Study On The Microstructure Evolution And Properties Of AlCr_1.6Fe_xNi_（32-x）Si_0.2 High Entropy Alloy

High entropy alloy（HEA）has the characteristics of multiple principal elements,and its mechanical properties,corrosion resistance and oxidation resistance are superior to those of traditional alloys due to its four effects on thermodynamics,dynamics,microstructure and properties,which have attracted the attention and exploration of the majority of researchers.The electrothermal alloys with good corrosion resistance and high temperature oxidation resistance contain the same chemical elements as the AlCr Fe Ni-series high entropy alloys which have been studied more.According to the performance requirements of electrothermal alloys,there are few studies on the effects of different Fe and Ni contents on the properties.Therefor,Therefore,in this thesis,the alloy applied in high temperature and alkaline environment is designed by adding Cr element with improved corrosion resistance and Si element with improved oxidation resistance.AlCr_1.6Fe_xNi_（3.2-x）Si_0.2（x=1.0,1.2,1.4,1.6,1.8,2.0）HEA prepared by vacuum arc melting was used to explore the influence of different Fe and Ni element content ratios on the microstructure evolution and properties of alloys,which provided reference for further improving the application performance of HEA,and drew the following main conclusions:The microstructure of the as-cast AlCr_1.6Fe_xNi_（3.2-x）Si_0.2 alloys changed from floral and cellular eutectic structures to dendritic structures.The cellular eutectic structures were distributed in the interdendritic structures.The eutectic structure of the as-cast alloy changes from B2+σphase to B2+BCC phase with the increase of Fe element.At the same time,the circular B2 phase and the square BCC phase were separated from theσphase and the B2 phase.After homogenizing annealing,the alloys grew into dendritic structure,and the lamellar structure grew into coarse bar and network structure.And the grains of B2 phase precipitation grew into filamentous structure and distribute among the bar and strip structures.With the increase of Fe content,solid phase reaction occurred in the disordered saturated BCC phase at high temperature,resulting in more stable and moreσ-phase.Due to the influence ofσphase volume fraction,the hardness of as-cast AlCr_1.6Fe_xNi_（3.2-x）Si_0.2 alloys decreased from 584.1 HV to 365.7 HV with the increase of Fe content,while the hardness of annealed alloys increased from 492.4 HV to 592.8HV with the increase of Fe content.The mechanical properties of the alloys were improved by homogenizing annealing,and the existence ofσphase and lattice distortion were beneficial to the mechanical properties of the alloys.However,due to the hard body-centered cubic phase andσphase,the fracture section of AlCr_1.6Fe_xNi_（3.2-x）Si_0.2 alloys appeared obvious river pattern and rock candy shape,resulting in brittle fracture.The AlCr_1.6Fe_xNi_（3.2-x）Si_0.2 alloys were corroded by oxygen absorption in 1 mol/L Na OH alkaline solution.Due to the differences in the microstructure size of the alloys,the corrosion resistance of the as-cast alloys was better than that of the alloys after homogenization annealing.The oxidation dynamic curve of AlCr_1.6Fe_xNi_（3.2-x）Si_0.2alloys at 900℃were parabolic,and the resulting oxide film consisted of Al₂O₃、Cr₂O₃and Fe Cr₂O₄.After annealing,the volume fraction ofσphase of the alloys increased,so that the Cr-rich area on the alloys surface increased.More oxygen diffuses between the alloys and the oxide film through the holes in the Cr₂O₃ oxide on the alloys surface,which destroied the integrity of the oxide film and reduced the oxidation resistance of the alloys.This thesis has 53 figures,14 tables and 116 references.