Study On The Microstructure,antibacterial And Mechanical Properties Of Fe-based Medium-entropy Alloy

In daily production environments,bacteria like E.Coli and S.Aureus can be present,making it crucial to maintain a clean and healthy living space.As a result,there is a growing need for materials that exhibit exceptional mechanical properties,corrosion resistance,processing capabilities,and potent,broad-spectrum antibacterial properties.Steel is the dominant structural material today,and the exploration of new antimicrobial high-performance structural steel with integrated antimicrobial functionality will bring significant social and economic benefits.At present,the traditional design concepts of alloyed materials based on the concept of“enthalpy”are reaching their limits,while the new metal materials designed based on the concept of"entropy"have overturned the traditional material design ideas and continuously made breakthroughs in performance.For example,medium-entropy alloys,with only2～4 main elements and conformational entropy usually between 1 R～1.5 R,have comparable or even better mechanical properties than high-entropy alloys and are easy to be applied industrially,and are rapidly developing and gaining widespread attention.In this paper,Fe-based medium alloys with excellent mechanical and antibacterial properties were prepared,and the effects of the addition of Cu and Ag elements on the microstructure,mechanical properties and antibacterial properties of two Fe-based medium-entropy alloy systems were systematically investigated.First,two medium entropy alloy systems,(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_99.5-XCu _XAg_0.5（X=1,2,3,4,5 at.%）and(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_88-XCu₁₂Ag _X（X=1,2,3,4,5 at.%）,were prepared by magnetically suspended water-cooled copper crucible melting and negative-pressure copper mold suction casting.Alloy(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_99.5-XCu _Xg_0.5（X=1,2,3,4,5 at.%）was subjected to antibacterial ageing heat treatment,and(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_88-XCu₁₂Ag _X（X=1,2,3,4,5 at.%）are cast alloys.The phase and microstructure of the two medium-entropy alloy systems were studied,and it was found that two different FCC str-uctures in the alloys,namely FCC1 phase and FCC2phase,and the FCC2 phase was more obviously enriched between the dendrites as the content of Cu and Ag elements increased.The compressive mechanical properties of the two alloy systems were studied,and it was found that the yield strength of the(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_99.5-XCu _Xg_0.5（X=1,2,3,4,5 at.%）alloy system gradually decreased with the increase of Cu content,and the compressive strength and plasticity showed a trend of first increasing and then decreasing.The overall mechanical properties of(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_95.5Cu₄g_0.5alloy were better,with yield strength,compressive strength and plasticity of 861 MPa,2881 MPa and 30.8%,respectively.In the(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_88-XCu₁₂Ag _X（X=1,2,3,4,5 at.%）alloy system,with the increase of Ag content,the yield strength of the medium entropy alloy first increases and then decreases,the compressive strength first increases and then decreases,and the plastic deformation gradually decreases.Among them,(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)₈₆Cu₁₂Ag₂possesses better combined mechanical properties,with yield strength,compressive strength and plasticity of 1100 MPa,1921 MPa and27.0%,respectively.Then,the antimicrobial properties of the medium entropy alloy(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_99.5-XCu _XAg_0.5（X=1,2,3,4,5 at.%）were examined by the overlay method,and it was found that with the increase of Cu elements,the antimicrobial rate of the entropic alloy(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_99.5-XCu _XAg_0.5（X=1,2,3,4,5 at.%）against two bacteria at 6 h first increased and then decreased,and the antimicrobial rate at 12 h and 24 h basically stabilized,but still showed an increasing trend,in which the best effect was achieved by the alloy(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_97.5C u₂Ag_0.5,with the antimicrobial rate at 6 h of 99.49%（Escherichia coli）and 98.35%（S.aureus）,and 99.92%and 99.93%for both bacteria at 12 and 24 hours,respectively.And the SEM results found that with the increase of Cu,the size of the antibacterial phase enriched with Cu and Ag in the alloy gradually increased,and the larger antibacterial phase was sparsely distributed on the substrate,which led to the difficulty of the antibacterial ions to quickly interact with the bacteria,so the short time antibacterial ability of the medium entropy alloy decreased.Finally,the antimicrobial properties of the(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_88-XCu₁₂Ag _X（X=1,2,3,4,5 at.%）medium entropy alloy were studied by the same method,and the results showed that with the increase of Ag element,the antimicrobial rate of the(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_88-XCu₁₂Ag _X（X=1,2,3,4,5 at.%）medium entropy alloy against E.coli and S.aureus for 2 hours gradually decreased,and the antimicrobial rate against E.coli for 6 hours,showed a trend of increasing and then decreasing,and the antimicrobial rate against S.aureus for 6 hours gradually increased,and the antimicrobial rate against both bacteria for 12 and 24 hours The antibacterial rate basically tends to be stable with a small increase.The best antibacterial rate of(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)₈₇Cu₁₂Ag₁medium entropy alloy was 86.95%（E.coli）and91.03%（S.aureus）at 2 h.The best antibacterial rate of(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)₈₆Cu₁₂Ag₂medium entropy alloy was 99.91%（E.coli）and 99.90%（S.aureus）at 6 h.The best antibacterial rate of(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)₈₃Cu₁₂Ag₅（X=1,2,3,4,5 at.%）was99.97%（E.coli）and 99.98%（S.aureus）at 12 h and 24 h,respectively.,99.98%（S.aureus）and 99.99%（E.coli and S.aureus）.According to the SEM analysis,it was found that with the increase of Ag,antimicrobial phases with larger size and sparse distribution appeared,which led to a decrease in the antimicrobial effect of the alloy for a short time.Similarly,based on the mechanical and antimicrobial properties of the medium entropy alloy of this system,the(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)₈₆Cu₁₂Ag₂alloy was found to possess superior overall properties.Combining the antimicrobial properties of the two medium entropy alloy systems,it is found that the overall antimicrobial properties of the(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_88-XCu₁₂Ag _X（X=1,2,3,4,5at.%）medium entropy alloy are better than those of the(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)_99.5-XCu _XAg_0.5（X=1,2,3,4,5 at.%）alloy,and without complicated antimicrobial aging heat treatment processes.