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2020 Research Highlight: Mitigating Stress-induced Amorphization in Boron Carbide via Silicon Doping

Mitigating Stress-induced Amorphization in Boron Carbide via Silicon Doping

Mr. Qirong “Bruce” Yang
Rutgers University
Dr. Sisi Xiang
Texas A&M University
Dr. Luoning Ma
Johns Hopkins University
Dr. Chawon Hwang
Rutgers University
Dr. Jun Du
Rutgers University
Dr. Jerry C. LaSalvia
CCDC Army Research Laboratory
Professor Kelvin Y. Xie
exas A&M University
Professor Kevin J. Hemker
Johns Hopkins University
Professor Richard A. Haber
Rutgers University

Consolidated boron carbide ceramics experience accelerated fragmentation when subjected to high applied pressures such as achieved in a ballistic event. The large shear stress triggers the collapse of boron carbide structure, manifesting in a network of nano-sized amorphous bands. These amorphous bands act as “the path of least resistance” for crack propagation, leading to a catastrophic failure of the ceramic.

Theoretical model suggests Si doping can be an effective strategy to suppress stress-induced amorphization in boron carbide. Si doping modifies the boron carbide structure by altering the C-B-C linear chain to a C-Si-C kinked chain, as shown in Fig. 5. Si-doped boron carbide ceramics were processed through reaction sintering using boron carbide, amorphous boron, and silicon hexaboride powder mixtures. Preliminary indentation and Raman spectroscopy studies demonstrated that Si doping can suppress amorphization by 31% (Fig. 5a and 5b). Complementary transmission electron microscopy (TEM) carried out in the quasi-plastic zones under the nano-indentation reveals salient differences in the deformation behavior between the undoped and Si-doped boron carbide. The undoped boron carbide deforms by nucleating amorphous shear bands, which facilitates crack formation (Fig. 5c). In contrast, Si-doped boron carbide deforms through micro-cracking rather than amorphization (Fig. 5d). Our findings suggest Si doping alters the deformation behavior of boron carbide by promoting micro-cracking, which dissipates strain energy leading to less amorphization.