HF DIFFUSION IN DILUTE FE-FREE ZR(NB) ALLOYS

Hf diffusion coefficients D have been measured in the a-phase of the F e-free binary alloys Zr-1.0at.% Nb and Zr-2.5at.% Nb in the temperatur e range 830-1100 K. The D values for the two alloys are essentially in distinguishable and little different from extant Hf diffusion coeffici ents measured in Fe-free polycrystalline alpha-Zr. The temperature dep endence of D in the alloys is characteristic of intrinsic alpha-Zr bul k behaviour: D(T)=5x10(-7)exp(-2.7 eV/kT)m(2)s(-1). The present Hf D v alues are much lower than corresponding values measured in commercial Zr-2.5 Nb. The difference is attributable to the influence of solid-so lution Fe. In addition, the absence of a strong enhancement of Hf diff usion in alpha-Zr by Nb suggests that intrinsic Nb diffusion in alpha- Zr may not be controlled by a normal vacancy mechanism.