Research Of The Plasma Arc Spraying Al₂O₃ Ceramic Coatings

In this paper, the process parameters of plasma arc spraying Al2O3 ceramic coatings is adjusted further, and then the stretching experiment and thermal shock resistance experiment of coatings are performed.Two coating samples, which one is the single Al2O3 ceramic coating, the other is the Al2O3 ceramic coating with FeCrAl bond coat, are conducted in the stretching experiment of coatings. The results are indicated that the coating bond strength of the latter is distinctly better than the one of the former. The reason for it is that FeCrAl bond coat alleviate change abruptly of the thermal expansion coefficient between the metal substrate and the ceramic coatings, and then debase the thermal stress of the surface between the substrate and the ceramic coating, therefore increase the bond strength of coatings.The thermal shock resistance experiment at the 600℃ is performed in order to studying resistance property to thermal shocks of plasma arc spraying A12O3 ceramic coatings, and then the failure mechanisms of thermal shock resistance are analyzed and discussed. The results are indicated that the nature of coatings' failure is the fatigue failure under the thermal cycling stress, and the failure process consist mainly of cracks formation, cracks spread and coatings' shedding. The accession of FeCrAl or Al bond coat alleviate efficiently thermal stress in the coatings, and restrict cracks formation and spread in the coatings, thus increase the resistance property of thermal shocks of coatings. The thermal shocks failure of coatings is caused by in or between coatings. To the coatings without bond coat, the main reason of coatings failure that is broken off from the interface between the substrate and coatings is the initiation and spread swiftly of interlaminar cracks; but to the coatings with bond coat, the main reason of coatings failure that is impaired partially in the ceramic coatings is the initiation and spread of cracks between lamellar particles in the ceramic coatings.In the end , the residual stress in the plasma arc spraying Al2O3 and Al-Al2O3 ceramic coatings is calculated appropriately by ANSYS analysis software, and stress distribution inthe two sorts of coatings is gained. The results is indicated that residual stress in the coatings is mainly the one parallel to coatings' interface. Thus in the circulations of thermal shocks> the cracks perpendicular to the surface of coatings are initiated easily, and result in coatings' premature failure. The analysis is indicated that accession of Al bond coat reduce the thermal stress of the surface between the substrate and the ceramic coating, alleviate abrupt change of thermal stress between them, and consequently height the bond between them. Thus Al-Al2O3 coatings have better bond and thermal shock resistance in comparison with Al coatings.