航空发动机高温固体润滑耐磨涂层的制备与性能研究
文献类型：学位论文
| 作者 | 曹玉霞 |
| 学位类别 | 博士 |
| 答辩日期 | 2012-06-01 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 张伟刚 |
| 关键词 | NiCr/Cr3C2-BN涂层 NiCoCrAlY/Al2O3涂层 NiCoCrAlY/Cr2O3涂层 热喷涂 力学性能 摩擦磨损 |
| 其他题名 | Preparation and Performance Study on the Solid Lubricating and Wear-Resistant coatings in Turbo-engine at Elevated Temperatures |
| 学位专业 | 化学工程 |
| 中文摘要 | 新一代航空发动机的高压压气机和涡轮部位开始采用刷式封严结构，以提高封严效率和减少重量。为了降低机轴和刷丝的磨损，减小两者之间的摩擦系数，通常采用热喷涂技术在机轴表面喷涂高温固体润滑耐磨涂层材料，以满足航空发动机上述刷式封严部件苛刻工作条件的要求。本论文采用加氢还原、固态合金化和离心喷雾造粒技术制备了NiCr/Cr3C2-BN、NiCoCrAlY/Al2O3和NiCoCrAlY/Cr2O3三种复合粉体，并采用等离子喷涂技术和超音速火焰喷涂技术制备了NiCr/Cr3C2-BN、NiCoCrAlY/Al2O3和NiCoCrAlY/Cr2O3高温抗氧化复合涂层材料，研究了涂层的结构与性能。主要研究内容和结果如下：（1）以CaB2O4为助熔剂制备了片状颗粒BN，研究了BN在干空气和水蒸汽气氛下的摩擦磨损性能。研究发现：CaB2O4的加入可以促进BN的结晶长大。BN块体在空气和水蒸汽气氛下的摩擦系数均随着温度的增加先增大后减小，且在水蒸汽气氛下的摩擦系数明显低于在空气气氛下的摩擦系数，主要原因是：在室温下，水蒸汽加入后会在BN与摩擦副的摩擦表面形成一层水膜，降低BN与摩擦副之间的剪切强度，进而降低了BN的摩擦系数；高温下，BN可以与水蒸汽发生反应，生成层状结构的H3BO3，进一步降低其摩擦系数。（2）以颗粒BN为固体润滑剂，采用等离子喷涂技术制备了NiCr/Cr3C2-BN复合涂层。研究发现：随着BN含量的增加涂层的孔隙率逐渐增大，显微硬度和结合强度逐渐降低，涂层的显微硬度HV0.2在570~857之间，结合强度在15~30MPa之间。涂层的主要结合机理是机械结合，同时还可能存在部分冶金结合。制备的涂层抗热震性能良好，氧化动力学曲线基本遵循抛物线增长规律。发现涂层的外部和内部同时氧化是涂层氧化失效的主要机制，因此涂层适用于800℃以下的温度环境。不含BN的NiCr/Cr3C2涂层的摩擦系数随温度的升高缓慢降低，最小值在0.56左右。磨损率随温度的升高而增大，在10-5~10-4mm3/Nm数量级之间。含有BN的等离子喷涂NiCr/Cr3C2-BN涂层的摩擦系数和磨损率均随温度的升高先增大后减小，相同测试条件下，涂层的摩擦系数随着BN含量的增加呈逐渐下降的趋势，而涂层的磨损率则呈逐渐升高的趋势，说明BN的加入可以有效的降低涂层的摩擦系数。综合考虑，当BN质量含量为10%时，涂层综合性能最好。（3）对NiCoCrAlY/Al2O3高温抗氧化复合涂层的研究发现：采用两种方法制备的涂层主晶相为NiCrAl合金相和Al2O3相，但是等离子喷涂涂层中还存在少量的Cr2O3相和CoCr2O4相，说明在热喷涂过程中金属发生了少量的氧化。与等离子喷涂涂层相比，超音速火焰喷涂涂层表面更为光滑，结构更加致密，孔隙率仅为0.41%，是等离子喷涂涂层的1/7左右；显微硬度HV0.2达到550左右，比等离子喷涂涂层提高了25%；结合强度为48MPa，比等离子喷涂涂层提高了70%。等离子喷涂涂层为典型的脆性断裂，裂纹主要沿着层与层之间的孔隙进行扩展，而超音速火焰喷涂涂层裂纹沿着NiCoCrAlY合金与未熔融的Al2O3颗粒的界面处扩展。两种方法制备的涂层主要结合机理是机械结合，同时还存在部分冶金结合。两种方法制备的涂层在700~850℃抗热震性能良好；氧化增重曲线分为大斜率直线、抛物线和小斜率直线三个阶段，超音速喷涂涂层抗氧化性能优于等离子喷涂涂层。两种方法制备的涂层摩擦系数相差不大，但是超音速火焰喷涂涂层的磨损率明显低于等离子喷涂涂层。NiCoCrAlY/Al2O3涂层低温下的主要磨损机制是脆性断裂和磨粒磨损；高温下涂层的主要磨损机制是氧化磨损、粘着磨损、磨粒磨损、塑性变形和涂层的转移。（4）对NiCoCrAlY/Cr2O3高温抗氧化复合涂层的研究发现：与等离子喷涂涂层相比，超音速火焰喷涂涂层表面更为光滑，结构更加致密，具有更高的显微硬度和结合强度，以及更好的抗氧化性能和抗热震性能，涂层氧化增重曲线与NiCoCrAlY/Al2O3相似，相同喷涂方法相比NiCoCrAlY/Cr2O3涂层抗氧化性能显著优于NiCoCrAlY/Al2O3涂层。两种方法制备的涂层摩擦系数均随着温度的升高呈下降的趋势，800℃时摩擦系数最低，分别为0.27（等离子喷涂涂层）和0.3（超音速火焰喷涂涂层），明显小于相同温度下NiCoCrAlY/Al2O3涂层的摩擦系数。NiCoCrAlY/Cr2O3涂层低温下的主要磨损机制是脆性断裂和磨粒磨损；高温下涂层的主要磨损机制是由氧化磨损、塑性变形和金属氧化物的转移共同作用造成的 |
