Monitoring eutectoid decomposition process of metastable phases in Al-Sm alloy via in-situ X-ray sca
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Meng, Fanqiang↗
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Unveiling the mechanism of phase and morphology selections during the devitrification of Al-Sm amorphous ribbon
The complex interplay between energetic and kinetic factors that governs the phase and morphology selections can originate at the earliest stage of crystallization in the amorphous parent phases. Because of the extreme difficulties in capturing the microscopic nucleation process, a detailed picture of how initial disordered structures affect the transformation pathway remains unclear. Here, we report the experimental observation of widely varying phase selection and grain size evolution during the devitrification of a homogeneous melt-spun glassy ribbon. Two different crystalline phases, θ-Al 5 Sm and ε-Al 60 Sm 11 , are found to form in the different regions of the same metallic glass ribbon during the devitrification. The grain size of ε-Al 60 Sm 11 phase shows a strong spatial heterogeneity. Coarse-grained ε-Al 60 Sm 11 phase coupled with the small volume fraction of θ-Al 5 Sm phase is preferably formed close to wheel side of the melt-spun ribbon. Combining experimental characterization and computational simulations, we show that phase selection and microstructure evolution can be traced back to different types and populations of atomic clusters that serve as precursors for the nucleation of different crystalline phases. Inhomogeneous cooling rates cause different structure orders across the glass sample during the quenching process. Our findings provide direct insight into the effect of structural order on the crystallization pathways during the devitrification of metallic glass. It also opens an avenue to study the detailed nucleation process at the atomic level using the metallic glass as a platform and suggests the opportunity of microstructure and property design via controlling the cooling process.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Enhanced Phase Stability of Sm 2 (Fe, Al) 17 C x
Aluminum doping can improve the phase stability of metastable compound Sm 2 Fe 17 C x with a high carbon content (x > 1.5). We investigated the preferential site substitution of Al, chemical bonding, and structural stability in Sm 2 (Fe,Al) 17 C 3 using first-principle calculations. Our results reveal a strong correlation between the preferential substitution of Fe by Al and the atomic site chemical environment, which affects the overall phase stability. Specifically, Al preferentially occupies the 9d site in Sm 2 (Fe,Al) 17 C 3 . At the same time, Al prefers the site 6c in its parent phase Sm 2 (Fe,Al) 17 . Partial replacement of Fe with Al leads to a more negative formation energy, indicating enhanced thermodynamic stability. Crystal Orbital Hamilton Population (COHP) and Crystal Orbital Bond Index (COBI) analysis suggest that insertion of carbon weakens the bonding strength of Sm-Fe (18f) and Sm-Fe (18h), resulting in metastability of Sm 2 Fe 17 C x . Doping Al strengthens Al-Fe, Al-Sm, Sm-Fe (18f, 18h) and Fe–C bonding in Sm 2 (Fe,Al) 17 C 3 , as revealed by calculated COHP and COBI. These effects contribute to improved phase stability in the Al-doped 2:17 interstitial compound.
chemical bonding↗
Materials Data on SmAl by Materials Project
SmAl is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Sm is bonded in a body-centered cubic geometry to eight equivalent Al atoms. All Sm–Al bond lengths are 3.18 Å. Al is bonded in a body-centered cubic geometry to eight equivalent Sm atoms.
36 MATERIALS SCIENCE↗
Materials Data on Sm3Al by Materials Project
Sm3Al is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Sm is bonded to eight equivalent Sm and four equivalent Al atoms to form distorted SmSm8Al4 cuboctahedra that share corners with twelve equivalent SmSm8Al4 cuboctahedra, edges with eight equivalent AlSm12 cuboctahedra, edges with sixteen equivalent SmSm8Al4 cuboctahedra, faces with four equivalent AlSm12 cuboctahedra, and faces with fourteen equivalent SmSm8Al4 cuboctahedra. All Sm–Sm bond lengths are 3.43 Å. All Sm–Al bond lengths are 3.43 Å. Al is bonded to twelve equivalent Sm atoms to form AlSm12 cuboctahedra that share corners with twelve equivalent AlSm12 cuboctahedra, edges with twenty-four equivalent SmSm8Al4 cuboctahedra, faces with six equivalent AlSm12 cuboctahedra, and faces with twelve equivalent SmSm8Al4 cuboctahedra.
