Effect of titanium on bcc Fe grain boundary cohesion

First-principles DMol method within the framework of density functional theory is used to study the effect of Ti on bcc Fe∑3 [110](111) grain boundary cohesion. The difference of segregation energies of a Ti atom at the grain boundary and at the free surface equals to -0.372 eV indicating that Ti is a cohesion enhancer. Further analyses show that the chemical and mechanical effects equal to -0.713 eV and +0.341 eV, respectively. The chemical effect plays a major role but mechanical effect can not be neglected in the computation. At the same time, the effect of Ti on bond is also analyzed. When Ti segregates on grain boundary, it can make the bonds across grain boundary stronger than that of clean grain boundary, that reflects the strenghthening action of Ti.