MECHANICAL-PROPERTIES OF TIAL-TYPE P/M INTERMETALLICS AT ELEVATED-TEMPERATURES

TiAl P/M intermetallics bearing Si less-than-or-equal-to 3.1 %, B less-than-or-equal-to 0.12 % and Nb less-than-or-equal-to 13.3 % were surveyed in respect of mechanical and oxidation behavior in the range: 600-1 200-degrees-C. The oxidation resistance of TiAl alloy is appreciably improved by Si and/or Nb addition, probably due to the protective aluminum-rich oxide on surface. Siliconizing instead of Si alloying will be recommended for good mechanical properties. In general, the tensile strength has a peak value of more than 350 MPa at 800-degrees-C or so nearly corresponding to brittle-ductile transition. The creep-rupture strength of TiAl alloy is more or less improved by Nb addition. Consequently, TiAl alloy bearing 1.5 % Si and 3-6 % Nb will be preferable for use in hot air up to 900-degrees-C. A further survey on superplasticity is required for alloy design and microstructural control.