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| HOT CORROSION AND PROTECTION OF CAST NICKEL-BASE SUPERALLOY K-3 FOR GAS TURBINE |
| Xiao Xuchang Yang Zhonglin Wu Fengjun Xiong Jiyuan (Institute of Aeronautical Materials;Beijing;China) |
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Abstract The corrosion products on both corroded blades from service and corro- ded specimens from test rig as made of cast nickel-base superalloy K-3 and coated with aluminide are examined by optical microscope,X-ray diffraction, SEM,EDAX and chemical analyses to explore failure mechanism.It is shown that sulphurization and hot corrosion caused by molten salt are responsible to the failure of the blades,and it is suggested that the mechanism of hot eorro- sion of low chromium,refractory metal-rich K-3 superalloy is the synergism of sulphidation,basic fluxing and acidic fluxing.When the temperature is raised to about 900℃,the weight change during the hot corrosion propagation stage of this superalloy obeys a linear relationship with time after an incuba- tion period.In order to improve the hot corrosion resistance of conventional aluminide coatings,two kinds of aluminium-silicon coating technique are deve- loped.A diffusion-type slurry coating and a sintered slurry coating based on aluminium-silicon are evaluated in RFL burner rig tester by comparing with pack aluminide coatings.It is interesting to note that sintered Al-Si slurry coating as well as the diffusion-type Al-Si slurry coating exhibit a much better hot corrosion resistance than conventional pack aluminide coating. When specimens are exposed to combustion gases containing 50ppm sea salt,the Al-Si coatings protected K-3 superalloy for more than 200 hrs with- out any indication of hot corrosion,while the Al-coated K-3 snperalloy lasted only less than 50 hrs.
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Received: 25 June 1983
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