Oxidation behaviour of a Ti-46Al-1Mo-0.2Si alloy: the effect of Mo addition and alloy microstructure

The influence of molybdenum addition and alloy microstructure on the oxidat ion behaviour of a Ti-46.8Al-1Mo-0.2Si alloy was studied in air at temperat ures ranging from 600 to 900 degrees C. The alloy produced by are melting e xhibited a structure of coarse lamellar grains in as-cast condition that tr ansformed to a duplex microstructure after hot extrusion at 1300 degrees C. Oxidation rate and scale spallation resistance were not affected by the ty pe of microstructure. The effect of molybdenum addition was related to the formation and thickening of a protective continuous nitride layer. The low mass gain measured can be associated with the low oxidation rate of the nit ride layer. Finally, the poor spalling resistance of the oxide scale at 900 degrees C was attributed to the mismatch in thermal expansion coefficients of the oxide scale and the nitride layer. (C) 2000 Elsevier Science S.A. A ll rights reserved.