*3.1. SEM Images and EDS Analysis Results of Coarse Particles in Cast Alloy*

Figure 1 shows the SEM images and the results of the EDS analysis of coarse particles in cast Cu-Cr-Zr-Ni-Si alloy. It can be seen from the figure that there are a large number of dispersed micron particles both in the grain and at the grain boundary in the as-cast alloy. In the enlarged SEM image, near-spherical and short rod-like particles with a size of about 0.5–3 μm can be observed, as indicated by the arrows in Figure 1b. The corresponding EDS analysis showed that these micron particles mainly contain Si, Cr, Ni and Cu elements.

## *3.2. SEM Images and EDS Analysis Results of Coarse Particles in Solution-Treated Alloy*

Figure 2 shows the SEM images and EDS analysis results of Cu-Cr-Zr-Ni-Si alloy treated by solution. As can be seen from Figure 2a, after high-temperature solution treatment, the large number of micron particles which occurred in the as-cast alloy disappear, and only some coarse particles are distributed both in the grain and at the grain boundary, as shown in Figure 2a,b. This indicates that most of the as-cast micron particles were dissolved into the copper matrix during the high-temperature solution treatment. Two different characteristic particles can be observed in the backscattering electron image, as shown in Figure 2b. Bright white lath particle "A" with a length of about 3 μm and a width of about 1.5 μm was located inside the grains. The results of the EDS analysis showed that the particle is composed of elements of Si, Zr, Cr and Cu. The cross-sectional of dark black particle "B" exhibits a nearly circular shape, and mainly contains Cu, Cr and a small amount of Si (about 1.77 at. %). Since the contrast in a backscattering electron image relates to the atomic number (a conspicuous Z-contrast for Fe*x*Sn1−*x*/MgO can be seen due to the great difference in atomic numbers of Fe, Sn, Mg and O [30]), the contrast of particle A mainly contained Zr element (atomic number is 40) and is obviously brighter than particle B, which mainly contains Cr element (atomic number is 24).

**Figure 1.** SEM images and EDS analysis results of coarse particles in cast Cu-Cr-Zr-Ni-Si alloy. (**a**) secondary electron image; (**b**) magnified secondary electron image; (**c**) EDS analysis results of selected particle in (**b**).

**Figure 2.** SEM image and EDS analysis results of coarse particles in solution-treated Cu-Cr-Zr-Ni-Si alloy. (**a**) secondary electron image in grain; (**b**) backscattering electron image at the grain boundary; (**c**) EDS analysis results of particle "A"; (**d**) EDS analysis results of particle "B".
