Research On Mechanical And Corrosion Properties Of Fe-based Medium Entropy Alloys

At present,the traditional alloying material design concept based on the concept of"enthalpy"is approaching its limit,and the new metal materials designed based on the concept of"entropy",high and medium entropy alloys and amorphous alloys,subvert the traditional design ideas of materials and are in terms of performance.Continuous breakthroughs have been made,and the non-isoatomic ratio heterogeneous second-generation high-entropy alloy developed from the first-generation high-entropy alloy with equal atom ratio has greater design freedom and the"cocktail"effect in performance is more fully developed.In this paper,In this paper,magnetic levitation smelting-negative pressure copper mold suction casting method was used to prepare single-phase Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8 and two-phase Fe_54.1Mn_23.2Si_9.1Cr_9.8C_3.8 two medium entropy alloys with different Mn content.AISI304 is used as a comparative material.The corrosion behavior is studied in1mol/L HCl and 1mol/L Na OH solutions.The corrosion phenomena and corrosion products of neutral salt spray corrosion under different time lengths are studied.Explore the composition-organization-performance relationship.Choose Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8medium entropy alloy with better corrosion resistance,add1%Ag,Cu,Ce elements.Explore the effects of Ag,Cu,Ce on alloy entropy,enthalpy,atomic size difference and other thermodynamic parameters,microstructure,hardness,electrochemical corrosion in 1mol/L HCl and 1mol/L Na OH.Analyze the relationship between composition-organization-performance,and summarize the laws and influencing factors of the corrosion resistance of the alloy.Studies have shown that the entropy values of Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8and Fe_54.1Mn_23.2Si_9.1Cr_9.8C_3.8 alloys are 1.14R and 1.31R,respectively,which belong to medium-entropy alloys.When x=14,the alloy structure is FCC structure,when x=23.2,the alloy structure is FCC+HCP structure,and the elements are evenly distributed in the alloy.Fe_54.1Mn_23.2Si_9.1Cr_9.8C_3.8 has a largeδ,large lattice distortion energy,and excellent comprehensive mechanical properties,with a maximum hardness of 650.26 Hv,a fracture strength of 2332 MPa,and a yield strength of 1526MPa.The corrosion resistance of the two medium-entropy alloys in 1mol/L HCl and1mol/L Na OH solutions is better than AISI304,Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8 alloy has the best corrosion resistance,the content of Mn increases,and the corrosion process Atom substitution migration occurs,the corrosion products contain Mn oxides,the content of corrosion-resistant Cr decreases,and the oxide film is more likely to be destroyed.The H⁺and Cl^-in HCl continue to corrode the oxide film,and the corrosion marks on the alloy surface are heavy.In 1mol/L HCl,Ecor is-0.586 V,Icorr is 7.908×10^-8A·cm^-2,and Rp is 5.1775×10⁶Ω·cm².Corrosion pits appeared on the surface of the alloy in Na OH solution.In 1mol/L Na OH solution,Ecor is-0.465 V,Icorr is7.023×10^-8 A·cm^-2,and Rp is 6.7545×10⁵Ω·cm².Carry out 0、48、120、240、480h salt spray corrosion.With the extension of the salt spray corrosion experiment time,the tested surface of the alloy begins to corrode.At 240h,obvious corrosion marks can be observed on the surface of the alloy.At 480h,Fe_54.1Mn_23.2Si_9.1Cr_9.8C_3.8 and AISI304 alloy corroded severely,and obvious corrosion pits appeared.The corrosion weight loss curve shows that the corrosion rate is greater in the later stage of the salt spray corrosion experiment.The XPS total spectrum analysis shows that the spectrum of Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8 is located at the bottom,and the less excited energy can form a passivation film faster.The split-peak XPS spectra of Fe2p,Mn2p,and Cr2p show that the corrosion products are roughly the same,and the corrosion resistance mainly comes from the compounds formed by Cr.The electrochemical corrosion study of the 0h and 480h samples in 3.5%Na Cl solution shows that the passive film containing Cr on the salt spray corrosion surface has a protective effect on the internal alloy.The 480h Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8 medium entropy alloy Ecor is-0.367 V,Icorr is 2.860×10^-8A·cm^-2,and Rp is 2.535×10⁶Ω·cm²,which has the best corrosion resistance.After adding 1%of Ag,Cu,Ce,the alloy entropy value is between 1R and 1.5R,which belongs to the category of medium entropy alloy.The mixed alloy is negative,and the atomic size difference,electronegativity difference and valence electron concentration value are small so it has the single FCC structure.(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)₉₉Ce₁alloy has the largestδand large lattice distortion energy.Ce has the best comprehensive mechanical properties by purifying the melt and grain refinement.The fracture strength is 2815 MPa,and the yield strength is 854MPa,the elongation rate is 22.89%,and the maximum hardness can reach 658.4 Hv.The alloy system has lower energy,finer grains,and enrichment of rare earth Ce on the surface,so a dense and uniform passivation film is formed after corrosion.In(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)₉₉Cu₁,the Cu-rich phase and Cr-rich phase form micro galvanic cells.The Cu-rich phase will corrode preferentially,and Cu deteriorates the corrosion resistance of the alloy.(Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)₉₉Ce₁ alloy has the best corrosion resistance in 1mol/L HCl and Na OH solutions.The self-corrosion potential in 1mol/L HCl Ecorr is-0.443 V,Icorr is 8.436×10^-9A·cm^-2,Rp is 5.2571×10⁶Ω·cm².In 1mol/L Na OH solution,Ecorr is-0.379 V,Icorr is 4.226×10^-8A·cm^-2,and Rp is4.7376×10⁷Ω·cm².