In search of amorphization-resistant boron carbide

Abstract

2016-11-03T14:11:40

Amorphization‐induced volume change and residual stresses in boron carbide

“…As a ceramic, the compressive strength of boron carbide is significantly higher than its tensile strength, and so even though the overall pressure in the region appears to be compressive, localized circumferential tension may exist along the boundary of the expanded amorphized region. This circumferential tensile stress may explain observations of cracks initiating from amorphized bands as well as the link between amorphization and comminution …”

“…(A) TEM images show amorphized regions of various sizes and shapes near the tip of an indentation on boron carbide. (B) Amorphized islands appear close to the indentation . (C) Lattice rotations formed about an amorphized island and (D) a dislocation along one of the long, thin amorphized bands [Color figure can be viewed at wileyonlinelibrary.com]…”

“…These anomalies in the high‐pressure performance of boron carbide spurred numerous investigations into the evolution of short‐range disorder in the material, often referred to as “amorphization”. Subsequent studies have also documented amorphization under Berkovich and Vickers indentations, laser shock impact, mechanical scratching, and nonhydrostatic loading in diamond anvil cell experiments . Postmortem TEM of the deformed regions revealed inhomogeneous distributions of nanoscale amorphized zones within the crystalline matrix of boron carbide …”

The role of ceramic and glass science research in meeting societal challenges: Report from an NSF‐sponsored workshop

“…These include operation at ultrahigh pressures or contact loads (10 GPa‐1 TPa), such as those generated within diamond anvil cells (DACs), machining tools (eg, cutting, drilling, grinding) which benefit from super‐ and ultrahard materials, and operation under highly dynamic loads found, for example, in armor applications, where impact pressures can exceed 10 GPa . While phase transformations under pressure can lead to the discovery of new structures with novel properties, they may also be deleterious to the expected performance, as in the solid‐state amorphization of B 4 C under high‐velocity impacts . As is the case with ballistic armor, the discovery and fundamental understanding of superhard materials is still in its early stages of identifying and leveraging advanced simulation, synthesis, and characterization tools.…”

The effect of boron and aluminum additions on the microstructure of arc‐melted boron carbide

“…B 4 C consists of 12‐atom icosahedra (mostly B 11 C) connected via 3‐atom linear chains (eg, ‐CBC‐). Subhash et al suggested that doping Si, Ni and B into boron carbide could prevent the icosahedra from collapsing, thus mitigating amorphization in boron carbide. An et al performed density functional theory calculations and proposed that replacing ‐CBC‐ chain with Si–Si chain (Si‐doping) would stabilize the icosahedra, so that the system could shear without breaking the icosahedra and alleviating amorphization .…”