Heat Treatment And Laser Surface Treatment Of CoCrCu_0.1FeMoNi High Entropy Alloy

High entropy alloys are composed of a variety of different metal or non-metal elements.Compared with traditional alloys,high entropy alloys have better properties.However,the system of high entropy alloys still needs to be improved.In-depth understanding of the influence of different treatment methods on the microstructure of the alloy is also of great significance to the development of the alloy.Therefore,the aim of this work is to study the influence of conventional heat treatment and surface laser remelting treatment on the microstructure and properties of CoCrCu_0.1FeMoNi high entropy alloy.On this basis,laser cladding was utilized to explore the application of CoCrCu_0.1FeMoNi high entropy alloy in surface modification of H13 steel.FCC,σandμwere detected in as-cast CoCrCu_0.1FeMoNi alloy,which show the microstructure of petal-like dendrite and lamellar eutectic structure.After holding at 800,900,1000 and 1100℃for 2 hours,CoCrCu_0.1FeMoNi high entropy alloy still consisted of FCC,σandμphases.With the increase of heat treatment temperature,many particles ofμphase were observed in the petal-like dendrites and the lamellar eutectic microstructure was necked and spheroidized continuously.Compared with the as-cast alloy,the phase structure of the heat-treated alloy is stable,but the hardness,corrosion resistance and friction and wear properties are not significantly improved.On this basis,the microstructure and properties of the alloy are improved by using surface laser remelting.The laser power was set to 240W,the scanning speed was changed in range of 200-800mm/min,and the surface of CoCrCu_0.1FeMoNi high entropy alloy was remelted by laser.Due to the characteristics of rapid melting and solidification,BCC solid solution appears in the remelted alloy.After laser remelting,the grain size of the alloy reaches100nm,and the microstructure shows"coral-like"meophology.The hardness of the remelting layer reaches 750-850HV,which is 34%to 56%higher than that of the as-casted high entropy alloy.The strengthening mechanism is mainly attributed to fine grain strengthening and precipitation strengthening.When the scanning speed is 200mm/min,the remelted alloy exhibits optimal corrosion resistance.The i_corr and i_p^′of the corrosion current density decrease by 84%and 21%,respectively.The wear resistance of laser remelting layer is improved,when the scan speed is 800mm/min,the friction coefficient and wear rate decrease 12%and 65%respectively,compared with the as-cast alloy.Moreover,its wear mechanism is abrasive wear and oxidation wear.Therefore,surface laser remelting can effectively improve the microstructure and properties of the alloy.Based on this,laser cladding technology was used to prepare CoCrCu_0.1FeMoNi high entropy alloy cladding layer on the surface of H13 steel to realize the surface optimization of H13 steel.Laser cladding CoCrCu_0.1FeMoNi high entropy alloy cladding layer consists of FCC,σandμphases.The forming indexes of single pass cladding layer are directly proportional to laser power and inversely proportional to scanning speed.When the energy density is less than 160J/mm²,the microstructure of the cladding layer tends to be feathery.When the energy density is more than 180J/mm²,the microstructure of the cladding layer is dendrite+equiaaxial.The hardness of cladding layer is increased by 108%-168%compared with H13 steel due to the combination of solution strengthening,second phase strengthening and fine grain strengthening.In 3.5%Na Cl solution,the cladding layer shows better corrosion resistance than H13 steel.When the laser power is 2000W and the scanning speed is 2mm/s,the corrosion potential E_corr of the cladding layer increases by 67%,the corrosion current density i_corr and the dimension obtuse current density i_p^′decrease by 98%and 96%respectively.It indicates that H13 steel can be optimized by means of laser cladding.