| 1. |
- Hu, Q., et al.
(författare)
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Anomalous thermal expansion in the deep super-cooled liquid region of a ZrCuAlAg bulk metallic glass
- 2018
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Ingår i: Materials Research Letters. - : Informa UK Limited. - 2166-3831. ; 6:2, s. 121-129
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Tidskriftsartikel (refereegranskat)abstract
- Bulk metallic glasses (BMGs), like other glasses, soften in the super-cooled liquid region (SCLR). Here in this work, surprisingly, a large expansion is reported occurring in the deep SCLR of a Zr 47 Cu 37 Al 8 Ag 8 BMG. Nano-crystals (NCs) are found precipitated during the anomalous expansion of Zr 47 Cu 37 Al 8 Ag 8 , but also in the SCLR of Zr 43 Cu 41 Al 8 Ag 8 that exhibits a conventional softening. It is found that there is a steep composition and density change at the NCs/amorphous matrix transition region in the former alloy, and this transition region exerts a thermal stress of about 0.15 MPa to the surrounding super-cooled liquid (SCL) and drives the soft SCL to expand severely. (Figure presented) IMPACT STATEMENT An anomalous expansion, and particularly a large expansion instead of softening, is reported occurring in the deep SCLR of a Zr-based bulk metallic glass for the first time.
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| 2. |
- 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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| 3. |
- Seelam, Rajasekhar Reddy, et al.
(författare)
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Microstructural design by severe warm-rolling for tuning mechanical properties of AlCoCrFeNi2.1 eutectic high entropy alloy
- 2019
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Ingår i: Intermetallics. - : Elsevier BV. - 0966-9795. ; 114:nov.
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Tidskriftsartikel (refereegranskat)abstract
- The influence of severe warm-rolling and subsequent annealing on the microstructure and mechanical properties in an AlCoCrFeNi2.1 high entropy alloy consisting of a lamellar arrangement of ordered L1(2) and B2 phases was studied. For this purpose, the as-cast EHEA was severely warm-rolled up to 90% reduction in thickness at selected temperatures of 400 degrees C, 600 degrees C, and 750 degrees C. The severely warm-rolled EHEAs were further annealed at temperatures ranging from 800 degrees C to 1200 degrees C for 1 h. Warm-rolling resulted in a unique disordering behavior of the L1(2) depending on the temperature of warm-rolling. However, the B2 phase maintained the ordered structure irrespective of the warm-rolling temperature. The EHEA warm-rolled at 400 degrees C and 600 degrees C showed a predominantly lamellar microstructure, while the EHEA warm-rolled at 750 degrees C showed a novel heterogeneous microstructure featured by a mixture of lamellar and non-lamellar regions. Annealing of the 90% warm-rolled materials resulted in the formation of predominantly duplex microstructures consisting of disordered FCC and B2 phases. The EHEA warm-rolled at 400 degrees C and 600 degrees C showed high strength but rather limited ductility, which could be improved upon annealing. Remarkably, the EHEA warm-rolled at 750 degrees C showed the most outstanding properties featured by exceptional strength-ductility combination owing to the novel heterogeneous microstructure. Annealing of the heterogeneous EHEA resulted in the deterioration of the strength-ductility balance owing to the annihilation of the heterogeneous microstructure, being replaced by a microduplex structure.
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| 4. |
- Bhattacharjee, T., et al.
(författare)
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Simultaneous Strength-Ductility Enhancement of a Nano-Lamellar AlCoCrFeNi2.1 Eutectic High Entropy Alloy by Cryo-Rolling and Annealing
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Nano-lamellar (L1 2 + B2) AlCoCrFeNi 2.1 eutectic high entropy alloy (EHEA) was processed by cryo-rolling and annealing. The EHEA developed a novel hierarchical microstructure featured by fine lamellar regions consisting of FCC lamellae filled with ultrafine FCC grains (average size ∼200-250 nm) and B2 lamellae, and coarse non-lamellar regions consisting of ultrafine FCC (average size ∼200-250 nm), few coarse recrystallized FCC grains and rather coarse unrecrystallized B2 phase (∼2.5 μm). This complex and hierarchical microstructure originated from differences in strain-partitioning amongst the constituent phases, affecting the driving force for recrystallization. The hierarchical microstructure of the cryo-rolled and annealed material resulted in simultaneous enhancement in strength (Yield Strength/YS: 1437 ± 26 MPa, Ultimate Tensile Strength/UTS: 1562 ± 33 MPa) and ductility (elongation to failure/e f ∼ 14 ± 1%) as compared to the as-cast as well as cold-rolled and annealed materials. The present study for the first time demonstrated that cryo-deformation and annealing could be a novel microstructural design strategy for overcoming strength-ductility trade off in multiphase high entropy alloys.
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| 5. |
- Lu, Yiping, et al.
(författare)
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Promising properties and future trend of eutectic high entropy alloys
- 2020
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462. ; 187, s. 202-209
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Tidskriftsartikel (refereegranskat)abstract
- Eutectic high-entropy alloys (EHEAs), as a sub-group of high-entropy alloys (HEAs), are becoming a new research hotspot in the metallic materials community because of their excellent castability, fine and uniform microstructures even in the as-cast state, high strength, and good ductility. Some of the EHEAs have shown promising potentials for industrial applications. Here, the history, interesting solidification microstructure and mechanical properties, and the design strategy of EHEAs are reviewed, and their future prospects are outlined.
