCoCrFeNi eutectic high entropy alloy. The load was transferred from the L1 to the B2 phase during the yielding process, and the changing load distribution within the L1 phase with increasing temperature strongly suggests that <110>{001} cube slip is activated at room temperature and above. This points towards alloying design for delayed octahedral-to-cube slip transition as a possible strategy for increasing the high temperature strength of material. 2.1 2 2
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| 3. |
- Lozinko, Adrianna, 1992
(författare)
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Characterization and Modification of Microstructure in Al-Co-Cr-Fe-Ni Eutectic High-Entropy Alloys
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The recently emerging high-entropy alloys (HEAs) present a novel alloying strategy, significantly expanding the scope of metal alloy design. HEAs are defined as alloys consisting of at least four principal elements in equi- or near equiatomic ratios, with a possibility of small amounts of alloying elements. For the past 15 years, most researchers focused on HEA compositions forming simple FCC or BCC solid solutions. However, such compositions have been found to suffer from a trade-off of strength and ductility. Many of the FCC HEAs can provide high ductility at room and elevated temperatures, however, they are unable to withstand high loads and their tensile strength is unimpressive. On the other hand, BCC HEAs are usually characterized by high strength, with unfortunately low ductility. Therefore, for HEAs to be truly considered as potential structural materials, alloys with a good balance of strength and ductility must be developed. A possible solution is found in the recently developed eutectic HEAs (EHEAs), which borrow the concept of using lamellar structures as in-situ composites to improve mechanical properties. The first such alloy, AlCoCrFeNi2.1, with an FCC+BCC lamellar microstructure remains as the most studied of EHEAs. Despite much work put into its characterization, much remains to be understood. The first part of this work focuses on the as-cast microstructures of the eutectic and near-eutectic compositions of the AlCoCrFeNix system. Quantification of the phase volume and lamellar spacing is performed as a function of the Ni content. Orientation relationship and misorientation angle-axis changes in the five investigated alloys are also studied, with the previously unknown dependency of misorientation angle on the Ni content revealed. The second part of this work studies the recrystallization process in the cold-rolled AlCoCrFeNi2.1 alloy. Development of the microstructure at various stages of recrystallization and the associated changes in mechanical properties are studied. Distinctive behavior of the two constituent phases during recrystallization, with varying rates of recrystallization and grain growth is observed. These findings show there is a possibility to further improve the EHEAs via careful thermo-mechanical processing.
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| 4. |
- Lozinko, Adrianna, 1992, et al.
(författare)
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Evolution of microstructure and mechanical properties during annealing of heavily rolled AlCoCrFeNi2. 1 eutectic high-entropy alloy
- 2022
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Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 833
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Tidskriftsartikel (refereegranskat)abstract
- Changes in the microstructure and mechanical properties during annealing at 800 °C have been characterized in a 90% cold-rolled AlCoCrFeNi2.1 eutectic high-entropy alloy containing the FCC and B2 (ordered BCC) phases. In the as-rolled condition, the FCC phase is found to contain a high frequency of finely spaced deformation-induced boundaries, which provides a high driving force for recrystallization within this phase. Quantitative analysis of electron backscatter diffraction data from the annealed samples indicates that recrystallization progresses faster in the FCC phase than in B2 regions. Although recrystallization leads to substantial coarsening of the microstructure, the average recrystallized grain size remains in the submicron range even after 2 h at 800 °C. Tensile test data demonstrate that combinations of high yield strength and good ductility are obtained in partially recrystallized samples produced by annealing for 2.5–10 min. However, the work-hardening capacity of each annealed sample is lower than that of the cold-rolled sample. Furthermore, for the samples annealed for at least 5 min a yield drop is observed soon after the onset of plastic deformation. Analysis of the microstructure and mechanical behavior in several annealed AlCoCrFeNi2.1 samples indicates a clear correlation between the magnitude of the yield drop and the recrystallized fraction. The mechanical behavior of the AlCoCrFeNi2.1 alloy studied in this work is compared with that reported in previous publications.
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| 5. |
- Lozinko, Adrianna, 1992, et al.
