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Title: Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals

When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. We demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. Furthermore, this “cyclic healing” of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising from increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. Our results point to a versatile pathway for controlledmore » mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [5] ;  [1] ;  [3] ;  [6] ;  [1] ;  [7]
  1. Xi'an Jiaotong Univ. (China). Center for Advancing Materials Performance from the Nanoscale and Hysitron Aplied Research Center in China
  2. Johns Hopkins Univ., Baltimore, MD (United States). Dept. of Materials Science and Engineering
  3. Tsinghua Univ., Beijing (China). School of Aerospace
  4. Xi'an Jiaotong Univ. (China). Center for Advancing Materials Performance from the Nanoscale and Hysitron Aplied Research Center in China; Johns Hopkins Univ., Baltimore, MD (United States). Dept. of Materials Science and Engineering
  5. Xi'an Jiaotong Univ. (China). Center for Advancing Materials Performance from the Nanoscale and Hysitron Aplied Research Center in China; Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Nuclear Science and Engineering and Dept. of Materials Science and Engineering
  6. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Materials Science and Engineering
  7. Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Materials Science and Engineering
Publication Date:
Grant/Contract Number:
FG02-03ER46056; DMR-1120901; DMR-1410636; FG02-09ER46056
Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 112; Journal Issue: 44; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Johns Hopkins Univ., Baltimore, MD (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; fatigue; dislocation motion; pristine materials; yield strength; cyclic mechanical healing
OSTI Identifier:
1235115
Alternate Identifier(s):
OSTI ID: 1356195