Behavior and mechanism for Boron atom diffusing across tungsten grain boundary in the preparation of WB coating: A first-principles calculation

Abstract For improving the thickness and property of WB coating prepared using atomic diffusion theory, the behavior and mechanism for B atom diffusing across W grain boundary (GB) were investigated. The result indicates that, no matter which W GB for B atom diffusing across, stage I (Obulk → S1) decides the diffusion rate, and the energy barrier is not depended on the boundary itself, but controlled by the atomic arrangement structure near GB. W GBs have neighboring octahedral interstices connected by their edges, such as Σ5(2 1 0)[0 0 1] GB, Σ7(2 1 3)[1 –2 0] GB and Σ11(3 2 3)[1 –3 1] GB, are the fast diffusion channels for B atom diffusion because of the smaller energy barriers at stage I (≦2.476 eV). While W GBs have neighboring octahedral interstices connected by their faces, including Σ3(1 1 1)[1 –1 0] GB, Σ3(1 1 2)[1 –1 0] GB, Σ5(2 1 0)[0 0 1] GB and Σ9(1 1 4)[1 –1 0] GB, are the two-dimensional barriers due to the larger energy barriers (＞2.476 eV). Both ionic bonding and covalent bonding between B atom at saddle point and the surrounding W atoms at stage I on two-dimensional barriers are stronger than those on fast diffusion channels, which is the reason two-dimensional barriers show the larger energy barriers and the smaller diffusion coefficient for B atom diffusing across.