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Title: Hall–Petch strengthening limit through partially active segregation in nanocrystalline Ag-Cu alloys

Journal Article · · Acta Materialia
 [1];  [2]
  1. University of Vermont, Burlington, VT (United States); OSTI
  2. University of Vermont, Burlington, VT (United States)

The breakdown from grain-size strengthening to softening mechanisms is generally well understood for high-purity nanocrystalline materials when the mean grain size decreases to the nanometer range. In nanocrystalline alloys, however, the stabilization of nanosized grains by grain-boundary solute segregation complicates the above mechanisms. Moreover, current segregation models have little predictive power for determining the optimal solute content that maximizes Hall-Petch strengthening effects. In this article, using large-scale hybrid Monte-Carlo/molecular dynamic simulations, we present a systematic study of the Hall–Petch breakdown in Cu-segregated Ag alloys with grain sizes ranging from 8 nm to 59 nm, where three concentration-dependent regimes of plasticity are described: (1) Classical segregation strengthening behavior at low solute contents, (2) shear band-induced softening at high solute contents, and (3) a previously unknown, but extended plateau of maximum strengths for intermediate solute contents from 4 to 15 at.%, which we term as nanocrystalline Sterling silver. We find that flow strengths in nanocrystalline Sterling alloys naturally exhibit a zero-slope limit at the smallest grain sizes that is well below the ideal Hall–Petch strengthening trend. This phenomenon results from partially active grain-boundary segregation that acts to influence interfacial plasticity in some, but not all, grain boundary regions. Our findings amplify the atomic nature of solute segregation and interaction at grain boundaries and its complex roles on grain boundary-mediated plasticity mechanisms in nanocrystalline alloys.

Research Organization:
University of Vermont, Burlington, VT (United States); University of California, Oakland, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC); National Science Foundation (NSF)
Grant/Contract Number:
SC0016270; SC0020054; AC02-05CH11231
OSTI ID:
1976780
Journal Information:
Acta Materialia, Journal Name: Acta Materialia Journal Issue: C Vol. 225; ISSN 1359-6454
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

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