Microstructure And Corrosion Performance Of Inconel 718 Alloy Fabricated By Selective Laser Melting

Inconel 718 alloy is one of the most commonly used alloy materials for selective laser melting.Selective laser melted Inconel 718 alloy（SLM Inconel 718 alloy）has been widely used in aerospace,nuclear power,shipbuilding and chemical industries.Corrosion performance is one of the important performance indicators of Inconel 718 alloy for selective laser melting,which directly affects the durability and service safety of alloy components.Due to the special forming process of selective laser melting,the microstructure and composition distribution of materials are different from those of traditionally processed materials,resulting in different corrosion behaviors.Therefore,the corrosion behavior of SLM Inconel 718 alloy was systematically investigated by using a variety of electrochemical testing techniques combined with composition and morphology characterization techniques in the typical corrosive medium at room temperature,and compared with commercial rolled Inconel 718 alloy（R Inconel 718 alloy）,it was observed that:In 3.5 wt.% NaCl solution,the corrosion resistance of SLM Inconel 718 alloy is inferior to that of R Inconel 718 alloy.SLM Inconel 718 alloy suffers from severe localized corrosion,which preferentially occurs at the melt-pool boundary and dendrites are severely corroded.The reason is that the carrier density of the passive film formed on the surface of the SLM Inconel 718 alloy is higher than that of the R Inconel 718 alloy,and the content of porous Ni O in the passive film is higher and the content of compact Cr2O3 is less,resulting in a decrease in protective performance and corrosion resistance for the passive film decreased.In 0.1 mol/L NaOH solution,pitting corrosion observed in both SLM Inconel 718 alloy and R Inconel 718 alloy.SLM Inconel 718 alloy underwent four stages of corrosion process:passivation,dissolution,secondary passivation,and pitting corrosion.Pitting corrosion preferentially occurred at melt-pool boundaries and defect sites.Compared with R Inconel718 alloy,SLM Inconel 718 alloy exhibited lower activity,lower corrosion rate,and thus lower corrosion susceptibility.The main reasons are that the carrier density of the passive film formed on SLM Inconel 718 alloy was lower,and the content of Cr2O3 with high protection in the passive film was relatively higher,the content of porous Ni O is relatively lower,and the passive film was more compact.Therefore,the passive film formed on SLM Inconel 718 alloy exhibited high protection performance and excellent corrosion resistance.In 0.05 mol/L H₂SO₄ solution,the corrosion resistance of SLM Inconel 718 alloy is better than that of R Inconel 718 alloy.SLM Inconel 718 alloy underwent uniform corrosion,which preferentially occurred at the melt-pool boundary and phase boundary with the dendrite/cellular interface.Compared with R Inconel 718 alloy,SLM Inconel 718 alloy exhibited lower corrosion current density and passive current density,resulting in excellent corrosion resistance.The main reasons are that the value of polarization resistance for SLM Inconel 718 alloy increased and was higher than that of R Inconel 718 alloy with the increase of immersion time.Ni O,Cr2O3 and Fe2O3 were the main components of the passive film for SLM Inconel 718 alloy and R Inconel 718 alloy,but the content of compact Cr2O3 in the passive film of SLM Inconel 718 alloy increased with the increase of immersion time,while the content of porous Ni O decreased,and its passive film was relatively compact and stable,thus providing better protection.