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Investigating the Effect of Chemical Composition on the Anisotropy of Solid-Liquid Interfacial Energy of Nickel-Niobium Alloy

Ehsani, Mohammad Hossein | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56912 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Tavakoli, Rouhollah
  7. Abstract:
  8. Although the anisotropy of the solid-liquid interfacial free energy for most metal alloys is small, this anisotropy plays a significant role in the growth rate, morphology, and preferred crystallographic directions in dendritic growth. In recent research, the binary nickel-niobium alloy has been suggested as a suitable substitute for studying the solidification behavior of the superalloy Inconel 718. In this study, using molecular dynamics simulation with the LAMMPS software, pure nickel and Ni-%1Nb, Ni-%5Nb, and Ni-%10Nb alloys were examined (composition is based on atomic percent). After equilibrating the liquid and solid phases at the melting temperature, the interfacial phase was studied using the theory of capillary fluctuation, and using a local order parameter, the stiffness was calculated for different orientations of the interface in nickel-niobium compounds. According to the results obtained, in pure nickel, the interfacial energy is 369.31 (mJ/m^2 ) and the anisotropy is 3.62%. These results are in good agreement with previous studies, confirming the accuracy of the calculations. Similarly, in nickel-1% niobium, the interfacial energy is 222.31(mJ/m^2 ) and the anisotropy is 8.01%. In the nickel-5% niobium alloy, the interfacial energy is 158.58 (mJ/m^2 ) and the anisotropy is 6.89%, and for the nickel-10% niobium alloy, the interfacial energy is 123.68 (mJ/m^2 ) and the anisotropy is 8.13%. Accordingly, with an increase in the percentage of niobium in the alloy, the interfacial energy significantly decreases (up to 65 percent for adding 10 percent atomic niobium). Moreover, the degree of anisotropy of the interface increases with the increase of the alloying element. It is predicted that the reduction in interfacial energy along with an increase in anisotropy will increase the alloy's propensity for interface instability and the formation of dendritic structures in this alloy. Furthermore, considering the significant variations in interface properties resulting from alloying, it is possible that the preferred crystal growth directions change with an increase in the percentage of the alloying element
  9. Keywords:
  10. Molecular Dynamic Simulation ; Nickel Alloy ; Solid-Liquid Interface Anisotropy ; Metals Solidification ; Inconel 718 Nickel Based Superalloy

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