Study On Structure Evolution And Antimicrobial Properties Of Copper Bearing Stainless Steel Produced By Laser Additive Manufacturing

Copper-bearing stainless steel exhibits a long-term and stable antibacterial ability,so it has a very broad application prospect in the field of medical and health.Generally,the forming process and alloy composition have great influence on the corrosion resistance and antibacterial property of copper-bearing stainless steel.As such,it is necessary to optimize the alloy composition on the basis of exploring the forming process and heat treatment to improve the comprehensive properties of copper-bearing stainless steel.In this paper,Laser Melting Deposition（LMD）and Selected Laser Melting（SLM）combined with heat treatment were used to prepare the copper-bearing 316L stainless steels.The effects of copper content and heat treatment temperatures on the corrosion resistance,strength and toughness and antibacterial properties of laser additive manufacturing copper-bearing stainless steels were investigated systematically.The main conclusions are listed as follows:（1）In LMD-produced copper-bearing stainless steel（0-7.5 wt.%Cu）,the addition of Cu can refine the austenite dendritic and increase the grain boundary densities,which is favorable to the growth of passivation film at grain boundaries and promote the thickening of passivation film.With the increase of copper content,the impedance values of copper-bearing stainless steels increase,which is consistent with the change trend of Cr₂O₃ and Cu₂O in XPS.Under the synergistic action of Cr and Cu,the self-corrosion current density of LMD-produced 316L-7.5Cu is as low as 0.119μA·cm^-2 and the self-corrosion potential is as high as-0.320 V.（2）The subgrain size of SLM copper-bearing stainless steels increases after heat treatment（500℃ and 700℃ for 6 h）,which is attributed to the growth and recrystallization of grains promoted by the release of residual stress.The addition of Cu can further reduce the ferrite content in copper-bearing stainless steels,which has a positive effect on enhancing the corrosion resistance of stainless steels.Therefore,when the copper content is increased to 4.5 wt.%and the heat treatment is conducted at 500℃,the copper-bearing stainless steel has fine grains,less ferrite and dense passivation film,and the self-corrosion current density is as low as 1.44μA·cm^-2 and the self-corrosion potential is as high as-0.489 V.（3）The tensile strength and elongation of SLM-produced copper-bearing stainless steels with the same composition increase with the increase of heat treatment temperature.At the same heat treatment temperature,the tensile strength and elongation of the samples decrease with the increase of copper content,which is attributed to the interaction between dislocation and twins andε-Cu precipitated phase.The deformation twins can hinder the movement of the slip zone,resulting in the increase of the tensile strength.The dislocations can be decomposed into movable dislocations at the twin boundaries,which can enhance the ductility.The copper-rich precipitated phases are dispersed within the matrix and can hinder the dislocation movement,which can improve the strength.Dislocation cutting through copper-rich precipitated phases can continue to move to improve the plasticity.After heat treatment at 700℃,the tensile strength and elongation of SLM-produced 316L-4.5Cu rise abnormally,indicating that the effect of heat treatment on stacking fault energy is greater than that of alloy composition.The tensile strength and elongation of SLM-produced 316L-4.5Cu is increased to～693.32 MPa and～56.94%.（4）With the increase of copper content and heat treatment temperature,antibacterial rate of SLM-produced copper stainless steel.As such,the S.aureus antibacterial effect is better than that of the antibacterial effect of E.coli,the Cu²⁺and the negatively charged bacterial cell wall or membrane together.Therefore,the cell wall and cell membrane permeability can be increased so that bacteria matter inside a large number of leakage caused by the death.