Cavitation Erosion Performance And Mechanismof Thermal Sprayed Co-based Coatings In Three Liquids

MCrAlY alloy coatings with a series of excellent properties such as oxidation resistance and corrosion resistance are widely used in surface protection.However,the mechanical properties such as the hardness of the conventional MCrAlY coatings are still low,which results in that their wear resistance and cavitation erosion resistance cannot meet the increasingly harsh operating conditions.In this thesis,two kinds of new hard particle reinforced CoCrAlYTaCSi and CoCrAlYTaCSi-Al₂O₃ coatings were prepared by high velocity oxygen fuel spraying technique?HVOF?.The effects of spraying different parameters on the phase composition,microstructure and mechanical properties of the coatings were investigated.Its corrosion performance in seawater and cavitation erosion performance in different liquids were also investigated.The cavitation erosion mechanism and corrosion-cavitation erosion coupling mechanism were analyzed.The main research results are as follow:1.The CoCrAlYTaCSi and CoCrAlYTaCSi-Al₂O₃ coatings were prepared by HVOF.The effects of different spraying parameters on the microstructure and mechanical properties of the two coatings were investigated.The results showed that the composition of CoCrAlYTaCSi and CoCrAlYTaCSi-Al₂O₃ coatings prepared by different spraying parameters were not significantly different,while the compactness and mechanical properties of the coating were significantly improved with the increase of spraying power.2.The cavitation erosion properties of two types of Co-based coatings and cast aluminum substrate?ZL101?in deionized water and aviation kerosene were compared and studied by using an ultrasonic vibration cavitation erosion test machine.The results showed that CoCrAlYTaCSi-Al₂O₃ powders with high molten degree were hard to melt under a low spraying power,resulting in more pores in the coating.Therefore,its cavitation erosion resistance was lower than the CoCrAlYTaCSi coating prepared at the same spraying power.However,the CoCrAlYTaCSi-Al₂O₃ coating prepared at a high spraying power showed the best anti-cavitation erosion performance due to its high compactness and mechanical properties.Cast aluminum showed very poor cavitation resistance due to its uneven structure and low mechanical propertie.In aviation kerosene,the cavitation with high impact force was difficult to form easily,so the loss of cavitation erosion of the materials was significantly reduced,and the reduction of coating material with better anti-cavitation erosion performance is larger.3.The corrosion performance of Co-based coating in seawater was studied using an electrochemical workstation.The results showed that the small amount of oxides pregenerated during the coating process could make the coating more capable of passivating film formation and impeding the charge transfer in the coating,thus improving the corrosion resistance of the coating.In addition,the moderate corrosion film formed on the coating surface in sea water could reduce the damage degree of cavitation erosion to some extent,and showed higher cavitation erosion resistance than in deionized water.