Nb、Al协同合金化MoSi2材料的燃烧合成与组织结构

摘要

以Mo、Nb、Si、Al元素粉末为原料，采用燃烧合成法制备名义成分分别为(Mo0.97Nb0.03)(Si0.97Al0.03)2、(Mo0.94Nb0.06)(Si0.97Al0.03)2、(Mo0.91Nb0.09)(Si0.97Al0.03)2与(Mo0.88Nb0.12)(Si0.97Al0.03)2等4种不同化含量的合金，研究其燃烧合成行为，分析燃烧合成过程中粉末压坯的燃烧模式、燃烧温度、燃烧波前沿蔓延速率以及产物组成。结果表明：随 Nb 含量增加，燃烧合成反应模式由螺旋燃烧逐渐转变为稳态燃烧。添加 Nb、Al 后，合金的最高燃烧温度升高，并随Nb含量增加呈现先升高后降低的变化趋势，其中(Mo0.91Nb0.09)(Si0.97Al0.03)2的燃烧温度最高，达到1924 K，但燃烧波蔓延速率随Nb含量增加而逐渐降低。XRD结果表明：(Mo0.97Nb0.03)(Si0.97Al0.03)2合金主要由 MoSi2构成，含有少量 Mo(SiAl)2和 Mo5Si3；(Mo0.94Nb0.06)(Si0.97Al0.03)2中开始出现 NbSi2相，(Mo0.91Nb0.09)(Si0.97Al0.03)2和(Mo0.88Nb0.12)(Si0.97Al0.03)2合金中Mo5Si3的衍射峰强度进一步降低，而NbSi2的衍射峰略有增强，因而添加Nb有利于形成C40结构的NbSi2，同时抑制Mo5Si3的产生。SEM观察表明合金为多孔结构。%The alloys with the nominal composition of (Mo0.97Nb0.03) (Si0.97Al0.03)2, (Mo0.94Nb0.06) (Si0.97Al0.03)2, (Mo0.91-Nb0.09) (Si0.97Al0.03)2 and (Mo0.88Nb0.12) (Si0.97Al0.03)2 were prepared by combustion synthesis method,and Mo, Nb, Si, Al powders were used as the starting materials. The combustion mode, combustion temperature, velocity of the flame-front propagation and combustion products were investigated. The results indicate that the combustion mode depends on the content of Nb. With the increase of the content of Nb, the combustion mode gradually transits from a spinning combustion to a stable combustion. The combustion temperature of pure MoSi2 is the lowest in all the alloys. With the increase of the content of Nb, the combustion temperature grows up first and then drops down. The specimen of the nominal composition (Mo0.91Nb0.09) (Si0.97Al0.03)2 has the highest combustion temperature of 1 924 k. However, the velocity of the flame-front propagation is inversely proportional to the content of Nb. The X-Ray diffraction patterns show that the combustion products of (Mo0.97Nb0.03) (Si0.97Al0.03)2 specimen are mainly MoSi2, and a small amount of Mo (SiAl)2 and Mo5Si3 are also detected. The NbSi2 phase appears in (Mo0.94Nb0.06) (Si0.97Al0.03)2 specimen. The intensity of the Mo5Si3 peak decreased obviously in (Mo0.91Nb0.09) (Si0.97Al0.03)2 and (Mo0.88Nb0.12) (Si0.97Al0.03)2 specimens, so it is reasonable to speculate that the addition of Nb promotes the formation of NbSi2 and suppresses the formation of Mo5Si3. The SEM photographs show that the combustion products are porous structure materials.