EFFECTS OF ADDITIONS OF Y-METALS AND RARE -EARTH-METALS ON THE CYCLICOXIDATION OF TIAL ALLOYS

Oxidation behavior of the intermetallic compound TiAl with additions o f Y and REM (Ce, Nd, Sm, Tb, Dy) as third elements has been investigat ed at 1173 K in air by means of cyclic oxidation tests. A small amount of Y addition restrains surface segregation of S and is effective for reducing spalling and breaking of oxide scale. The addition of a larg e amount of Y (2 mol%), however, increases an invasion of oxygen, and accordingly the mass gain by oxidation increases. The addition of REM also restrains surface segregation of S, and leads to suppression of b reaking and spalling of oxide scale, then the oxidation resistance is improved. However, the effect of REM addition to TiAl alloys is not so remarkable as that to Fe- and Ni-base alloys. This fact suggests that the scale spalling on TiAl-base alloys is controlled not only by S se gregated at the scale-alloy interface, but also by other several facto rs.