Multi-material processing of metallic components by direct additive manufacturing methods: technologies, scientific insights, and industrial applications

Inspired by the surrounding natural patterns, multi-material structures play a significant and integral role in contemporary life because of their multi-functionality and tailored site-specific properties for diverse service requirements. Although conventional manufacturing methods have brought the primary concept of multi-materials into the engineering world, additive manufacturing (AM) technology has overcome long-standing limitations and has significantly flourished in its research and development. Its layer-wise mechanism provides a unique opportunity to integrate highly flexible materials design and manufacturing of highly complex geometries. Over the past decade, many attempts have been made to develop multi-material additive manufacturing (MM-AM) as an innovative and reliable solution for critical materials. Therefore, this review comprehensively covers and criticizes recent advances in processing multi-material metallic components through direct AM technologies. By clarifying the dimensions of the multi-material concept, different direct metal AM processes for multi-material fabrication are described in this context. Then, case studies on MM-AM are classified based on AM technology and discussed, focusing on the most recent and notable research. Furthermore, practical applications of MM-AM in various sectors, such as aerospace, automotive, biomedical, and electronics, are addressed. Lastly, a perspective and a summary are provided to offer insights into the current status and future directions of this field.