Research Of AlCoCrNiFe High Entropy Alloy Coating Prepared By Surface Mechanicle Attrition Treatment

Surface mechanical attrition treatment(SMAT)is a new surface treatment method.A coating can be formed on the surface of the substrate by ball-milling.In this paper,AlCoCrNiFe high entropy alloy(HE A)coatings are prepared on surface of 304 stainless steel substrate,in order to improve the surface properties.The phase,microscopic structure and elements distribution of HEA coatings are analyzed by using XRD,SEM,and EDS.Effect of process parameters on the formation of coatings and the formation mechanism of the coatings were also studied.Micro-hardness test,friction and wear experiment are carried out to inspect the mechanical property of the coating layer.The corrosion resistance and the corrosion mechanism of the coating are analyzed by electrochemical corrosion workstation.The results show that milling time and rotational speed have significant influence on the coating roughness,thickness and density in the preparation of AlCoCrNiFe HEA coating.With the increase of milling time,the roughness and thickness of the coating increased and then decreased.but increase rotational speed also increase the roughness and thickness of the coating.It is revealed that increasing of milling time and proper rotational speed can enhance the density of the coating.The formation mechanism of the coating can be deposited on four stages as follows:(1)Particles hammered into substrate.(2)Powder substrate through cold welding.(3)Element diffused between the coating and the substrate.(4)Work hardening leads to spalling fatigue.Coating performance tests show that the microhardness of AlCoCrNiFe high entropy alloy coating prepared by different milling parameters is significantly higher than that of 304 stainless steel.The highest hardness was 759.17HV,which is about 3 times as much as that of the matrix,which is obtained by milling time at 9h and rotational speed of 400r/min.The microhardness shows gradient-like distribution of the coating cross section,and the closer to the coating surface,the greater the microhardness.The friction coefficient of the coating prepared by different milling time increases with the increase of the surface roughness of the coating.The wear resistance of the coating prepared at 400r/min rpm is the best.The polarization curves of alloy coatings with different ball milling parameters are analyzed.The corrosion current density of the HEA coating is positively correlated with the roughness of the coating under the condition of the milling speed of 400r/min,The corrosion resistance of the coating obtained by ball milling 9h is the optima,and the corrosion resistance of the coating is lower than that of 304 stainless steel.The 9h coating of 400r/min is immersed for a long time,and the polarization curves and AC impedance spectroscopy are analyzed in different periods The corrosion rate of AlCoCrNiFe HEA coating becomes faster as the surface oxide film becomes thinner and thinner.Then,with the increase of immersion time,the formation of passive film and corrosion products,which hinder the further corrosion of the alloy coating,decrease the corrosion rate.