Study On Microstructure, Strengthening Mechanism And Properties Of FeCoNiCrAl Based High-entropy Alloys

With the rapid development of the machinery manufacturing industry,the problems of material wear,fracture and corrosion are becoming more and more prominent,and the traditional metallic materials with one or two elements as the main constituents are no longer able to meet the performance requirements.High-entropy alloys are composed of 5～13elements,and the atomic percentage of each element is between 5%～35%,which is a new alloy emerging at present.As a new engineering structural material,this alloy has a broad development prospect in the fields of aviation,navigation and construction.Numerous studies have shown that the comprehensive performance of FeCoNiCrAl high-entropy alloys has great potential for application.Concurrently,the shape,size and volume fraction of the precipitated phases can be adjusted by a simple aging process to optimize the overall performance of the alloy.Therefore,in this study,FeCoNiCr_0.8Al_0.2 and FeCoNiCr_0.6Al_0.4 high-entropy alloys were prepared and the effects of aging treatment on the microstructure,phase structure and properties of these two alloys were explored.The results show that:（1）The FeCoNiCr_0.8Al_0.2 high-entropy alloys were held at 600℃,700℃,800℃and900℃for 24h,then all the alloys were tested for tensile mechanical properties and frictional wear properties.The results showed that the FeCoNiCr_0.8Al_0.2 high-entropy alloy with 24h holding time at 800℃had both excellent tensile properties and frictional wear resistance.In order to further optimize the mechanical properties and frictional wear resistance of FeCoNiCr_0.8Al_0.2 high-entropy alloy,the aging time of FeCoNiCr_0.8Al_0.2 high-entropy alloy at 800°C was explored,and it was found that the alloy kept simple FCC phase after 6h～168h of holding at 800°C,consisting of disordered FCC phase+L1₂ phase.When the aging time exceeds 12h,as the aging time continues to increase,it will not only lead to the coarsening of the L1₂ precipitated phase particles within the alloy,but also cause its average volume fraction to continuously decrease,which eventually makes the hardness,tensile properties and frictional wear resistance of the alloy continuously decrease.（2）The phase composition,microstructure and tensile properties of FeCoNiCr_0.6Al_0.4high-entropy alloy at different aging temperatures were explored.The results show that the phase structures of the alloys all consist of FCC phase+L1₂ phase+B2 phase as the aging temperature increases.The increase of aging temperature causes the volume fraction of L1₂and B2 phases within the alloy to show an increase followed by a decrease.The volume fractions of L1₂ and B2 phases reach their maximum values when the aging temperature is700°C,while the best tensile properties are obtained.The increase in the volume fractions of L1₂ and B2 phases is the main reason for the improvement of the tensile properties of the alloy.Subsequently,reciprocal frictional wear tests were performed on FeCoNiCr_0.6Al_0.4high-entropy alloy with the optimal combination of mechanical properties under different loads.The average friction coefficient of the alloy decreases when the load keeps increasing,while the wear loss keeps increasing and the size of the abrasive debris on the wear surface of the alloy also increases.（3）The FeCoNiCr_0.8Al_0.2 high-entropy alloy and FeCoNiCr_0.6Al_0.4 high-entropy alloy with the best frictional wear resistance and the best mechanical properties were selected,and the corrosion resistance of the alloy in 3.5ωt.%Na Cl solution and 10ωt.%HNO₃ solution was investigated.The results showed that the corrosion resistance of FeCoNiCr_0.8Al_0.2 high-entropy alloy was the best in both corrosion solutions,the cast FeCoNiCr_0.8Al_0.2 high-entropy alloy was the second best,and the corrosion resistance of FeCoNiCr_0.6Al_0.4 high-entropy alloy was the worst.This is because the B2 phase in the FeCoNiCr_0.6Al_0.4 high-entropy alloy（held at 700°C for 24h）shows high activity in either 3.5ωt.%Na Cl solution or10ωt.%HNO₃ solution,and selective dissolution occurs preferentially.At the same time,the B2 phase in the alloy may form a local primary cell with the L1₂ phase,leading to a faster corrosion process of the passivation film.However,the diffusely distributed L1₂ phase in the FeCoNiCr_0.8Al_0.2 high-entropy alloy（held at 800°C for 12h）can form a more continuous barrier layer to retard the corrosion process of the alloy.