**5. Conclusions**

(1) The microstructure of as-SLM Ti-6Al-4V appears as a needle-like martensitic α' phase. Depending on different heat treatment temperatures, there are different phase compositions. The phase composition of 400 ◦C is α' + α, 600 ◦C is α' + α + β, and at 800 ◦C, the α' phase is completely transformed into the lamellar α + β phases. The phase composition of 800-AC is α + β.

(2) For the SLM Ti-6Al-4V specimen, the high temperature strength decreases as the temperature continues to increase after 400 ◦C, and the ductility increases as the temperature rises. The as-SLM Ti-6Al-4V could maintain a certain strength under 400 ◦C. Among the specimens, the highest UE is at 350 ◦C, so the tensile properties at 350 ◦C are most appropriate for the application of interest.

(3) Both AS and 800-AC had maximum erosion rates at 30◦ impact, and minimum erosion rates at 90◦ impact, where ductile failure dominated the erosion behavior. The continuous lamellar α + β phases of 800-AC were tough enough to limit the ability of the erosion particles to scrape off the material at all impact angles.

**Author Contributions:** Methodology, J.-R.Z. and Y.-L.W.; investigation, J.-R.Z. and Y.-L.W.; data curation, J.-R.Z.; writing—original draft preparation, J.-R.Z.; writing—review and editing, F.-Y.H. and T.-S.L.; supervision, F.-Y.H. and T.-S.L.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors are grateful to The Instrument Center of National Cheng Kung University and the Ministry of Science and Technology of Taiwan (Grant No. MOST 107-2221-E-006-012-MY2) for their financial support for this research.

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