Design,Strengthening Mechanism And Properties Of Fe-Co-Cr-Ni-Based Interstitial Solid-Solution Strengthened High-Entropy Alloys

In recent years,with the development of materials genome engineering,the application of machine learning has provided new methods and ideas for the design and development of high-entropy alloys with excellent properties,and the guiding role of the computational phase diagram（CALPHAD）method for material design and development.It is more and more recognized by people,which can greatly shorten the development cycle of new materials and reduce the cost of research and development.High-entropy alloys have a series of excellent properties and show broad application prospects.The addition of interstitial atoms in high-entropy alloys makes the alloys form interstitial solid solutions,especially the addition of C and B elements plays a very important role in the mechanical properties of metal materials.important role.In this study,the hardness and tensile strength of Fe-Co-Cr-Ni system high-entropy alloys were predicted by machine learning to obtain a matrix high-entropy alloy Ni₃₅Fe₂₀Co₂₀Cr₁₁Al₇Ti₇ with better comprehensive mechanical properties,and experimental verification was carried out.At the same time,the CALPHAD method was used to preliminarily predict the change of phase composition and volume fraction with temperature after adding interstitial elements（C and B）to the matrix high-entropy alloy Ni₃₅Fe₂₀Co₂₀Cr₁₁Al₇Ti₇,and then systematically study the effect of interstitial atoms（C and B）on high-entropy alloys.The effect of Ni₃₅Fe₂₀Co₂₀Cr₁₁Al₇Ti₇ on the microstructure,tensile properties,friction and wear properties,electrochemical corrosion properties and high temperature oxidation properties,the main conclusions are as follows:（1）Based on the prediction of the machine learning model,the Ni₃₅Fe₂₀Co₂₀Cr₁₁Al₇Ti₇high-entropy alloy with better comprehensive mechanical properties was obtained by iterative optimization and screening,and the CALPHAD calculation and test results showed that the alloy was composed of FCC,L2₁ and L1₂ phases.The results have good consistency;（2）The effect of interstitial atoms（C and B）content on the microstructure of Ni₃₅Fe₂₀Co₂₀Cr₁₁Al₇Ti₇high-entropy alloys:the base alloy without interstitial atoms is composed of FCC,L2₁ and L1₂ phases.MC carbide phase and MB2 boride phase are generated in the entropy alloy.At the same time,interstitial atoms are solid-dissolved into the matrix,causing lattice distortion,and the diffraction peaks tend to shift to the left;homogenization and aging treatment The high-entropy alloys are the same.Ti,B and C elements are mainly concentrated and distributed along the grain boundaries,and other elements are mainly uniformly distributed in the matrix,with less content at the grain boundaries;there are a large amount of Ti C and Ti B₂ hard at the grain boundaries.Phase formation,which plays a"pinning"role at the grain boundary,thereby strengthening the grain boundary and improving the mechanical properties of the alloy;（3）The effect of interstitial atom（C and B）content on the friction and wear properties Ni₃₅Fe₂₀Co₂₀Cr₁₁Al₇Ti₇ high-entropy alloy:with the increase of interstitial atom content,the hardness of the alloy increases first and then decreases,and the wear first decreases and then increases.The wear rate and hardness inversely proportional relationship.When the C content is 0.1 at.%and the B content is 1.0 at.%,the wear resistance of the alloy is the best,and the wear mechanism is mainly abrasive wear and adhesive wear;（4）The effect of interstitial atom（C and B）content on the electrochemical corrosion properties of Ni₃₅Fe₂₀Co₂₀Cr₁₁Al₇Ti₇ high-entropy alloys:in 3.5 wt.%Na Cl solution,with the increase of interstitial atom content,the corrosion potential and corrosion current density of high-entropy alloys did not change much.When the B content was 2.5 at.%,the electrochemical corrosion performance of the alloy was the worst;（5）The effect of interstitial atom（C and B）content on the high-temperature oxidation performance of Ni₃₅Fe₂₀Co₂₀Cr₁₁Al₇Ti₇ high-entropy alloys:after high-temperature oxidation at different temperatures for 80 h,the thickness of the oxide layer formed on the surface of the alloy decreased with the increase of interstitial atom content first and then increase,the oxide layer is composed of Ti O₂ and Fe₂O₃ in the outermost layer and Cr₂O₃and Al₂O₃ in the inner layer,and the structure distribution of the oxide layer is relatively uniform.The variation law of oxide layer thickness with interstitial atom content at each temperature is similar,and it is consistent with the oxidation kinetics curve.When the C content is 0.1 at.%and the B content is 2.5 at.%,the high temperature oxidation performance of the alloy is the best.This study shows that the interstitial solid solution strengthening method by adding interstitial atoms（C and B）to Ni₃₅Fe₂₀Co₂₀Cr₁₁Al₇Ti₇ high-entropy alloys in Fe-Co-Cr-Ni matrix is an effective strengthening method,which can further improve the performance of high-entropy alloys.