*3.4. TEM Images and Electron Diffraction Results of Coarse Particles in Solution-Treated Alloy*

Figure 4 displays TEM images and the electron diffraction pattern of a coarse particle in the Cu-Cr-Zr-Ni-Si alloy. The bright field image and dark field image clearly show a needle-like particle that has a length of 820 nm and width of about 100 nm in Figure 4a, with the corresponding electron diffraction pattern shown in Figure 4c. Two sets of patterns can be distinguished from the electron diffraction pattern: one set of diffraction spots has higher intensity and smaller spacing between crystal planes, while the other set of diffraction spots shows slightly lower intensity and larger crystal face spacing. Angles between the adjacent diffracted spots and the transmitted spot of the two patterns were both measured to be about 54◦ and 36◦, and the distance ratios were both determined to be about 1.1. The results fully comply with the diffraction pattern characteristic of f.c.c crystals under the <011> zone axis. Therefore, it can be inferred that the two sets of diffraction patterns are both induced by f.c.c crystals under <011> zone axes diffraction. The patterns were indexed as shown in Figure 4d. According to the spots distance, the lattice parameters of the two crystals were calculated as 0.3612 nm and 0.687 nm, respectively, and the two phases were identified with reference to the PDF card as follows: one is the Cu matrix and

the other is the Cu5Zr intermetallic phase, which belongs to F − 43 m (216) space group and has an f.c.c structure with a lattice parameter of 0.687 nm. The red-circled spot shown in Figure 4c was selected for an operation of central dark field, and the central dark field image is presented in Figure 4b. It can be further confirmed that the set of patterns is induced by the f.c.c structure Cu5Zr intermetallic phase.

**Figure 4.** TEM images and electron diffraction pattern of needle-like particle in the Cu-Cr-Zr-Ni-Si alloy (-*•* Cu; -• Cu5Zr). (**a**) bright filed image; (**b**) dark filed image; (**c**) electron diffraction pattern; (**d**) indexing result of (**c**).

According to the electron diffraction pattern and TEM bright field image, it can be ascertained that the Cu5Zr phase grows along the <111> direction of the Cu matrix. The orientation relationship between the Cu5Zr phase and the matrix can also be determined as follows:[011]*Cu*//[011]*Cu*5*Zr*, ( − 31<sup>−</sup> 1)*Cu*//( − 11<sup>−</sup> 1)*Cu*5*Zr*.

Another nearly spherical particle with a size of approximately 40~120 nm in diameter can be observed in Figure 4. A bright field image and a dark field image of the particle are shown in Figure 5a,b, and the corresponding electron diffraction pattern is presented in Figure 5c. It can be inferred that the extra diffraction is caused by the <001> zone axis of a b.c.c structure phase, and the lattice constant of the phase is 0.288 nm, calculated by the diffraction pattern. Based on the energy spectrum analysis results, which indicate a nearly

spherical phase containing Cr and Si elements, it can be concluded that the extra diffraction is induced by a Cr9.1Si0.9 intermetallic phase. The indexing result is shown in Figure 5d. According to the indexing result, a Nishiyama–Wassermann (N–W) orientation relationship can be found between the Cr9.1Si0.9 phase and Cu matrix, which is that:[011]*Cu*//[001]*Cr*9.1*Si*0.9, − − − − − −

( 1 11)*Cu*//(1 10)*Cr*9.1*Si*0.9, ( 42<sup>−</sup> 2)*Cu*//( 1 10)*Cr*9.1*Si*0.9//( − 2 − 20)*Cr*9.1*Si*0.9.

**Figure 5.** TEM images and electron diffraction pattern of nearly spherical phase in the Cu-Cr-Zr-Ni-Si alloy (-*•* Cu; -• Cr9.1Si0.9). (**a**) bright filed image; (**b**) dark filed image; (**c**) electron diffraction pattern; (**d**) indexing result of (**c**).

#### **4. Discussion**
