Role of Sintering Additives in Si-Ti-C Composites

为了提高碳化硅的断裂韧性，研究了TiC颗粒分散碳化硅基复合材料。掺2wt% Ti的SiC-Tic复合材料在2000℃时可热压至接近理论密度，且其抗弯强度直到1200℃时才下降。然而，掺入Ti的SiC-TiC复合材料的抗弯强度在1400℃时急剧下降。本研究的目的是阐明在1400℃时强度下降的原因，并寻找一种即使在高温下也具有高强度的复合材料的制备方法。在低碳复合材料中，除SiC和TiC为主相外，还存在游离Si和Ti_3SiC_2。随着碳含量的增加，Si和Ti_3SiC_2的x射线衍射峰强度和试样密度均呈下降趋势。而掺杂Ti的单片SiC则不能致密化。因此，认为Si和Ti_3SiC_2的存在有助于Ti掺杂SiC-TiC复合材料的致密化。复合材料中自由Si的存在以及SiC与TiC之间弱界面层的存在以及在1400℃时的化学反应可能是导致材料强度较差的原因。SiC-TiC复合材料的抗氧化性能优于TiC。最后指出，采用火花等离子烧结或热压法制备的SiC-TiC复合材料在化学计量TiC的基础上添加硼，有望获得优异的高温抗弯强度。

To improve the fracture toughness of SiC,TiC particle dispersed SiC matrix composites have been studied. SiC-Tic composite doped with 2wt% Ti could be hot-pressed to nearly theoretical density at 2000ﾟC, and its bending strength did not degrade until 1200ﾟC.However, the bending strength of the SiC-TiC composite doped with Ti decreased severely at 1400ﾟC.The purpose of this study is to clarify the reason of degradation of the strength at 1400ﾟC,and to find a fabrication method of a composite which has high strength even at high temperature.It was observed that free Si and Ti_3SiC_2 existed in the composites containing lower carbon content, besides SiC and TiC as principal phases. The intensity of X-ray diffraction peaks of Si and Ti_3SiC_2 and the density of specimens decreased with the increment of carbon content. Whereas monolithic SiC doped with Ti could not be densified. Therefore, it is believed that the existence of Si and Ti_3SiC_2 contributes to the densification of the SiC-TiC composites doped with Ti.The existence of free Si in the composite and weak interface layr between SiC and TiC and a chemical reaction at 1400ﾟC could be a reason of poor strength at 1400ﾟC.Oxidation resistance of the SiC-TiC composite was better than TiC.Finally, it is suggested that a SiC-TiC composite fabricated by spark plasma sintering method or by hot-pressing method with addition of boron using stoichiometric TiC could be expected to possess superior high temperature bending strength.