INTERDIFFUSION IN THE BODY CUBIC CENTERED BETA-PHASE OF TA-TI ALLOYS

Interdiffusion in the beta-phase of Ta-Ti alloys is studied in the tem perature range 1000-1900 degrees C. Interdiffusion coefficients are ca lculated with Den Breeder's method from concentration profiles determi ned by EPMA. These coefficients depend strongly on the composition: th e interdiffusion coefficient for the lower tantalum concentrations is approximately 1000 times greater than the one for the higher concentra tions. The activation energy (150-240 kJ/mol) is characteristic of a m onovacancy diffusion mechanism. Except for the impurity diffusion of t antalum in titanium, determined by the Vignes and Birchenall method, a nomalous behaviour of the diffusion in the beta-phase of titanium is n ot observed. The diffusion in these alloys is characterized by an impo rtant 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 th e composition of the Kirkendall plane, by Heumann's method: the intrin sic diffusion coefficient of titanium is approximately five times grea ter than that of tantalum. (C) 1998 Acta Metallurgica Inc.