TEM investigation was carried out to further explore the microstructure of the β/Zn lamellar structure (Fig. 4). Bright field (BF) TEM image is shown in Fig. 4a, revealing that lath-like precipitates with paralleled long axes distribute in the matrix. The reproducible long axes of the precipitates indicate there exist reproducible orientation relationship (OR) between the two phases. HRTEM image in Fig. 4b shows the interface in the red square marked region in Fig. 4a, and the insets show enlarged fast Fourier transformed (FFT) filtered micrograph of the two phases. Both of them are HCP structured. Lattice parameters of Zn are a = 0.2665 nm, c = 0.4949 nm, with c/a = 1.86, while those of β phase are a = 0.278 nm, c = 0.439 nm, with c/a = 1.58. In Fig. 4b, the HCP structure of the lath-like precipitate is oriented along [2110] zone axis, while that of the matrix is orientated along [1213] zone axis. Measured from the HRTEM image, lattice parameters in the region of the lath-like precipitate are a = 0.27 nm, c = 0.49 nm, with c/a ≈ 1.8, indicating it is Zn. By contrast, those in the matrix are measured to be a = 0.27 nm, c = 0.43 nm, with c/a ≈ 1.6, indicating it is β phase. To determine the OR between the two phases, their FFT diffraction patterns are given in Fig. 4c. In order to guide pattern indexing, their FTT patterns are illustrated with green or red dots overlapped on it. It can be measured in Fig. 4c that (1010)β deviates about 4.5° anticlockwise from (0002)Zn. Hence the OR between the two phases can be described as[1213] //[2110] β Zn, (1010)β 4.5° from (0002)Zn. It is evidenced that the lamellar structure forms due to solid-state phase transformation.
