Study On Laser Deposited Al_xTiCrMnCu High Entropy Alloy

Attribute to the high mixing entropy,sluggish diffusion,severe lattice-distortion and cocktail effect for the multi-component high-entropy alloys(HEAs),HEAs tend to form stable single-phase structures and have wide application prospect due to their high strength and hardness,high temperature oxidation resistance,outstanding resistance to wear and corrosion.In this paper,Al_xTiCrMnCu lightweight HEAs were prepared by laser deposition.The microstructure and crystal structure of HEAs were investigated by utilizing the metallographic microscope,scanning electron microscope,and X-ray diffractometer.The microhardness,wear resistance and corrosion resistance of HEAs were studied by utilizing the microhardness teste,friction and wear measurement and electrochemical workstation.The results showed that the optimal parameters for laser deposition of Al_xTiCrMnCu-based lightweight HEAs were that laser power was 600W,laser scanning speed was250mm/min,defocus amount was 5mm and powder feed rate was 15g/min.The morphology of the microstructure of Al_xTiCrMnCu-based HEAs were mainly composed of dendrites.The numbers of phases were reduced in Al_xTiCrMnCu-based HEAs due to the high mixing entropy.With the increase of Al element,The phase structure changes from the coexistence of HCP1 phase and FCC phase to a single HCP1 phase.And When the Al content is 1,the phase structure transforms into a single HCP2 phase.The microhardness of the TiCrMnCu HEA deposit is 630HV.The microhardness of HEAs is gradually increased with the increasing of Al.This is mainly because laser deposition has the characteristics of fast heat and rapid cooling,and has the effect of fine grain strengthening.The rapid solidification of laser raises the solid solution limit of the solid solution in the alloy.Secondly,the addition of Al atoms increases the degree of lattice distortion,which enhances the effect of solid solution strengthening.With the increasing of Al,the friction coefficient tends to decrease firstly and then increase.Among them,the friction coefficient of Al_0.75TiCrMnCu alloy reaches a minimum of 0.46.The wear mechanism changes from the exfoliation wear and abrasive wear to the abrasive wear with the increasing of Al.And when the Al element content is 1,the wear mechanism is coexistence of the exfoliation wear and oxidation wear.The main reason was that the addition of Al element promotes the increase of the proportion of HCP1 and HCP2 phases in the alloy,and the close-packed hexagonal structure slip system is less,which increases the hardness of the alloy and has a certain effect on its friction coefficient.In the process of abrasive wear of the material,the surface and near surface of the material were subject to the pressure on the grinding pair,and at the same time,they are hindered by the grinding pair during the sliding process,which leads to the plastic deformation of the alloy surface.TiCrMnCu alloy has a large amount of FCC phase and has a certain plasticity.It can absorb more energy during friction and wear and has a large ability to deform with repeated cycles.Therefore,the wear mechanism is mainly abrasive wear.In the 3.5%Na Cl solution,it is easy to form dense passivation films such as Al₂O₃ and Cr₂O₃ on the surface of Al_xTiCrMnCu high-entropy alloy during the electrochemical corrosion process to protect the alloy from being attacked by Cl ions because Al and Cr in Al_xTiCrMnCu high-entropy alloy have strong corrosion resistance.However,with the increase of Al,the corrosion resistance tends to increase firstly and then decrease.The corrosion resistance of Al_0.25TiCrMnCu alloy is optimal.This is mainly because when no Al element is added,the Cu-rich FCC phase and HCP1 phase of the TiCrMnCu high-entropy alloy form a microbattery,and then galvanic corrosion occurs,therefore the corrosion resistance of the alloy decreases.With the increasing of Al,the phase structure changes to a single HCP phase,the microbattery effect is weakened,and the corrosion resistance becomes better.As the Al content continues to increase,a large amount of Al₂O₃ oxide film is formed on the surface of the alloy.However,the density and protection are not as good as Cr₂O₃,so the corrosion resistance of alloy decreases.