Spatio-temporal dynamics of jerky flow in high-entropy alloy at extremely low temperature

ABSTRACT

Despite a large body of literature, mechanisms contributing to low temperature jerky flow remain controversial. Here, we report a cross-over from a smooth at room and liquid nitrogen temperatures to serrated plastic flow at 4.2 K in high-entropy CrMnFeCoNi alloy. Several complimentary investigations have been carried out to get a coherent physical picture of low temperature jerky flow in these alloys. Microstructural characterisations at 77 K and 4.2 K show that the number of Lomer-Cottrell (L-C) locks at 4.2 K is much higher than that at 77 K, inducing stronger barriers for dislocation glide at 4.2 K. A stability analysis shows that the jerky flow results from an interaction between dislocation inertial motion with L-C locks. The instability results from a competition between inertial and viscous time scales characterised by a Deborah number. A detailed nonlinear time series analysis of experimental serrated stress signals shows that jerky flow is chaotic characterised by the existence of a finite correlation dimension and a positive Lyapunov exponent. Further, the minimum degree of freedom required for the chaotic dynamics turns out to be four, consistent with four collective modes degrees of freedom used in our model equations. These results highlight the crucial ingredients for jerky flow at liquid helium temperatures.

KEYWORDS:

• High-entropy alloy
• cryogenic temperature
• jerky flow
• linear perturbation analysis
• chaotic

Acknowledgments

This research was supported by the NSFC (Nos. 11790292 and 11572324), the National Key Research and Development Program of China (No. 2017YFB0702003), the Strategic Priority Research Program of the Chinese Academy of Sciences (Nos. XDB22040302 and XDB22040303), the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (No. QYZDJSSW-JSC011), the opening project of State Key Laboratory of Explosion Science and Technology (Beijing Institute of Technology, No. KFJJ18-14M), and the Science Challenge Project (No. TZ2016001). G. Ananthakrishna wishes to acknowledge Indian Nation Science Academy for Honorary Emeritus Scientist position.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Key Research Program of Frontier Sciences of the Chinese Academy of Sciences [QYZDJSSW-JSC011] and Science Challenge Project [TZ2016001] and National Key Research and Development Program of China [2017YFB0702003] and NSFC [11572324,11790292] and Strategic Priority Research Program of the Chinese Academy of Sciences [XDB22040302,XDB22040303] and opening project of State Key Laboratory of Explosion Science and Technology [KFJJ18-14M].