- PAR ID:
- 10293177
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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To obtain thorough understandings of precipitation process in heat-treatable Mg-Ca-Zn alloy, we revisited the precipitation process of a Mg-0.3Ca-0.6 Zn (at.%) dilute alloy during isothermal aging at 200 °C using an aberration-corrected scanning transmission electron microscope, atom probe tomography, and first-principles calculations. The monolayer G.P. zones form on the (0002)α plane in the peak-aged condition and transform into tri-atomic layer η'' and η' plates with a thickness of a single unit-cell height. The η' plates, then, form in pairs and stacks with energetically favorable 4–5 atomic layers of pure magnesium between the plates. While such a transformation path is similar to that seen in Mg-RE-Zn alloys (RE: rare-earth elements), the unique structure of coarse η1 plates that precipitate after the η' plates leads to a different precipitate microstructure evolution from the Mg-RE-Zn system. The η1 phase (Mg7Ca2Zn3) is unevenly distributed in the matrix after 100 h of aging and finally evolves to the equilibrium η phase (Mg10Ca3Zn6) phase with a hexagonal structure. First-principles calculations of energetics were performed to further identify the crystal structure and stability of the precipitates, supporting the following new precipitation sequence: S.S.S.S. → G.P. zones → η'' → η' → η' pairs and stacks / η1 → ηmore » « less
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Abstract Multicomponent high‐entropy alloys (HEAs) can be tuned to a simple phase with some unique alloy characteristics. HEAs with body‐centered‐cubic (BCC) or hexagonal‐close‐packed (HCP) structures are proven to possess high strength and hardness but low ductility. The faced‐centered‐cubic (FCC) HEAs present considerable ductility, excellent corrosion and radiation resistance. However, their strengths are relatively low. Therefore, the strategy of strengthening the ductile FCC matrix phase is usually adopted to design HEAs with excellent performance. Among various strengthening methods, precipitation strengthening plays a dazzling role since the characteristics of multiple principal elements and slow diffusion effect of elements in HEAs provide a chance to form fine and stable nanoscale precipitates, pushing the strengths of the alloys to new high levels. This paper summarizes and review the recent progress in nanoprecipitate‐strengthened HEAs and their strengthening mechanisms. The alloy‐design strategies and control of the nanoscale precipitates in HEAs are highlighted. The future works on the related aspects are outlined.
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Recent advancements in the severe plastic deformation process called accumulative roll bonding (ARB) can help to address the long‐standing need for manufacturing lightweight, high‐strength Mg sheet materials. However, the fabrication of Mg alloy‐based laminates via ARB remains a challenge due to the intrinsically poor formability of Mg. Herein, it is shown that Mg‐based composite laminates with refined layers can be fabricated via several room‐temperature ARB cycles with appropriate intermediate annealing and alloy selection. The final laminates made here consist of equal volume fractions of a dilute Mg–Zn–Mn–Ca alloy phase and a pure Nb phase with fine 150 μm layer thicknesses. Deformation texture evolution in both phases within the composite is analyzed via neutron diffraction measurements taken at different stages in the process. The analysis suggests that the annealing step recrystallizes the Mg‐alloy phase. It is also shown that for both phases, the stabilized deformation textures within the composite correspond to the classic stable textures of the individual constituents. Polycrystal texture modeling implies that {10–12} <‐1011> extension twinning developed in the Mg alloy during rolling.
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Maier, P. ; Barela, S. ; Miller, V.M. ; Neelameggham, N.R. (Ed.)Mg-Sn and Mg-Zn alloys exhibit a strong age-hardening effect and have become promising bases for high-strength and low-cost Mg alloys. However, the atomic structures and phase stabilities of various precipitates and intermetallic compounds during the heat treatment in these systems remain unclear. Here we use a combined approach of first-principles calculations and cluster expansion (CE) to investigate the atomic structures and thermodynamic stabilities of the experimentally reported precipitates as well as orderings on the FCC and HCP lattices in Mg-Sn and Mg-Zn alloys. From the low energy structures searched by CE, potential Guinier–Preston (GP) zones are identified from preferred HCP orderings. The slow convergence for CE of HCP Mg-Zn, compared with that of Mg-Sn system, is attributed to the long-ranged interactions resulting from the larger lattice mismatch. This study could help design better age-hardened Mg alloys.more » « less
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