Study On The Preparation Of Iron-based Amorphous Composite Coatings By Thermal Spraying And Their Properties

Amorphous alloys have the advantages of high strength,good wear resistance and corrosion resistance due to their structural properties of atomic arrangement.However,the amorphous alloy itself has high brittleness,poor toughness defects,and high cooling rates,which limit its size,which limits its industrial applications.The use of thermal spraying to heat the powder and quickly cool deposited on the substrate can make the amorphous alloy break through the size limit,on the other hand,due to the fast cooling rate of the thermal spraying method,the amorphous alloy retains the structural characteristics and excellent performance of the amorphous alloy.This will effectively improve the application of amorphous alloys in the industrial field.In this dissertation,AT13（87 wt.%Al₂O₃-13 wt.%TiO₂）ceramic particles and TiO₂powder were introduced into the iron-based amorphous coating,and two kinds of iron-based amorphous composite coatings were prepared by supersonic flame spraying technology.Electron microscope,friction and wear testing machine,electrochemical workstation,XPS and XRD were used to study the microstructure and wear resistance and corrosion resistance of the two composite coatings.The surface melting state of AT13 composite coating and TiO₂composite coating prepared by supersonic flame spraying is better,and there are a few pores on the coating surface.The internal structure of TiO₂ composite coating is relatively dense,and there are TiO₂ and amorphous phases at the same time,and the coating density is high.Through friction and wear experiments,it is shown that under the same wear experimental conditions,the wear morphology of TiO₂ composite coating is mainly composed of peeling pits and plough grooves,and its wear mechanism is mainly fatigue wear and abrasive wear,and the AT13 composite coating is significantly less than that of TiO₂ composite coating due to the addition of AT13 ceramic particles,and the plow groove phenomenon on the surface of the coating is significantly less than that of TiO₂composite coating,and the wear mechanism is mainly fatigue wear.The friction coefficients of the two composite coatings are presented as first rising and then decreasing and then tending to be stable,the AT13 composite coating friction coefficient is small,the wear marks are the shallowest and the wear rate is the smallest,and the wear stability is the best and the wear resistance is optimal in the two composite coatings.Through potentiodynamic polarization and open circuit potential tests,the differences in specific corrosion behavior of two different iron-based amorphous composite coatings and Q235 and 304 stainless steel in artificially simulated seawater were studied.The results show that the corrosion resistance of AT13 composite coating and TiO₂ composite coating is obviously better than that of Q235 substrate,and lower than that of 304 stainless steel.The corrosion resistance of AT13 composite coating in artificial seawater is better than that of TiO₂ composite coating.The AT13 composite coating and the TiO₂ composite coating were subjected to long-term artificial seawater immersion experiments.Through electrochemical impedance spectroscopy analysis,the corrosion rate of the AT13 composite coating showed a trend of first decreasing and then increasing.The entire corrosion process of the TiO₂ composite coating is divided into Three periods:pre-corrosion,mid-corrosion,and post-corrosion.The corrosion mechanism of the two composite coatings in artificial seawater was expounded by establishing an equivalent circuit model.In this paper,through the long-term immersion experiment of AT13 composite coating and TiO2 composite coating in sulfate reducing bacteria（SRB）,the corrosion process of AT13 in SRB 31d can be divided into two stages,the corrosion pre-corrosion（0-10d）and the late corrosion（17d-31d）.In the early stage of corrosion,the corrosion medium continued to penetrate the pores of the coating,and the corrosion rate of the coating increased.With the increase of immersion time,metabolic and corrosion products accumulated on the coating surface to form a biofilm.The holes and crevices of the coating are filled,thereby blocking the transmission channel of the corrosive medium,so that the corrosion rate of microorganisms on the coating surface is reduced.Under the action of SRB on the coating surface in the later stage of immersion,the biofilm attached to the coating surface gradually decomposed,and the metabolism of SRB would produce a large number of metabolites and acid products,which changed the structure between the solution and the electrode,and the corrosion showed a trend of gradually increasing.When the TiO₂ composite coating was immersed in the SRB solution for a long time,the corrosion rate was firstly fast,then slow,then fast,and finally slowed down,and the overall trend was slowed down.Through fluorescence microscopy and SEM photos,it was found that the surface of the TiO₂ composite coating had less SRB,and the corrosion resistance in the SRB was significantly better than that of the AT13 composite coating,mainly because TiO₂had a good antibacterial effect.By fitting the circuit and analyzing the corrosion products,the corrosion mechanism of the two composite coatings in SRB solution is expounded.