Microstructure dependent electrochemical corrosion behavior of SLM inconel 625 alloys in the presence of a molten KCl–Na2SO4 film at 600 °C in air

The influence of the microstructure of IN625 alloys fabricated by selective laser melting (SLM), both in the as-built condition and after being heat-treated at 980°C (HT-I) and 1100°C (HT-II), on their corrosion behavior beneath a molten KCl-Na 2 SO 4 film at 600°C in air was investigated through electrochemical impedance spectroscopy (EIS), comparing with the forged counterpart. The as-built and HT-I alloys formed compact, multilayered Cr 2 O 3 /sulfide scales that appeared to act as diffusion barriers, suppressing chloride-induced self-sustaining reactions and sulfur ingress, as evidenced by the double capacitive loops in EIS. By contrast, HT-II and forged alloys exhibited porous mixed oxide–sulfide scales and obvious Cr-depleted zones, with Warburg-type impedance indicating diffusion-controlled corrosion. High sub-boundaries and low-angle grain boundaries (LAGBs: 31.5% and 42.1%) fractions in as-built/HT-I enable rapid outward Cr transport and continuous chromia repair, whereas CSL/TB-rich networks in HT-II/forged alloys ( CSL: 55.34% and 48.36%; TB: 33.3% and 35.6% ) impede Cr supply, promote internal sulfidation, and magnify fluxing/oxychlorination porosity. This work highlights the microstructure-dependent corrosion mechanisms of SLM IN625 alloys and suggests that tailoring grain boundary character can enhance hot corrosion resistance in molten salt environments.