Tracer diffusion and mechanism of non-Arrhenius diffusion behavior of Zr and Nb in body-centered cubic Zr-Nb alloys

Tracer diffusion of Zr-95 and Nb-95 has been measured in a set of beta-Zr-N b alloys (Zr-5.5 at. % Nb, Zr-16.3 at. % Nb, and Zr-28.1 at. % Nb) in a wid e temperature range from 1035 to 1871 K. All experimental concentration pro files revealed a Gaussian-like behavior over two to three decades in logari thm of concentrations. Experimental data were analyzed in terms of the Mann ing's random alloy model and the partial correlation factors were calculate d as functions of temperature. The partial correlation factors vary smoothl y over the whole temperature range, whereas the diffusivity shows a pronoun ced curvature of the Arrhenius plots. A correlation was found between the d egree of deviation from the Arrhenius behavior of the diffusion coefficient s of both components and the lattice dynamics features of the measured phon on dispersions in their dependence on the Nb content in these alloys. The t emperature dependence of the isotope effect parameter E of Zr diffusion was measured in the Zr-5.5 at.% Nb alloy. E essentially increases with tempera ture and the energy transfer factor Delta K deduced for the alloy was found to be somewhat larger than the corresponding values for pure beta-Zr, espe cially at low temperatures. The whole set of experimental data leads to the conclusion that only one diffusion mechanism-the vacancy mechanism-is oper ating in the whole investigated temperature range. (C) 1999 American Instit ute of Physics. [S0021-8979(99)01312-2].