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Development of NbSi_2-Based Duplex Silicides for Turbine Blade Operating at Ultra High-Temperature

超高温涡轮叶片用NbSi_2基双相硅化物的研制

基本信息

批准号：
10555232
负责人：
UMAKOSHI Yukichi
金额：
$ 7.74万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

项目摘要

NbSi_2-based silicides with the C40 structure had superior high-temperature strength and showed anomalous strengthening behavior at high-temperatures accompanied by a peak around 1500℃. Addition of Mo and W which are expected to stabilize the C11_b structure as a disilicide induced an increase in high-temperature strength and peak temperature. In contrast, MoSi_2 with the C11_b structure showed the lower high-temperature strength than NbSi_2. However, a large number of slip systems were operative and good ductility was obtained for MoSi_2. In order to use good mechanical properties of both silicides, duplex silicides composed with the C11_b and C40 phases were developed. If the silisides were prepared by conventional melting and casting processes, the C11_b and C40 phases form lamellae but it is not easy to control the orientation of lamellae. It is very difficult to obtain single crystals because there is a peritectic reaction in the NbSi_2-MoSi_2 psuedo binary system. Single crystals with the C40 structure were growned by controlling the crystal growth rate using the floating zone furnace. During annealing at 1500℃ for long period, the phase transformation from the C40 to the C11_b phase occurred forming a single set of lamellae. In the lamellar structure, the phase boundary between the C40 and C11_b phases maintained a good coherency and displayed good thermal stability. The mechanical properties of these silicides depended strongly on the angle (φ) between the lamellar boundary and stress axis. When stress is applied at φ=45°, good ductility was obtained in the duplex silicides. At φ=0, the duplex silicides showed high strength at high temperatures and 900MPa for the yield stress was obtained at 1400℃. If the lamellar structure is aligned to the longitudinal direction of the turbine blades, these blades can be operative at ultra high temperatures.

具有C40结构的NbSi_2基硅化物具有良好的上级高温强度，并在1500℃附近表现出反常的高温强化行为。添加Mo和W，这是预期稳定的C11_b结构作为二硅化物诱导高温强度和峰值温度的增加。相反，具有C11_b结构的MoSi_2显示出比NbSi_2低的高温强度。然而，大量的滑移系统是有效的，并获得良好的塑性为MoSi_2。为了利用这两种硅化物的良好机械性能，开发了由C11_b和C40相组成的双相硅化物。采用传统的熔铸工艺制备硅化物时，C11_b和C40相形成层状结构，但层状结构的取向不易控制。由于NbSi_2-MoSi_2准二元系中存在包晶反应，很难获得单晶。通过控制晶体生长速率，用浮区炉生长了具有C40结构的单晶。在1500℃长时间退火过程中，发生了由C40相向C11_b相的相变，形成了单一的层状结构。在层状结构中，C40和C11_b相之间的相边界保持了良好的共格性，并显示出良好的热稳定性。这些硅化物的力学性能强烈地依赖于片层边界与应力轴之间的角度（φ）。在φ=45°应力作用下，双相硅化物具有良好的塑性。当φ=0时，双相硅化物具有较高的高温强度，在1400℃时屈服应力达到900 MPa。如果层状结构与涡轮机叶片的纵向对齐，则这些叶片可以在超高温下工作。