Investigation of mutual diffusion in titanium-vanadium and titanium-niobium systemts

The interdiffusion was studied in the Ti-V- and Ti-Nb systems in which the elements from continuous rows of solid solutions. The concentrational and temperature dependences of the interdiffusion coefficients have been obtained and investigated. The curves of the component quantity distribution in the diffusion zones have been obtained by a local X-ray spectrum analysis. The interdiffusion coefficient has been computed by the Matano method. The interdiffusion coefficient in the investigated systems increases with the titanium concentration, the Ti-Nb system being characterized by a very strong concentrational dependence of the interdiffusion coefficient D tilde (within the whole concentrational region D tilde varies by more than four orders). The latter fact agrees with the concentrational dependence of the solidus temperature, decreasing with the titanium concentration increase. But for the Ti-V alloy system, in which the solidus curve has the minimum at the Ti concentration about 70 at.%, the direct correlation between the alloy melting point and the interdiffusion coefficient is broken. The curves of D tilde(c) in the Ti-V system have no maximum while growing monotonously within the whole concentration range. To express the relation between the diffusion characteristics and the melting point of the alloy in case of binary systems of bcc lattice, a formula is obtained of the Wisnes-Birchenall type but with a numerical multiplying factor K=22 cal/molxdeg, in variance with K=16 cal/molxdeg for the fcc lattice. The expression for the concentrational dependence of the self-diffusion coefficients in continuous solid solutions of bcc lattice has been changed in similar way (K=22 cal/molxdeg). The results of the computations performed are in a satisfactory agreement with the experimental data by the Darken formula from the data on the component self-diffusion (m - a thermodynamic multiplying factor)