Ab initio Studies on the Effects of Si and S Impurities on Al Grain Boundary

Abstract

The electronic structure of Al grain boundary with segregated Si and S impurity atoms, respectively, is calculated by first principles pseudopotential method. It is found that the segregated Si atom bonds the neighboring Al atoms, forming the metallic-covalent character mixing bonds. These bonds will prevent the rearrangement of atoms, such as sliding under stress. Therefore the embrittlement promoted by Si segregation should be classified into ‘bond mobility model’. However, the segregated S atom bonds only one of the neighboring Al atoms, forming a metallic-covalent character mixing bond. Other Al–S bonds in the boundary may become weaker than the former Al–Al bonds. Therefore it can’t be decided that the mechanism of the embrittlement promoted by S segregation is classified into ‘bond mobility model’ or ‘decohesion model’.