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8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Experimental characterization and atomistic simulation of grain boundary segregation in Mg-Y alloys

As a rare earth solute element in Mg alloys, Y has the beneficial effects of increasing both the strength and the ductility as well as weakening the crystallographic texture. To achieve a more fundamental understanding on how Y addition affects the microstructural evolution and mechanical properties, the Y segregation behavior at grain boundaries was investigated in Mg-1wt.%Y and Mg-7wt.%Y alloys at different conditions. The segregation intensity and its dependence on the grain boundary misorientation angle were experimentally characterized and computationally predicted. Strong segregation at grain boundaries was observed in both low and high Y-containing alloys. Y segregation was found to remain in alloy Mg-7Y after high-temperature annealing heat treatment at 540 °C. No direct correlation between the Y segregation intensity and the grain boundary misorientation angle could be established based on either the experimental characterization or the atomistic simulation with a spectral model. We thus conclude that grain boundary segregation of Y is independent of grain boundary misorientation angle.

Grain boundary↗
DOE OSTI2020

Revealing the Subsurface Basal $\langle$a$\rangle$ Dislocation Activity in Magnesium Through Lattice Rotation Analysis

A method was proposed in this study to reveal the subsurface basal dislocation activity in Mg-Y alloy and determine the corresponding Burgers vector. This is achieved by correlating the slip directions of dislocations to the lattice rotation represented by the {0001} pole figure. The identified basal slip system by this approach was verified by micro-Laue diffraction. This method can be applied as a complementary method to the conventional slip trace analysis to study the dislocation behavior of Mg alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Activation of dislocations in Mg with solute Y

Mg-Y cast alloy shows excellent ductility (elongation to failure > 15%) compared with pure Mg and commercial Mg cast alloys. By monitoring the microstructure evolution during an in situ tensile test of a Mg-2.5 wt%Y alloy, we identify the activation of prismatic slip, which is rare in Mg. Synchrotron X-ray micro-beam Laue diffraction (μ-Laue) and transmission electron microscopy revealed the morphology of prismatic slip bands and individual dislocations. Density functional theory and molecular dynamics calculations indicate that solute Y can significantly reduce the stacking fault energy (SFE) along direction on prismatic plane in Mg lattice and thus facilitate the nucleation of dislocations during deformation. The presence of free dislocations in the Mg lattice can also lead to nucleation of {10–12} twins even under unfavorable geometric conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Formation of I 1 stacking fault by deformation defect evolution from grain boundaries in Mg

I 1 stacking faults (SFs) in Mg alloys are regarded as the nucleation sites of $\langle \text{c+a} \rangle$ dislocations that are critical for these alloys to achieve high ductility. Previously it was proposed that the formation of I 1 SFs requires the accumulations of a large number of vacancies, which are difficult to achieve at low temperatures. In this study, molecular dynamics (MD) and molecular statics (MS) simulations based on empirical interatomic potentials were applied to investigate the deformation defect evolutions from the symmetric tilt grain boundaries (GBs) in Mg and Mg-Y alloys under external loading along $\langle c \rangle$-axis. The results show the planar faults (PFs) on Pyramidal I planes first appear due to the nucleation and glide of $\langle {\frac {1}{2}}c + p\rangle$ partial dislocations from GBs, where $\langle p\rangle$ = ${\frac {1}{3}} \langle10\bar{1}0\rangle$. These partial dislocations with pyramidal PFs interact with other defects, including pyramidal PFs themselves, GBs, and $\langle p\rangle$ partial dislocations, generating a large amount of I 1 SFs. Detailed analyses show the nucleation and growth of I 1 SFs are achieved by atomic shuffle events and deformation defect reactions without the requirements of vacancy diffusion. Our simulations also suggest the Y clusters at GBs can reduce the critical stress for the formation of pyramidal PFs and I 1 SFs, which provide a possible reason for the experimental observations that Y promotes the $\langle{\text{c+a}}\rangle$ dislocation activities.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on YMg2 by Materials Project

Mg2Y is Hexagonal Laves structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded to six equivalent Mg and six equivalent Y atoms to form a mixture of corner, edge, and face-sharing MgY6Mg6 cuboctahedra. All Mg–Mg bond lengths are 3.05 Å. All Mg–Y bond lengths are 3.56 Å. In the second Mg site, Mg is bonded to six Mg and six equivalent Y atoms to form a mixture of corner, edge, and face-sharing MgY6Mg6 cuboctahedra. There are two shorter (2.95 Å) and two longer (3.11 Å) Mg–Mg bond lengths. There are two shorter (3.53 Å) and four longer (3.54 Å) Mg–Y bond lengths. Y is bonded in a 12-coordinate geometry to twelve Mg and four equivalent Y atoms. There are one shorter (3.65 Å) and three longer (3.72 Å) Y–Y bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on YMg by Materials Project

