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在SiC粉中添加MoSi2粉,采用模压成型、无压烧成方法制备MoSi2–再结晶SiC(RSiC)复合材料。利用扫描电子显微镜、X射线衍射和等温氧化法研究复合材料的高温抗氧化性能及氧化机理。结果表明,所得复合材料中SiC为6H型,部分MoSi2转变为六方结构Mo4.8Si3C0.6,添加MoSi2前后样品的氧化产物均为方石英,样品表面生成的氧化膜形貌相似。氧化过程中样品质量变化与时间关系遵循抛物线规律,随MoSi2添加量增加,复合材料的抗氧化性能显著提高,其中,添加20%(质量分数)MoSi2所得复合材料在1500℃循环氧化100h后质量增加量仅为未添加MoSi2样品的37%。当MoSi2添加量为10%时,复合材料的抗氧化性能随样品烧成温度的升高先提高后降低,2 300℃烧成所得材料有较好的高温抗氧化性能,其氧化速率常数为0.99mg2/(cm4.h)。在氧化初始阶段,Mo4.8Si3C0.6和MoSi2首先发生氧化反应,随氧化时间增加,Mo4.8Si3C0.6和MoSi2消耗殆尽,此后的氧化则主要为Mo5Si3和SiC的氧化。SiO2膜的致密性和膜厚度与膜中Mo5Si3的含量有关。
MoSi2 powder was added to SiC powder, and MoSi2-recrystallized SiC (RSiC) composite was prepared by compression molding and pressureless sintering. The high temperature oxidation resistance and oxidation mechanism of the composites were investigated by scanning electron microscopy, X-ray diffraction and isothermal oxidation. The results show that SiC in the obtained composite is 6H and some MoSi2 is transformed into hexagonal Mo4.8Si3C0.6. The oxidation products of the samples before and after the addition of MoSi2 are cristobalite, and the oxide films formed on the sample surface are similar in morphology. The change of the sample mass during the oxidation process follows the parabolic law. With the increase of MoSi2 content, the oxidation resistance of the composites increases significantly. The composite with 20% (mass fraction) MoSi2 is oxidized at 1500 ℃ for 100h, The amount was only 37% of MoSi2 samples that were not added. When the additive amount of MoSi2 is 10%, the oxidation resistance of the composites first increases and then decreases with the increasing of the calcination temperature of the composites, and the material obtained after calcination at 2300 ° C has better high temperature oxidation resistance with an oxidation rate constant of 0.99 mg2 / (cm4.h). In the initial stage of oxidation, Mo4.8Si3C0.6 and MoSi2 first oxidized. With the increase of oxidation time, Mo4.8Si3C0.6 and MoSi2 were depleted. The subsequent oxidation was mainly the oxidation of Mo5Si3 and SiC. The denseness and film thickness of SiO2 film are related to the content of Mo5Si3 in the film.