|Initiation of fatigue cracks in ultrafine-grained copper|
LUKAS, P., KUNZ, L., NAVRÁTILOVÁ, L.
vol. 50 (2012), no. 6, pp. 407 - 413
Ultrafine-grained copper of commercial purity produced by ECAP technique was tested in fatigue in the range of lives from 5×103 to 2×1010 cycles. The fatigue strength of ultrafine-grained copper is by a factor of 2 higher than that of conventional-grained copper. The density of surface slip bands decreases with the decreasing stress amplitude and is extremely low in the very-high-cycle region. Fatigue microcracks were found to initiate in cyclic slip bands, which run across many grains in regions of near-by oriented grains. The very first fatigue damage in high-cycle and very-high-cycle regions consists in formation of cavities and elongated voids representing crack nuclei. No grain coarsening was observed either in bulk or in areas underneath the surface slip markings.
ultrafine-grained microstructure, fatigue, slip bands, microcrack initiation, grain coarsening
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