Abstract
With the continuing development of aviation and navigation, the demand for the materials with higher performance for gas turbine and the internal combustion engine is increasing. Conventional coating and cathodic protection cann't meet the protection demand especially for the components in the severest corrosion environment. So the materials with high-temperature resistant and corrosion-resistant have been developed continuously, and, at present, spraying mental/ ceramic coating is the most effective way to improve the economy and reliability of the gas turbine and the internal combustion engine.
Mental/ceramic coatings have been widely used in the high temperature environment for its good thermal insulation, corrosion resistant and wear resistant properties. The interlayer is introduced into the mental/ceramic coating to decrease the high thermal stress caused by the mismatch of the thermal expansion coefficient, it is able to improve the combination, thermal-shock resistance and service life of coating.
First, the ansys software was used to implement the theoretical calculation of temperature fields and thermal stress fields in the mental/ceramic coating. The influence of the material, structure and thickness on the thermal insulation and thermal stress of the coating was studied.
Second, the accelerating behaviors of the CoNiCrAlY and ZrO2 particals were simulated through Gambit and Fluent software. The influence of different process parameters and nozzle structure on the accelerating behaviors was investigated, the appropriate spray parameters were obtained, gas temperature: 450～500℃ , gas pressure: 1.5～3.0Mpa, spray distance: 15～30mm, expansion ratio:5～10. The impinging simulation in the spray process of the CoNiCrAlY and ZrO2 particals was also studied through the ansys software.
Third, the coatings were prepared with the appropriate spray parameters,CoNiCrAlY , ZrO2-CoNiCrAlY and Al-CoNiCrAlY coatings are prepared with helium gas. Because the helium gas is very expensive, the CoNiCrAlY coating with air gas was studied for decreasing spray cost, though it was difficult at the beginning,and finally, the Al-CoNiCrAlY coating was prepared successfully with air gas.At last, the performances of the coatings were also studied. The apperarance of coating was observed through SEM and EDS. The results showed that the coating was deposited through intensive plastic deformation of the spray particles by high-speed impact, and no oxidation phenomena discovered in the cold spray process. The microhardness of the coating is high because of the shot peening strengthening in the cold spray. With optical microscopy, it is found that the coating has lower porosity,and can avoid crrosive medium penetrating into the coating. The combination test showed that the adhesion strength between coatings is higher than that between coating and substrate, and the coating combined physically to the substrate through the plastic deformation of spray particles.
The thermal shock resistance test showed that the coating has high thermal shock resistance, particle spalling occurred for the ZrO2-CoNiCrAlY coating after 12 times thermal shock resistance test, the Al-CoNiCrAlY coatings endured 12 times thermal shock were perfect without any defects, such as crack and spalling. In order to study the corrosion resistance of the coating, the seawater corrosion resistance test and the neutral salt spray test were performed. The results indicated that the steel can be effectively protected by the cold-sprayed coating.
In order to put this process into industrial use, there are still many problems waiting for further research and improvement.
KEY WORDS: numerical simulation, cold spray, mental/ceramic coating, process parameter, performance
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