【作者】 张梦贤；

【导师】 李建国；

【作者基本信息】 上海交通大学 ， 材料加工工程， 2011， 博士

【摘要】 CS （combustion synthesis）技术具有产物纯度高、操作简单、省时节能等优点,已广泛被应用于金属间化合物、复合材料、陶瓷材料等的制备。然而人们对CS合成材料的力学性能及应用的研究较多,而对其形成机制和生长行为的研究却相对有限。因此,本文通过CS技术合成了TiC、ZrC陶瓷颗粒,并利用差热分析（DTA）,X射线衍射（XRD）,微区X射线,场发射扫描电镜（FE-SEM）,能谱（EDS）及透射电镜（TEM）等分析手段,研究了原位合成TiC、ZrC的反应特征、组织形貌、反应过程及生长行为。热力学计算结果表明,TiC、ZrC分别为Fe-Ti-C和Fe-Zr-C体系中最稳定的相。SHS （Self-propagating high-temperature Synthesis）反应制备TiC时,随着Fe-Ti-C混合粉末中Fe含量的增加,绝热燃烧温度、反应温度和燃烧波速降低,合成的TiC颗粒尺寸逐渐减小。通过DTA分析和燃烧波淬熄实验揭示了Fe-Ti-C体系SHS过程中的反应机制。首先,Fe和Ti相互扩散发生固态反应形成FeTi相;当温度升高到1085℃时,FeTi和Ti发生反应形成Fe-Ti液相,随后C原子溶解进入Fe-Ti熔体中并与Ti反应生成热力学上更稳定的TiC相。TE （Thermal explosion）较SHS具有更快的反应速度和冷却速度,合成的TiC颗粒更为细小,40wt.% Fe-Ti-C混合粉末TE产物中残留少量的Fe₂Ti化合物。Fe-Zr-C体系SHS制备ZrC时,随着体系中Fe含量的增加,绝热燃烧温度、反应温度和燃烧波速降低,产物中ZrC的颗粒尺寸明显减小,直至纳米级。体系中Fe含量为30wt.%时,SHS反应不完全,少量的Fe₂Zr化合物驻留在产物中。DTA分析和燃烧波淬熄实验表明,ZrC的形成机制主要为反应-析出机制。首先,Fe与Zr发生固-固反应生成Fe₂Zr化合物,Fe₂Zr形成时所释放的热量会促使Fe与C反应形成Fe-C液相,随后Zr溶解进入Fe-C熔体内与C反应生成ZrC,同时释放出大量的热量而导致Fe与Fe₂Zr反应形成Fe-Zr液相。最后,C扩散溶解进入Fe-Zr液相中并与Zr反应生成大量的ZrC颗粒。TE合成时,Zr和C通过固态反应生成ZrC颗粒,由于TE较SHS具有更高的反应温度,合成的ZrC颗粒尺寸略大。当Fe-Ti-C混合粉末中Fe含量为10³0wt.%时,SHS合成的TiC颗粒呈金字塔型层层堆砌形态,其生长模式为二维形核台阶生长。混合粉末中Fe含量为40wt.%时,高过饱和度与过冷度导致液/固界面由原子尺度光滑向原子尺度粗糙转变,其生长机制转变为连续生长。C粉颗粒尺寸能影响SHS的反应放热速度和放热量,从而改变合成产物中TiC颗粒尺寸。TE点火方式合成TiC时,体系中Fe含量的增加能降低TE的反应温度,但不影响TiC的生长机制。SHS点火方式合成ZrC时,0¹0wt.% Fe-Zr-C混合粉末中ZrC以固态扩散形式长大,一旦Fe含量超过20wt.%,液/固界面结构转变为原子尺度粗糙界面,ZrC以连续生长方式长大。采用石墨为碳原时,C向Fe-Zr液相中扩散需要的能量较高,不利于ZrC的持续形成及放热,使得SHS反应难以维持。TE点火方式合成过程中,不规则ZrC颗粒亦是以固态扩散方式长大。在Fe-Ti-C混合粉末中,添加物Cr₇C₃和V₈C₇粉仅作为稀释剂降低了SHS反应温度,减小了TiC颗粒尺寸。在Cu-Zr-C体系中SHS合成了纳米级ZrC颗粒,添加物Cu粉参与并促进了ZrC的形成。更多还原

【Abstract】 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.更多还原