Diffusion of Hf and Nb in Zr19%Nb

Diffusion of Hf and Nb in large-grained bcc Zr19%Nb has been studied. Diffusion coefficients of Hf, D(Hf), were measured in the range 620–1173 K and D(Nb) was measured at 920 and 1167 K. The Elf diffusion profiles were determined by SIMS and the Nb profiles by microtome sectioning and radio-tracer counting. The Hf data show a smooth, temperature-dependent behaviour through the monotectoid temperature, 875 K, and may be characterised by D ≃ 10 −9 × exp(−1.4(eV/ kT)m 2/s. D(Nb) tends to be lower than the corresponding values for D(Hf). Overall, diffusion of Hf and Nb are characteristic of diffusion in bcc Zr. Surface hold-up (oxide film) at low temperatures was overcome by using ion-implanted Hf diffusion sources. The results are compared with earlier work and discussed in terms of diffusion mechanisms and the β-phase transformation of commercial Zr2.5Nb.