Substitutional and Interstitial Diffusion in alpha2-Ti3Al(O)The reaction between Al2O3 and alpha2-Ti3Al was studied with a series of Al2O3/alpha2-Ti3Al multiphase diffusion couples annealed at 900, 1000 and 1100 C. The diffusion-paths were found to strongly depend on alpha2- Ti3Al(O) composition. For alloys with low oxygen concentrations the reaction involved the reduction of Al2O3, the formation of a gamma-TiAl reaction-layer and diffusion of Al and O into the alpha2-Ti3Al substrate. Measured concentration profiles across the interaction-zone showed "up-hill" diffusion of O in alpha2-Ti3Al(O) indicating a significant thermodynamic interaction between O and Al, Ti or both. Diffusion coefficients for the interstitial O in alpha2-Ti3Al(O) were determined independently from the interdiffusion of Ti and Al on the substitutional lattice. Diffusion coefficients are reported for alpha2-Ti3Al(O) as well as gamma-TiAl. Interpretation of the results were aided with the subsequent measurement of the activities of Al, Ti and O in alpha 2-Ti3Al(O) by Knudsen effusion-cell mass spectrometry.
Document ID
20070010751
Acquisition Source
Glenn Research Center
Document Type
Conference Paper
Authors
Copland, Evan (Case Western Reserve Univ. Cleveland, OH, United States)
Young, David J. (New South Wales Univ. Sydney, Australia)
Gleeson, Brian (Iowa State Univ. of Science and Technology Ames, IA, United States)
Jacobson, Nathan (NASA Glenn Research Center Cleveland, OH, United States)