مشخصه‌يابي اتصال فولاد زنگ‌نزن 316 كم‌كربن به سوپر آلياژ اينكونل 718 به روش جوشكاري پلاسماي جرقه‌اي

Abstract Spark Plasma Welding (SPW) is among the most advanced methods for joining dissimilar materials. This process enables precise control over atomic diffusion, phase transformation, an‎d grain boundary modification, making it suitable for the fabrication of critical components. The joining of dissimilar materials, such as low-carbon 316 stainless steel an‎d Inconel 718 superalloy, presents significant challenges in the production of components exposed to high temperatures an‎d corrosive environments in aerospace, marine, energy, an‎d petrochemical industries. The joining of these alloys by conventional fusion welding techniques, such as Gas Tungsten Arc Welding (GTAW), is often hindered by the formation of brittle intermetallic phases, heat-induced cracking, an‎d chemical segregation due to considerable differences in chemical composition, thermal expansion coefficients, an‎d alloy element diffusivities. Fusion welding methods cause extensive melting, rapid cooling rates, an‎d severe microstructural heterogeneity; consequently, a significant accumulation of niobium an‎d titanium at elevated temperatures leads to the formation of compounds such as Fe₂Nb, Ni₃Nb, an‎d unstable brittle carbides, severely reducing the tensile strength, bending resistance, impact toughness, an‎d ductility of the joint—rendering the joining of such alloys practically impossible by these processes.Given all these considerations, solid-state welding processes offer the best solution for achieving this joint. Although various solid-state techniques like diffusion bonding, friction welding, an‎d explosive welding have been previously examined, they have shown limited success. Spark Plasma Welding, by generating pulsed electrical discharge an‎d simultaneous pressure, facilitates joining in a quasi-solid-state regime without full melting of the joint area.The present study aims to investigate the microstructure an‎d mechanical properties of the joint between low-carbon 316 stainless steel an‎d Inconel 718 using Spark Plasma Welding. The joining process was studied at temperatures ranging from 800 to 1000 °C, pressures of 40 to 60 MPa, an‎d process times of 5 to 10 minutes. The resulting joint microstructure was characterized by optical microscopy, an‎d grain boundaries an‎d structure were assessed. For detailed analysis of intermetallic phases an‎d reaction layers at the joint interface, X-ray diffraction (XRD) was employed for phase identification, an‎d scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM/EDS) was used to determine layer morphology an‎d thickness. Analysis revealed that the thickness of reaction layers increased with higher process temperatures, an‎d distinctive intermetallic phases with notable continuity were observed at the interface. At 900 °C, a continuous Fe-Ni intermetallic phase formed at the joint boundary. Microhardness at the interface was measured at the aforementioned temperatures. Tensile an‎d bending strengths of the joint were eva‎luated at 850, 900, an‎d 950 °C, yielding maximum tensile strength of approximately 960 MPa an‎d bending strength of 19 MPa at 900 °C. Fracture surfaces were also examined using scanning electron microscopy. Keywords: Spark Plasma Welding, Inconel 718, Low-Carbon 316 Stainless Steel, Mechanical Properties, Microstructure, Dissimilar Joint.

علي شفيعي

محمدحسين مصلي‌نژاد , محمدرضا طرقي نژاد