Study On Microstructure And Properties Of Directional Solidification Of AlCoCrFeNi_2.1 Eutectic High Entropy Alloy

Eutectic high-entropy alloy is a new type of alloy with great advantages in high-entropy alloy.It combines the advantages of high-entropy alloy and eutectic material,balances the contradiction between strength and plasticity of metal material,has good forming ability,overcomes the phenomenon of component segregation,and has good high temperature stability.The emergence of eutectic high-entropy alloys has made high-entropy alloys an important step towards high-temperature structural materials.In this paper,AlCoCrFeNi2.1,eutectic high-entropy alloy was selected,and the preparation method was changed to further optimize the properties of the eutectic high-entropy alloy,and the thermal stability of its structure and mechanical properties after heat treatment were studied.In this paper,AlCoCrFeNi2.1 eutectic high-entropy alloy master alloy was prepared by vacuum induction melting,and the eutectic high-entropy alloy with different drawing rates(6?m/s-120?m/s)was prepared by directional solidification.The solidification growth law of the eutectic high-entropy alloy at different drawing rates was studied.The law of solidification growth of alloys at different drawing rates,and the thermal stability and mechanical properties of the eutectic high-entropy alloy were studied by high temperature heat treatment of different processes.The main conclusions are as follows:The microstructure of AlCoCrFeNi2.1 eutectic high-entropy alloy by vacuum induction melting is composed of eutectic dendrites,which are composed of FCC and BCC phases.After directional solidification,with the increase of drawing rate(6?m/s-120?m/s),the morphology of solid/liquid interface undergoes a flat-cell-dendrite transition from the longitudinal interface during directional solidification.From the cross-section structure,the structure changes from plane eutectic to cellular eutectic,and the lamellar spacing of cell center decreases gradually.The phase composition of directionally solidified AlCoCrFeNi2.1 eutectic high-entropy alloy does not change with the change of drawing rate.The phase composition is always two-phase eutectic structure of FCC and BCC.The fracture strength and elongation of eutectic high-entropy alloy with directional solidification of 60 um/s are 1139 MPa and 37.3%,both of which have been improved.The strengthening mechanism and plasticizing mechanism are discussed in terms of fracture morphology and fracture specimen profile.The corrosion resistance of eutectic high-entropy alloy is the best when directionally solidified at 30?m/s.The above results indicate that directional solidification technology has great potential in improving the properties of eutectic high-entropy alloy materialsFor AlCoCrFeNi2.1 eutectic high-entropy alloy,heat preservation treatments were carried out at 900 ?,1000 ? and 1100?,respectively.The results showed that there was no significant change in the lamellar tissue at 900 h and 400h,but the local coarsening and stability of the inner lamellar tissue at 1000/400h and 1100/400h were worse.With the increase of heat treatment temperature,the compressive strength of eutectic high-entropy alloy decreases gradually,and the plasticity of eutectic high-entropy alloy is generally higher than that of induction melting alloy.