**Preface to "Additive Manufacturing of Metals"**

Additive manufacturing (AM), through which products are digitally manufactured from their 3D design data in a layer-by-layer manner, is an exciting and rapidly growing family of manufacturing technologies, offering a unique capability to realize 'impossible' structures, and providing the flexibility to make low-volume production cost effective. Originally developed in the mid-1980s, for many it is seen as a polymer-based technology; however, with the developments in CAD/CAM and laser technology, AM has moved into the metal arena, and new metal AM technologies, materials and applications are emerging at an ever-increasing rate, and are among the most dynamic and exciting research frontiers in AM. The additive nature of AM also enables unprecedented process control over the microstructure and performance of metals, and ever-increasing demands from industry, for AM processed materials offering excellent mechanical properties, is driving research to elucidate the often complex relationships that exist between process parameters and material structure and properties. This Special Issue on the additive manufacturing of metals offers an insight into the cutting-edge research that is currently being carried out in metal AM, bringing together an interesting set of contributions that make it possible to understand some of the phenomena that are directly related to the AM processing conditions and the resulting microstructural and mechanical properties, as well as the impact that these have had on the industrial application of materials. Over two-thirds of this book follow the laser powder bed fusion (PBF) of a range of alloys, from steels through to titanium alloys, with PBF being the most widely adopted metal AM technology both in academia and in industry, having been the founding technology for metal AM in the mid-1990s. More recently, other methods have emerged that offer the potential for the larger-scale higher-rate AM of components. Principally directed energy deposition (DED), with its unrivaled range of applications, is leading as one of the most promising advanced AM technologies for the future, and the remainder of the book is devoted to exciting new developments in this technology. This book has strength in being a collection of articles from different authors, with the knowledge being brought by true specialists in each area and rigorously reviewed by their expert peers in their field. This book will be of interest and bring added value in terms of knowledge to the entire scientific community, both academic and industrial, providing insight into these exciting developments. The authors hope that their contributions will be of grea<sup>t</sup> benefit and an inspiration to those who study and research in this field, as well as to those who wish to exploit the benefits of metal AM in their research and for commercial enterprise.

> **Gregory John Gibbons** *Editor*

*Article*
