A diffusion couple similar to that shown in Figure 5.1a is prepared using two hypothetical...

A diffusion couple similar to that shown in Figure 5.1a is prepared using two hypothetical metals A and B. After a 20-h heat treatment at 800°C (and subsequently cooling to room temperature) the concentration of B in A is 2.5 wt% at the 5.0-mm position within metal A. If another heat treatment is conducted on an identical diffusion couple, but at 1000°C for 20 h, at what position will the composition be 2.5 wt% B? Assume that the preexponential and activation energy for the diffusion coefficient are 1.5 × 10–4 m2/s and 125,000 J/mol, respectively.

Figure 5.1 (a) A copper–nickel diffusion couple before a high-temperature heat treatment.