36 MATERIALS SCIENCE↗
Materials Data on SmAl2 by Materials Project
Al2Sm is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Sm is bonded in a 12-coordinate geometry to four equivalent Sm and twelve equivalent Al atoms. All Sm–Sm bond lengths are 3.45 Å. All Sm–Al bond lengths are 3.31 Å. Al is bonded to six equivalent Sm and six equivalent Al atoms to form a mixture of edge, corner, and face-sharing AlSm6Al6 cuboctahedra. All Al–Al bond lengths are 2.82 Å.
36 MATERIALS SCIENCE↗
Materials Data on SmAl3 by Materials Project
Al3Sm crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Sm is bonded to twelve equivalent Al atoms to form a mixture of distorted face and corner-sharing SmAl12 cuboctahedra. There are six shorter (3.13 Å) and six longer (3.22 Å) Sm–Al bond lengths. Al is bonded in a 10-coordinate geometry to four equivalent Sm and six equivalent Al atoms. There are two shorter (2.76 Å) and four longer (2.81 Å) Al–Al bond lengths.
36 MATERIALS SCIENCE↗
Materials Data on SmAl by Materials Project
SmAl crystallizes in the orthorhombic Pbcm space group. The structure is three-dimensional. there are two inequivalent Sm sites. In the first Sm site, Sm is bonded in a 2-coordinate geometry to eight Al atoms. There are a spread of Sm–Al bond distances ranging from 3.13–3.43 Å. In the second Sm site, Sm is bonded in a 6-coordinate geometry to eight Al atoms. There are a spread of Sm–Al bond distances ranging from 3.13–3.57 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to eight Sm and two equivalent Al atoms. Both Al–Al bond lengths are 2.75 Å. In the second Al site, Al is bonded to eight Sm and four Al atoms to form a mixture of distorted corner, edge, and face-sharing AlSm8Al4 cuboctahedra. Both Al–Al bond lengths are 2.85 Å.
36 MATERIALS SCIENCE↗
Materials Data on Sm3Al by Materials Project
Sm3Al is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Sm is bonded in a 12-coordinate geometry to eight equivalent Sm and four equivalent Al atoms. There are a spread of Sm–Sm bond distances ranging from 3.30–3.72 Å. There are two shorter (3.29 Å) and two longer (3.51 Å) Sm–Al bond lengths. Al is bonded to twelve equivalent Sm atoms to form a mixture of corner and face-sharing AlSm12 cuboctahedra.
36 MATERIALS SCIENCE↗
Materials Data on SmAl4 by Materials Project
Al4Sm crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. Sm is bonded in a 1-coordinate geometry to thirteen Al atoms. There are a spread of Sm–Al bond distances ranging from 3.12–3.20 Å. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to three equivalent Sm and seven Al atoms. There are a spread of Al–Al bond distances ranging from 2.65–2.93 Å. In the second Al site, Al is bonded in a 6-coordinate geometry to four equivalent Sm and two equivalent Al atoms. In the third Al site, Al is bonded in a 3-coordinate geometry to three equivalent Sm and six equivalent Al atoms.
36 MATERIALS SCIENCE↗
Materials Data on Sm2Al by Materials Project
Sm2Al is Cotunnite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Sm sites. In the first Sm site, Sm is bonded in a 5-coordinate geometry to five equivalent Al atoms. There are a spread of Sm–Al bond distances ranging from 3.13–3.46 Å. In the second Sm site, Sm is bonded in a 3-coordinate geometry to five equivalent Al atoms. There are a spread of Sm–Al bond distances ranging from 3.21–3.65 Å. Al is bonded in a 10-coordinate geometry to ten Sm atoms.
36 MATERIALS SCIENCE↗