The Research Of Al₂O₃/Ag-Cu-Ti Composite Coating Prepared By Plasma Spraying

The way to combing the excellent properties of ceramic and metal is always thefocus of the study at home and abroad. Generally, due to the mechanicalcombination between the ceramic coatings and the metal substrate, the ceramicconatings prepared by plasma spraying will be easily fall off from the metalsubstrate. In this paper, by the way to adding Ag-Cu-Ti mixture powder to thealumina ceramic powders, and then using the mixture powder to carrying plasmaspraying on the GCr15steel. After that, taking heat treatment to the sample preparedby plasma spraying, finally, the metallurgical combination between theAl₂O₃/Ag-Cu-Ti composite coatings and the GCr15steel has been successfullyreached.In the experiment, the Ag-Cu-Ti mixture powder is making as the compositionof Ag-26Cu-3Ti alloy. In order to reducing the oxidation degree of the metal duringthe plasma spraying, using Ar to form a inert gas atmosphere to protect thecomposite coatings. The results shows that voltage:30V, current:280³40A, massratio of Al₂O₃:（Ag-Cu-Ti）=5:1is the best spraying parameters in the experiments.The Al₂O₃/Ag-Cu-Ti composite coatings are typical layer structure and the primaryphases are Ag、Cu and α-Al₂O₃. Due to the presence of alumina ceramic in thesurface of the composite and the lubrication caused by Ag and Cu，the compositecoatings shows excellent wear resistance.The bonding strength of Al₂O₃/Ag-Cu-Ti composite coatings prepared byplasma spraying is not very well. In order to enhancing the bonding strength of thecomposite coatings, the composite coatings are shelved in the furnace to bere-heated, the heating processing is carried out in vacuum and atmosphericenvironment. The experiment which is done in the vacuum environment shows thatwhen the heating temperature exceeding800℃, the composite coating is made up ofAg-Cu eutectic, Ag based solid solution, Cu based solid solution and α-Al₂O₃.During the heating process, the layer structure of the composite disappears and thetissue becomes dense and uniform. The heat treatment can not change the phase ofthe Al₂O₃, but small portion of the alumina ceramic have diffused and lost theoxygen content which caused small amount of aluminum diffusing into the coatingaround the alumina ceramic. When the temperature exceeds850℃, the interfacialreaction products will be formed at the junction between the composite coating andthe GCr15steel, the products are mainly made up of TiC. With the rising of the temperature, the thickness of the interfacial reaction products will increases, but t hethickness of the interfacial reaction products will show little change when thetemperature over1000℃. The heating experiment that under the atmosphericenvironment shows that due to the oxidation of the metal elements, there are someporous oxide layer formed in the composite coating, as a result, the performance ofthe composite coating are seriously damaged.The impact test results show that the composite coating prepared by900℃and10min in the vacuum environment has the highest bonding strength.