期刊
ACTA MATERIALIA
卷 59, 期 5, 页码 1974-1985出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2010.11.063
关键词
Nickel; Severe plastic deformation (SPD); Grain boundary diffusion; Non-equilibrium defects
资金
- Deutsche Forschungsgemeinschaft
Grain boundary self-diffusion in Ni severely deformed by equal-channel angular pressing has been investigated. The radiotracer technique was applied by using the Ni-63 isotope and high-precision mechanical grinding. Ultra-fast diffusion rates, which exceed those along general high-angle grain boundaries in annealed coarse-grained Ni by orders of magnitude, were observed. Such high diffusivities were attributed to a non-equilibrium state of grain boundaries produced by severe plastic deformation. A significant downward deviation from an Arrhenius plot for ultra-fast diffusivity for temperatures above 400 K was found. This was interpreted in terms of a partial relaxation of the non-equilibrium grain boundary structure. Additionally, the formation of ultra-fast diffusion channels, presumably in the form of percolating porosity as a result of stepwise annealing of the material, was observed. This phenomenon is discussed in terms of the free volume redistribution in grain boundaries. It is proposed to quantify the excess energy of interfaces in terms of the observed enhancement of diffusivity. This approach allows the excess energy of non-equilibrium grain boundaries to be determined from diffusion measurements. (c) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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