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Studying of Micro-structure and Mechanical Properties of Resistant Spot Welds of Nickel Base Super Alloys

Bemani, Milad | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51896 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pouranvari, Majid
  7. Abstract:
  8. Resistance spot welding is one of the fabrication processes of gas turbines. Due to few published works about using RSW for joining participation hardened nickel base super alloys like Nimonic C263 and solid solution hardened ones like Hastelloy X, this work tries to investigate the microstructure and mechanical properties of RSW joints of these super alloys. In phase one, effect of welding current on structural properties of welds, hardness profile from the center of the weld to the edge of it, failure mod and failure energy were investigated. In phase two, effect of standard heat treatment of Nimonic C263 and the initial microstructure of the base metal on the micro-structure and mechanical properties of the welds were under study. In phase three, properties of Hastelloy X RSW weldment and finally in phase four, the mechanical and micro-structure of the dissimilar weldment of Nimonic C263 and Hastelloy X were investigated and the best welding current were proposed.In phase one, it is shown that welds with welding currents higher than 7KA, in constant other welding parameters, pass the minimum requirements of deferent industries. In phase two, it is concluded that the initial micro-structure of the base metals (Annealed or participated hardened) has almost no effect on the tensile strength and hardness profile of the welds, but the volume fraction of the gamma prime and structure matching in annealed specimen which were heat treated with the standard heat treatment cycle of Nimonic C263 were greater.In phase three, it was shown that if welding currents of 8KA or higher are used to joint Hastelloy X sheets, the mechanical and metallurgical properties will be reached.In phase four, it was observed, by investigating the mechanical properties and micro-structure of dissimilar RSW weldments of Nimonic C263 and Hastelloy X, that the best welding current for joining Nimonic C263 and Hastelloy X is 9KA in order to pass both the mechanical requirements and weld nugget and micro-structure requirements
  9. Keywords:
  10. Resistance Spot Welding ; Nickel-Base Superalloy ; Nimonic C263 Superalloy ; Hastelloy X Superalloy

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