Study On Microstructures And Properties Of Al_xCrFeNi Quaternary Component Alloys

AlCrFeNi-M alloys?M includes Co,Mo,Ti,et al?developed for high entropy alloys?HEAs?earliest have been investigated in many aspects.Among those,there exists a common feature for some HEAs,which is that the variation of M element type has no influence on the basic phase compositions of HEAs.Therefore,if the microstructures and properties of Al_xCrFeNi alloys excluding M elements could be investigated,new insight would be provided for developing five or more component HEAs based on Al-Cr-Fe-Ni alloys.In the part of microstructure investigation of Al_xCrFeNi alloys,it is verified that Alx Cr FeNi alloys were all eutectic alloys with NiAl intermetallic and [Fe,Cr] solid solution.With the increase of Al content,NiAl decreased and [Fe,Cr] increased.After homogenization,Ostwald ripening occurred: NiAl nano particles precipitated in [Fe,Cr] disappeared and the size of alloy phases increased.Compared to some other high entropy alloys,Al_xCrFeNi alloys were superior in regarding of compressive mechanical properties.For example,the fracture strength of as-cast Al_1.2Cr FeNi alloy was 3607.6 MPa and compressive strain was 31.4%,which showed excellent combination of fracture strength and ductility.With the increase of Al content,the strength increased and plasticity decreased.Due to solid solution strengthening and fine grain strengthening,mechanical properties of homogenized Al_xCrFeNi decreased in some degree but showed similar changes to those of as-cast alloys.In addition,the fracture types of these alloys were mainly cleavage fracture and mixed fracture.In order to explore the potential of thermal applications,the oxidation behaviors of Al_1.3CrFeNi alloy at 900 °C and 1000 °C for 100 h were investigated,respectively.The results showed that 900 °C oxidation curve fitted with the quartic parabolic rate law and 1000 °C oxidation followed the cubic one.This difference between the two oxidation curves was owing to the composition of oxidation scales: after 900 °C oxidation for 100 h,the oxides were Al₂O₃/Cr₂O₃ and FeCr₂O₄ oxides from the outside to the inside;but for 1000 °C oxidation,the oxides were composed of FeCr₂O₄/Cr₂O₃/Al₂O₃,Cr₂O₃/Al₂O₃ and single Al₂O₃.Electrothermal properties play an important role in expanding application fields of HEAs.Thus physical properties including electrical resistivity and thermal conductivity of Al_xCrFe Ni alloys were studied.With Al addition,the amount of phase boundaries and crystal defects increased,which led to the electron scattering when electrons move across the alloys.As a result,the electrical resistivity of alloys increased.Besides,the thermal conductivity of alloys showed irregular change laws with little Al addition.But temperature obviously exerted positive effect on thermal conductivity.Main reason is that rising temperature could decrease the inhibition electrons suffered from thermal resistance of defects.