| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 101 === This study investigates the weldability, solidification cracking susceptibility, ductility-dip cracking(DDC) susceptibility and corrosion resistance of Inconel Alloy 52 with different Niobium(Nb) content. By GTAW process, different dilution rates with different Nb content weldments were studied. Trans. Varestraint Test was used to predict the solidification cracking susceptibility. Microstructure and EDX analysis was used to realize the change of metallurgical behavior. Finally, combine the above results, the corrosion resistance was discussed after SL-EPR and Modified Huey Test.
After the Trans. Varestraint Test, it was indicated that the susceptibility of solidification cracking in 2.53% Nb weldment is the highest,. Because of the eutectic Laves phase precipitating, it lowers the melting temperature and increase the size of the crack susceptible solid + liquid mushy zone. Besides, the sensitivity of ductility-dip cracking in 0.02% Nb weldment is the highest. Due to the lack of extensive GB pinning by the medium size eutectic NbC-like precipitates, it cause GBs migrating, sliding and creep-like phenomenon in cladding.
Inspection on the fusion zone of weldments with different Nb content, it was shown that the alloy 52 without Nb content was cellular dendrite mainly. Owing to the unrestrained grain boundary migration in cladding, the DDC phenomenon occurred often at alloy 52. The alloy 52 with Nb content was columnar and equiaxed dendrite. The more Nb, the bigger size of eutectic NbC-like precipitates.The results of corrosion displayed that the alloy 52 weldment has worse IGC resistance because the entectic TiN precipitated at GBs. The more Nb content, the worse corrosion resistance because of the galvanic effect when the size of NbC is becoming bigger.
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