The effect of W on the structural stability of TiAl intermetallic systems and the site preference of W in $B2\mathrm{}$ and ${L1\mathrm{}}_0$ TiAl were studied based on first-principles calculations. It was found find that about 15 at. % W addition, in good agreement with experiment, is required to stabilize the $B2\mathrm{}$ structure in a TiAl base alloy. W was predicted to occupy Al sites in the $B2\mathrm{}$ phase, but Ti sites in the ${L1\mathrm{}}_0$ phase. The $B2\mathrm{}$-stabilizing effect of W and its site preference can be explained perfectly on the basis of the pseudogap effect and the strong covalent W-Ti bonding. The strong W-Ti bonding pairs are maximized when W occupies Al sites in $B2\mathrm{}$ TiAl. But when W occupies Al sites in ${L1\mathrm{}}_0$ TiAl, the W-Ti bonding is weakened by the existence of Al in the alternating (002) plane, which can, however, strengthen the in-plane W-Ti bonding when W occupies Ti sites.

• Received 11 December 2001

DOI:https://doi.org/10.1103/PhysRevB.65.184102