On the analysis of diffusion anomalies in Ti alloys

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Abstract
Existing experimental data for diffusion in Ti alloys are analysed in terms of the recently proposed Ω-embryo mechanism for anomalous diffusion in the group IVB transition metals. An expression for the diffusion coefficient is derived starting from a phenomenological expansion for the free energy in terms of the atomic displacements and assuming that the Ω instability results from softening of the 2/3〈111〉 longitudinal mode. The β to Ω instability temperature is an important physical parameter that can be obtained from the model by fitting diffusion data. General agreement is found between the model and experimental diffusion data. All fitting parameters are found to fall well within the expected ranges, and in particular the β to Ω instability temperature estimated from the model shows reasonable agreement with the available experimental data.