Microalloying Effects in TiAl+Mo Alloys

Ti–48.5Al–1.5Mo (at.%) and Ti–48.5Al–1.5Mo–X (X=0.3, 1.0 and 2.0C or N) alloys were prepared by vacuum arc melting and homogenized at 1390°C for the lamellar microstructure and then aged at 900°C. It was found that C (or N) additions decreased the grain size of the lamellar structure. In particular, 1.0 and 2.0%C (or N) additions refined the grain size to 1/10 of that of the mother alloy. Tensile elongation at room temperature decreased for the alloys with 0.3%C (or N) but recovered with 1.0% and 2.0%C (or N) additions compared to the value of the mother alloy. The yield stress at room temperature for these alloys containing 1.0% and 2.0%C (or N) increased up to twice that of the mother alloy, and this high stress was maintained up to 800°C. The aged alloys showed much higher tensile elongation at room temperature than did the alloys with only heat-treatment. Moreover, the alloy with 1.0%N added exhibited better creep resistance than did the mother alloy, in spite of its much smaller grain size.