Study On Prepare And Properties Of Amorphous Alloy Coatings On The T91 And 304H Boiler Tubes

Fe-based metallic glasses have high hardness and excellent corrosion resistance and relatively low material cost, Fe-based amorphous coatings that large surface coatings are prepared by thermal spraying processes are considered to be extremely viable candidates as surface protective coatings to metal structure parts for corrosion protection. In this paper, depending on the service environment and heating surface corrosion failure of boiler convection tube bank, Fe-based amorphous alloy powder was prepared, which provides fundamental material to prepare amorphous coatings on the 304 H and T91 substrates via plasma spraying processes, and the regular relation with coating structure, spraying process and corrosion resistance was studied.The different microstructure amorphous coatings were obtained by changing the spraying power and the thickness of coating. The results show that, under different plasma sprayings, a uniform microstructure of Fe-based amorphous coating with a coating wavy like multi-layer structure is prepared, the coating and the substrate are combined with mechanical bonding, and the bonding is closely. The XRD diffraction peak of coatings show obvious diffuse diffraction peaks and a small amount of sharp peaks, and coatings express high amorphous phase content more than 70%. With the increase in spraying power, the amorphous phase content reduces, but amorphous phase content increases with increase in coating thickness.In addition, increasing in plasma spraying power and coating thickness, the porosity of coatings decreases and the microhardness of coatings increases. The porosity and microhardness of amorphous coating what is prepared under spraying power of 40 KW and coating thickness of 200μm is 2% and 762.4HV, respectively.Electrochemical studies show that, electrochemical corrosion behavior of amorphous coatings is active dissolution- passive- transpassivation in 0.5mol/L H2SO4 and 3.5% NaCl solution. And polarization curves showed wide passive region and low corrosion current density in H2SO4 and NaCl solution, respectively. And passive region is more significantly, corrosion potential tends to move forward, corrosion current density decreases with spraying power and coating thickness increase, therefore, indicating that the corrosion resistance of coatings is improved. The constituent elements of amorphous coating and porosity are the main factors in corrosion resistance of the coating, and a slight change in the amorphous component content of the coating has little effect on corrosion resistance.Amorphous coatings exhibit excellent resistance high temperature oxidation and high temperature corrosion performance compared to the metal substrate. Furthermore the coating represents low porosity and excellent resistance high temperature oxidation and high temperature corrosion performance with increasing spraying power and coating thickness. Chromium and oxygen element form Cr2O3, dense and stable protective film, while inhibiting oxygen diffusion and corrosive medium at high temperature, the sample is fully protected. In addition, Mo, P, Ni, Si and other elements improve the structure and properties of amorphous coating, and resistance high temperature oxidation high temperature corrosion of the amorphous coating is improved in high temperature and corrosive environment.