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

The self-diffusivities of Ti and Cr were determined in (TixWyCrz)B-2 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)B-2, (Ti0.5W0.3Cr0.2)B-2, and (Ti0.4W0.5Cr0.1)B-2 were studied in the temperature interval between 1100 and 1500 degrees C, using ion implanted stable Ti-49 and Cr-14 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 x 10(-7) m(2)/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 (TixWyCrz)B-2 solid solutions are discussed. (c) 2006 Springer Science + Business Media, Inc.