The influence of the alloy microstructure on the oxidation behavior of Ti-46Al-1Cr-0.2Si alloy

The influence of microstructure of the two-phase alloy Ti-46Al-1Cr-0.2Si on the oxidation behavior in air between 600 and 900 degrees C was studied. The oxidation rate, type of scale, and scale spallation resistance were strongly affected by the type of microstructure, i.e., lamellar in as-cast material and duplex after extrusion at 1300 degrees C. The oxidation rate was affected by the size and distribution of the alpha(2)-Ti3Al. The type of oxide scale determines the spalling resistance. Cast material developed a uniform scale that spalled off after short exposure times at 800 and 900 degrees C when a critical thickness was reached. The extruded material presented a heterogeneous scale with predominant thick regions formed on gamma-TiAl-alpha(2)-Ti3Al grains and thin scale regions formed on gamma-TiAl grains. This type of scale could permit an easier relaxation in the matrix of stresses generated by both thermal-expansion mismatch between scale and alloy and oxide growth, resulting in a higher spallation resistance.