The statistical and dynamic analyses of the serrated-flow behavior in the nanoindentation of a high-entropy alloy, Al0.5CoCrCuFeNi, at various holding times and temperatures, are performed to reveal the hidden order associated with the seemingly-irregular intermittent flow. Two distinct types of dynamics are identified in the high-entropy alloy, which are based on the chaotic time-series, approximate entropy, fractal dimension, and Hurst exponent. The dynamic plastic behavior at both room temperature and 200 °C exhibits a positive Lyapunov exponent, suggesting that the underlying dynamics is chaotic. The fractal dimension of the indentation depth increases with the increase of temperature, and there is an inflection at the holding time of 10 s at the same temperature. A large fractal dimension suggests the concurrent nucleation of a large number of slip bands. In particular, for the indentation with the holding time of 10 s at room temperature, the slip process evolves as a self-similar random process with a weak negative correlation similar to a random walk.

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Published in Scientific Reports, v. 6, article no. 29798, p. 1-10.

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J.R. is very grateful for the support from the financial support from the NSFC (Grant No. 11271339), the Plan for Scientific Innovation Talent of Henan Province (164200510011) and the ZDGD13001Program. P.K.L. appreciates the financial support from the U.S. National Science Foundation (CMMI1100080). P.K.L. is very grateful for the support from the US Department of Energy (DOE), Office of Fossil Energy, National Energy Technology Laboratory (Grant No. DE-FE-0008855, No. DE-FE-0011194, and No. DE-FE0024054), and the U.S. Army Research Office (Grant No.W911NF-13-1-0438).