Diffusion and Segregation in Grain and Interphase Boundaries
Tracer Diffusion and Linear and non-Linear Segregation in Cu Poly- and Bicrystals
Recently we have developed the radiotracer techniques to measure very successfully solute segregation at grain
boundaries by performing grain boundary diffusion experiments in different kinetic regimes. Usually
GB diffusion is measured in the so-called type B-regime where only the product P = s d Dgb can be determined; s is the segregation coefficient and
Dgb is the diffusion coefficient in the grain boundary and d its width which is a fairly well known quantity, ≈ 0,5 nm.
The key are so-called type C regime measurements which directly yield Dgb at
lower temperatures. We have shown that these tracer measurements are so sensitive that s can be
determined in the true dilute (Henry) conditions. By changing the specific activity of the applied tracer the
conditions of non-linear segregation can be achieved experimentally in a quantitative manner in selected
cases.
Thus this technique is superior to all other techniques so far applied to the segregation
phenomenon.
Following our extensive investigation of Ag segregation in Cu, we have extended these
experiments to Cu-bicrystals to guarantee a stable GB and have quantitatively proven the transition from linear
to non-linear segregation.
Furthermore type B and C measurements were performed for diffusion of
Ge and Bi in Cu polycrystals. In this way the segregation coefficients and the segregation enthalpies for
both solutes could reliably be determined. The behaviour of the Bi solute is of special interest, because the
embrittlement of Cu by Bisegregation is a well known and frequently investigated topic.
Drittmittelgeber:
Beteiligte Wissenschaftler:
Veröffentlichungen:
| 
