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Study and Controlling Microstructure of Rapidly Solidified Multiprinciple Fe, Co and Ni Alloy

Ghiasi Afjeh, Mohammad Bagher | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53144 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Tavakoli, Rouhollah; Aashuri, Hossein
  7. Abstract:
  8. Multi-principle alloys exhibit microstructure and different properties from most conventional alloys due to their high entropy, very slow diffusion and distorted crystal structure properties. Heat treatment, thermomechanical treatment, addition of alloying elements and control of solidification process are common methods of microstructure modification and property improvement. Among the solidification parameters, undercooling and cooling rate is one of the most suitable methods to obtain semi-stable and fine-grained phases. These parameters have been less studied in multi-principle alloys, while in the case of ferrous and cobalt alloys has been much studied. The main purpose of this type of study is to understand the mechanisms of solidification behavior of multi-principle alloys and to understand the problem of favorable formation of different phases under fast quenching conditions in complex multi-principle alloy systems.In this study, high purity iron, nickel and cobalt were alloyed with vacuum arc remelting (VAR), then the samples were produced by two processes: 1- melt spinning and 2- suction casting. Finally, the effect of cooling rate and partial addition of chromium on their microstructure was investigated.In this study, it was found that due to non-equilibrium solidification in the average cooling rate, some separation occurs, and if a BCC-producing element is found in the separation section, the thermodynamics of the chemical composition of that area dictates that a BCC phase form occurs; If the concentration of BCC is not enough to produce BCC, then due to the presence of that particular element, the hardness of those areas changes. In the simulation of multi-principle alloys that should be thermodynamically single-phase FCC, it was found that hard sphere model is not suitable, but using the semi-thermodynamic method used to determine the type of phases of high entropy alloys can be useful for comparing alloys with different chemical compositions and is close to the answer
  9. Keywords:
  10. Rapid Solidification ; Microstructure ; Vacuum Arc Re-Melting ; Multi-Principle Alloys ; Thermomechanical Treatment ; Cobalt-Nickel-Ferrum Alloy

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