Abstract
The subscale formed during high temperature rapid oxidation of γ-titanium aluminum is revealed by transmission electron microscopy and microanalysis to consist of two phases: one hexagonal with unit cell dimensions a = 0.58nm, c = 0.47nm (±0.005nm), and a composition close to Ti 6Al 3O 4; the other simple cubic with a = 0.69nm (±0.005nm) and composition of Ti 3Al 2O 3, with oxygen concentration known to about 10% accuracy. The results strongly suggest that the hexagonal phase is a solid solution of O in Ti 3Al, while the cubic phase is a novel ternary compound with space group P4 232. These subscale phases exhibit some tendency for a crystallographic orientation relationship with (110) cubic//(01 1 0) hexagonal and [0 1 1] cubic//[ 2 112] hexagonal, and the hexagonal phase is less stable than the cubic phase as the distance to the sample surface decreases and oxygen level increases.
Published Version
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