Preparation Of Fe-based Amorphous Coating By HVOF And Study On Its Properties

Fe-based amorphous alloys has excellent properties due to its structural characteristics,such as high strength,high hardness,excellent wear and corrosion resistance,and secondly Fe-based amorphous is inexpensive,so it has great application prospects.In this paper,high velocity oxy-fuel（HVOF）is used to prepare Fe-based amorphous coatings,which effectively overcomes the disadvantage that bulk amorphous is prone to brittle fracture and cannot be used as a structural material,The prepared Fe-based amorphous coating by HVOF has uniform microstructure and good bonding force,which breaks through the application limitations of bulk Fe-based amorphous.The specific research contents of this paper include:firstly,the nano-indentation creep test was carried out on the spraying and heat treatment Fe-based amorphous coating,the creep mechanism of the coating and the stress exponent（n）under different holding time and peak load was analyzed,it was further explained with free volume model and shear zone model.Secondly,the electrochemical corrosion test of the Fe-based amorphous coating and the substrate material under different etching solutions is carried out to analyze the corrosion resistance,and the effect of heat treatment on the corrosion resistance of the coatings was further explored.Finally,the friction and wear test of Fe-based amorphous coating was carried out to analyze the influence of environment,heat treatment temperature,wear time and applied load on the wear resistance of Fe-based amorphous coating,and the mechanism of friction and wear was discussed.The main conclusions obtained are:（1）Compared with the holding time,creep deformation is more sensitive to the applied peak load.At the same holding time,the stress exponent（n）at a peak load of10 mN is less than 6 mN,this is due to the large number of free volumes produced under high peak load which cause the decrease of stress exponent value.At the same peak load with the increase of holding time,the stress exponent value decreases.When the peak value is 6 mN and holding time is 10 s,higher stress exponent value indicates that the amorphous coating is more resistant to creep deformation.The heat-treated amorphous coating produces structural relaxation,which reduces structural defects and free volume,so it is compared with the original amorphous coating,the heat treated amorphous coating is insensitive to holding time and exhibits a higher stress exponent,indicating that the heat treated coating has greater resistance to creep deformation than the original coating.（2）The heat treated coating is amorphous coating obtained from XRD spectrum,the porosity of the amorphous coating near the glass transition temperature（T_g）is the smallest.The electrochemical corrosion test of the heat treated coating in the same corrosive solution（artificial seawater）shows that the corrosion current density is I_250℃<I_150℃<I_{original coating},which means that the Fe-based amorphous coating heat treated at 250℃has the strongest corrosion resistance in artificial seawater.It can be seen that the smaller the porosity is,the better the corrosion resistance is.In artificial seawater conditions,hydrochloric acid,sulfuric acid etching solution,corrosion current density I_{corr coating}<I_{corr substrate},R_{p coating}>R_{p substrate},so the corrosion resistance of the Fe-based amorphous coating is better than that of 304 stainless steel.（3）The friction coefficient of 304 stainless steel is more sensitive to the change of load,while the friction coefficient of amorphous coating is sensitive to the friction environment.Under dry friction conditions,the surface of the amorphous coating peels off very little,mainly due to adhesive wear.The amorphous coating induces fatigue peeling wear at the defects such as pores,with a small amount of oxidative wear,And the surface of the amorphous coating in the dry friction environment is more oxidatively worn than in the artificial seawater environment.The wear rate of stainless steel is 7 times higher than that of Fe-based amorphous coating.That is to say,the wear resistance of Fe-based amorphous coating is better than that of 304stainless steel;the wear rate of the coating decreases with the increase of the wear time,and increases with the increase of the applied load,indicating the amorphous coating can withstand long-term wear,and the wear rate of the coating in dry friction environment is greater than that in artificial seawater environment.Heat treatment will increase the hardness of the amorphous coating,and with the increase of hardness,the wear rate of the coatings will decrease.However,the effects of different wear mechanism and structural relaxation should be considered.By calculating the wear rate of the amorphous coatings heat treated at 150℃is the highest,followed by the original coatings,and the wear rate of the coatings heat treated at 250℃is the lowest.It can be seen that the proper heat treatment temperature（close to T_g）can be not only improve the hardness of the coating but also reduce the wear rate of the coating and improve its wear resistance.