Research On Microstructure And Properties Of Plasma Sprayed Iron-based Metallic Glass Coatings

By using gas atomization technique, fully amorphous FeCrMoCB powders were prepared. We produced atmospheric plasma spray (APS) coatings by using these powders. The coatings were sprayed on various substrates, and all of them exhibited fully amorphous state by X-ray Diffraction (XRD) analysis. The morphologies and microstructures of powders, splats, coatings and interfaces were systematically investigated by scanning electron microscope (SEM). Then a series of experiments were taken to test bonding strength, dry friction properties and electrochemical corrosions of coatings and substrates.The gas atomized FeCrMoCB powders showed quite spherical shape. No clear porosities can be found inside the powders. On the surface of coatings, some microcracks were found due to the release of thermal stress during the spraying process. The porosity of coating was about 7 percent. Single glassy splats were collected by quickly passing the torch over the polished substrates while spraying. The formation mechanism of the bubble inside the splats was analyzed through SEM observation of the single splat on the substrate. It is expected that this work will provide insight into the quality control of APS coatings.SEM observation of the interface between the substrate and the coating reveal that, the main bonding mechanism of APS coating is mechanical bonding. The bonding strength between single amorphous coating and substrate was 27.93 MPa. NiAl or NiCrAl was selected as the interlayer between the metallic glass coating and the substrates. For the bi-layer coating with NiAl interlayer, its bonding strength is 5% higher than that for the single metallic glass layer due to the metallurgical reaction between NiAl and metallic glass layer or substrate. However, for the bi-layer coating with NiCrAl interlayer, its bonding strength is 20 % lower than that for the single metallic glass layer, which is attributed to the formation of the oxidation on the interface between the NiCrAl layer and metallic glass layer or substrate.The wear resistance of FeCrMoCB coatings and 921A steel was examined by the dry friction tests. The wear mechanisms for the 921A steel and FeCrMoCB are adhesive wear and abrasive wear, respectively. FeCrMoCB coating has the better wear properties than 921A steel when weared in short-distance tests. However, the friction coefficient of FeCrMoCB coating is almost same with that for 921A steel when weared in long-distance tests.The electrochemical corrosion behavior of FeCrMoCB amorphous coating, 921 A steel and Ti-6Al-4V alloy were studied by potentiodynamic polarization in 0.5 mol/L, 1 mol/L and 4 mol/L sulfuric acid solution. Among the three materials studied, the FeCrMoCB coating exhibits the best corrosion resistance. The concentration of sulfuric acid solution plays a crucial role on the corrosion behaviors of amorphous coatings. The corrosion resistant ability of FeCrMoCB amorphous coating changes in the descending order of 0.5, 4, and 1 mol/L in the concentration.