Interdiffusion in the body cubic centered β-phase of Ta-Ti alloys

Interdiffusion in the beta-phase of Ta-Ti alloys is studied in the temperature range 1000-1900 degrees C. Interdiffusion coefficients are calculated with Den Breeder's method from concentration profiles determined by EPMA. These coefficients depend strongly on the composition: the interdiffusion coefficient for the lower tantalum concentrations is approximately 1000 times greater than the one for the higher concentrations. The activation energy (150-240 kJ/mol) is characteristic of a monovacancy diffusion mechanism. Except for the impurity diffusion of tantalum in titanium, determined by the Vignes and Birchenall method, anomalous behaviour of the diffusion in the beta-phase of titanium is not observed. The diffusion in these alloys is characterized by an important Kirkendall effect, materialized by a marker's shift towards the titanium rich part of the sample. The intrinsic diffusion coefficients have been calculated between 1000 degrees C and 1600 degrees C, at the composition of the Kirkendall plane, by Heumann's method: the intrinsic diffusion coefficient of titanium is approximately five times greater than that of tantalum. (C) 1998 Acta Metallurgica Inc.