MoSi_2–再结晶SiC复合材料的高温抗氧化性能及氧化机理

Oxidation Resistance and Mechanism of MoSi_2–Recrystallized SiC Composites at Elevated Temperature

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。

The MoSi2-recrystallized SiC （RSiC） composites were obtained in the mixed powders of SiC and MoSi2 by pressing forming and pressureless firing. The scanning electron microscope, X-ray diffraction and isothermal oxidation method were used to study the oxidation resistance and mechanism of the composite at elevated temperatures. The experimental results showed that the 6H-SiC, MoSi2 and Mo4.8Si3C0.6 with hexagonal structure were the main crystal phases of the composite. The main oxidation product of both RSiC and MoSi2-RSiC was SiO2. The mass change of the composite with oxidation time obeyed the Parabola＇s law. With the increase of MoSi2 content, the oxidation resistance of the composite increased, and the composite with 20% （mass fraction） MoSi2 exhibited the excellent oxidation resistance. The mass gain of the composite after cyclic oxidation at 1 500 ℃ for 100 h was only 37% compared with that of RSiC. When the content of MoSi2 equaled to 10%, the oxidation resistance of the composite increased first and then decreased with the increase of the firing temperature. The composite with 10% MoSi2 fired at 2 300 ℃ exhibited excellent oxidation resistance, showing a reaction rate constant of 0.99 mg^2/（cm^4·h）. The oxidation process of the composite was complex, the MoSi2-Mo4.8Si3C0.6 was oxidized first and then the M05Si3 and SiC followed. The thickness and compact properties of SiO2 film were affected by the Mo5Si3 content in the film.