| Fe based amorphous alloys have been widely used in the field of surface engineering due to their unique long-range disordered and short-range ordered atomic arrangement structure and a series of excellent physical,chemical and mechanical properties,such as high strength,high hardness,good wear and corrosion resistance and relatively low material cost.In this paper,commercial Fe Cr Mo CB amorphous powder is used as the spraying material,and the Fe-based amorphous coating is prepared on the surface of the AZ31B magnesium alloy substrate by detonation spraying technology.The microstructure,thermal stability,microhardness,friction and wear properties and electrochemical corrosion performance of Fe-based amorphous coating were investigated by X-ray diffraction(XRD),transmission electron microscopy(TEM),differential scanning calorimetry(DSC),scanning electron microscopy(SEM),Vickers microhardness tester and electrochemical workstation.The results of the study on the microstructure of the coating show that the coating is dense and uniform,showing a typical layered structure of thermal spray coating,with a low porosity of about 1%.The coating is well bonded with the substrate,the XRD diffraction results show a typical amorphous“steamed bread peak”,and the TEM selscted area electron diffraction pattern shows a diffuse halo ring,which indicates that the coating well retains the amorphous phase structure of the original powder.The amorphous phase content of the Fe-based amorphous coating prepared by detonation spraying is calculated by software to be about 89.3±2%,which is significantly higher than that of Fe-based amorphous coating prepared by other thermal spraying techniques.DSC result show that the coating has good thermal stability,and the initial crystallization temperature is about 612?.The microhardness of the coating(825±15 Hv)is about 11 times higher than that of AZ31B magnesium alloy substrate(76±5 Hv).Compared with the stainless steel coating on the surface of magnesium alloy,the amorphous coating also has very high microhardness,almost twice as high as that of stainless steel coating(?400 Hv).Dry sliding friction and wear test were carried out on Fe-based amorphous coating and magnesium alloy substrate.The results show that the coating has more stable friction coefficient than the substrate under 5 N and 0.25 m/s friction condition,and the wear rate of the coating(3.51×10-6 mm3 N-1 m-1)is nearly two orders of magnitude lower than that of the substrate(6.67×10-4 mm3 N-1 m-1).The wear mechanism of the coating is mainly fatigue wear and oxidative wear,accompanied by slight adhesive wear,while the wear mechanism of the magnesium alloy substrate is mainly abrasive wear and oxidation wear.With the increase of load and sliding speed,the wear scar width of the coating increases from413?m(2 N,0.1 m/s)to 1260?m(8 N,0.5 m/s),and the wear rate increases from 3.14×10-6 mm3 N-1 m-1 to 11.5×10-6 mm3 N-1 m-1,which is still lower than that of most other thermal spraying Fe-based amorphous coating.In addition,compared with other metal coating or high-entropy alloy coating on the surface of magnesium alloy,Fe-based amorphous coating can still maintain a relatively low wear rate,making it reliable and stable for engineering applications.The wear mechanism of the coating changes from oxidation wear with slight adhesive wear and fatigue wear at lower load and lower sliding speed to delamination wear accompanied by oxidative wear and fatigue wear.The excellent wear resistance is mainly due to the extremely low porosity and ultra-high content of amorphous coating of the Fe-based amorphous coating prepared by detonation spraying,which prevent the generation and propagation of cracks and the spalling of coating during dry sliding wear.The electrochemical tests of Fe-based amorphous coating and magnesium alloy substrate were carried out in 3.5%Na Cl solution.The results of polarization curve and impedance spectroscopy show that the coating have a very wide passivation zone and very low corrosion current density,and the corrosion current density(5.36±3?A/cm2)is only1/20 than that of the substrate(99.02±12?A/cm2).Compared with other thermal spraying coatings and metal coatings on magnesium alloy surface,Fe-based amorphous coating prepared by detonation spraying show relatively low corrosion current density and relatively high corrosion potential,indicating that corrosion resistance is better than most other surface coatings.Only a small amount of pitting pits were observed on the surface of the corrosion morphology,which indicated that the Fe based amorphous coating could resist the invasion of chloride ions,indicating that it had good pitting resistance.In addition,the impedance modulus of the coating is about 70 times than that of the magnesium alloy substrate,indicating that the coating has excellent corrosion resistance.The Fe based amorphous coating has almost no crystal defects such as grain boundaries and dislocations.A uniform passive film can be formed in the corrosion medium,and there is no sensitive part caused by pitting.At the same time,the chemical composition of amorphous coating is also helpful to improve its corrosion resistance.The introduction of Cr element is helpful to the formation of passive film,which effectively inhibits the dissolution of amorphous phase,so the corrosion resistance is improved.It provides good corrosion protection for magnesium alloy in structural or functional applications. |
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