Study On The Temperature Field And Micro-structure In The Solidification Process Of Bulk Nanocrystalline Fe₃Al Materials Prepared By Aluminothermic Reaction

In this thesis, the recent development of computer digital simulation of solidification, ANSYS software and aluminothermic method to prepare nanocrystalline Fe3Al was reviewed, and the difference between our country and the foreign was pointed out. On the same time, the accordance,purpose,and the meaning abouts electing the subject had been analyzed. Adiabatic temperature, temperature field, thermodynamic parameters of homogeneous nucleation and grain size in aluminothermic reaction to prepare nanocrystalline Fe3Al were calculated, which provided a theoretical basis for process parameters optimization to prepare different nanostructured Fe3Al.The main conclusions were given in the following.1.With the increase of preheating temperature To, the reaction adiabatic temperature Tad increased linearly; with the increase of alloying elements contents and Al2O3, Fe3Al diluents contents, the reaction adiabatic temperature decreased.2.Heat conduction of the Cu substrate was the main way of heat transfer in aluminothermic reaction to prepare nanocrystalline Fe3Al.Along the height direction, the closer to the Cu substrate, the temperature of Fe3Al melt was lower; The farther away from the substrate, the superheating time of Fe3Al melt was longer, and the melt purification was better. Along the radial direction, the temperature and cooling rate of Fe3Al melt were almost same. The calculated results were in good coincident with the measured results, proving the correct of the simulation.3.The effects of different process parameters on the temperature, cooling rate and superheating time of Fe3Al melt indicates that, at the elected point, with the increase of substrate thickness and reduction of reactant's quantity, the cooling rate of Fe3Al melt at the initial cooling stage became larger, while the melt purification became worse. With the increase of argon pressure, the cooling of Fe3Al melt increased a little; The cooling rate of Fe3Al melt cooled by quartz glass substrate was lower than the melt cooled by 45 steel and Cu substrate, while the melt purification became better. With the increase of Al2O3,Fe3Al diluents content, the cooling rate at the initial cooling stage became lower, and the melt purification became worse. 4.With the increase of undercooling, the critical necleus radius and the activation energy of bulk nanocrystalline Fe3Al became smaller, while the nucleation rate increased.5.With the increase of undercooling, the calculated average grain size of Fe3Al decreased, and remained 37nm when reaching a certain undercooling, which was in good coincident with the average grain size calculated by XRD in experiment.