Effects of Co and Cr on bcc Fe grain boundaries cohesion from first-principles study

The segregation effects of Co and Cr on the bcc Fe ∑ 3 [ 1 1 ¯ 0 ] ( 1 1 1 ) grain boundary cohesion are investigated based on the Rice–Wang thermodynamics model by the first-principles DMol method within the framework of density functional theory. The electronic properties are studied for Co/Fe and Cr/Fe systems. The calculated segregation energy difference between the grain boundary and the corresponding free surface is 0.25 eV for solute Co and −0.43 eV for solute Cr, which indicates that Co could weaken and Cr enhance the grain boundary cohesion in bcc Fe. In these systems the chemical effect induced by Co and Cr play crucial effects, but the geometry effect can be neglected. In addition, an anti-parallel spin island is formed around the central of GB.