**4. Conclusions**

The combination of different materials by SLM makes it possible to combine the excellent properties of different materials. In this paper, the selective laser melting technology was used to form CuSn10 alloy on the formed NiTi alloy. The microstructure, element diffusion, microhardness change, and phases at the interface were studied. Tensile parts were formed to test the interfacial bonding properties, and the conclusions were drawn as follows:

(1) Different interfacial structures can be obtained by adjusting the forming energy density input of the interface by adjusting process parameters. Columnar grains can form along the boundary of molten pool in the interfacial region and can effectively improve the interfacial bonding. Grain refinement in the interfacial region can also play a strengthening role.


In general, the interfacial bonding is still weak, but on the premise of the large gap between the physical and chemical properties of CuSn10 and NiTi alloy, it can be said that the interfacial bonding strength has reached a good level with a value of 309.7 ± 34.4 MPa. This direction still has good application prospects. In addition, how different process parameters affect the interfacial Ni4Ti<sup>3</sup> strengthening phase, columnar grain, and grain refinement, thus affecting the interfacial bonding strength still needs further quantitative research.

**Author Contributions:** Conceptualization, C.S.; Investigation, C.S. and Y.X.; Methodology, Z.H.; Resources, Y.L. and Y.Y.; Validation, Z.H. and Y.X.; Writing—original draft, Z.H. and Y.X.; Writing review & editing, C.S. and Y.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was financially supported by Key-Area Research and Development Program of Guangdong Province (2020B090923001), National Natural Science Foundation of China (U2001218), Guangdong Province Special Support Plan for High-Level Talents (2019TQ05Z110), Capital's Funds for Health Improvement and Research (CFH 2020-2-5131).

**Acknowledgments:** The authors gratefully acknowledge China-Ukraine Institute of Welding.

**Conflicts of Interest:** The authors declare no conflict of interest.
