NiAl-Cr(Mo)共晶合金微观组织的热稳定性研究

NiAl-Cr(Mo) eutectic alloy possesses a vast application prospect due to some advantages, such as high melting temperature, relatively low density, good thermal conductivity and excellent oxidation resistance. However, the poorly thermal stability of lamellar structure and nanoscale particles in lamellar structure restricts the application of serving as the aeroengine hot end components. The research shows that the lamellar spacing and the solid solution element have an effect on the thermal stability, and the investigation of ripened rule of axioliticly nanoscale particles in lamellar structure is important for the thermal stability of axiolitic particle. We can control the lamellar spacing by directional solidification in this project and then clarify the effect of lamellar spacing on the thermal stability of lamellar structure to obtain a critical lamellar spacing in which there is a transition from unstable lamella to stable lamella. For the solid solution element, it is necessary to ascertain the effect of Fe and Co on the thermal stability of lamellar structure and reveal the unstable mechanism of lamellar structure. Furthermore, the morphology of axioliticly nanoscale particles is observed by TEM, and then the ripened rule of particles is concluded by the measurement of particle size at different time, and the coarsening mechanism of particles is revealed. Based on the preliminary work, the relation between the thermal stability of NiAl-Cr(Mo) eutectic structure and elevated temperature strength is investigated to provide the experimental basis and theoretical support for obtaining an excellent elevated temperature property.

NiAl-Cr(Mo)共晶合金因熔点高、密度低、导热性好和优异的抗氧化性能等优点具有广阔的应用前景，但是其组织(层片组织和层片内纳米级颗粒)的热稳定性较差，限制了其作为航空发动机热端部件材料的应用。研究发现层片组织的热稳定性主要与层片间距和固溶元素有关，对于层片内椭球状纳米级颗粒的热稳定性，讨论其熟化规律更为重要。本申请项目拟采用定向凝固技术对层片间距进行控制，研究层片间距与层片组织热稳定性的关系，明确作为高温下层片组织稳定依据的临界间距；针对固溶元素，需探明Fe和Co分别对层片组织热稳定性的作用规律，并揭示层片组织不稳定机制；采用TEM观察椭球状颗粒在尺寸和形貌上的变化，通过测量不同时间段内的颗粒尺寸来总结其熟化规律，并揭示其粗化机制。在此基础上，探索该共晶合金组织的热稳定性与高温强度的关系，为实现优异的高温性能提供实验依据和理论支持。

NiAl-Cr(Mo)共晶合金因熔点高、密度低、导热性好和优异的抗氧化性能等优点具有广阔的应用前景，但是其组织(层片组织和层片内纳米级颗粒)的热稳定性较差，限制了其作为航空发动机热端部件材料的应用。本项目通过采用定向凝固技术对NiAl-Cr(Mo)共晶层片组织进行控制，研究了层片组织的热稳定性与层片间距、温度和固溶元素的关系，也探究了层片内椭球状纳米级颗粒的热稳定性。结果表明，在抽拉速率2.5μm/s以及对应层片间距为3.7μm时，层片组织相对稳定，随着抽拉速率增大，热稳定性降低，也随温度的升高，热稳定性降低，例如层片发生粗化、迁移、局部溶解、圆柱化等；研究表明Fe对层片组织的热稳定性没有明显影响；采用TEM观察沉积物颗粒为椭球状，高温处理后发生了Ostwald粗化，椭球状颗粒更加扁平，通过形貌上的改变也能判断该合金中椭球状颗粒平均尺寸的变化不再服从球状颗粒的t1/3规律。这些研究为该合金是否能够应用于高温环境提供了依据。