Self-diffusion of transition metals in (Ti,W,Cr)B2 solid solutions

The self-diffusivities of Ti and Cr were determined in (Tix Wy Crz )B2 ceramics which are a model system for the development of in-situ reinforced boride ceramics by tailored precipitate formation. Homogeneous solid solutions of composition (Ti0.3W0.5Cr0.2)B2, (Ti0.5W0.3Cr0.2)B2, and (Ti0.4W0.5Cr0.1)B2 were studied in the temperature interval between 1100 and 1500◦C, using ion implanted stable 49Ti and 54Cr isotopes and secondary ion mass spectrometry (SIMS). The diffusivities of each element obey an Arrhenius law. The Cr diffusivities of all three compounds can be fitted to a unique Arrhenius line with an activation enthalpy of 3.5 eV and a low pre-exponential factor of 2×10−7 m2/s. The Ti diffusivities are smaller by 1–2 orders of magnitude than the Cr diffusivities, showing, however, higher activation enthalpies of 3.9 eV and approximately the same pre-exponential factors. The consequences of the results for the formation kinetics of precipitates in supersaturated (Tix Wy Crz )B2 solid solutions are discussed. C 2006 Springer Science + Business Media, Inc.