Corrosion Study of Selective Laser Melted IN718 Alloy upon Post Heat Treatment and Shot Peening

Abstract

Selective laser melted (SLM) IN 718 alloy specimens are subjected to heat treatment and shot peening to assess the effect of post processing on the corrosion performance of the alloy in a 3.5 wt % NaCl solution. The four conditions used in this analysis are as-built material (AB), heat-treated as-built material (HT), shot-peened as-built material (SP), and heat-treated and shot-peened as-built material (HTSP). Microstructural studies revealed the presence of a 500 nm sized cellular structure with a γ matrix surrounded by the Laves phase in the AB material. Shot-peening reduced the surface roughness of the AB and HT samples to almost 80%. The potentiodynamic experiments revealed a highest Icorr value of 0.21 µA/cm2 for the AB material and the lowest Icorr value of 0.04 µA/cm2 for the HTSP material. In the Electrochemical Impedance Spectroscopy (EIS) analysis, the Nyquist plot substantiated the increasing corrosion resistance in the same order of decreasing corrosion rate. The Bode plot exhibited two resistance–capacitance (RC) time constants for all four conditions. The solution resistance measured around 30 Ω, with the HTSP specimen exhibiting the highest passive film resistance of 676 kΩ cm2 and the AB specimen exhibiting the lowest passive film resistance of 234 kΩ cm2. This study has shown that elimination of the network of the Laves phase in SLM material through heat treatment and smooth surface morphology achieved through shot peening improves the corrosion resistance of Inconel 718 alloy.