Study On The Microstructural Refinement And Oxidation Behavior Of γ-TiAl Alloys

Two methods, namely alloying and heat treatment were used to investigate the refinement of lamellar structure in Ti-46Al alloy in this paper.The as cast microstructures of Ti-46Al alloy were coarse full lamellar structures. With increasing of the content of W, the microstructures of the as cast button-ingots were refined. After adding a little amount of Si, the size of the dentrites in the alloys of Ti-46Al-xW(x=0.5, 2) decreased greatly. It was found that the alloying elements W and Si were enriched in the interdentritic and grain boundary regions. Coarse intermetallic phase B2 forms during the solidification, and the content of which increases with increasing the content of alloying elements W and Si.After solution treatment and quenching of the alloys with W and Si, the alloying elements distributed homogeneously. Coarse full lamellar structures usually form in the alloys. However, after the annealing above 1200℃, the grain size decreases greatly. The refined full lamellar structures forms. The influences of W and Si on the microstructures after heat treatment are quite different. The element W increases the refinement effect, whereas the element Si decrease the effect.The oxidation behaviors of Ti-46Al, Ti-46Al-0.5W, Ti-46Al-2.5W and Ti-46Al-0.5W-0.5Si alloys were investigated. It was found that: (1) the oxidation rate decreased with the increasing of the content of W; (2) the addition of Si decreased the oxidation rate furthermore; (3) the oxidation layer of the Ti-46Al-0.5W-0.5Si alloy is thinner than that of Ti-46Al-0.5W alloy, that is to say, the addition of Si decreased the thickness of oxidation layers and impeded the oxidation of the alloy greatly.