| 1. |
- Liu, Xiongjun, et al.
(author)
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Metastable high entropy alloys
- 2022
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 120:12
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Journal article (other academic/artistic)abstract
- High entropy alloys (HEAs) are a new family of alloys usually made up of five or more metallic elements in approximately equal proportions to maximize the configurational entropy, also termed as the multi-principal-element alloys or complex concentrated alloys. The unique features of structure and property render HEAs exciting potential for structural and functional applications, particularly for those cases under extreme conditions, which spark intense research activities in this area, ranging from the fundamental issues, such as phase formation and stability, to the engineering-related problems, such as fabrication, processing, and usage performance. HEAs are the focus of intense research in the fields of materials science and condensed matter physics. Compositional metastability in HEAs leads to decomposition of the complex concentrated solid solution via thermally activated processes, which results in the development of local chemical ordering, the precipitation of second phases, and the formation of a complex multi-phase microstructure.
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| 2. |
- Sousa, Ronaldo, et al.
(author)
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The role of anthropogenic habitats in freshwater mussel conservation
- 2021
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In: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 27, s. 2298-2314
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Journal article (peer-reviewed)abstract
- Anthropogenic freshwater habitats may provide undervalued prospects for long-term conservation as part of species conservation planning. This fundamental, but overlooked, issue requires attention considering the pace that humans have been altering natural freshwater ecosystems and the accelerated levels of biodiversity decline in recent decades. We compiled 709 records of freshwater mussels (Bivalvia, Unionida) inhabiting a broad variety of anthropogenic habitat types (from small ponds to large reservoirs and canals) and reviewed their importance as refuges for this faunal group. Most records came from Europe and North America, with a clear dominance of canals and reservoirs. The dataset covered 228 species, including 34 threatened species on the IUCN Red List. We discuss the conservation importance and provide guidance on how these anthropogenic habitats could be managed to provide optimal conservation value to freshwater mussels. This review also shows that some of these habitats may function as ecological traps owing to conflicting management practices or because they act as a sink for some populations. Therefore, anthropogenic habitats should not be seen as a panacea to resolve conservation problems. More information is necessary to better understand the trade-offs between human use and the conservation of freshwater mussels (and other biota) within anthropogenic habitats, given the low number of quantitative studies and the strong biogeographic knowledge bias that persists.
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| 3. |
- Zhang, Fan, et al.
(author)
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Effects of Ni and Al on precipitation behavior and mechanical properties of precipitation-hardened CoCrFeNi high-entropy alloys
- 2022
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In: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 839, s. 142879-
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Journal article (peer-reviewed)abstract
- Morphology and volume fraction of precipitates are crucial for mechanical properties of precipitation-hardened high-entropy alloys (HEAs). In this study, we systematically examined the effects of Ni and Al on precipitation behavior and mechanical properties of (FeCoCr)(98-x-y) NixTi2Aly (x = 25, 30, 35; y = 4, 6, 8) HEAs. It was found that an increase of Ni and Al can effectively promote the formation of coherent gamma' precipitates, but an incoherent Heusler phase (Ni2AlTi) also inevitably appeared once the Al content exceeds 6%. Both gamma' and the Heusler phases could strengthen the materials, however, since they shared the same constituent elements, the two phases produced synergistic effects. For instance, excessive Heusler phase not only restrains the formation of gamma', but also reduces the ductility. Our analysis indicated that the ratio of Ni over Al played a pivotal role on the Heusler phase formation, and the Heusler phase could be completely eliminated when the Ni/Al ratio is larger than 5. In such a case, the maximum volume fraction of gamma' in (FeCoCr)(57)Ni35Ti2Al6 reaches 33% and the alloy exhibits tensile strength over 1 GPa with a decent ductility of about 35%. Our findings provide a useful guideline for the optimal design of precipitation-hardened HEAs, it also shed light on understanding precipitation behavior in highly concentrated alloys.
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| 4. |
- Zhou, Jie, et al.
(author)
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Simultaneously enhancing the strength and plasticity of Ti-based bulk metallic glass composites via microalloying with Ta
- 2019
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In: Materials Research Letters. - : TAYLOR & FRANCIS INC. - 2166-3831. ; 8:1, s. 23-30
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Journal article (peer-reviewed)abstract
- Characteristics of deformation-induced transformation under loading dictate the mechanical performance of TRIP (transformation-induced plasticity)-reinforced bulk metallic glass composites (BMGCs), which have shown great potential as engineering materials. Here, we report that the addition of 0.3 at.% Ta in the Ti45Cu41Ni9Zr5 alloy could induce the formation of uniform glassy composite structure with B2-(Ti,Zr)(Ni,Cu) precipitates. More interestingly, nanosized A2-(Ti,Zr)(Ni,Cu) particles also formed inside B2 grains which effectively impede rapid propagation of martensite plates and lead to the formation of multi-oriented martensites, eventually homogenizing the involved plastic flow during deformation-induced transformation. Consequently, high fracture strength (similar to 3000 MPa), large plasticity (similar to 25%) and pronounced work-hardening ability were achieved. [GRAPHICS] IMPACT STATEMENT Microalloying of Ta not only homogenizes the B2 distribution, but also facilitates formation of multi-orientated martensites during deformation, resulting in simultaneously enhanced strength and plasticity of a Be-free Ti-based BMGC.
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