Experimental studies on fabricating functionally gradient material of stainless steel 316L-Inconel 718 through hybrid manufacturing: directed energy deposition and machining

Directed energy deposition (DED) is an important approach to fabricate metallic functionally gradient materials (FGMs). During DED process, two kinds of metallic powder are blown into molten pool with gradually changing powder feed rates to achieve material gradients in FGM. DED process always causes poor surface roughness and limited dimensional accuracy, which have to be overcome by machining. Different mechanical properties of two powder materials generate heterogeneous mechanical properties in FGM, which seriously influence cutting mechanism, such as cutting temperature, surface roughness, and tool wear, especially if one material is a hard-to-cut material. However, so far, there has not been any research particularly focused on this problem. This work investigated hybrid manufacturing FGMs involving DED and machining. SS316L and IN718 were fabricated into FGM specimen with DED process. Then, a tungsten carbide (WC) milling cutter machined the FGM specimen under dry peripheral milling condition. A series of material tests were performed to characterize the material properties of FGM specimen. Additionally, surface roughness, machining temperature observations, and tool wear were studied to investigate machining mechanism. Based on the experimental results, it is found that the cutting temperature close to IN718 region was higher than the cutting temperature close to the SS316L region. After machining, the surface colors of IN718 and SS316L regions were bright blue and bright silver, respectively. The surface roughness of SS316L region was greater than that in the IN718 region. In FGM (from 100% SS316L to 100% IN718) after machining, the machined surface colors were shown as yellow, bright yellow, and purple, with the surface roughness found decreasing gradually. Since IN718 is a typical hard-to-cut material, milling cutter is also observed to have obvious wear close to IN718 side. This work firstly studied the fabrication of FGM part with hybrid manufacturing (DED and machining) and provided valuable experimental data of machining the SS316/In718 FGM.

Automated summary

This study investigates the fabrication of functionally gradient materials (FGMs) using hybrid manufacturing (DED and machining) and provides valuable experimental data for machining SS316/In718 FGM. The study reveals that the heterogeneous mechanical properties in FGM due to different materials greatly influence cutting mechanism.