Tracer grain boundary diffusion of silver in α-zirconium polycrystals

Grain boundary (GB) diffusion of 110mAg was measured in polycrystalline α-Zr in the temperature range 574 to 1024 K using microtome sectioning and γ-spectrometry to evaluate the diffusion profiles. An Arrhenius relation was determined for the GB diffusion parameter P = sδDgb, (s is the segregation coefficient, δ the GB width and Dgb the GB diffusion coefficient) with an activation enthalpy Qgb = 152 ± 3 kJmol-1 and a pre-exponential factor P0 = 6.4-2.3+3.6 . 10-13 m3s-1. The microstructure of the well annealed Zr material of low impurity content was examined by transmission electron microscopy. A fine subgrain network built by dislocation walls was found. In the temperature interval 733 to 786 K the penetration profiles were evaluated in terms of subgrain boundary (SB) diffusion characterised by the parameter Psb = ssbδsbDsb as well as by the parameter P. The results of the measurements are compared with our previous results on GB diffusion of Zr and Co in α-Zr. The influence of SB diffusion on GB tracer diffusion measurements is discussed. The value of the segregation enthalpy of Ag in α-Zr grain boundaries is estimated. (orig.)