Control of chemical composition of tracer layers in diffusion experiments : The Example of 70Zn diffusion in α-Cu64Zn36

For tracer diffusion experiments in metal alloys, the deposition of a suitable isotope enriched tracer layer is necessary. In this context, the chemical composition of the tracer layer and of the sample under investigation have to be identical. This can be achieved using ion-beam sputtering with segmented sputtering targets for tracer deposition. In the present study, the tracer diffusion of zinc in the copper zinc alloy α-Cu64Zn36 was investigated using the rare stable isotope 70Zn. The composition of the tracer layer was specifically adjusted by varying the Zn area fraction on the segmented copper target in contact to the sputtering zone. A model was developed to describe the relationship between Zn area fraction and chemical composition. The difference between the calculated chemical composition and the chemical composition measured by EDX in the coating is only 3 %. First diffusion experiments were carried out at 500 °C using secondary ion mass spectrometry and the diffusivity was determined to 1.7  0.3  10−16 m2/s in agreement with extrapolated values from the literature.