Study On The Mechanism Of The Electric Field Induced Combustion Synthesis Of Iron-based Composites

Both of TiC and VC are the ideal reinforcement in iron-based composites. Although there are many reports on combustion synthesis of TiC/Fe composites, the temperatures of synthesis reaction in these reports are higher than 1000℃. However, at present, there is no any report on combustion synthesis of VC/Fe composites. Therefore, this research of combustion synthesis of TiC and VC reinforced iron-based composites at relatively low temperature has its own novelties and important scientific value.In this paper, the system is heated rapidly by the great electric current through it directly. In this process, the electric field play the roles not only in inducing the reaction, but also in maintaining and controlling the process of combustion synthesis. The co-effect of electric and thermal field can provide the additional contribution for the solid diffusion among reactant at low temperature, and then reduce the staring temperature of reaction, realize combustion synthesis of iron-based composites at relatively low temperature eventually, which is the academic idea of this paper. The research objects were Fe-Ti-Cand Fe-V-C systems, and the thermal simulation instrument Gleeble-1500D was used in this experiment. There are many merits of this instrument, such as controlling the procedure easily, realizing the organic combination of dynamic process and phase analysis, obtaining the message of microstructure and micrograph inversion, high level of automation and information etc. So the macroscopic kinetic process of combustion synthesis can be made known by this instrument, which is one of the novelties of this method. In addition, the results of the process of combustion synthesis and its mechanism can provide a new synthesis method and theory not only for iron-based composites, but also for metal-ceramics composites.Firstly, the combustion synthesis of Fe-Ti-C system under the induction of electric field was studied. On one hand, the investigation for combustion behaviors indicated that the induction roles of the electric field were mainly in two points: one is supplying Joule heat to system, and another one is promoting diffusion process among the reactants at low temperature. The solid diffusion of the system at low temperature could be promoted by the co-effect of electric and thermal field. And then, the field emission under the electric field with great current would supply additional energy to the system and additional contribution to the solid diffusion among reactants at low temperature. As a result, the ignition temperature of the system could be decreased to a considerable degree. Moreover, the instantaneous fluid phase in micro-zone, which appeared during the process of combustion synthesis, could promote the diffusion of reactants. For FT44 system, when the preset heating rate was 600℃/s, the low-temperature combustion synthesis reaction could occur at 393. 69℃ in synchronism with the shrinkage of the compact, which indicated that the densification of compact could be realized to a certain degree in this process. And thepossibility and trend of the reaction at low temperature could be verified further by thermodynamic calculation and analysis. On the other hand, comparing the results of the electric field induced combustion synthesis process with that of the thermal analysis and high-temperature XRD, which are under the simple thermal field, the conclusion could be verified further that the ignition temperature could be decreased to a considerable degree under the electric field induction. In conclusion, the results demonstrated that the synthesis process under the coupling action of electric and thermal field was different from that under the simple thermal field, and the kinetic process of the electric field induced combustion synthesis could be describe as: Firstly, in the early period of heating process, the solid diffusion among reactants was strengthened under the common effect of electric field and great thermal density. In this period, although there was no reaction occurred in the system, the micro...