Study On The FeCoNiB Eutectic High-entropy Alloy Composition Design And Deep Undercooling Solidification

High-entropy alloys have the characteristics of high entropy effect,delayed diffusion,lattice distortion and"cocktail effect".Compared with traditional alloys,they have a simple structure and excellent comprehensive properties;eutectic alloys have better phase stability and interfacial energy.Low,stable dislocation structure,usually with high fracture strength and high temperature creep resistance.Therefore,eutectic high-entropy alloys can combine the advantages of high-entropy alloys and eutectic materials to achieve a balance between strength and plasticity.The current research on eutectic high-entropy alloys mainly focuses on composition design and performance improvement,and the study of its solidification mechanism still needs to be in-depth.In this paper,Fe-Co-Ni-B quasi-eutectic high-entropy alloys with different compositions are prepared in a vacuum high-frequency induction melting furnace.The smelted samples are analyzed and tested by XRD,SEM,TEM,etc.,and then the Fe Co Ni B quasi-eutectic alloy is studied by the method of molten glass+cycle overheating.The influence of the cooling curve and solidification structure of the eutectic high-entropy alloy under different undercooling degrees to determine the solidification path,and the following conclusions are drawn:（1）Fe-Co-Ni-B quasi-eutectic high-entropy alloy containing non-metallic principal element B is obtained.When the Fe,B,Co and Ni elements are 7%,18%,37.5%and 37.5%respectively,the microstructure presents a typical lamellar eutectic structure,and its phase composition is Fe Co Ni FCC solid solution and intermetallic compound（Fe Co Ni）₃B.（2）In Fe_x（Co Ni）_82-xB₁₈ alloy,it is found that the change of Fe element content has a great influence on the microscopic morphology and phase composition of Fe Co Ni B alloy.When the Fe element content is from 28%to 7%,the morphology changes from coarse The dendrite structure transforms into a fine dendritic structure,and finally into a eutectic layered structure.In the Fe₇（Co Ni）_93-xB_x alloy design,it is found that as the B content increases from 6%to 22%,the primary phases in the alloy microstructure gradually decrease,and the intermetallic compound phases gradually increase,a fully lamellar quasi-eutectic high-entropy alloy（Fe Co Ni primary phase+eutectic layer sheet）forms.（3）The alloy has reached a supercooling degree of over 200 K through the method of molten glass+cycle overheating.Fe₇（Co Ni）₇₇B₁₆ hypoeutectic alloy has two reblows during the deep subcooling experiment,and the distribution corresponds to the nucleation growth of FCC phase and the formation of eutectic phase,while Fe₇（Co Ni）₇₅B₁₈ eutectic alloy has only one recalescence,and as the degree of undercooling increases,the maximum recalescence temperature gradually decreases,the corresponding isothermal plateau time is shortened,and the recalescence rate increases.The solidification structure transforms from a complete lamellar eutectic to FCC solid solution+lamellar eutectic inclusions and point and rod eutectic.When the undercooling reaches 200 K,the regular eutectic morphology has completely disappeared,and the eutectic structure is heavy.Melting and solidification structure is irregular eutectic.