**3. Conclusion and Outlook**

The current Special Issue of *Metals* provides a comprehensive insight into current research in the field of SPD. The papers cover several research topics and we hope that this Special Issue will be a starting point for future scientific discussions. As Guest Editors of this Special Issue, we hope that the papers will catch the interest of many scientists and will be useful for their future work.

**Acknowledgments:** We would like to express our deep gratitude to all the authors for their contributions. We further thank the anonymous reviewers for their efforts to ensure high-quality publications were accepted. Sincere thanks are also due to the editors and editorial assistants of *Metals* for their help and support during the preparation of this Special Issue.

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