Study On Properties Of Fe_xCrMnAlCu High-entropy Alloy And Preparation Of Coating

High-entropy alloys（HEAs）are a new type of multi-principal element alloys that can be widely used in extreme environments due to their high hardness and excellent wear-resistance.However,the limitation of preparation technology and cost hampers their large-scale promotion.The HEA coating with simple preparation processes and low cost is an excellent solution to this problem.If the HEA coating is directly studied,issues will arise such as different effective deposition rates of element particles during cold-spray deposition,leading to discrepancies between the actual coating and the theoretical design,requiring extensive experimentation to modify the powder composition prior to spraying.Therefore,this article first uses vacuum melting to prepare Fe_xCrMnAlCu（x=0,0.5,1,1.5,2）bulk HEA,and studies the effect of Fe element content on the microstructure,phase structure and mechanical properties of the alloy to determine the optimal Fe content.Then,molecular dynamics simulation is used to study the deposition rule of mixed metal powders during cold-spray deposition,to guide the preparation of mixed metal coatings by cold-spray deposition.Finally,guided by the simulation results,HEA coatings are prepared using cold-spray deposition and induction remelting,and the microstructure and all properties of the coatings before and after remelting are measured to verify the simulation conclusions and compare with the comprehensive properties of bulk HEA.The study found that the Fe_xCrMnAlCu HEA is composed of dendrites and interdendritic regions,where the dendrites are in a disordered BCC structure and the interdendritic regions are in a disordered FCC structure.There is a uniformly distributed rod-shaped precipitate（Φ50 nm×300 nm）rich in Al and Cu（ordered BCC）in the dendrites.As the Fe element content increases,the volume fraction of dendritic regions gradually increases,but the content of precipitates in the dendrites gradually decreases.The content of precipitate has an important effect on the strength and hardness of the Fe_xCrMnAlCu HEA.With the increase of Fe content,the strength of the alloy decreases gradually,and the hardness increases first and then decreases.When x=0.5,the volume fraction of the precipitates in the alloy reaches its maximum,and the yield strength,compressive strength,deformation rate,hardness and wear rate of the alloy are 978 MPa,1428 MPa,0.16,405 HV and 1.75×10^-5 mm³·N^-1·mm^-1,respectively,with a high performance-to-cost ratio.Numerical simulation of the cold-spray deposition process showed that the higher the spray temperature,the greater the degree of particle deformation and the better the adhesion with the substrate.Simulation results of the single-particle deposition showed that Mn particles can be effectively deposited at 600 K,Fe particles require a spraying temperature of 700 K or higher,and Cr particles require a spraying temperature of 1100K or higher;while Al and Cu particles can be effectively deposited in the temperature range of 500 K-800 K.Moreover,the flattening ratio of these two particles exceeds 0.6,which means that in the deposition process of mixed metal powders,the particles can effectively fill the gaps between other particles,greatly improving the coating density and its properties.Different from the single-element particle deposition,simulation results of the deposition of mixed-element particles at 700 K showed that even if the Cr particles did not meet the deposition conditions due to the subsequent changes in the deposited substrate and the compaction of the particles,effective bonding still formed in the coating.Therefore,it is not necessary to meet the Cr deposition conditions in the preparation of mixed metal coatings by cold-spray deposition.For elements that do not meet the deposition conditions,their proportions in the mixture can be appropriately increased during preparation to ensure that the coating composition matches the design value.The distribution of each element particle in the Fe_0.5CrMnAlCu pre-fabricated mixed metal coating is uniform,and Al and Cu particles fill the gaps between the particles,making the coating extremely dense,which is consistent with the simulation results.After remelting,it was found that unlike the Fe_0.5CrMnAlCu bulk HEA,the pre-fabricated mixed metal coating quickly cooled after induction remelting,and transformed into a single BCC phase structure HEA coating,with no element segregation in the coating and the element content nearly the same as the design value.Because the entire coating is composed of a hard phase of BCC structure,the hardness of the coating is higher than that of the same composition alloy,reaching 556 HV.The increase in hardness promotes the improvement of wear resistance.The wear rate of the Fe_0.5CrMnAlCu HEA coating prepared by cold-spray deposition and induction remelting is only 2.0×10^-6 mm³·N^-1·mm^-1,which means that under the same composition,the wear resistance of the coating prepared by the cold-spray deposition and induction remelting method is superior to that of the alloy.