Ab initio pseudopotential studies on an Al Σ = 9 grain boundary: Effects of Na and Ca impurities

The electronic properties of an Al ‡ = 9 tilt grain boundary with segregated Na and Ca impurity atoms have been calculated by a first-principles pseudopotential method. The results show that the boundary expands and the charge density decreases significantly over the whole boundary by the segregation of Na and Ca, and there are no stronger bonds than those associated with metallic bonding in the boundary even with the impurities. It is concluded that the embrittlement promotion mechanism by Na or Ca segregation in the Al boundaries is one kind of 'decohesion model'.