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Investigation of Microstructural Evolutions During Dissimilar TLP Bonding of IN792 and Hastelloy X Nickel Based Superalloys

Ghasemi, Ali | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50215 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pouranvari, Majid
  7. Abstract:
  8. In this thesis, macrostructural evolutions in dissimilar TLP bonding of as-cast nickel based supperalloy IN792 to wrought HX was investigated. In the first step of this study solidification behavior of Ni-Cr-Fe-Si-B (MBF-15) interlayer in presence of HX as base metal at 1120 °C was surveyed. In second step, bonding of HX/HX, IN792/IN792 and HX/IN792 systems with MBF-15 interlayer at 1120 °C and different times were studied and isothermal solidification time and factors that affect this stage were discussed. In third step, synchronization of dissimilar bonding with standard heat treatment cycle of IN792 was investigated and effect of this cycle on aging response of different zones, isothermal solidification and DAZ borides was examined. Then the effect of PBHT as a solution for dissolution of DAZ borides was discussed. It has been shown that in wide gap TLP bonding process, presence of ASZ is inevitable and MBF-15 interlayer is suitable according to gamma solid solution fraction. Microhardness of the ASZ is much lower than typical Ni-B-(Si)-(Cr) interlayers. PBHT temperature is dictated by Solidification path of the interlayer. It has been shown that formation of Boride pricipitates in DAZ during isothermal solidification causes depletion of boron from austenitic nickel based matrix and results in higher flux of B and lower isothermal solidification time. On the other hand, presence of alloying elements that increase the liquid phase temperature can help isothermal solidification as well. Response of different microstructural regions to the standard heat treatmet cycle of IN792 has shown that this cycle is good enough for dissolution of IN792-DAZ side and development of gamma prime precipitates in bonding region. But this cycle is not fully useful for dissolution of HX-DAZ side. Mechanical properties of joint region are controlled by solid solution and precipitation hardnenning mechanisms. Suitable gamma prime and alloying elements gradinent in bonding region proves good low and high temperature mechanical properties
  9. Keywords:
  10. Mechanical Properties ; Isothermal Solidification ; Precipitation Hardening ; Transient Liquid Phase Boneling (TLPB) ; Nickel-Base Superalloy ; Microstructure Evolution

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