Quasi-plastic deformation mechanisms and inverse Hall–Petch relationship in nanocrystalline boron carbide under compression

Abstract

Grain boundary (GB) plays a significant role in the deformation behaviors of nanocrystalline ceramics. Here, we investigate the compression behaviors of nanocrystalline boron carbide (n-B4C) with varying grain sizes, using molecular dynamics simulations with a machine-learning force field. The results reveal quasi-plastic deformation mechanisms in n-B4C: GB sliding, intergranular amorphization, and intragranular amorphization. GB sliding arises from the presence of the soft GBs, leading to intergranular amorphization. Intragranular amorphization arises from the interaction between grains with unfavorable orientations and the softened amorphous GBs, finally causing structural failure. Furthermore, the n-B4C models with varying grain sizes from 4.07 nm to 10.86 nm display an inverse Hall-Petch relationship due to the GB sliding mechanism. A higher strain rate in n-B4C often leads to higher yield strength, following a 2/3 power relationship. These deformation mechanisms are critical for the design of ceramics with superior mechanical properties.