Functionally graded multi-materials by laser powder bed fusion: a review on experimental studies

In the rapidly developing manufacturing industry, there are emerging needs for complex and diverse requirements in a single part , which urged the invention of functionally graded materials (FGMs). In recent years, the rapid development of additive manufacturing has presented a new flexible and promising production method compared with the traditional methods. This technology provides the maximum control over point-to-point material composition and structure, which is strongly in favor of the manufacturing complex FGMs. The proven ability of the laser powder bed fusion (LPBF) for producing nearly fully dense 3D parts made it a popular method for various materials. However, there is not enough focus on multi-material FGM processing using this method. LPBF is normally used for single (or mono-) material processing, and producing a functionally graded material by this method is much easier by grading porosity compared to grading material composition. To facilitate further advancements in this area, this article tends to collect all the important metallurgical concepts and statistical points of the researches on functionally graded multi-materials manufactured using laser powder bed fusion. Different material systems based on the nature of the constituents including Metal/Metal and Metal/None metal are categorized and studied in deep. Then, potential applications and challenges are presented. Finally, there is a summary of the important points of the reviewed articles in the section of material systems, and future directions for the research in this area is given. This review study presents the applications, challenges, summary of investigations, and LPBF printing parameters of multi-material FGMs as brief as possible to be easily found and referenced.