Observed Mitigation of Local Amorphization in Boron-Rich Boron Carbide

Abstract

Boron carbide is extremely hard but has been shown to undergo stress-induced amorphization when subjected to large nonhydrostatic stresses. This localized amorphization has been associated with the sudden loss of shear strength and poor ballistic performance. Recent quantum mechanics predictions suggest that boron-enrichment may be used to mitigate amorphization in boron carbide. As a means to test this hypothesis, stoichiometric boron carbide (nominally B4C) and a novel composition of B-rich boron carbide (nominally B6.3C) were investigated. Nanoindentation followed by Raman spectroscopy revealed an obvious reduction in the Raman peaks associated with amorphization in the B-rich material. Transmission electron microscopy observations of the region below the nanoindents facilitated direct observation of amorphization, confirmed the Raman result that amorphization is reduced in the B-rich specimens, and provided additional insight into deformation mechanisms. It is concluded that boron-rich alloys offer one path to mitigating local amorphization in boron carbide.