*3.4. Quasi-Stationary Strength of 8/12Cu-Zr*

The circles in Figure 10 indicate the quasi-stationary strengths of ufg Cu-Zr at the grain/phase structure present at the beginning of creep. Their choice results from a compromise of


Taking into account that subgrain growth by migration of LABs is a relatively fast process needing strains in the order of 0.05 to 0.1 and that only limited subgrain growth is possible before all LABs were absorbed at the HABs of mean spacing *d*<sup>0</sup> (Figure 7), we expect that at the rather low strains of the qs states marked by circles in Figure 10 only marginal grain coarsening will have happened and that sufficiently small grains will have become subgrain-free by subgrain coarsening, except perhaps at the lowest stresses. Figure 12a shows the circles from Figure 10 as function of stress *σ* for ufg 8Cu-Zr. Within scatter, the qs strengths confirm the power law with a stress exponent *n*qs = 6, already mentioned in Section 3.1, for the stress range 70 MPa < *σ* < 260 MPa. The square symbols from the load change test demonstrate the moderate softening effect resulting from dynamic (sub)grain coarsening mentioned before (Figure 7). An analogous procedure as for 8Cu-Zr leads to Figure 12b for ufg 12Cu-Zr. There is no significant difference between 8Cu-Zr and 12Cu-Zr except lesser scatter for 12Cu-Zr at (true) stresses near 270 MPa (corresponding to *σ*eng = 250 MPa), probably due to better homogeneity of the grain structure of 12Cu-Zr.

**Figure 12.** Quasi-stationary strengths of (**a**) 8Cu-Zr (symbols from Figure 7) and (**b**) 12Cu-Zr; grey dotted lines connect data from the same test.
