## 3 Results and Discussion  
Figure 1a shows the backscattered electron imaging (BEI) of the furnace-cooled Cu-23 Ti-17 Sn specimens, which include Cu\({}_{2}\)SnTi\({}_{3}\) (Phase A), Phase B, Cu-9 at. %Sn (Phase C), and Cu\({}_{41}\)Sn\({}_{11}\) (Phase D) identified using the XRD patterns. The compositions and average atomic mass of Phases A, B, C, and D are presented in Table 1. Figure 1b shows the BEI of the water-quenched Cu-23 Ti-17 Sn specimens, which include Phase A, Phase B, and Cu-14 at. %Sn (Phase M) for which the composition and average atomic mass of Phase M are listed in Table 1. Our results show that when the Cu-23 Ti-17 Sn alloy is heated to 900 \({}^{\circ}\)C and the base phase of the alloy is a solid solution phase of Cu-Sn. The phase separation occurs to form two phases with different tin contents, namely the C phase and the D phase, because the solubility of tin in solid solution is temperature-dependent and the tin atoms have enough time to diffuse in the furnace-cooled Cu-23 Ti-17 Sn sample. In contrast, when cooling at a very fast rate (water quenching), no phase separation occurs, and only a single solid solution phase, Phase M, is formed. We noted that Cu\({}_{2}\)SnTi\({}_{3}\), Phase A, is a new phase and has never been reported before. Figure 1: Microstructures of the Cu-23 at. %Ti–17 at. %Sn alloy under (**a**) furnace-cooled and (**b**) water-quenched. To further analyze the structures of the ternary intermetallic phases, the sample was immersed in a solution of 20 vol. % sulfuric acid and connected to the positive pole of the DC power supply, resulting in the remaining Cu\({}_{2}\)SnTi\({}_{3}\) and CuSn\({}_{3}\)Ti\({}_{5}\). The XRD plot contains two sets of peaks corresponding to Cu\({}_{2}\)SnTi\({}_{3}\) and CuSn\({}_{3}\)Ti\({}_{5}\). The crystal structure of CuSn\({}_{3}\)Ti\({}_{5}\) has been identified and found in JCPDS [10; 16], while Cu\({}_{2}\)SnTi\({}_{3}\) has not been reported yet. We use the regression to estimate the unknown Cu\({}_{2}\)SnTi\({}_{3}\), showing that Cu\({}_{2}\)SnTi\({}_{3}\) could be a hexagonal structure with \(a\) = 4.708 A and \(c\) = 6.756 A, which in turn determines the diffraction angle of hexagonal Cu\({}_{2}\)SnTi\({}_{3}\) and matches bulklike CaCu\({}_{5}\) structure (space group: 191 \(P\)6/\(mmm\)) [12]. Table 2 compares the measured and regression diffraction angles of Cu\({}_{2}\)SnTi\({}_{3}\), and the relative intensity of each individual peak in the measured XRD pattern. The measured and regressed diffraction angles of the crystal plane of (002) are 27.08\({}^{\circ}\) and 26.36\({}^{\circ}\), respectively, showing the largest uncertainty. Figure 2 shows a TEM bright image of Cu\({}_{2}\)SnTi\({}_{3}\) and its corresponding SAD patterns. The composition analysis based on EDS in TEM shows that this domain is composed of Cu of 32.1-34.7 at. %, Sn of 15.2-17.1 at. %, and Ti of 49.3-52.6 at. %, which the stoichiometry of the domain \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Phase**} & \multirow{2}{*}{**Chemical Formula**} & \multicolumn{3}{c}{**Composition (at. \%)**} & \multirow{2}{*}{**Average Atomic Mass**} \\ \cline{3-3} \cline{5-5}  & & **Cu** & **Sn** & **Ti** \\ \hline A & Cu\({}_{2}\)SnTi\({}_{3}\) & 32.92 & 15.95 & 51.13 & 64.34 \\ B & CuSn\({}_{3}\)Ti\({}_{5}\) & 12.15 & 32.25 & 55.60 & 72.63 \\ C & Cu-9 at. \%Sn & 90.95 & 8.84 & 0.21 & 68.39 \\ D & Cu\({}_{41}\)Sn\({}_{11}\) & 79.68 & 20.02 & 0.30 & 74.54 \\ M & Cu-14 at. \%Sn & 85.35 & 14.38 & 0.27 & 71.10 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The chemical formula and composition of the Phases A, B, C, D, and M in the Cu-23 at. %Ti–17 at. %Sn alloy. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Diffraction Angles 2\(\theta\) (deg.)**} & \multirow{2}{*}{\(\mathbf{h\ k\ l}\)} & \multirow{2}{*}{\(\mathbf{\text{Intensity}}\)} \\ \cline{1-1} \cline{3-4}
**Measured** & & **Regressive** & **Error (\%)** & & **1/10 (\%)** \\ \hline  
\hline \hline \end{tabular}
\end{table}