The atomic diffusion of chromium in the titanium-chromium system

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Abstract
Diffusion rates of chromium in the body centred cubic phase of the titanium—chromium system have been measured by an autoradiographic tracer technique using the radioactive isotope 51Cr. Two alloys, Ti + 10% Cr and Ti+18% Cr (by weight), in addition to two grades of Ti metal, ‘iodide’ and ‘commercial’, were used as solvents so that tracer diffusion coefficients at essentially 0, 10 and 18% Cr concentration were measured, over the temperature range 900°c to 1200°c. The results are expressed in equations of the form D=D o exp (− Q/RT). The most significant feature is that the activation energy Q for tracer diffusion at zero solute concentration is very much lower than that expected for self-diffusion in pure Ti. An extension of the Johnson model of solute diffusion in face centred cubic metals to the body centred cubic lattice is proposed as an explanation of this divergence.