Combustion Synthesis And Growth Behaviors Of The Fe-Ti(Zr)-C Systems

compounds, composites and ceramic particles due to due to the high purity of the products, low production cost and simplicity of the operation and equipment. However, the mechanical properties and applications of in-situ materials have been paid more attention, while few works have been focused on its formation mechanism, especially its growth behaviors. Therefore, in this paper, TiC and ZrC ceramic particulates were fabricated by the CS technology. The reaction characteristics, crystal morphologies, formation mechanisms and the growth behaviors of TiC and ZrC ceramics were investigated in detail by using the modern analyzing methods such as differential thermal analyzer (DTA), X-ray diffractometer (XRD) and micro-diffractometer, field emission scanning electron microscopy (FE-SEM), energy dispersive spectrometer(EDS), as well as transmission electron microscopy(TEM).The results of thermodynamic calculation showed that TiC and ZrC are the most thermodynamically stable phase in Fe-Ti-C and Fe-Zr-C systems, respectively. When producing TiC ceramic particles by SHS (Self-propagating high-temperature synthesis), with increasing Fe content in Fe-Ti-C system, the Tad (Adiabatic temperature), reaction temperature and combustion wave rate decreases, and also the synthesized particles sizes reduces. The formation mechanism of TiC in Fe-Ti-C system was studied DTA analysis combining with combustion wave quenched experiments. After being preheated, the solid-state reaction between Fe and Ti initially occurred and produced a few FeTi phase. With increasing temperature, FeTi would react with Ti and formed Fe-Ti liquid. Then C diffused and dissolved into the Fe-Ti liquid and reacted with Ti to synthesize the thermodynamically stable TiC phase. Compared with SHS, TE (Thermal explosion) synthesis possesses higher reaction rate and cooling rate, which led to synthesis of finer TiC particles and Fe₂Ti compound residual in the 40wt.%Fe-Ti-C powder mixtures.When preparing ZrC through SHS route, with increasing Fe content in Fe-Zr-C system, the Tad, reaction temperature and particles sizes decreased, and also the synthesized ZrC particles sizes reduces to nano-order. In 30wt.% Fe-Zr-C powder mixtures, SHS reaction failed to complete and a amount of Fe₂Zr phase resided in the final product. The formation mechanism of ZrC in Fe-Zr-C system is reaction-precipitation mechanism. The solid-state reaction between Fe and Ti initially occurred and synthesized a few Fe₂Zr compounds. The formation of Fe₂Zr would release some heat and resulted in the formation of Fe-C liquids through the reaction between Fe and C powders. Subsequently, Zr atoms would diffuse and dissolve into Fe-C liquid phase and reacted with C to form ZrC phase. Utilizing the heat released by ZrC-forming reaction, Fe would react with Fe₂Zr to form Fe-Zr liquids. Finally, C atoms dissolved into Fe-Zr melt and reacted with Zr to form a number of ZrC particles.During the processing of TE synthesis, ZrC particles were formed by the solid-sate reaction between C and Zr particles. Compared with SHS synthesis, TE synthesis has higher reaction temperature, which led to the coarsening of ZrC particles.As Fe content ranges from10 to 30wt.% in the Fe-Ti-C powder mixtures, the growth morphology of TiC particles in the SHS products appear layer by layer growth mode through two-dimensional method. Due to high supersaturation and undercooling, liquid/solid interface of TiC changes from smooth interface to coarse interface in atom scale, and its growth mechanism of TiC also changes to continuous growth. The particles sizes of C atoms could influence exothermic rate and amount and the particles sizes of TiC. For synthesizing TiC by TE ignition method, the increasing of Fe content in the Fe-Ti-C system could decrease the TE reaction temperature, and has no influence on the growth mechanism of TiC.When fabricating ZrC with SHS ignition method, the growth of ZrC particles was controlled by the solid-diffusion method. Once Fe content exceeded 20wt.%, the growth mode of ZrC changed from lateral to continuous growth modes. When graphite acted as carbon resource, higher diffusion activity energy is need for the diffusion of C atoms into the Fe-Zr liquids, which would prevent the formation of ZrC. As a result, the SHS reaction is hard to self-sustain. In TE ignition modes, the irregular ZrC particles also grow up in solid diffusion mode.As a dilution agent, the additive of C₇C₃ and V₈C₇ decreased SHS reaction temperature and reduced the particles sizes of TiC. In Cu-Zr-C system, nano-meter ZrC particles were synthesized by SHS method. The addition of Cu participated and promoted the formation of ZrC.