Zr diffusion in BCC refractory high entropy alloys: A case of ‘non-sluggish’ diffusion behavior

Single phase (BCC solid solution) HfTiZrNbTa and HfTiZrNbV refractory high entropy alloys are synthesized and characterized. For the first time for BCC refractory high entropy alloys, tracer diffusion is measured using the short-living radioactive isotope 89 Zr in the temperature range of 1123 to 1423 K. A ’non-sluggish’ diffusion behavior is clearly observed, highlighted by an enhancement of the measured diffusion rates with respect to the geometric mean of the diffusivities in the corresponding pure elements. The factors influencing self-diffusion in BCC multi-principal element alloys are discussed, including the chemical complexity, atomic size mismatch and the phonon broadening.