Diffusion, the Kirkendall effect and vacancy jump frequency ratios in dilute Al-Zn alloys

Abstract

The method of vapour-solid couples was applied in order to investigate interdiffusion and intrinsic diffusion in dilute Al-Zn alloys. Although an aluminium oxide layer could not be avoided in our experiments, typical concentration-penetration curves were measured by electron probe microanalysis. The Boltzmann-Matano evaluation of the profiles yielded interdiffusion coefficients in agreement with previously published results. Contrary to the expected behaviour, bulges were observed by metallographic inspection at those regions of surfaces where zinc diffused into the samples. From results of interdiffusion and from measurements with only 1h diffusion time, it is deduced that the penetration of Zn atoms is nearly unaffected by the surface oxide layer and shows no local differences. Therefore, the reason for the growth of the bulges is the diffusion of the host component Al, which is possible only at preferred sites of the oxide layer. The ratio DZn/DAI was determined at those sites where the oxide layer was penetrated by both Zn and Al atoms. From the value measured for an infinitely dilute solution, (DZn/Dl))0=1.70+or-0.25, the vacancy flow factor (LAlZn/ZnZn)0=-0.19+or-0.13 was derived. Vacancy jump frequency ratios according to the five-frequency model were calculated which differ from unity only slightly and are similar to those obtained for the systems Ag-Zn and Cu-Zn. A weak binding between vacancies and Zn impurity atoms was estimated by means of two different methods.

Study of diffusion mobility of Al−Zn solid solution

“…The first example describes the semi-infinite vapor-solid diffusion couple con-structed by Hagenschulte and Heumann. [38] The calculation (Fig. 7) is in remarkable agreement with the measured concentration curve.…”

“…Though their data appear to be comparatively scattered, the same concentration tendency was confirmed. The last chemical diffusion coefficient measurement by Hagenschulte and Heuman [38] was accomplished by extracting data from a Boltzmann-Matano evaluation of the penetration profile; however, a comparison indicates this set of data does not extrapolate to the proper tracer diffusivity of Zn and was therefore excluded from the present assessment. …”

“…6(a). A comparison of the calculated chemical diffusion coefficient with the experimental values [15,38,45] is shown in Fig. 6(b).…”

“…4(a) seldom differ greatly from the measured points at low temperature, particularly not in the region of low Zn content. Because the difference between calculated and observed chemical diffusion coefficients are greatest for the results of Hagenschulte and Heuman [38] at 556°C, those results are singled out for a more detailed examination in the next section.…”

Intermetallic formation and interdiffusion in diffusion couples made of uranium and single crystal iron

“…Previous studies showed no chemical interaction at UO 2 /Fe interface after 1000-hour annealing at 1000 o C [12]. As to be discussed, the existence of UO 2 will influence interface reaction by introducing an incubation time period for diffusion and this effect must be considered in data interpretation.…”