Study of Intermetallic Compounds task A:Dispersion-Hardened TiAl.

摘要

The feasibility of increasing the high-temperature tensile and creep strength, the high-temperature oxidation resistance, and the low temperature ductility of the titanium aluminide, TiAl, by means of a dispersion of inert particles of yttria, has been studied. Alloys containing 1.5 and 3 volume percent Y2O3 were produced by attritor milling of TiAl and Y2O3 powders and hot extruding to bar stock. The major findings of the study are: (1) Attritor milling of TiAl powders for total milling times in excess of 100 hrs can be accomplished without problems. Milling for more than 80 hrs was required to achieve a uniform dispersion of yttria with the REP powder used in this program. (2) The oxygen and nitrogen contents of TiAl increased with increasing attritor milling time. (3) The microstructures of the Y2O3-containing TiAl alloys comprised a predominantly basket-weave structure of gamma and lamellar alpha 2, with uniformly dispersed particles. (4) The yttria-containing alloys exhibited considerably increased tensile strength at room temperature and at 1652 F compared to yttria-free TiAl. (5) The tensile creep strengths of Y2O3-containing TiAl and Y2O3-free TiAl at 900 C were similar. (6) No effect was observed of the dispersoid on the room-temperature ductility of TiAl. (7) the oxidation behavior of the yttria-containing alloys was variable, some specimens oxidizing more slowly than the equivalent dispersion-free TiAl specimens, and most specimens exhibiting adherent scale.