Graded Inconel 625 – SUS316L Joint Fabricated Using Directed Energy Deposition

The joining of dissimilar materials is an important process to produce a large production. In other words, the reliability of such a production is determined by the joining technique because the joint interface often becomes the weakest point against stress. In case of metals, welding and riveting are popular approaches for joining dissimilar materials. However, these techniques generally involve manual and complex operations; therefore, the production quality cannot be maintained, because the accuracy and efficiency of these operations strongly depend on the worker’s skill. From this viewpoint, additive manufacturing (AM) can be useful to produce parts using a combination of dissimilar metals. Metal AM has attracted considerable attention from aerospace and automobile industries recently because of its flexibility and applicability in the production of various complex-shaped parts. Directed energy deposition (DED), one such metal AM method, forms a deposit of powder material and simultaneously irradiates a laser beam on the baseplate. DED can be applied to cladding and repairs as it can be conducted on the surface of the part. In particular, a combined part of dissimilar metals can be easily and directly produced from scratch by changing the powder material of the process. A graded material can also be produced by blending different powders and changing their ratios appropriately. In order to realize such applications of DED, the mechanical properties of the produced part must be evaluated in detail. In this study, a part combining a nickel-based superalloy (Inconel 625) and a stainless steel alloy (SUS316L) is produced using DED; the produced part is evaluated through a tensile strength test, Vickers hardness measurement, metal structure observation, and element distribution analysis. In addition, a graded material is also produced to evaluate the basic characteristics of the joint produced using DED. The experimental results show that the produced joint is sufficiently stiff against tensile stress and its hardness is increased because of the solid solution of niobium in the stainless steel area. The results of the elemental distribution analysis and the Vickers hardness test indicate that a graded joint of Inconel 625 and SUS316L can certainly be produced using DED.