A DFT study of the influence of Al doping on the mechanical properties of boron carbide

Boron carbide (B₄C) is one of the hardest lightweight ceramics, but its application is limited by abrupt failure under high stresses caused by amorphization of intericosahedral chains. Aluminum doping has been proposed as a strategy to improve its mechanical resilience. In this work, Density Functional Theory (DFT) calculations were used to investigate the influence of aluminum substitution on the elastic and compressive behavior of boron carbide. Elastic constants were calculated from the numerical first derivative of the stress with respect to strain, while uniaxial compression simulations were performed on 180-atoms supercells oriented perpendicular to the (001) plane. The results show that Al-doped B₄C has a uniform distribution of elastic properties across its modifications, in contrast to the variability observed in undoped polytypes. Although the maximum stress values for Al-doped structures are reduced compared to unmodified boron carbide, their failure mechanisms are markedly different: instead of abrupt collapse, Al-doped configurations undergo gradual, multistep deformation involving local distortions, tubular reconstructions, and delayed structural breakdown. Consequently, modifications of boron carbide with Al substituted into the intericosahedral chains sustain larger ultimate strains, highlighting enhanced ductility and toughness. These findings demonstrate that aluminum substitution into boron carbide fundamentally alters its failure response, offering a pathway to mitigate its intrinsic brittleness and extend its applicability in extreme environments.