(författare)
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Microstructural characterization of eutectic and near-eutectic AlCoCrFeNi high-entropy alloys
- 2020
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 822
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure and orientation relationships in five AlCoCrFeNix alloys with eutectic (x = 2.1) and near-eutectic compositions (x = 1.9, 2.0, 2.2 and 2.3) have been characterized in this work. The eutectic and near-eutectic AlCoCrFeNix alloys have microstructures consisting of face-centered cubic (FCC) and ordered body-centered cubic (BCC) B2 phases, where the volume fraction of the FCC phase is found to increase with increasing Ni content. It is found that each eutectic colony consists of several parallel lamellae in the colony center and peripheral irregular labyrinth-like structures. The frequency of the irregular structures appears to be higher in the near-eutectic alloys than in the eutectic alloy. The ratio of the average widths of FCC and BCC lamellae is observed to be sensitive to the chemical composition and increases with the increasing Ni content. The two phases in the studied alloys display relationships close to the Kurdjumov-Sachs orientation relationship. The distribution of misorientation angles between the interphase boundaries changes as a function of the Ni content. The result of this change is a small increase in the average misorientation angle across the FCC/BCC interphase boundaries with increasing Ni content. The differences in the morphological crystallographic characteristics between the alloys are briefly discussed.
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| 6. |
- Lozinko, Adrianna, 1992
(författare)
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Microstructure development and mechanical properties of cast and thermo-mechanically treated eutectic high-entropy alloys
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The recently emerging high-entropy alloys (HEAs) present a novel alloying strategy, significantly expanding the scope of metal alloy design. Single-phase HEAs, nevertheless, suffer from the strength-ductility trade off as seen in conventional metallic materials. A possible solution is found in the recently developed eutectic HEAs (EHEAs), which borrow the concept of using lamellar structures as in-situ composites to balance mechanical properties. The first such alloy, AlCoCrFeNi2.1, with an FCC(L12) + BCC(B2) lamellar microstructure, remains the most studied EHEA. Despite much work put into its characterization, much remains to be understood. For example, more efforts have been given to optimize the mechanical properties while less are given to quantitatively describe the microstructure. Various thermo-mechanical treatments have been used to modify the mechanical properties of the AlCoCrFeNi2.1 alloy, however, previous studies mainly focused on the fully recrystallized materials, while a clear understanding of the recrystallization process is still missing, and the potential of partial recrystallization remains to be explored. The first part of this thesis work focuses on the as-cast microstructures of the eutectic and near-eutectic compositions of the AlCoCrFeNi2.1 system. Quantification of the phase volume and lamellar spacing is performed as a function of the Ni content. Orientation relationship and misorientation angle-axis changes in the five investigated alloys are also studied, with the previously unknown dependency of misorientation angle on the Ni content revealed. Some attention is also given to irregular microstructures in eutectic and near-eutectic compositions, which have not been discussed in previous studies. In the second part of this thesis work, a systematic study of the recrystallization process and the correlation between microstructure and mechanical properties in the thermo-mechanically treated AlCoCrFeNi2.1 alloy is undertaken. Distinctive behavior of the constituent phases during recrystallization, with varying rates of recrystallization and grain growth are observed, providing new insights to the recrystallization process in this alloy. Furthermore, it is shown that by controlling the annealing temperature and time, hetero-deformation induced hardening could lead to abnormal hardening in the as-rolled alloy, providing a new strategy to achieve high-strength with acceptable ductility in EHEAs.
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| 7. |
- Lozinko, Adrianna, 1992, et al.
(författare)
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Quantification of microstructure in a eutectic high entropy alloy AlCoCrFeNi2.1
- 2019
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Ingår i: IOP Conference Series: Materials Science and Engineering. - 1757-8981 .- 1757-899X. ; 580:1
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Konferensbidrag (refereegranskat)abstract
- Eutectic high entropy alloys (EHEAs) are a new class of metallic alloys with good mechanical properties at various temperatures. In the present investigation, microstructural parameters such as the volume fraction of two phases (FCC (L12) and BCC (B2)) forming the eutectic, the orientation relationship between these phases and interphase boundary spacings in as-cast EHEA AlCoCrFeNi2.1 were quantified using electron microscopy. It is found that the two phases have a Kurdjumov-Sachs orientation relationship, i.e., {111} fcc || {110} bcc and 〈110〉 fcc || 〈111〉 bcc . It is also found that both regular semi-coherent lamellar and irregular curved interphase boundaries are present within individual eutectic colonies. The habit planes for the semi-coherent lamellar interfaces are {224} and {123} for the FCC and BCC phases, respectively. Quantitative microstructural analysis shows that the ratio of volume fractions of the FCC and BCC phases within the regular lamellar regions differs to that within irregular regions, which suggests a local chemistry difference between the two regions. Finally, the solidification process of EHEAs is discussed, and possible ways to optimize the mechanical properties by microstructural design are suggested.
