Oxidation behavior of TiAl at high temperatures in purified oxygen

Abstract

Oxidation behavior of a TiAl coupon was studied in a temperature range 1100 to 1400 K in a flow of purified oxygen at atmospheric pressure using thermogravimetry and standard metallographic techniques. The oxidation kinetics initially follows approximately a linear rate law. The oxidation rate decreases gradually as the oxidation proceeds. However, they never follow the parabolic rate law. This is attributable to the crack formation near the scale/substrate interface. The oxide scale has two layers: an outer layer consisting mainly of rutile and an inner porous layer consisting of a mixture of rutile and α-alumina. The preferential growth of rutile is responsible for the initial kinetics. Large voids are developed near the interface between the outer and inner oxide layers. Thin alumina platelets grow almost normal to the substrate surface as an internal oxide near the scale/substrate interface. The lamellar structure thus developed is maintained in the scale near the interface.