Study On Solid Phase Transformation Behavior Of AlCoCrFeNi High-entropy Alloy During Heat Treatment

Emerging multi-principal high-entropy alloys are characterized by high entropy effect,lattice distortion effect,hysteresis diffusion effect and cocktail effect,etc.,and exhibit excellent physical,chemical and mechanical properties more,which have important theoretical research value and potential broad industrial application prospects.Studies have shown that in addition to regulating the alloy organization by changing the composition or deformation heat treatment process or using the principle of phase change induced plasticity and other schemes,the solid state phase change during the heat treatment of cast alloys can also change the microstructure and mechanical properties of the alloy,however,there are still relatively few related studies.In this paper,the behavior of solid-state phase transformation during heat treatment of high-entropy alloys of different compositions is systematically studied by differential thermal analysis(DTA),scanning electron microscopy(SEM),X-ray diffraction analysis(XRD),universal tensile testing machine and other characterization methods,the system has systematically studied the high entropy of different components.The solid-state phase transition behavior of the alloy during heat treatment is compared and analyzed,and the difference and connection between reversible phase transition and irreversible phase transition are analyzed,and then the influence of the solid-state phase transition behavior during heat treatment on the mechanical properties of the alloy is revealed.Al_xCo CrFeNi,Al Co_xCrFeNi,Al Co Cr_xFe Ni,AlCoCrFe_xNi and AlCoCrFeNi_xalloys were prepared by varying the content of single components using the isoatomic ratio AlCoCrFeNi high-entropy alloy as the model alloy.The results of differential thermal analysis show that when Al is between 0.8 and 1.4,Co is between 0.4 and 1.6,Cr is between 0.2 and 2.0,Fe is between 0.4 and 2.0,and Ni is between 0.8 and 1.6,the alloy undergoes complex solid-state phase transformation during heat treatment at600°C.The type of phase transformation contains both reversible and irreversible phase transformation.The alloy phase composition and microstructure analysis results before and after heat treatment show that both reversible and irreversible phase changes are related to the disordered BCC phase,and the corresponding phase change products are relatively complex but show certain regularity.Among them,the reversible phase transition process mainly precipitates?phase,and the irreversible phase transition process mainly precipitates FCC phase.The hardness test results show that the hardness of the Al,Fe and Ni alloys is influenced by the change of elemental content,while the hardness of the Co and Cr alloy alloys is not greatly influenced by the change of alloy composition.Among them,with the increase of Al content,the hardness of Al_xCo CrFeNi alloy gradually increased from 157.8 HV(x=0.2)to 522.4 HV(x=1.8).With the increase of Fe content element,the hardness of AlCoCrFe_xNi alloy decreases from 676.5 HV(x=0.2)to 476.7 HV(x=2.0).The results of the high temperature heat treatment experiment at 1100?show that the plasticity of Al,Co and Cr alloys is less affected,while the mechanical properties of Fe and Ni alloys are more affected.Among them,the strength of AlCoCrFe_1.8Ni alloy remained basically unchanged after high-temperature heat treatment,and the elongation increased from 0.56%to 3.98%.On the contrary,the comprehensive mechanical properties of AlCoCrFeNi_x(1.4?x?2.0)in the heat-treated state decreased.