Studies on Electron Beam Surface Remelted Inconel 718 Superalloy
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Studies on Electron Beam Surface Remelted Inconel 718 Superalloy Sumit K. Sharma1 · K. Biswas1 · J. Dutta Majumdar1 Received: 11 April 2020 / Accepted: 17 September 2020 © The Korean Institute of Metals and Materials 2020
Abstract The present study aims at a detailed investigation of microstructure, residual stress and evaluation of microhardness of electron beam surface remelted Inconel 718 alloy using an indigenously developed electron beam welding unit (with a capacity of 80 kV acceleration voltage and a power of 12 kW). Electron beam surface remelting has been carried out at a constant voltage of 40 kV with varying scan speed from 500 to 1000 mm/min. The detailed study involves understanding of the effect of process parameters on the surface roughness, microstructure, residual stress, and hardness of the melt zone. Surface remelting leads to a significant refinement of microstructure with the presence of γ primary dendrites, fine precipitates of Ni3(Al,Ti) (γ′), and MC (metallic carbides). Due to microstructural refinement and presence of fine precipitates, there is an introduction of residual compressive stress and improvement in hardness. Finally, a detailed study of the effect of process parameters on the microstructure, residual stress and microhardness has been undertaken to optimize the process parameters for electron beam remelting of INCONEL718. Keywords Electron beam surface remelting · Surface roughness · Microstructure · residual stress · microhardness · Inconel 718
1 Introduction Inconel 718 is a nickel based super alloy with the composition of 50–55 wt% Ni, 17–21 wt% Cr, 0.2–0.8 wt% Al, 0.65–1.15 wt% Ti, 4.75–5.5 wt% Nb, 2.8–3.3 wt% Mo, 0.35% Mn 0.35 wt% Si, 0.006 wt% B, 0.08 wt% C, 0.15 wt% S, and balance Fe. It is widely used as components for jet engines, gas turbine blades, vanes, combustion chamber, and shells of gas generators because of its capability to withstand very high temperatures (400–700 °C), and high pressures complemented by excellent mechanical strength due to presence of a Ni phase (γ) along with disordered gamma phase (gamma prime-γ′). Though Inconel 718 is an important alloy for structural applications in aerospace and * J. Dutta Majumdar [email protected] Sumit K. Sharma [email protected] K. Biswas [email protected] 1
Department of Metallurgical and materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
marine sector, it often undergoes failure due to wear, and hot erosion. Wear and erosion may be minimized by a suitable modification of surface microstructure and composition. Akca [1] investigated the effect of strengthening heat treatment on the microstructure and mechanical properties of Inconel 718. Zhao et al. [2] investigated the evolution of Ni3Al phase in Ni based superalloy. Salma and Abdellaui [3] also reported the presence of gamma (γ), gamma prime (γ′) and gamma double prime (γ″) phases in the microstructure of Inconel718 superalloy, though the nature of precipitations were reported to be strong
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