Material transport in (Ti0.3W0.5Cr0.2)B2 ceramics: simultaneous diffusion of ion implanted 49Ti and 54Cr

Self-diffusion studies of Ti and Cr were carried out in a two-phase ceramic compound with nominal composition (Ti0.3W0.5Cr0.2)B2, which is a model system for the development of in situ reinforced boride ceramics, via precipitation of a supersaturated host matrix. In the temperature interval 1000 °C⩽T⩽1400 °C, the diffusivities were determined with secondary ion mass spectrometry (SIMS) using co-implanted and simultaneously diffusing stable 49Ti and 54Cr isotopes. This procedure minimizes systematic errors, reduces experimental time, and enables a direct comparison of the results. The two- phase nature of the material is directly reflected in non-uniform Cr depth profiles, while for Ti, uniform depth profiles indicate nearly the same diffusivities in both phases. The diffusivities of both elements obey an Arrhenius behaviour with activation enthalpies of ΔHTi=3.1 eV and ΔHCr=3.3 eV, respectively, and very low pre-exponential factors of about D0Ti=1×10−9 m2/s and D0Cr=6×10−8 m2/s, which is a hint that no simple vacancy mechanism is operating in the material. The experimental results also suggest that the growth of the precipitates at 1600 °C is controlled by the volume diffusion of Cr and Ti.