Simulation On The Temperature Field And Micro-structure Of Large Bulk Nanocrystalline Fe₃Al Based Materials Prepared By Aluminothermic Reaction

This thesis summerized the development of simulation,the fabrication methods oflarge bulk nanocrystalline materials, the research about computer simulation and theapplication of finite element analysis software ANSYS. The purpose and the meaningof selecting the subject have been discussed. It provides a theoretical basis forparameters selection and optimization of preparing nanostructured Fe-Al-Cr indifferent grain size and microstructure control by the temperature field analyses duringthe big bulk nanocrystallic Fe-Al-Cr and the changes of temperature distribution underthe different parameters. The study of thermodynamic parameters calculation ofhomogeneous nucleation during solidification and grain size and their effects onnucleation. The main conclusions were given in the following.1. Mould is the main heat conductor in aluminothermic reaction to preparenanocrystalline Fe-Al-Cr. Along the height direction, the closer to the substrate, thelower was the temperature of Fe-Al-Cr melt and the cooling rate of Fe-Al-Cr melt waslarger; the farther from the substrate, the longer was the superheating time of Fe-Al-Crmelt,and the purification effect was better. Along the radial direction, the temperatureand cooling rate of Fe-Al-Cr melt were almost uniform. At the measuring point, thesimulation temperature was in accordance with the experiment temperature, whichproves the reliablity of simulation results2. The effects of different processing parameters on the temperature, cooling rateand superheating time of Fe-Al-Cr melt are at the selected point.With the increase ofsubstrate thickness, the cooling rate of Fe-Al-Cr melt at the initial cooling stagebecame larger, while the melt purification became worse. With increase of argonpressure and the number of1045steel, the cooling rate of Fe-Al-Cr melt varied a little.The cooling rate of Fe-Al-Cr melt cooled by glass substrate was much lower than themelt cooled by1045steel and Cu substrate, while the melt purification became better;The cooling rate of Fe-Al-10wt%Cr melt was largest than5wt%,15wt%and20wt%melts, while the purification of Fe-Al-5wt%Cr was the best. With the increase of Fe3Aldiluents content, the cooling rate at the initial cooling stage became lower, and themelt purification became worse. The temperature of Fe-Al-10wt%Cr was lower thanthe temperature of Fe-Al-10wt%Mo, Fe-Al-10wt%Ni, Fe-Al-10wt%Mn and Fe-Al-10wt%Cu, and the cooling rate at the initial cooling stage was larger than others.3. With the increase of undercooling extent, the critical nucleation work andcritical nucleus radius became lower, while thermodynamic energy and nucleation rate increased. With the increase of the undercooling extent, the calculated average grainsize of the Fe-Al-Cr nanocrystalline alloy decreased. When reaching a certainundercooling, the grain size kept in the nanometer level, which was in good coincidentwith the experimental results.4. The culculation indicates that, under the same undercooling, with the increaseof Cr content, the average grain size decreased. When reaching a certain Cr content,the average grain size decreased with the undercooling increase. At the sameundercooling, in the order of Fe-Al-Mn、Fe-Al-Cr、Fe-Al-Mo、Fe-Al-Ni and Fe-Al-Cu, the average grain size of the large nanocrystilline decreased. At the same alloysystem, with the increase of undercooling, the average grain size always decreased.5. The calculated average grain size of simulation was roughly the same toexperimental measured grain size, which indicated the computational feasibility,andthe average grain size of prepared materials can be forecasted by this simulation.