Nanotwins soften boron-rich boron carbide (B_(13)C_2)
Extensive studies of metals and alloys have observed that nanotwins lead to strengthening, but the role of nanotwins in ceramics is not well established. We compare here the shear strength and the deformation mechanism of nanotwinned boron-rich boron carbide (B_(13)C_2) with the perfect crystal under both pure shear and biaxial shear deformations. We find that the intrinsic shear strength of crystalline B_(13)C_2 is higher than that of crystalline boron carbide (B_4C). But nanotwins in B_(13)C_2 lower the strength, making it softer than crystalline B_4C. This reduction in strength of nanotwinned B_(13)C_2 arises from the interaction of the twin boundary with the C-B-C chains that connect the B_(12) icosahedra.
© 2017 AIP Publishing. Received 26 November 2016; accepted 26 February 2017; published online 16 March 2017. This work was supported by the Defense Advanced Research Projects Agency (W31P4Q-13-1-0010 and W31P4Q1210008, program manager, John Paschkewitz), by the Army Research Laboratory under Cooperative Agreement Number W911NF-12-2-0022, and by the National Science Foundation (DMR-1436985, program manager, John Schlueter). Q.A. was also supported by the U.S. Nuclear Regulatory Commission (NRC-HQ-84-15-G-0028). The authors declare no competing financial interests.
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