In this paper, two kinds of MCrAlY coatings were prepared by atmospheric plasma spraying. The powders and coatings were characterized with scanning electron microscopy and energy dispersive spectrometry. X-ray diffraction and thermogravimetry differential thermal analysis were used to qualitatively analyze the phase. The change of powder mass with time and the change of heat absorption and exothermic were measured, and then the generation of new material was analyzed. It was found that the melting effect of the two kinds of powder by plasma spraying was good, and coating with high temperature oxidation resistance and hot corrosion resistance can be prepared. Both powders weight increased when heated in air, which indicates that oxidation occurs when the temperature rose. The main composition of NiCrAlY coating was γ′-Ni3Al, while NiCoCrAlYTa coating contained several kinds of NiAl composites.

NiCrAl-diatomite coatings, nickel graphite coatings and Ag-Cu alloy coatings prepared by thermal spraying were used to study the reaction mechanism. The compositions of NiCrAl-diatomite, nickel graphite and Ag-Cu alloy powders and coatings were investigated by X-ray diffraction. The powders were analyzed by thermogravimetric differential thermal analysis and scanning electron microscopy. The powders and coatings were compared and found to have the same phase by X-ray diffraction. Thermogravimetric differential thermal analysis of the powders showed that NiCrAl-diatomite was almost stable below 800 °C. Ag-Cu alloy coating and nickel graphite coating cannot be used at temperatures above 700 °C and 400 °C, respectively.

AlSi-polyester seal coatings and aluminum bronze/polyester seal coatings prepared by plasma spraying were used to study their reaction mechanism. The composition of AlSi-polylester and aluminum bronze/polyester powders and coatings were investigated by X-ray diffraction. The powders were analyzed by thermogravimetric differential thermal analysis and scanning electron microscopy. Comparing the powder with the coating, it is found that they have the same phase by X-ray diffraction. Thermogravimetric differential thermal analysis of the powders show that the service temperature should not exceed 500oC, otherwise the polyester constituent begins to degrade. It is also found that the aluminum bronze/polyester seal coatings have a lower porosity than the AlSi-polyester seal coatings.

In this paper, Cr2O3-2TiO2 and Al2O3 coatings are prepared by atmospheric plasma spraying (APS), and WC-10Co4Cr was prepared by high velocity oxygen fuel (HVOF). The powders and coatings are characterized with scanning electron microscopy (SEM) and energy dispersive spectrometry. X-ray diffraction (XRD) is used to qualitatively analyze the phase. The generation of new material is analyzed. The Vickers hardness of each coating is tested by microhardness tester. The tribological properties of the coatings are tested with the multifunctional material surface tester and the friction coefficient curves are drawn with the collected data. It is found that the friction and wear properties of the Cr2O3-2TiO2 coating are good due to the high degree of flattening during spraying. Cr2O3-2TiO2 coating has the highest average hardness. The phase structure is stable before and after spraying. Compared with the powder, the X-ray diffraction peaks of Al2O3 coating are seriously widened, some diffraction peaks are offset, and the intensity of the derived peaks is significantly reduced. Al2O3 coating has the largest hardness and lowest average hardness. However, compared with the other two coatings, Al2O3 coating has the worst wear resistance. It is also found that decarburization occurred during HVOF of WC-10Co4Cr. However, CoCr phase will wrap the WC, which can greatly reduce decarburization of WC during spraying. The bonding strength, wear resistance and toughness of the coating will be significantly enhanced. Compared with Al2O3 coating and Cr2O3-2TiO2 coating, the wear resistance of WC-10Co4Cr coating is slightly better.

The Al coating was prepared on the surface of steel samples by arc spraying. The corrosion behavior of Al coating was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), electromotive potential polarization and electrochemical impedance spectroscopy (EIS). The impedance data were fitted into an appropriate equivalent circuit to explain the electrochemical corrosion behavior of the coating in different stages. The micro morphology of arc sprayed Al coating surface was observed by SEM. It was found that the Al coating surface was in tentacle and layered structure, and the coating was porous and rough, which was related to the process of thermal spraying coating. XRD results showed that the oxide content in the coating was very small, and Al was the main component. The corrosion resistance of the coating was tested by EIS. The results showed that the Al coating had high corrosion resistance at the initial stage of corrosion, and a large number of bubbles were generated on the surface of the coating when it was immersed. Because there were many pores in the coating, which facilitated the penetration of Cl- . However, with the extension of corrosion time, the coating first appeared pitting behavior. At this time, the outer surface of the corrosion hole formed an oxygen-rich area and became a cathode, and the concentration cell was formed outside the corrosion hole due to the decrease of oxygen concentration in the corrosion hole, which promoted the activation and dissolution of aluminum. The corrosion products of the coating will block the pores in the coatings, and the corrosion rate will decrease.