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Properties of the Cobalt Base Superalloys and the Effect of Remelting on Microstructure and Chemical and Physical Behavior

Mokhtar, Fatemeh | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41202 (07)
  4. University: Sharif University of technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Yoozbashizadeh, Hossein
  7. Abstract:
  8. Because of the importance and value of Superalloy, In this research has been treid to remelting scrap of gas turbine blades cobalt based Superalloy X-45, In order to restore it to the cycle of consumption. For this purpose, scraps were remelted under different conditions, for example changing the atmosphere, changing slag composition, changing type of the furnace for remelting and changing time of remelting process. Then in order to investigate effect of the above factors, microstructure were studied by optical microscope and Scanning Electron Microscopy (SEM) And also in order to investigate changings of element composition, chemical analysis were examined by atomic absorption analysis and carbon and sulfur analysis. to determine the type of inclusion found in microstructure, Energy Diffraction X-ray Analysis (EDAX) were taken and to evaluate the quantity of them Image analysis of the samples were taken. The results of carbon and sulfur analysis shows that the highest desulfurization will be achieved under reducing atmosphere and the vacuum. The results of this analysis shows that some of the carbon reacts with oxygen and burns so percentage of carbon samples decrease after melting. Also reduce of carbon percentage under vacuum atmospheric is less than air atmospheric. The results of microstructure studies show that the samples has dendritic structure and also in samples that had low cooling rate, solidification defects were observed. Carbide types was observed in the samples, depending on the type of used furnaces and cooling rate. Oxide and sulfide inclusions observed in the samples according to the Energy Diffraction X-ray Analysis and also the image analysis results show that most inclusion removing is done by slag with the highest ratio of CaO to Al2O3
  9. Keywords:
  10. Electroslag Refining ; Microstructure ; Turbine Blades ; Cobalt Base Superalloy

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