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High-temperature abradable coating technology is a key manufacturing technique for aero-engines,and the high-temperature scrapping properties are one of the critical indicators to evaluate coating quality.Taking Sc2O3-Y2O3-ZrO2-based wear-resistant coating as the object,the metallographic,phase,porosity,thickness,Rockwell hardness and high-temperature scraping properties of the coating were tested and analyzed using metallographic microscope,SEM,XRD,Rockwell hardness tester and high-temperature abrasion tester at 1 150 ℃.Results showed that after scraping tests at 1 150℃,the Sc2O3-Y2O3-ZrO2-based abradable coating was primarily composed of the t'-Sc2O3-Y2O3-ZrO2 and CaF2.The surface Rockwell hardness was 51.0 HR45Y,and the average Incursion Depth Ratio(IDR)of the blade was 5.98％,indicating excellent high-temperature scrapping properties of abradable coating.The excellent scraping properties were mainly attribu-ted to the following aspects:t'-Sc2O3-Y2O3-ZrO2 and CaF2 in the abradable coating exhibited good microstructural stability at 1 150℃ without phase transformation;the coating had relatively low Rockwell hardness,and CaF2 provided high-temperature self-lubrication,reducing wear on the blade material;meanwhile,the counterpart blade was made of IC10 superalloy,which exhibited good high-temperature stability and wear resistance.The inside of the wear scar of the abradable coating was uneven and contained cracks,with IC10 counterface material transferred in-to the scar during scraping.Besides,obvious linear wear marks appeared on the blade tip,and part of the abradable coating scraped off by the blade tip remained on the side of the blade tip.
Corrosion problem resulting from alternating ambient salt spray and high temperature oxidation poses a great threat to the safe service of aircraft engine during frequent start-stop in marine environment. In the present study，Ni25Cr5AlY coating is prepared on top of GH4169 superalloy substrate by direct-current（DC） magnetron sputtering. Corrosion behavior of the Ni25Cr5AlY coating is systematically studied by designing three different test conditions： high temperature oxidation at 1000 ℃，ambient salt spray，and alternating ambient salt spray and high temperature oxidation. The phase constitution and morphology of the corrosion products are analyzed by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The results indicate that after 168 h oxidation at 1000 ℃，the coating forms a dense and continuous Al2O3 scale which resists well against the oxidizing environment，while the coating suffers from pitting locally after 168 h salt spray test. After 168 h exposure to alternating ambient salt spray and high temperature oxidation test，the Al2O3 scale formed on the coating is damaged owing to the chlorine induced active oxidation mechanism，eventually resulting in Cr2O3 scale formation. In addition，the Cr2O3 scale is porous and cracks locally，which causes accelerated corrosion of the coating and internal oxidation of the coating and substrate. The corrosion degradation of the coating is accelerated under the synergistic effect of salt spray and high temperature oxidation. The GH4169 superalloy without the coating experiences severe scale spallation after 168 h exposure to the alternating test，featured by forming a poorly protective NiO scale with prevalent internal oxidation.
The finite element software ProCAST was adopted to numerically simulate the transition between the runner and the support plate with rounded corners of 3,5 and 7 mm of ZTC-4 titanium alloy intermediate casing,respectively.The results indicate that variation of fillet temperature field between different runners and support plate are basically consistent with the results of hot crack tendency.In the stress distribution of shunt ring,the stress field distribution formed by rounded angle value of 5 mm and 7 mm is superior to that of 3 mm.The residu-al stress on the surface of casing was measured by small hole method,and results basically coincide with simula-ted ones,verifying the simulation feasibility.
