Atomistic Origin of Brittle Failure of Boron Carbide from Large-Scale Reactive Dynamics Simulations: Suggestions toward Improved Ductility
Ceramics are strong, but their low fracture toughness prevents extended engineering applications. In particular, boron carbide (B_4C), the third hardest material in nature, has not been incorporated into many commercial applications because it exhibits anomalous failure when subjected to hypervelocity impact. To determine the atomistic origin of this brittle failure, we performed large-scale (∼200 000 atoms/cell) reactive-molecular-dynamics simulations of shear deformations of B_4C, using the quantum-mechanics-derived reactive force field simulation. We examined the (0001)/⟨101¯0⟩ slip system related to deformation twinning and the (011¯1¯)/⟨1¯101⟩ slip system related to amorphous band formation. We find that brittle failure in B_4C arises from formation of higher density amorphous bands due to fracture of the icosahedra, a unique feature of these boron based materials. This leads to negative pressure and cavitation resulting in crack opening. Thus, to design ductile materials based on B_4C we propose alloying aimed at promoting shear relaxation through intericosahedral slip that avoids icosahedral fracture.
© 2015 American Physical Society. (Received 19 May 2015; revised manuscript received 1 July 2015; published 31 August 2015) This work was supported by the Defense Advanced Research Projects Agency (W31P4Q-13-1-0010, program manager, Judah Goldwasser) and the National Science Foundation (DMR-1436985). The reaxff reactive force field simulation used here was developed with support provided by the Army Research Laboratory under Cooperative Agreement No. W911NF-12-2-0022 (MEDE).
Published - PhysRevLett.115.105501.pdf
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