| High-entropy alloy is a new alloy which has been rapidly developed in recent years.Comparing with the traditional alloys,high-entropy alloy has the characteristics of high strength,high hardness,high wear resistance and excellent corrosion resistance,and has an extensive application prospect of industrial field in the future.However,the defects such as coarse grains,voids and porosities are easily formed in high-entropy alloy during the smelting process,which will lead to low plasticity and toughness.For this reason,it is necessary to control the microstructure and improve the comprehensive mechanical properties of this alloy by the hot deformation processing method.Therefore,the hot deformation behavior of high-entropy alloy has gradually become a hot spot in this field.In this study,the self-developed AlFeCoNiMo0.2 high-entropy alloy was selected as the research target.The Gleeble-3800 thermal simulation machine was used to experiment on the thermal compression simulation under different deformation conditions.Based on the Arrhennius hyperbolic sine function model,the rheological stress constitutive equation of this alloy was established.The strain rate sensitivity indexes m and the thermal deformation activation energy Q during the thermal deformation process were acquired.The hot processing parameter was optimally determined by utilizing the theory of hot processing map.And combined with the results of the microstructure analysis and characterization,the mechanisation of the dynamic recrystallization during the hot deformation process was revealed.The main results are as follows:（1）With the increasing of the deformation temperatures,the strain rate sensitivity indexes m of AlFeCoNiMo0.2 high entropy alloy are increased under the deformation temperatures of900～1150℃,the strain rates of 1×10-3～1s-1,and the true strain of 0.6.The thermal deformation activation energy Q is 350.78k J·mol-1.The relationship between the flow stressσand the hot deformation process parameters is satisfied to the Arrhennius hyperbolic sine function constitutive model.The correlation coefficient R of the constructed model is 0.98633,and the average absolute relative error is 3.97%.（2）Based on the Prasad instability criterion,the hot processing maps of AlFeCoNiMo0.2high-entropy alloy are constructed by using the hot processing map theory.In the deformation region of high temperature and low strain rate,the value ofηis larger,and the hot workability of this alloy is better.In the deformation regions of low temperature high strain rate and high temperature high strain rate,the values ofξare less than 0,which fall into the rheological instability ranges.It should be avoided as much as possible during the hot processing.The optimized hot processing parameter of AlFeCoNiMo0.2 high-entropy alloy is under the deformation temperatures of 1090～1125℃ and the strain rates of 1×10-3～2×10-3s-1.（3）The work hardening and the dynamic softening is mainly included in the hot deformation process of AlFeCoNiMo0.2 high-entropy alloy.The change of the flow stress values are negatively correlated with the deformation temperatures and positively correlated with the strain rates.Under the deformation conditions of low deformation temperature and high strain rate,the phenomenon of the dislocation entanglement is evident.The feature of the true stress-true strain curves is work hardening.With the rise of the deformation temperature and the decline of strain rate,a large number of the dislocations are absorbed by the low-angle grain boundaries,and gradually transformed into the large-angle grain boundaries.With the progress of the deformation,the grain boundary sliding and the dynamic recrystallization are occurred at the high-angle grain boundaries.The characteristic of the true stress-true strain curves is dynamic softening.The dynamic recrystallization mechanism of AlFeCoNiMo0.2 high-entropy alloy is the dislocation-induced grain boundary sliding. |
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