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Title: EFFECTS OF CARBON CONTENT IN FERRITE AND MARTENSITE ON LATTICE PARAMETER AND ITS DIFFUSION PROCESS (COMPUTER SIMULATION)
Authors: Yilma, Mengistu
Advisors: Mulugeta Bekele(Dr.)
Keywords: CARBON
COMPUTER SIMULATION)
Copyright: Jan-2011
Date Added: 25-Jul-2012
Publisher: Addis Ababa University
Abstract: Molecular dynamics and molecular static simulation has been performed to investigate the structural transition of martensite and the diffusion properties of single carbon atom in the bulk of ferrite. For both types of simulations embedded atom potential was applied to describe atomic interaction. This potential considers short-range interaction of iron and non-interacting defects which can be valid only for small concentration. After carrying out molecular static simulation we found that octahedral sites are the preferential position of carbon that have lowest formation energy -6.277 eV with minimum energy configuration than tetrahedral sites which have -5.349 eV formation energy. The migration energy of carbon calculated using this method when carbon moves from one preferential position to the next preferential position is 0.89 eV. This result is in good agreement with Ab initio calculation of migration energy 0.90 eV and experimental results 0.83 eV. From direct molecular dynamics simulation result of equilibrium lattice constant at room temperature we found that ferrite that contains carbon less than 0.081 wt % have cubical structure (that have equal values of lattice constant in the three direction (100), (010) and (001)). When the amount of carbon contained reaches 0.081 wt % the equilibrium lattice constant of martensite started splitting in to two values a and c. This splitting shows ferrite-martensite structural transition. Thus this content in our case is the minimum concentration (critical point) at which structural transition of martensite from body centered cubic to body centered tetragonal occur at room temperature. The diffusion coefficient calculated using molecular dynamic method is 9.736 × 10−8m2/s.
Description: A THESIS SUBMITTED TO THE SCHOOL GRADUATE STUDIES OF ADDIS ABABA UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN MATERIALS SCIENCE
URI: http://hdl.handle.net/123456789/3477
Appears in:Thesis - Material Science

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