Hard nanocrystalline gold materials prepared via high-pressure phase transformation
Chenlong Xie, Wenxin Niu, Penghui Li, Yiyao Ge, Jiawei Liu, Zhanxi Fan, Xiaoxiao Liu, Ye Chen, Ming Zhou, Zihe Li, Mengdong Ma, Yonghai Yue, Jing Wang, Li Zhu, Kun Luo, Yang Zhang, Yingju Wu, Lin Wang, Bo Xu, Hua Zhang, Zhisheng Zhao, Yongjun Tian
As one of the important materials, nanocrystalline Au (n-Au) has gained numerous interests in recent decades owing to its unique properties and promising applications. However, most of the current n-Au thin films are supported on substrates, limiting the study on their mechanical properties and applications. Therefore, it is urgently desired to develop a new strategy to prepare n-Au materials with superior mechanical strength and hardness. Here, a hard n-Au material with an average grain size of ~ 40 nm is prepared by cold-forging of the unique Au nanoribbons (NRBs) with unconventional 4H phase under high pressure. Systematic characterizations reveal the phase transformation from 4H to face-centered cubic (fcc) phase during the cold compression. Impressively, the compressive yield strength and Vickers hardness (HV) of the prepared n-Au material reach ~ 140.2 MPa and ~ 1.0 GPa, which are 4.2 and 2.2 times of the microcrystalline Au foil, respectively. This work demonstrates that the combination of high-pressure cold-forging and the in-situ 4H-to-fcc phase transformation can effectively inhibit the grain growth in the obtained n-Au materials, leading to the formation of novel hard n-Au materials. Our strategy opens up a new avenue for the preparation of nanocrystalline metals with superior mechanical property.