**Jialin Liu 1, Xiaofeng Fan 1,\*, Yunfeng Shi 2, David J. Singh <sup>3</sup> and Weitao Zheng 1,4**


Received: 13 August 2020; Accepted: 17 September 2020; Published: 24 September 2020

**Abstract:** The strength of nanocrystalline (NC) metal has been found to be sensitive to strain rate. Here, by molecular dynamics simulation, we explore the strain rate effects on apparent Young's modulus, flow stress and grain growth of NC gold with small size. The simulation results indicate that the apparent Young's modulus of NC gold decreases with the decrease of strain rate, especially for strain rates above 1 ns<sup>−</sup>1. The rearrangement of atoms near grain boundaries is a response to the decrease of apparent Young's modulus. Indeed, the flow stress is also sensitive to the strain rate and decreases following the strain rate's decrease. This can be found from the change of strain rate sensitivity and activation volume with the strain rate. Temperature has little effect on the activation volume of NC gold with small grain size, but has an obvious effect on that of relatively large grain size (such as 18 nm) under low strain rate (0.01 ns<sup>−</sup>1). Finally, grain growth in the deformation process is found to be sensitive to strain rate and the critical size for grain growth increases following the decrease of strain rate.

**Keywords:** strain rate; molecular dynamics simulation; strain rate sensitivity; activation volume; grain growth
