High Temperature Oxidation Behaviors of Powder Metallurgical gamma-TiAl Based Alloys: Effects of Surface Defects on Morphology of the Oxide Scale

In the present work, gamma-TiAl-based alloys with nominal composition of Ti-48Al-2Cr-2Nb (at.%) were prepared by vacuum hot pressing sintering using pre-alloyed powders under different pressures. The alloys were oxidized under cyclic conditions at 900 degrees C in the air for up to 100 h. The effects of surface defects on the morphology of the oxide scale were investigated. It was found that the alloys with increased porosities had increased mass gains after oxidation as a result of the increased area of oxidation reaction and the thickness of the scale, as well as the formation of micro-oxide clusters with an increased amount and size. These micro-clusters, which made the oxide layer rough, grew in the positions of surface defects. The diffusion of elements to the inner face of the defects led to the formation of large TiO2 and Al(2)O(3 )particles and was responsible for the formation of oxide clusters. The phenomenon and corresponding mechanism proposed here have previously been unreported, and they may play a guiding role in investigations concerning the oxidation behaviors of TiAl alloys with defects.