Inconel 718 is a precipitation-strengthened Ni-based superalloy which finds applications across a wide temperature range (up to 650°C). It shows excellent yield strength, ductility, creep resistance and fatigue strength. Surface treatment is known to improve the fatigue life of materials via nano-crystallization of the surface layer. However, the precipitation behavior of the surface-treated layer is largely unexplored. In this regard, the present study aims to investigate and compare the precipitation in the surface-treated layer and the bulk solution-treated IN718. The material is subjected to surface mechanical attrition treatment (SMAT) after solution treatment and is followed by a two-step aging treatment which promotes the precipitation of γ″/γ′ in the alloy. The precipitation behavior shown by the bulk and SMAT layer was different. After aging, the bulk shows a microcrystalline γ matrix containing γ″ precipitates, whereas the microstructure of the surface layer consists of nanograins with nanotwins. No evidence of γ″/γ′ precipitates were observed in the SMAT layer. The formation of nanograins in the surface layer after aging is attributed to recrystallization with controlled grain growth. The differential microstructures due to the chosen processing route have resulted in increased hardness of the surface layer and increased wear life of the material.
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A. Bisht, Gaddam, S., Kumar, L., Dileep B. P., and Suwas, S., “Precipitation Behavior of IN718 After Surface Mechanical Attrition Treatment (SMAT) and Its Effect on Wear Properties”, JOM, 2018.