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| 8. |
- Patel, A., et al.
(författare)
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Strain-path controlled microstructure, texture and hardness evolution in cryo-deformed AlCoCrFeNi2.1 eutectic high entropy alloy
- 2018
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Ingår i: Intermetallics. - : Elsevier BV. - 0966-9795. ; 97, s. 12-21
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Tidskriftsartikel (refereegranskat)abstract
- The effect of strain path on microstructure, texture and hardness properties of AlCoCrFeNi 2.1 eutectic high entropy alloy containing ordered FCC (L1 2 ) and ordered BCC (B2) was investigated. The EHEA was cryo-rolled using UCR, MSCR (during which the samples were rotated by 90° around the ND between each pass) and TSCR(45°) (in which the samples were deformed by unidirectional rolling to half of the total strain and then diagonally rolled for rest half of the strain). The UCR processed material showed a rather heterogeneous microstructure. The textures of the L1 2 /FCC and B2 phases in the MSCR processed material agreed with the cross-rolling texture of the corresponding single phase materials, while the texture of the two phases in the TSCR(45°) processed materials appeared rather weak. Upon annealing at 800 °C, the UCR processed materials showed a novel heterogeneous microstructure, while the MSCR and TSCR(45°) processed materials revealed microduplex structure. The heterogeneous microstructure was replaced by the usual microduplex structure at higher annealing temperatures. The annealing texture of the L1 2 /FCC phase showed the presence of α-fiber (ND// < 011 > ) components while the B2 phase showed strong ND-fiber (ND// < 111 > ) components. The UCR processed material with novel heterogeneous microstructure showed much greater hardness as compared to the MSCR and TSCR(45°) processed materials. The present results indicate that strain path exerted significant influence in controlling microstructure, texture and hardness properties of EHEA.
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| 9. |
- Reddy, S. R., et al.
(författare)
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Microstructure and texture of a severely warm-rolled and annealed AlCoCrFeNi2.1 eutectic high entropy alloy
- 2019
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1270:1
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Konferensbidrag (refereegranskat)abstract
- The effect of warm-rolling and subsequent annealing on the evolution of microstructure and texture was systematically investigated in a lamellar (L12+B2) AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA). The EHEA was warm-rolled at 400°C up to 90% reduction in thickness and annealed at different temperatures. Ultra-fine lamellar microstructure evolved after heavy deformation with the characteristic textures of the two phases. Annealing treatments resulted in the gradual development of an ultrafine micro-duplex structure with increasing annealing temperature, even though the alloy showed significant resistance to grain growth. The annealing process was featured by concomitant microstructural and textural changes.
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| 10. |
- Reddy, S. R., et al.
(författare)
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Nanostructuring with Structural-Compositional Dual Heterogeneities Enhances Strength-Ductility Synergy in Eutectic High Entropy Alloy
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- A lamellar (L12 + B2) AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA) was severely deformed by a novel hybrid-rolling process. During hybrid-rolling, the deformation was carried out in two stages, namely cryo-rolling followed by warm-rolling at 600 °C. The strain (ε) imparted in each of these steps was identical ~1.2, resulting in a total strain of ε~2.4 (corresponding to 90% reduction in thickness). The novel processing strategy resulted in an extremely heterogeneous microstructure consisting of retained lamellar and transformed nanocrystalline regions. Each of these regions consisted of different phases having different crystal structures and chemical compositions. The novel structure-composition dual heterogeneous microstructure originated from the stored energy of the cryo-rolling which accelerated transformations during subsequent low temperature warm-rolling. The dual heterogeneous microstructure yielded an unprecedented combination of strength (~2000 MPa) and ductility (~8%). The present study for the first time demonstrated that dual structure-composition heterogeneities can be a novel microstructural design strategy for achieving outstanding strength-ductility combination in multiphase high entropy alloys.
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