MgY is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Mg is bonded in a body-centered cubic geometry to eight equivalent Y atoms. All Mg–Y bond lengths are 3.29 Å. Y is bonded in a body-centered cubic geometry to eight equivalent Mg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y2Mg by Materials Project

MgY2 crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded to four Mg and eight Y atoms to form distorted MgY8Mg4 cuboctahedra that share corners with six equivalent YY8Mg4 cuboctahedra, corners with twelve MgY8Mg4 cuboctahedra, edges with three equivalent MgY8Mg4 cuboctahedra, edges with fifteen YY8Mg4 cuboctahedra, faces with six MgY8Mg4 cuboctahedra, and faces with fourteen YY10Mg2 cuboctahedra. There are two shorter (3.48 Å) and two longer (3.51 Å) Mg–Mg bond lengths. There are a spread of Mg–Y bond distances ranging from 3.43–3.47 Å. In the second Mg site, Mg is bonded to four Mg and eight Y atoms to form distorted MgY8Mg4 cuboctahedra that share corners with six equivalent YY8Mg4 cuboctahedra, corners with twelve MgY8Mg4 cuboctahedra, edges with three equivalent MgY8Mg4 cuboctahedra, edges with fifteen YY10Mg2 cuboctahedra, faces with six MgY8Mg4 cuboctahedra, and faces with fourteen YY10Mg2 cuboctahedra. Both Mg–Mg bond lengths are 3.51 Å. There are a spread of Mg–Y bond distances ranging from 3.46–3.59 Å. There are four inequivalent Y sites. In the first Y site, Y is bonded to two equivalent Mg and ten Y atoms to form YY10Mg2 cuboctahedra that share corners with eighteen YY10Mg2 cuboctahedra, edges with eight equivalent MgY8Mg4 cuboctahedra, edges with ten YY6Mg6 cuboctahedra, faces with eight MgY8Mg4 cuboctahedra, and faces with twelve YY10Mg2 cuboctahedra. There are a spread of Y–Y bond distances ranging from 3.43–3.61 Å. In the second Y site, Y is bonded to four equivalent Mg and eight Y atoms to form YY8Mg4 cuboctahedra that share corners with eighteen YY10Mg2 cuboctahedra, edges with six YY6Mg6 cuboctahedra, edges with twelve MgY8Mg4 cuboctahedra, faces with six MgY8Mg4 cuboctahedra, and faces with fourteen YY10Mg2 cuboctahedra. There are four shorter (3.51 Å) and two longer (3.52 Å) Y–Y bond lengths. In the third Y site, Y is bonded to six Mg and six Y atoms to form YY6Mg6 cuboctahedra that share corners with eighteen YY10Mg2 cuboctahedra, edges with four equivalent MgY8Mg4 cuboctahedra, edges with fourteen YY10Mg2 cuboctahedra, faces with ten MgY8Mg4 cuboctahedra, and faces with ten YY10Mg2 cuboctahedra. Both Y–Y bond lengths are 3.51 Å. In the fourth Y site, Y is bonded to four Mg and eight Y atoms to form YY8Mg4 cuboctahedra that share corners with six equivalent YY8Mg4 cuboctahedra, corners with twelve MgY8Mg4 cuboctahedra, edges with six MgY8Mg4 cuboctahedra, edges with twelve YY10Mg2 cuboctahedra, faces with four MgY8Mg4 cuboctahedra, and faces with sixteen YY10Mg2 cuboctahedra. Both Y–Y bond lengths are 3.51 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y3Mg by Materials Project

MgY3 crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Mg is bonded to six equivalent Y atoms to form distorted MgY6 cuboctahedra that share corners with twenty-four YY12 cuboctahedra, edges with six equivalent MgY6 cuboctahedra, edges with twelve equivalent YY9Mg3 cuboctahedra, and faces with two equivalent YY12 cuboctahedra. All Mg–Y bond lengths are 3.51 Å. There are two inequivalent Y sites. In the first Y site, Y is bonded to twelve Y atoms to form YY12 cuboctahedra that share corners with six equivalent YY12 cuboctahedra, corners with twelve equivalent MgY6 cuboctahedra, edges with eighteen YY12 cuboctahedra, faces with two equivalent MgY6 cuboctahedra, and faces with eighteen YY12 cuboctahedra. There are six shorter (3.53 Å) and six longer (3.54 Å) Y–Y bond lengths. In the second Y site, Y is bonded to three equivalent Mg and nine Y atoms to form YY9Mg3 cuboctahedra that share corners with six equivalent MgY6 cuboctahedra, corners with eighteen equivalent YY9Mg3 cuboctahedra, edges with six equivalent MgY6 cuboctahedra, edges with twelve YY12 cuboctahedra, and faces with fourteen YY12 cuboctahedra. All Y–Y bond lengths are 3.54 Å.

36 MATERIALS SCIENCE↗