Role of Sintering Additives in Si-Ti-C Composites

为了提高碳化硅的断裂韧性，对TiC颗粒弥散的碳化硅复合材料进行了研究。掺钛2wt%的SiC-TiC复合材料在2000ﾟC下可热压至接近理论密度，其抗弯强度在1200ﾟC前不会下降，但在1400ﾟC时，抗弯强度严重下降。本研究的目的是阐明复合材料在1400ﾟC时强度下降的原因，并寻找一种在高温下仍能保持高强度的制备方法。随着碳含量的增加，Si和Ti3SiC2的X射线衍射峰强度和致密性降低。而掺钛的单块碳化硅不能致密化。因此，认为Si和Ti3SiC2的存在有助于TiC复合材料的致密化。复合材料中游离Si的存在和TiC界面弱界面层的存在以及1400ﾟC下的化学反应可能是导致1400ﾟC强度较低的原因。最后指出，采用放电等离子烧结法或添加硼的化学计量比热压法制备的SiC-TiC复合材料具有较好的高温弯曲强度。

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.