Study On Structure And Properties Of Fe-based Amorphous Coatings Improved By Adding Ni-clad Al Powders

Fe-based amorphous alloy coatings have been attracted more attention due to its unique structure,high strength,high hardness,excellent wear and corrosion resistance.However,a certain amount of pores exist in the coating prepared by plasma spraying due to its lamellarr structure,which seriously affect the performance of the coating.By analyzing the formation process of the plasma spray coating and the mechanism of pore formation,poor particle spreading and deformation ability are the main factors that significantly affect the nesting of the particles and the increase of porosity during the formation of the coating.In this paper,the Ni-clad Al self-bonding powders were clad on the surface of Fe-based amorphous particles by ball milling to prepare a composite powder with shell-core structure,which were applied to the preparation of plasma sprayed Fe-based amorphous composite coatings.The influences of the milling speed,time and the amount of Ni-clad Al powders on the microstructure and phase composition of the composite powder were studied to determine the best ball milling parameters for the preparation of the composite powders.The influence of the amount of Ni-clad Al powders on the porosity and amorphous contents of the composite coating ware systematically studied.The mechanism of the addition of Ni-clad Al powders to improve the micro-structure and properties of the Fe-based amorphous coating was obtained.It is desirable to find a method that can reduce the porosity of the coating without changing its amorphous content,providing theoretical and technical support for the engineering application of Fe-based amorphous coatings.The results of composite powders show that:?1?Increasing the ball speed can improve the efficiency of the cladding powder and the coating effect.?2?Increasing the milling time will increase the number of cladding powders in the composite powder and the density of its surface microstructure,but will increase the particle size of the composite powder and cause powders be contaminated and oxidized.?3?Increasing the addition amount of Ni-clad Al powder is beneficial to increase the amount of cladding powder in the composite powder and the thickness of the cladding layer,but will lead to a decrease in the amorphous content of the composite powders.The optimum ball milling parameters for preparing the cladding powders were:ball milling speed is 240 r/min,ball material ratio is 10:1,ball milling time is 3 h,and the amounts of Ni-clad Al powders are 10wt.%.The results of the composite coating structure show that:?1?The addition of Ni-clad Al powders are beneficial to improve the melting state of the Fe-based amorphous powders,the particles in the coating are basically eliminated,and the composite coating is constitute by Fe-based amorphous and Ni₃Al layers,the porosity of the coating was reduced from 6.69%to1.12%,and the amorphous content of the coating was not significantly reduced.?2?The greater the amount of Ni-clad Al powders added,the lower the amorphous content in the coating and when the addition amount is 15wt%,there are cracks in the coating.?3?TEM study shows that the composite coating is composed of amorphous phase inlaid with the crystallization phase,and the grain size of the crystallization phase is basically nanoscale.The results of composite coating property show that:?1?In spite of addition Ni-clad Al powders will make the microhardness of the coating reduced,the reasonable choice of the amount of added powder is beneficial to improve the wear resistance.The friction coefficient of the Fe-based amorphous coating is 0.3259,and the friction coefficient of the composite coating prepared by adding 10wt.%Ni-clad Al is 0.2561.Under the same load,the wear amount of the composite coating is 1/2 of the Fe-based amorphous coating.The wear mechanism of the composite coating is abrasive wear,adhesive wear and a small amount of coated particles that break off.The wear mechanism of the amorphous alloy coating is abrasive wear and cracking and shedding of the coating.?2?In the electrochemical corrosion system,the composite coating has a lower corrosion current density and more general zone than the Fe-based amorphous coating.The experimental results after soaking in saline for 120h that Fe-based amorphous coating samples etched approximately 5 times as heavy as composite coatings.The main corrosion of the composite coating was point corrosion,and the main corrosion of Fe-based amorphous coating was crevice corrosion.Corrosion products of both coatings mainly accumulate around the pores.