航空发动机封严用石墨/BN/Si3N4复合材料结构调控及摩擦磨损机制研究

In view of immediate contact between graphite seal material and high temperature transmission medium in aero-engine, the fluid medium will diffuse and permeate into the graphite seal material, even result in the seal leakage, which has disadvantage for stable and long space travel operation of the aerospace craft. As a seal material in end face and main shaft of aero-engine, the graphite should be provided with low penetration rate, excellent oxidation resistance and frictional wear. In this work, the liquid slurrying-mixing technology is suggested to perpare the graphite/BN/Si3N4 composite by the subjecting mixture of h-BN, Si3N4 and mesocarbon micrebeads (MCMB). Depanding on structural design and technical optimization, the h-BN, Si3N4 and MCMB in the composite will be strengthen during sintering process. The carbon coated h-BN, Si3N4 and MCMB was underwent uniform mixture, moulding and heatrteatment in order to obtain the graphite/BN/Si3N4 composite. The composite would have both low expansion coefficient, excellent thermal conductivity and self-lubricating property of graphite, and oxidation resistance and excellent frictional wear of BN and Si3N4 ceramics. The mutual relationship between preparing parameters and properties of graphite/BN/Si3N4 composite will be studied. The deposition, diffusion and transfer characteristics of transmission medium in the graphite/BN/Si3N4 composite will also be studied. Based on the distribution and diffusion characteristic of transmission medium in the composite, the relationship between infiltration feature and pore structure of composite will be clarified. After frictional wear test, the properties evolution, such as crystallite parameter, mechanical strength and thermal coefficient of expansion of composite will be evaluated, and corrosion behaviors and damage mechanism will also be investigated. It would be provided with an innovative candidate material for graphite seal material in aero-engine in the future.

在发动机工作中，与封严材料接触的高温燃料介质沿着材料孔隙进行扩散、渗透，将可能导致密封泄露。本项目针对航空发动机对封严材料低渗透、抗燃气氧化和摩擦磨损等要求，提出利用液相浆涂法制备石墨/BN/Si3N4封严材料的工艺路线。以六方氮化硼（h-BN）、氮化硅（Si3N4）和中间相碳微球（MCMB）为混合原料，首先将h-BN和Si3N4颗粒表面进行炭包覆，然后将包覆炭的h-BN、Si3N4与MCMB经混合、压型和热处理后制得石墨/BN/ Si3N4复合材料。该材料将兼具石墨自身的低膨胀系数、高导热和自润滑性，以及陶瓷的抗高温氧化和摩擦磨损性能。通过考察高温介质在石墨/BN/Si3N4复合材料中的分布和扩散行为，研究介质对复合材料的浸渗特性和对其孔结构与性能的依赖关系。结合复合材料在摩擦磨损前后性能和微晶参数的变化规律，探讨复合材料的损伤机制，为我国未来发动机用封严材料的制备或候选提供技术支撑。

在发动机工作中，与封严材料接触的高温燃料介质沿着材料孔隙进行扩散、渗透，将可能导致密封泄露。本项目针对航空发动机对封严材料低渗透、抗燃气氧化和摩擦磨损等要求，提出利用液相浆涂法或原位掺杂法制备石墨/BN/Si3N4封严材料的工艺路线。以六方氮化硼（h-BN）、氮化硅（Si3N4）、改制沥青和中间相碳微球（MCMB）为混合原料，首先将h-BN和Si3N4颗粒表面进行炭包覆，然后将包覆炭的h-BN与Si3N4直接压型或与MCMB经混合后压型，经过热处理后制得石墨/BN/Si3N4复合材料。该材料将兼具石墨自身的低膨胀系数、高导热和自润滑性，以及陶瓷的抗高温氧化和摩擦磨损性能。通过考察石墨/BN/Si3N4复合材料氧化前后结构与形貌的变化情况，研究复合材料的抗氧化机理。结合复合材料在摩擦磨损前后性能和微晶参数的变化规律，探讨复合材料的损伤机制，为我国未来发动机用封严材料的制备或候选提供技术支撑。