The fundamental processes that govern plasticity and determine strength in crystalline materials at small length scales have been studied for over fifty years1,2,3. Recent studies of single-crystal metallic pillars with diameters of a few tens of micrometres or less have clearly demonstrated that the strengths of these pillars increase as their diameters decrease4,5,6,7, leading to attempts to augment existing ideas about pronounced size effects8,9 with new models and simulations10,11,12,13,14,15,16,17. Through in situ nanocompression experiments inside a transmission electron microscope we can directly observe the deformation of these pillar structures and correlate the measured stress values with discrete plastic events. Our experiments show that submicrometre nickel crystals microfabricated into pillar structures contain a high density of initial defects after processing but can be made dislocation free by applying purely mechanical stress. This phenomenon, termed ‘mechanical annealing’, leads to clear evidence of source-limited deformation where atypical hardening occurs through the progressive activation and exhaustion of dislocation sources.
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Research performed at the National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, was supported by the Scientific User Facilities Division of the Office of Basic Energy Sciences, US Department of Energy under Contract No. DE-AC02-05CH11231. This work was also supported by an SBIR Phase II grant DE-FG02-04ER83979 awarded to Hysitron, which does not constitute an endorsement by DOE of the views expressed in this article. Chris Gilde is thanked for his assistance with video editing.
Supplementary movie S1: material and sample preparation procedures (MOV 8145 kb)
Supplementary movie S2: experimental testing methods (MOV 6347 kb)
Supplementary movie S3: mechanical data analysis (MOV 7255 kb)
Supplementary movie S4: crystallographic analysis (MOV 9638 kb)
Supplementary movie legends, supplementary figures and references (PDF 232 kb)
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Shan, Z., Mishra, R., Syed Asif, S. et al. Mechanical annealing and source-limited deformation in submicrometre-diameter Ni crystals. Nature Mater 7, 115–119 (2008). https://doi.org/10.1038/nmat2085
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