Functionally graded materials (FGMs): A review of classifications, fabrication methods and their applications

Functionally graded materials (FGMs) are new materials whose properties change gradually in respect to their dimensions. This group of materials shows a tremendous improvement of previously used composite materials. FGM consists of two or more materials whose combination enables the achievement of specified properties in accordance with the desired application. The article gives an overview of different classifications, various fabrication methods and applications of the FGMs. It could also provide insight and perspective for researchers, university students and research and development teams since it has brought together diverse aspects of FGMs. As mentioned in section two, we took all FGMs fabrication methods under consideration, giving the reader an insight into how to make a product while satisfying the conditions of financial and mechanical efficiency. The classification section specifically goes over structures, types of gradients, sizes/scales, state of matter and finishes with the manufacturing processes. Section two deep dives into the fabrication methods used in the FGMs, which are divided into three sub-sections, including gas-based, liquid-based and solid-based. Lastly, various applications of the FGMs in different fields and industries, namely aerospace, energy, medicine, military, manufacturing and eventually other applications, are demonstrated.