Laser Additive Manufacturing of Titanium-Based Functionally Graded Materials: A Review

Functionally graded materials (FGMs) refer to advanced engineering materials that exhibit exceptional thermo-mechanical characteristics due to their intrinsic spatial variation in properties across the volume. These materials provide an elegant solution for the cases where the parts are subjected to varying thermal or mechanical loads over a region of interest. For this reason, FGMs have found their applications in areas including aerospace, defense, mining and naval manufacturing sectors. Particularly in the aerospace industry, the properties of FGMs have been harnessed to develop heat-resistant surfaces for the space shuttle and aircraft engine components. One of the most relevant methods in the production of FGMs is the use of additive manufacturing (AM) techniques. Especially directed energy deposition (DED) method is one of the leading technologies to produce physical objects from the 3D CAD model. Titanium and nickel are one of the most efficient materials used in aerospace. Several studies have been carried out to develop suitable Ti- and Ni-based alloys and composites for specific applications. Moreover, several researchers have developed FGMs based on Ti or its alloys with materials like Al, Ni, Mo, Nb, etc. The current article presents a state of art conceptual understanding of additively manufactured FGMs, covering an overview of the DED technique and effects of the process parameters involved that can enable the manufacturing of FGM parts. The limitations of certain AM technologies are briefly discussed. In addition, possible strategies to overcome the challenges and future opportunities of AM technology to fabricate Ti-based FGMs and structures were presented.