Research On The Surface Treatment And Corrosion Behaviour Of 316L Stainless Steel Fabricated By Selective Laser Melting

Selective laser melting（SLM）technology is an additive manufacturing,which plays an important role in metal structure manufacturing.SLM has several advantages,such as forming rapidly,creating complex-shaped parts,mechanical properties,leading it is widely applied in aerospace,automotive,medical and mold.Conventional 316L stainless steel is widely used due to its low cost,superior corrosion resistance and strong oxidation resistance.Therefore,the mechanical properties and corrosion resistance of SLM 316L is studied extensivly.However,it is unclear that how the cold rolling affects the corrosion behaviour and microstructures of SLM 316L stainless steel.Furthermore,there is no an effective post-surface treatment technology to remove spheroidized particles,incomplete fusion,rough surface and other defects caused by SLM forming.On the one hand,the influence of cold rolling on the evolution of corrosion resistance of SLM 316L stainless steel was studied by electrochemical tests in this work.On the other hand,an effective surface treatment technology of SLM 316L parts was studied by a series of surface treatment experiments.Moreover,optical microscope,SEM,EBSD and XRD were also used in this study to characterize the microstructure,and roughness meter,nano indentation meter and other instruments were used to test the surface roughness,hardness and other properties of materials.It is found that the pitting resistance of cold-rolled SLM 316L stainless steel increased with the rolling degree,reached the peak at 20%rolling,and then decreased with further rolling.When the rolling degree less than 20%,MPBs and GBs are the dominant factors in the corrosion behavior.But,the dislocation density determined the corrosion behaviour of SLM 316L stainless steel with the rolling degree greater than20%.The interrupted MPBs,the increasedΣ3 boundaries and LAGBs improved the corrosion resistance of SLM 316L stainless steel,while the increased DD decreased its corrosion resistance.The corrosion behavior of the cold-rolled SLM 316L stainless steel is determined by the coupling effect of these microstructural changes induced by rolling.The celluar structure size and low angle grain boundaries changed with increasing the cold rolling degree,resulting the hardness of SLM 316L stainless steel increased.In this paper,an effective surface treatment technology was proposed to improve the surface quality of SLM 316L stainless steel.This technology included three steps of sandblasting,oxide removal and regeneration,and compound polishing.Sandblasting treatment removed the spheroidal particles,pores and other defects on the surface of SLM 316L stainless steel through the impact force and shear force of SiO₂sand at high speed and high pressure.Thus,after sandblasting treatment,the smoothness and uniformity of SLM 316L stainless steel was improved,and corrosion cracks on the surface were inhibited.Severe plastic deformation proposed when the sandblasting lead to the more compact surface structures of materials.After sandblasting,the new passivation film exposed is more stable and the original outermost passivation film is removed.Moreover,the grains in the surface/subsurface were refined and the molten pool boundary near the sandblasting surface was blurred,which could improve the corrosion resistance of SLM 316L stainless steel.