Study On Preparation And Wear And Corrosion Resistance Of CoCrFeMnNiM High-entropy Alloy Coatings

As a new type of alloy design concept,high-entropy alloy has a simple phase composition and good comprehensive properties.In order to adapt to the performance requirements under different working conditions,the performance control and optimization of high-entropy alloys has gradually become a research hotspot.For performance requirements and large grains of high-entropy alloys,the CoCrFeMnNiM(M=Ti_x,Mo_x;x=0.00,0.25,0.50,0.75,1.00)high-entropy alloy coatings were prepared on the surface of 45 steel,by laser cladding.The CoCrFeMnNiTi and CoCrFeMnNiMo coatings were treated by ultrasonic surface rolling extrusion(USRE).The microstructure,surface profile,residual stress,microhardness,wear resistance and corrosion resistance of the CoCrFeMnNiM coatings and the USRE coatings were analyzed.The specific content is as follows:CoCrFeMnNiTi_x high-entropy alloy coatings are mainly composed of FCC solid solution phase and TiC particle phase.With the increase of Ti content,the lattice distortion of the coatings and the volume fraction of TiC particle phase also gradually increase.The increase in the hardness of the coatings is mainly attributed to the enhancement of the solid solution strengthening and the second phase strengthening effect.The Ti_1.00 coating has the largest average hardness of 364.5 HV_0.3.Appropriate addition of Ti element can improve the wear resistance of the coatings.Among them,Ti_0.25 coating has the most excellent wear resistance.With the increase of Ti content,the wear mechanism of the coating changes from adhesive wear to abrasive wear and oxidative wear.Ti-containing coatings have excellent quality passivation film and good corrosion resistance.The introduction of Ti atoms changes the corrosion mechanism of the coating from pitting to intergranular corrosion.The CoCrFeMnNiMo_x high-entropy alloy coatings have a single FCC solid solution phase composed of Mo-rich interdendrites and Mo-poor dendrites.The introduction of Mo atoms enhanced the microstrain and lattice distortion effects of the coatings,and caused the Mo-rich dendrites to widen.The hardness of the coatings increases linearly with the content of Mo in the coatings.The strengthening mechanism of coatings hardness improvement is dominated by solid solution strengthening.The addition of Mo atoms can effectively improve the wear resistance of the coatings.The Mo_1.00 coating has the lowest volume wear rate(0.68×10^-4 mm³/(N·m)).The doping of Mo atoms changes the wear mechanism of the coatings from adhesive wear to oxidative wear and abrasive wear.The introduction of Mo atoms improves the corrosion resistance of the coatings,increases the generation rate of oxygen ions,promotes the generation of strong oxides.The introduction of Mo atoms changes the corrosion mechanism of the coatings from pitting to intergranular corrosion.USRE reduces the grain size and surface roughness of the coatings,and increases the surface residual stress and hardness of the coatings.USRE has no effect on the phase composition of the coatings.The increase of coatings hardness after USRE is attributed to the increase of fine grain strengthening,dislocation strengthening and residual stress.USRE expands the passivation region of the coatings and reduces the passivation current density,which significantly improves the corrosion resistance of the coatings.After the USRE,the wear resistance of the CoCrFeMnNiTi coating is significantly improved,and the corresponding volume wear rate is 0.71×10^-4 mm³/(N·m).USRE changes the wear mechanism of the coating from abrasive wear to oxidative wear and abrasive wear.The deterioration of the wear resistance of the CoCrFeMnNiMo coating after USRE is mainly due to the existence of microcracks in the coating and the transformation of the wear mechanism.USRE changes the wear mechanism of the coating from oxidative wear to abrasive wear and slight oxidative wear.There are 66 figures,26 tables and 99 references in this paper.