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Mechanical Properties of Two-Phase Microstructure in Nickel Based Superalloys with Molecular Dynamics Method

Shakibi, Saber | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52315 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khoei, Amir Reza
  7. Abstract:
  8. Nickel based superalloys are widely used in turbines since they are highly resistant to static, fatigue and creep loadings at high temperatures. Efficiency of turbines can be increase by application and development of these materials, which leads to reduced energy consumption. Nickel based superalloys constitutes of two phases, γ and γ' with multiscale behaviour. Thus to better understand the behaviour of this material, its behaviour should be studied across different scales.Molecular dynamics is used to model mechanical behaviour of this superalloy. This method is used for atomistic simulation of materials in which forces between atoms are modelled using an interatomic potential. Different phases of superalloys and dislocations therein is modelled using molecular dynamics.In this work, nickel based superalloy was modelled using atomistic simulations. Pattern of misfit dislocations at γ/γ' interface was extracted and validated. Stress-Strain response and evolution of dislocation density in this material under tensile uniaxial loading with different strain rates and temperatures were studied. It is observed that variation in temperature from 10 to 300 and 500 Kelvins did not alter neither dislocation densities nor the stress-strain response of the superalloy significantly. On the other hand increase in strain rate resulted in a considerable increase in yield stress and decrease in dislocation density. In addition the dislocations were mainly in [111] plane and in channels perpendicular to the loading direction. Lock formation process in γ phase, which is responsible for change in statistically stored dislocations in dislocation based crystal plasticity models, is also modelled in this work. Immobilization of mobile dislocations by interaction with forest dislocations is observed in molecular dynamics simulation of this process. Effect of this immobilization on the velocity of mobile dislocations is also quantitatively determined
  9. Keywords:
  10. Nickel-Base Superalloy ; Molecular Dynamics ; Dislocation ; Crystal Plasticity ; Finite Element Method

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