Abstract
We investigated the effects of size and interstitial elements of the L1(2)-type Al6Y8 cluster on the formation of the long-period stacking ordered (LPSO) structure in the 10H-type Mg-Al-Y alloy, Mg92Al12Y16-i(2) , i=interstitial elements, Mg, Al, Y or vacancy (no interstitial atom), by using first-principles calculations. We found that there exist two local minima of total energy (two stable states) in a function of the Al-Al distance of the vacancy-centered L1(2) cluster. The Al-type stacking is the most stable at the 1st energy minimum with the smaller Al-Al distance whereas the A3-type stacking is the most stable for the 2nd minimum with the greater Al-Al distance. Meanwhile, the Al-Y distances are identical at both minima. We also found that the sizes of the solute atom-centered L1 2 clusters in Mg92Al12Y16-i(2) (i=Mg, Al, Y) are similar to that for the 2nd minimum with the larger cluster size. The Al-Y distances are again identical for all the solute atom-centered clusters. We show that these behaviors in the Al-Al and Al-Y distances can be explained by the softness of the Al-Al bonds and the strong Al-Y bonds predicted from the distance dependence of the pair interaction energies between the solute atoms in the Mg-matrix. These results suggest that the Al-Y bond is a key factor to determine the structure in the solute-enriched layer in the Mg-Al-Y LPSO alloy, especially in the L1(2) cluster.
NSTL
Elsevier