Rheocasting techniques applied to intermetallic TiAl alloys and composites

An investigation was made on the homogenization of microstructures and improvement of mechanical properties in intermetallic TiAl binary, ternary and quaternary alloys and their composites produced by the rheocasting in which the solidifying alloy was vigorously agitated at rotation speeds of 15-70 s(-1) (900-4200 rpm) by a stirring rod immersed in the alloy in an argon gas atmosphere. In the microstructures of rheocast Ti-44at.%Al alloy, such a lamellar structure in the alloy cast without stirring was disappeared completely and an extremely refined microstructure was formed. The crystal grain size of the rheocast Ti-44at.%Al alloy was 2 mu m. The room temperature elongation of rheocast Ti-44%Al alloy exceeded 3%. The tensile strength of the alloy rheocast at 70 s(-1) and was 538 MPa at 1173 K and 439 MPa at 1273 K, respectively. Zirconium-rich lamellar grains and titanium-rich and carbon-rich precipitates, which were formed in the lamellar grains in a rheocast Ti-44at%Al-5vol.%ZrC alloy composite, were increased in a rheocast Ti-44%Al-10%ZrC alloy composite. Titanium-rich and carbon-rich precipitates, which were formed in the lamellar grains in a rheocast Ti-44%Al-10%TiC alloy composite, were increased in a rheocast Ti-46Al-10%TiC alloy composite, and were decreased in a rheocast Ti-49%Al-10%TiC alloy composite. The elongation at room temperature and the tensile strength at 1373 K were 4% and 280 MPa, respectively, in a Ti-44at.%Al-10vol.%ZrC alloy composite. (C) 1997 Elsevier Science S.A.