Strengthening boron carbide through lithium dopant

Abstract

The high strength of boron carbide (B4C) is essential in its engineering applications such as wear‐resistance and body armors. Here, by employing density functional theory simulations, we demonstrated that the strength of B4C can be enhanced by doping lithium to boron‐rich boron carbide (B13C2) to form r‐LiB13C2. The bonding analysis on r‐LiB13C2 indicates that the electron counting rule (or Wade's rule) is satisfied in r‐LiB13C2 whose formula can be written as r‐Li+(B12)2‐(CB+C). The shear deformation on r‐LiB13C2 indicates that its ideal shear strength is larger than that of B4C because of the existing of Li dopant. The failure process of r‐LiB13C2 under ideal shear deformation initiates from breaking the icosahedral‐icosahedral B‐B bonds. Then these B atoms react with the middle B in the C‐B‐C chain, resulting in the disintegration of icosahedral clusters and brittle failure. More interesting, the nanotwinned r‐LiB13C2 is even stronger than r‐LiB13C2 because of the directional nature of covalent bonding at the twin boundaries. This suggests that the nanotwinned r‐LiB13C2 has a significant enhanced strength compared to B4C. Our simulation results illustrate the deformation mechanism of Li‐doped boron carbide and its nanotwinned microstructure. We proposed to improve the strength of boron carbide by doping Li into B13C2 and increasing its twin densities.

Experimental observations of amorphization in multiple generations of boron carbide

“…An et al showed this to be the case by performing DFT simulations in which the -CBC-chains with microalloying elements such as -Si 2 -. 25,26 This review paper aims to describe and discuss the experimental observations of stress-induced amorphization in multiple generations of boron carbide, which are referred to as several variants. The first variant is the stoichiometric boron carbide with nominal B 4 C composition.…”

“…No references were found on modeling of the PIP process for CMCs, though experimental studies on this manufacturing process have been reported. Studies on polycarbosilanederived SiC ceramic 25 and SiC/SiC composite 26,27 have shown that porosity decreases and mechanical properties improve with the increasing number of PIP cycles. Zhu et al 28 show that increasing pyrolysis temperature and the concentration of SiC fillers in polycarbosilane polymer result in improved mechanical properties in two-dimensional Carbon/ SiC (C/SiC) composites fabricated using the PIP process.…”

“…If stress‐induced amorphization in boron carbide is dependent upon strong interaction of the B atom in the chain and a C atom in a nearby icosahedra, then altering the chain and icosahedral chemistries should reduce such interactions thereby making boron carbide more resistant to stress‐induced amorphization. An et al showed this to be the case by performing DFT simulations in which the –CBC– chains with microalloying elements such as –Si 2 – 25,26 …”

Strengthening boron carbide by doping Si into grain boundaries

“…Several approaches, such as microalloying, [12][13][14][15][16] stoichiometry control, [17][18][19] and addition of a second phase, [20][21][22] have been proposed to mitigate amorphous shear band formation. For microalloying, both non-metal dopants (P 23 and Si 24 ), as well as metal dopants (Li, 14,15 Mg, 12,16 and Ti 13 ) may decrease amorphization in B 4 C. Both experimental and theoretical studies have suggested that boron enrichment is helpful to mitigate amorphization. [17][18][19] Moreover, the addition of the second phase, such as SiC 25 and TiB 2 26 has been shown to improve the fracture toughness of B 4 C. Among these approaches, grain-boundary (GB) engineering is promising.…”

“…This suggests that adding Si or P to the grain boundaries might improve ductility. Several approaches, such as microalloying, [12][13][14][15][16] stoichiometry control, [17][18][19] and addition of a second phase, [20][21][22] have been proposed to mitigate amorphous shear band formation. For microalloying, both non-metal dopants (P 23 and Si 24 ), as well as metal dopants (Li, 14,15 Mg, 12,16 and Ti 13 ) may decrease amorphization in B 4 C. Both experimental and theoretical studies have suggested that boron enrichment is helpful to mitigate amorphization.…”