Substantial toughening by thick nanoscale amorphous intergranular films in nanocrystalline materials

Author:

Huang Yijing12ORCID,Qin Feng1ORCID,Dai Kaiqing1,Chen Shaohua3ORCID,Li Jiejie1ORCID,Li Jianjun12ORCID

Affiliation:

1. College of Mechanical and Electrical Engineering, Central South University 1 , Changsha, Hunan 410083, People’s Republic of China

2. State Key Laboratory of Precision Manufacturing for Extreme Service Performance, Central South University 2 , Changsha, Hunan 410083, People’s Republic of China

3. Institute of Advanced Structure Technology, Beijing Institute of Technology 3 , Beijing 100081, People’s Republic of China

Abstract

Amorphous intergranular films (AIFs) have been proven in experiments to improve the damage tolerance of nanocrystalline materials. However, a quantitative study is still lacking. Molecular dynamics simulations were performed here to investigate the effect of CuNb AIFs on the fracture toughness of nanocrystalline Nb. In order to clarify the role of AIFs, a bicrystal Nb model with one straight symmetrical tilt grain boundary and a mode-I crack in one of the grains was constructed, in which the AIF effect was introduced by replacing the normal grain boundary with a CuNb AIF. Then, AIF thickness-dependent tensile deformation of the bicrystal Nb samples was simulated. The work-of-fracture, which is defined as the released strain energy due to the newly generated unit area in the crack during stretching, was employed to quantify the fracture toughness of the bicrystal systems. The results show that the fracture toughness of the AIF sample can be tripled due to the blunted crack tip and the relieved stress concentration at the crack tip as compared to the AIF-free one that exhibits a brittle crack propagation behavior. Also, the thicker the AIFs, the more pronounced this reinforcing effect. More importantly, it is found that there exists a critical AIF width of 1.7 nm, below which the crack will eventually break through the AIF, and above which the crack failed to do this. It is revealed that the enhanced fracture toughness originated from the transformation of brittle crack propagation to abundant dislocation emission from AIFs.

Funder

National Natural Science Foundation of China

Department of Science and Technology of Hunan Province

Publisher

AIP Publishing

Subject

General Physics and Astronomy

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