|
Addis Ababa University Libraries Electronic Thesis and Dissertations: AAU-ETD! >
Faculty of Science >
Thesis - Material Science >
Please use this identifier to cite or link to this item:
http://hdl.handle.net/123456789/3477
|
| 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
|
Items in the AAUL Digital Library are protected by copyright, with all rights reserved, unless otherwise indicated.
|
