Design and Simulation of Diffusion Multiples for systems with the Fe-Al-C-Mn quaternary system
Independent thesis Basic level (degree of Bachelor), 15 credits / 22,5 HE creditsStudent thesis
This work is a subsection of the RFCS project “Precipitation in High Manganese Steel” which includes the octernary system Fe-C-Mn-Si-Al-V-Nb-N. To be able to understand and design a desired microstructure in such an elaborate system, all subsystems have to be analyzed. This analysis should include understanding of their kinetics and reaction processes as well as equilibrium states.
The evaluation of the quaternary system Fe-Mn-Al-C is of high importance to the design and manufacturing of steels, especially TWIP steels. The areas of interest, areas with a high content of both Al and Mn (15 respectively up to 40 mass-%), have not been looked at in detail before. Thus, experimental data in combination with simulations of atomic diffusion throughout the steel is necessary. In this work simulations are done to design diffusion multiples and to see what ranges in composition can be covered. The goal is to design the set-up of a diffusion multiple of the four elements as well as to acquire the parameter values for that specific set-up. From this, conclusions can be drawn about the set-up of an experimental procedure from which then properties of many different compositions can be determined. Prerequisites or “by-products” for this are the binary and ternary phase diagrams as well the diffusion coefficients of the different atom species through different lattices.
Phase diagrams which also show the diffusion path after certain annealing times, can be produced. The diagrams depend on the content of Al and Mn. The simulation of the diffusion path can also be modified to show the content ranges obtained when samples of dissimilar compositions are annealed while in contact with each other.
The phase diagrams are calculated using Thermo-Calc and the diffusion paths are simulated in Dictra, including calculations of thermodynamic state functions based on large databases. Those mobility and thermodynamic databases are developed using the Calphad approach, which depends on experimental values. Steel alloys are relatively well known, but for other alloy systems the calculated results may be less accurate and have to be improved by optimization using additional data. Here, an extended database was used which also includes the additional four elements necessary for the overall project.
Even though conclusions based on simulations have to be confirmed by experimental results, the number of samples can be highly reduced as the optimal parameters can be obtained much faster than by solely using the trial-and-error technique. This reduction is also valid in the case of the diffusion multiple technique, a combinatorial approach, to get many results in one sample.
Place, publisher, year, edition, pages
Dictra, ThermoCalc, Simulation, Diffusion Multiple
Other Materials Engineering
IdentifiersURN: urn:nbn:se:kth:diva-38039OAI: oai:DiVA.org:kth-38039DiVA: diva2:435853
Subject / course
Materials Design and Engineering
Master of Science in Engineering - Materials Design and Engineering