## 3 Results and Discussion
### DSC Phase Transformation Analysis  
The DSC exothermic/endothermic graphs of four different sections are shown in Figure 12a-d. For each section, the procedure was set as a heating and cooling cycle: heating to 120 \({}^{\circ}\)C from 0 \({}^{\circ}\)C with a constant heating rate of 10 \({}^{\circ}\)C/min (the lower part of each graph), and then cooling back to 0 \({}^{\circ}\)C with a constant cooling rate of 10 \({}^{\circ}\)C/min (the upper part of each graph). Peaks appear during the heating and cooling process, which reflects the heat absorption or release between martensite and austenite phase transformation. From Figure 12a-c, it can be observed that sections S12, S23, and S34 have one martensite-to-austenite (M\(\rightarrow\)A) peak during heating and one austenite-to-martensite (A\(\rightarrow\)M) peak during cooling, while no peak can be observed between the given temperature range in S45. The characteristic temperatures of S12, S23, and S34, including the austenite starting temperature (A\({}_{\mathrm{s}}\)), austenite finishing temperature (A\({}_{\mathrm{f}}\)), austenite peak temperature (A\({}_{\mathrm{p}}\)), martensite starting temperature (M\({}_{\mathrm{s}}\)), martensite finishing temperature (M\({}_{\mathrm{f}}\)), and martensite peak temperature (M\({}_{\mathrm{p}}\)) are determined from DSC graphs in Figure 12a-c. All of the phase starting and finishing temperature points were determined by the tangent method. These characteristic temperatures are all labeled in each DSC graph. From Figure 12a-c, it can be found that S12, S23, and S34 experience transformation during the heating and cooling temperature. In contrast, no transformation can be found in S45 in the given temperature range. This indicates that S12, S23, and S34 include the martensite TiNi phase before heating, while almost no martensite exists in S45. S12, S23, and S34 exhibit some portion of the martensite phase at room temperature (\(\sim\)25 \({}^{\circ}\)C) since their values of M\({}_{\mathrm{f}}\) and A\({}_{\mathrm{s}}\) are all higher than room temperature. For S45, it can be inferred that the martensite transformation may occur at a low temperature that is lower than 0 \({}^{\circ}\)C. Therefore, at room temperature, S45 consists of almost all austenite. This agrees well with what is found in the aforementioned XRD results. In XRD results, no strong diffraction pattern of the martensite phase can be detected in locations H4 and H5. From Figure 12a-c, peak widths of M\(\rightarrow\)A: 1A\({}_{\mathrm{f}}\)-A\({}_{\mathrm{s}}\)1, and A\(\rightarrow\)M: 1M\({}_{\mathrm{s}}\)-M\({}_{\mathrm{f}}\)1 can also be determined. The relation of peak widths among S12, S23, and S34 is S12 \(<\) S23 \(<\) S34. The temperature range for the phase transformation becomes longer when the location gets higher, which shows that the homogeneity of martensite is the highest at location H1, and it follows a descending trend when going up along the BD direction [42]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**UTS (MPa)** & **AM Processing Methods** & **Ref.** \\ \hline
622 for the horizontal sample & & DED (elemental powder) & This work \\
447 for the vertical sample & & \\
250 & DED (elemental powder) & [40] \\
320 & DED (elemental powder) & [41] \\
780 & DED (pre-alloyed) & [42] \\
601 & SLM & [43] \\
690 \(\pm\) 15 & SLM & [44] \\
571.4 \(\pm\) 18.6 & WAAM & [45] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of UTS of current work and other published AM TiNi alloys. Adding Cu to replace a certain atomic number of Ni was reported to be able to reduce the thermal hysteresis, which is usually defined by the difference between \(\rm A_{P}\) and \(\rm M_{P}\)[46], or the difference between \(\rm A_{f}\) and \(\rm M_{s}\)[47]. In this work, the thermal hysteresis calculated by \(\rm 1\,A_{P}-M_{P}\)1 of these three sections can be found for S12 (11 \({}^{\circ}\)C), S23 (12 \({}^{\circ}\)C), and S34 (16 \({}^{\circ}\)C).