Diffusion Kinetics of Oxygen in beta-Titanium Measured by Molten Flux Method

Abstract

The unidirectional diffusion model of oxygen in beta-titanium was investigated based on the molten flux method and was analyzed by combining thermodynamics and kinetics. The interfacial concentration of oxygen could uniformly be maintained by using the Ca(CaO)-CaCl2 flux. The diffusion coefficient of oxygen in beta-Ti has been measured at temperatures from 1273 to 1573 K. The diffusion coefficient of oxygen in beta-Ti was evaluated as a function of temperature, especially at the low oxygen content region (0.025 mass pct O). ... calcium and titanium do not form any intermetallic compound, and the solubility of calcium in β-Ti (body-centered-cubic) is about 60 mass ppm at 1273 K.[10] In the present study, the commercial pure titanium (0.055 mass pet C-0. 14 mass pet Fe-0.32 mass pet O-0.006 mass pet N) was reacted with the Ca-CaCl^sub 2^ flux at 1273 through 1573 K. The interfacial concentration of oxygen is determined by the activity of Ca and CaO in the Ca(CaO)-CaCl^sub 2^ flux at given temperatures. [5], it is known that the oxygen content in Ti is proportional to the activity of CaO but inversely proportional to the activity of Ca in the flux as well as the activity coefficient of oxygen in Ti. [...] we determined the composition of the molten flux in order to control the concentration of oxygen in titanium based on the thermodynamic conditions involving activities of Ca and CaO.