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The Study and Comparison of Serrated Flow in IN600, IN625, and MP35N

Nima Nikpoor Badr | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43974 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Asgari, Sirous
  7. Abstract:
  8. A large number of metals and alloys show an irregular plastic behavior called serrated flow when being deformed in a certain temperature and strain rate range. The occurrence of this phenomenon affects the mechanical properties of the material, such as work hardening rate and ductility; consequently, it exerts limitations on the service conditions in which the alloy can be used.
    IN600, IN625 and MP35N are wrought Ni based and Ni-Co based alloys which are thermo-mechanically processed. When these alloys are deformed in temperatures between 300-700 ˚C, serrated plastic flow occurs. In order to investigate the mechanisms responsible for irregularities, hot compression tests were conducted on solution-treated samples of IN600 and IN625 at 600, 650, 700 and 750 ˚C. Obtained data were compared with available data on mechanical behavior of MP35N at room temperature and 600 ˚C.
    Microstructural studies by optical microscope, SEM and TEM were conducted on samples. In micrographs obtained by optical microscope, deformation markings and signs of inhomogeneous deformation were observed in all samples. Micrographs obtained by SEM from IN600 samples deformed at 700 and 750 ˚C in which serrated flow was disappeared, revealed the formation of a second phase in grain boundary regions. This phenomenon was not observed in samples of IN625. In TEM micrographs obtained from IN600 deformed at 600 and 650 ˚C, planar array of dislocations was observed; Furthermore, stacking faults were identified by their characteristic fringe pattern running parallel to the intersection of the inclined fault plane with the sample free surfaces. These features were not observed in samples deformed beyond the temperatures in which serrated flow occurred.
    Based on microstructural observations, interaction of solute atoms with dislocations – Suzuki mechanism and Cottrell mechanism- was determined as the mechanism responsible for occurrence of serrated flow in both IN600 and IN625. Also, Suzuki mechanism is known to be the active mechanism operating in MP35N
  9. Keywords:
  10. Scanning Electron Microscopy (SEM) ; Transmission Electron Microscope ; Hot Compression ; Serrated Flow ; Suzuki Mechanism ; Inconel 625 Superalloy ; MP35N Superalloy ; Cottrel Mechanism

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