**4. Conclusions**

Continuous Ti coatings on steel and stainless steel ball substrates were prepared by mechanical coating technique. Greater revolution speed, providing larger collision force and energy, accelerated the formation of continuous Ti coatings. The substrate material plays an essential role in the formation of Ti coatings; specifically, Ti coatings or even other metal coatings are more easily formed on metal/alloy balls than on ceramic balls. Meanwhile, substrate hardness also markedly affected the formation of Ti coatings. The material with smaller surface hardness is more suitable as the substrate on which Ti coatings were prepared. The above conclusion can also be exerted on other metal or alloy coatings on metal/alloy and ceramic substrates.

**Acknowledgments:** This work is financially supported by the National Nature Science Foundation of China (No. 51404170), the Innovation Team Program of Tianjin University of Science & Technology (No. 10117) and the Scientific Research Foundation of Tianjin University of Science & Technology (No. 10220).

**Author Contributions:** Y. Lu conceived and designed the experiments; L. Hao performed the experiments; L. Hao and H. Yoshida analyzed the data; T. Itoi contributed analysis tools; L. Hao wrote the paper.

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