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| 6. |
- Prieto, E., et al.
(författare)
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Novel high entropy alloys as binder in cermets: From design to sintering
- 2021
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Ingår i: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 99
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Tidskriftsartikel (refereegranskat)abstract
- In recent years a new group of alloys has emerged breaking with the classical alloying concepts of physical metallurgy, high entropy alloys (HEA). Their main characteristic is that these alloys present 4 or 5 main elements increasing the entropy of the system and favouring the formation of a single phase. The disordered solid solution leads to develop an alloy with improved properties, in particular high thermal stability, hardness and strength. These properties make this group of alloys attractive as potential candidates for alternative binders in hard materials. In this work, two new compositions have been designed with the aim of obtaining a single BCC phase, reducing the cost and minimizing the presence of critical elements using elements that can present good potential properties for a cermet and with low toxicity and price such as Al, Cr, Mo, Ni, Fe and Ti. The design has been made based on the composition calculation applying the HEA phase formation empirical rules from literature in combination with thermodynamic simulations by Calphad method. The viability of the compositions has been studied through the processing of the compositions by casting and the study of wettability and solubility at high temperature on the hard phase of TiCN. Once the chosen compositions have been validated as competitive binders, cermets have been consolidated by spark plasma sintering (SPS) and the influence of the compositions on the mechanical properties of the compound materials has been studied.
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| 7. |
- Prieto, E., et al.
(författare)
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Processing of a new high entropy alloy: AlCrFeMoNiTi
- 2018
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Ingår i: Powder Metallurgy. - : Informa UK Limited. - 0032-5899 .- 1743-2901. ; 61:3, s. 258-265
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Tidskriftsartikel (refereegranskat)abstract
- This work, a new composition of high-entropy alloys (HEAs) was designed. The composition was carefully tailored with the aim to obtain a solid solution with a BCC crystalline structure to be an alternative binder in cermets. Thus, the composition of the HEA has been designed taking into account various criteria which has fulfilled a metallic binder of a Ti(C,N) cermet:(1) high hardness and oxidation resistance and (2) good wetting behaviour with Ti(C,N) particles because the processing of cermets is by LPS. The design of the alloy has been performed using theoretical calculations of physicochemical properties of the elements involved and the calculation of phase diagram by Thermocalc. The designed alloy has been processed by casting and powder metallurgy (PM) to study the influence of the processing route on the phases formed and on the resulting properties. The powders were produced by gas atomisation and then consolidated by hot pressing. Special theme block on high entropy alloys, guest edited by Paula Alvaredo Olmos, Universidad Carlos III de Madrid, Spain, and Sheng Guo, Chalmers University, Gothenburg, Sweden.
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| 8. |
- 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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| 9. |
- Ananthanarayanan, Durga, et al.
(författare)
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Grain refinement in additively manufactured ferritic stainless steel by in situ inoculation using pre-alloyed powder
- 2021
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 194
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Tidskriftsartikel (refereegranskat)abstract
- For ferritic stainless steels, TiN has effectively been used as an inoculant to produce equiaxed grain structures in casting and welding. However, it is not established whether TiN would be an effective inoculant in additive manufacturing. In this study, the effectiveness of TiN as an inoculant in a ferritic stainless steel processed by laser powder-bed fusion is studied. An alloy without Ti is fabricated and compared to an alloy designed to form a high amount of TiN early during solidification. The work shows that the presence of TiN provides general grain refinement and that TiN-covered oxide particles are effective in enabling columnar-to-equiaxed transition in certain regions of the meltpool. The applied approach of pre-alloying powders with inoculant-forming elements offers a straightforward route to achieving fine, equiaxed grain structures in additively manufactured metallic materials. It also shows how oxygen present during the process can be utilized to nucleate effective inoculating phases.
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| 10. |
- Balpande, A. R., et al.
(författare)
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Excellent specific strength-ductility synergy in novel complex concentrated alloy after suction casting
- 2024
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Ingår i: Materials and Design. - 1873-4197 .- 0264-1275. ; 242
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Tidskriftsartikel (refereegranskat)abstract
- Lightweight alloys are known to improve the fuel efficiency of the structural components due to high strength-to-weight ratio, however, they lack formability at room temperature. This major limitation of poor formability is most of the time overcome by post-fabrication processing and treatments thereby increasing their cost exponentially. We present a novel Ti50V16Zr16Nb10Al5Mo3 (all in at. %) complex concentrated alloy (Ti-CCA) designed based on the combination of valence electron concentration theory and the high entropy approach. The optimal selection of constituent elements has led to a density of 5.63 gm/cc for Ti-CCA after suction casting (SC). SC Ti-CCA displayed exceptional room temperature strength (UTS ∼ 1.25 GPa) and ductility (ε ∼ 35 %) with a yield strength (YS) of ∼ 1.1 GPa (Specific YS = 191 MPa/gm/cc) without any post-processing treatments. The exceptional YS in Ti-CCA is attributed to hetero grain size microstructure, whereas enormous strength-ductility synergy is due to the concurrent occurrence of slip and deformation band formation in the early stages of deformation followed by prolonged necking event due to delayed void nucleation and growth. The proposed philosophy of Ti-CCA design overcomes the conventional notion of strength-ductility trade-off in such alloy systems by retaining their inherent characteristics.
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