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Title: Spatially-correlated Site Occupancy in the Nonstoichiometric Meta-stable ε -Al 60Sm 11 Phase during Devitrification of Al-10.2 at.% Sm Glasses

A metastable ε-Al 60Sm 11 phase appears during the initial devitrification of as-quenched Al-10.2 at.% Sm glasses. The ε phase is nonstoichiometric in nature since Al occupation is observed on the 16 f Sm lattice sites. Scanning transmission electron microscopic images reveal profound spatial correlation of Sm content on these sites, which cannot be explained by the “average crystal” description from Rietveld analysis of diffraction data. Thermodynamically favorable configurations, established by Monte Carlo (MC) simulations based on a cluster-expansion model, also give qualitatively different correlation functions from experimental observations. On the other hand, molecular dynamics simulations of the growth of ε-Al 60Sm 11 in undercooled liquid show that when the diffusion range of Sm is limited to ~4 Å, the correlation function of the as-grown crystal structure agrees well with that of the scanning transmission electronic microscopy (STEM) images. Furthermore, our results show that kinetic effects, especially the limited diffusivity of Sm atoms plays the fundamental role in determining the nonstoichiometric site occupancies of the ε-Al 60Sm 11 phase during the crystallization process.
Authors:
ORCiD logo [1] ;  [2] ; ORCiD logo [2] ;  [2] ; ORCiD logo [2] ;  [2] ;  [2] ;  [2] ;  [2] ;  [1]
  1. Iowa State Univ., Ames, IA (United States); Ames Lab., Ames, IA (United States)
  2. Ames Lab., Ames, IA (United States)
Publication Date:
Report Number(s):
IS-J-9660
Journal ID: ISSN 1359-6454; PII: S1359645418303847
Grant/Contract Number:
AC02-07CH11358
Type:
Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Name: Acta Materialia; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Research Org:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; nonstoichiometric compound; cluster expansion; Monte Carlo simulation; molecular dynamics simulation
OSTI Identifier:
1441002