A copper-nickel diffusion couple similar to that shown in Figure 5.1a is fashioned. After a 700-h heat treatment at 1100?C (1373 K) the concentration of Cu is 2.5 wt% at the 3.0-mm position within the nickel. At what temperature must the diffusion couple need to be heated to produce this same concentration (i.e., 2.5 wt% Cu) at a 2.0-mm position after 700 h? The preexponential and activation energy for the diffusion of Cu in Ni are given in Table 5.2.

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Cu Ni (a) Activation Energy Qa Calculated Values Host Diffusing Species Dalm?1s) D(m²ls) тес) Metal kJ/mol eVlatom 3.0 x 10-21 1.8 x 10-15 2.8 x 10-4 Fe a-Fe 251 2.60 500 (BCC) 900 1.1 x 10-17 7.8 x 10-16 y-Fe (FCC) 5.0 x 10-5 284 2.94 900 Fe 1100 2.4 x 10-12 1.7 x 10-10 6.2 x 10-7 a-Fe 80 0.83 500 900 5.9 x 10-12 5.3 x 10-11 2.3 x 10-3 r-Fe 148 1.53 900 1100 4.2 x 10-19 Cu Cu 7.8 x 10-5 211 2.19 500 18 2.4 x 10-5 4.0 x 10- Zn Cu 189 1.96 500 2.3 x 10-4 6.5 x 10-5 Al 144 500 Al 1.49 4.2 x 10-14 4.1 x 10-14 Cu Al 136 1.41 500 10-4 Mg Al 1.2 131 1.35 500 1.9 x 10-13 2.7 x 10-5 1.3 x 10-22 Cu Ni 256 2.65 500