First-Principles Predicting Improved Ductility of Boron Carbide through Element Doping

Boron carbide (B4C) is a superhard material, whose wide engineering applications are limited by its brittleness under impact. Doping various impurity elements into B4C may lead to a significant change in its mechanical properties and deformation behaviors. To study this effect, density functional theory was employed to examine how different doping elements and doping content affect the mechanical properties and failure mechanism of B4C. The results show that doping Mg, N, or Si into B4C could improve its ductility, but the newly doped B11CP-CMgC and B11CP-NBC structures are not stable because of the bending of 3-atom chains after structural optimization. Si was selected to illustrate the effect of doping content on the mechanical properties and deformation mechanism of B4C. The results show that, with the increase of doping content, the ductility of xSi-B4C is increased, whereas its thermodynamic stability and mechanical stability are both decreased. The a-axis uniaxial compression of 6Si-B4C indicates that its failure strain is increased by 39.1% relative to that of B4C. Doping Si into B4C can enhance its ductility, which arises from the modified failure mechanism through stabilizing the icosahedra. Our study suggests that doping an element into B4C is a promising way to tune the mechanical properties and deformation mechanism of B4C.