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Phys Rev Lett. 2007 Mar 30;98(13):135505. Epub 2007 Mar 28.

Colossal shear-strength enhancement of low-density cubic BC2N by nanoindentation.

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Department of Physics, Shanghai Jiao Tong University, Shanghai 200030, China.

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  • Phys Rev Lett. 2007 Apr 6;98(14):149905.


Recently synthesized low-density cubic BC2N exhibits surprisingly high shear strength inferred by nanoindentation in stark contrast to its relatively low elastic moduli. We show by first-principles calculation that this intriguing phenomenon can be ascribed to a novel structural hardening mechanism due to the compressive stress beneath the indenter. It significantly strengthens the weak bonds connecting the shear planes, yielding a colossal enhancement in shear strength. The resulting biaxial stress state produces atomistic fracture modes qualitatively different from those under pure shear stress. These results provide the first consistent explanation for a variety of experiments on the low-density cubic BC2N phase across a large range of strain.

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