The Effect of Rhenium Addition on Microstructure and Corrosion Resistance of Inconel 718 Processed by Selective Laser Me
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ODUCTION
SELECTIVE laser melting (SLM) is an additive manufacturing (AM) technique which enables the production of nearly fully dense 3D metal parts in a layer-by-layer fabrication process. Subsequent 50- to 100-lm-thick powder layers are melted and consolidated by a focused laser beam to obtain a given computer-aided design (CAD) model.[1–4] Such processing allows the direct manufacture of metal parts with complex geometries with little to no further machining. This significantly reduces the material waste and investment cost for machining tools.[5]
KAMIL MAJCHROWICZ, ZBIGNIEW PAKIEŁA, JANUSZ KAMIN´SKI and MAGDALENA PŁAOCIN´SKA are with the Faculty of Materials Science and Engineering, Warsaw University of Technology, WołAoska 141, 02-507 Warsaw, Poland. Contact e-mail: [email protected] TOMASZ KURZYNOWSKI and EDWARD CHLEB are with the Faculty of Mechanical Engineering, Centre for Advanced Manufacturing Technologies/Fraunhofer Project Center, Wrocław University of Science and Technology, Łukasiewicza 5, 50-371 Wrocław, Poland. Manuscript submitted March 16, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
For the above reasons, the aircraft industry has become increasingly interested in the fabrication of Ni-based components by SLM. Extensive work has thus been conducted in recent years on SLM-processed Inconel 718 (IN718).[6–17] IN718 is a common Ni-based (Ni-Cr-Fe) austenite (c) alloy that combines high strength at elevated temperatures up to 700 C with excellent corrosion resistance. For these attributes, it is widely used for turbine engines or high-speed airframe parts in the aircraft industry as well as for valves, packers, or fasteners in the oil and gas industry.[18–20] IN718 is an age-hardenable alloy strengthened by precipitates of c¢ (Ni3(Al,Ti)) and c¢¢ (Ni3Nb) phases. However, some undesirable phases, i.e., NbC, d-Ni3Nb and Laves phase represented by (Ni,Cr,Fe) (Nb,Mo,Ti), can be also formed in IN718 alloy which leads to a degradation of its ductility and creep properties.[8,18,19] Rhenium, as a refractory metal with an excellent creep strength and resistance to a wide range of corrosive environments,[21] is highly effective in modifying the properties of Ni-based superalloys. It has been shown that Re addition significantly improves their high-temperature durability by decreasing the creep deformation rate.[22,23] This results from the fact that Re is a slow-diffusing element in nickel[24,25] and has a strong tendency to segregate in the c matrix.[26–28] During
high-temperature exposure, Re tends to pile up at the c/ c¢ interface which leads to a reduced c¢ coarsening rate[29,30] and the retardation of the dislocation climb at the c/c¢ interface.[31] Thereby, the creep resistance of Re-containing Ni-based superalloys is significantly enhanced. Recently, the effect of Re on mechanical properties has been also investigated in the case of SLM-processed Ni-based superalloys. Brynk et al.[10] have found that Re addition reduces the fatigue crack growth rate of IN718 alloy fabricated by SLM, wh
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