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Improvement Of Hot Corrosion Resistance Of Casted Nickel-base Superalloy M17L

Posted on:2009-07-18Degree:MasterType:Thesis
Country:ChinaCandidate:F F HanFull Text:PDF
GTID:2121360245999427Subject:Materials Processing Engineering
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M17L is a new turbine blade superalloy with low density. In order to improve its hot corrosion resistence for application in the oceanic atmosphere and civilian industries, modified M17L superalloys were prepared by adjusting the M17L alloying composition. High temperature corrosion, thermal fatigue behavior and creep rupture strength of the modified M17L were investigated by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Chemistry analysis. The studies are significance for development of new high temperature alloys and practical application of modified M17L superalloy.It is indicated on the alloys with high content of Cr and refining grain size that a protective oxide scale formed easily and the MC carbide could be preferentially attacked because of higher content of C. The hot corrosion behavior of modified M17L alloys with 75wt%Na2SO4+25wt%NaCl at 900℃was investigated by completely immersion crucible test. The results indicated that G7 alloy has excellent hot corrosion resistance, G1,G2 alloys have better hot corrosion resistance than G3 and G4 alloys, 06-M17L alloy's worst.The hot corrosion behavior of modified G1 and G2 alloys with lower C content was studied through depositing salt film of 75wt%Na2SO4+25wt%NaCl at 900℃. It is indicated that the hot corrosion resistance of modified G2 alloy with Nb addition is improved, possibly because in G2 alloy Nb substitutes for some W, which prolongs the incubation period of acid solution and promotes formation of Cr2O3 and Al2O3 scales. The thermal fatigue performance of modified G1 and G2 alloys with lower C content during cyclic from 1100℃to room temperature (RM) is worse than M17L alloy by reasons of the grain boundary and microscopic structure's discrepance. All of the primary fatigue cracks and the secondary cracks at elevated temperature propagate intergranularly and high temperature oxidation plays role in the crack propagation.The stress property of modified M17L superalloys totally meets the challenge of M17L alloy. The creep rupture strength of G7 alloy with high Cr content is equivalent to M17L. The fracture way is intergranular crack.
Keywords/Search Tags:M17L, hot corrosion, thermal fatigue, stress rupture property
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