| A high-entropy alloy is a new type of alloy composed of five or more elements in equal or nearly equal atomic ratios.The appearance of this alloy has greatly expanded the alloy design space and provided more ideas for strengthening and toughening of metal structural materials.Since high-entropy alloys have the characteristics of diverse components and complex structures,their strengthening effects are often the result of the coupling of multiple mechanisms.At present,since a large number of research results are obtained under different compositions and process conditions,it is difficult to quantitatively analyze the effect of alloy composition on the strengthening and toughening mechanism of high-entropy alloys.In order to solve this problem,CoCrFeNi is used as the base alloy in this paper.By controlling the alloying degree,hot working process and other factors,four high-entropy alloys,CoCrFeNi,CoCrFeNi-4at.%Al,CoCrFeNi-4at.%Mo,CoCrFeNi-4at.%Ti,were prepared under the same experimental conditions,and their microstructures and mechanical properties were systematically studied,focusing on different Influence of alloying elements on the strength and toughening mechanism of high-entropy alloys.The main findings and conclusions of this paper are as follows:(1)By comparing the microstructure characteristics of different composition systems,the influence of Al,Mo and Ti elements on the microstructure of CoCrFeNi matrix alloy was clarified.When the annealing temperature is 1000-1100 °C,the four high-entropy alloys are all single-phase FCC structures.When the annealing temperature drops to 800-900 °C,the CoCrFeNi and CoCrFeNi-4at.%Al alloys are still single-phase FCC structures.In the CoCrFeNi-4at.%Mo alloy,Cr-rich and Mo-rich σ phases appeared,Ni3 Ti type η phase appeared in CoCrFeNi-4at.%Ti alloy.(2)The effects of Al,Mo and Ti elements on the mechanical properties of CoCrFeNi matrix alloys are revealed by comparing the results of uniaxial tensile experiments under different composition systems.The addition of Al,Mo and Ti can improve the strength of CoCrFeNi alloy to different degrees;the addition of Al will not affect the elongation of the alloy,while the addition of Mo and Ti will cause the elongation to decrease when the alloy is annealed at 800-900℃.(3)By comparing the deformation mechanism and failure mechanism of four CoCrFeNibased high-entropy alloys,the contributions of solid solution strengthening,grain boundary strengthening and second phase strengthening to yield strength are clarified.The solid solution strengthening effect of Mo is the best;Al and Ti can greatly reduce the stacking fault energy of CoCrFeNi alloy,and then maintain a high geometrically necessary dislocation density during the deformation process,effectively achieving grain boundary strengthening;CoCrFeNi with a second phase exists The yield strength of-4at.%Mo,CoCrFeNi-4at.%Ti alloy is much higher than other alloys.(4)By comparing and analyzing different solid solution strengthening models(Labusch model,Fleischer model),it is clarified that the solid solution strengthening of CoCrFeNibased high-entropy alloys satisfies the Labusch model,and the value of the dimensionless parameter f in the model is determined,which can change the concentration range.Quantitative prediction of solid solution strengthening effect on a wide range of CoCrFeNibased high-entropy alloys. |
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