| 英文摘要 | Brush seal system was used on the high-pressure compressor and turbine blades in advanced turbo-engine. The solid lubricating and wear-resistant coating prepared on the turbo-engine by thermal spraying technology would not only reduce the wear rates of the rotor shaft and brushes, but also satisfy the harsh service environment need for the brush seal parts. In this study, the NiCr/Cr3C2-BN, NiCoCrAlY/Al2O3 and NiCoCrAlY/Cr2O3 composite powders were prepared by hydrogen reduction, solid state alloying and spray granulation technologies. Then the NiCr/Cr3C2-BN composite coatings were prepared by atmospheric plasma spray (APS), the NiCoCrAlY/Al2O3 and NiCoCrAlY/Cr2O3 composite coatings were prepared by atmospheric plasma spray (APS) and high velocity oxygen fuel (HVOF), and the microstructure and properties of the coatings were systematically investigated. The main conclusions are summarized as follows: (1) Granular BN was prepared by hot-temperature under nitrogen with CaB2O4 as an additive to promote its crystallization, and the friction coefficients of the sintered BN were investigated under atmosphere ambience and water vapor ambience, it was found that CaB2O4 can effectively promote crystal growth of BN at 2000℃ for 5h in N2 ambience. The friction coefficients of the sintered BN increased as the temperature increasing from room temperature to 400℃, and then decreased with the temperatures increasing from 400℃ to 800℃ under atmosphere ambience and water vapor ambience. The friction coefficients of the sintered BN under water vapor ambience were much lower than those under an atmosphere ambience. The reason is probably that the water film forms on the sliding surface and the presence of the condensed liquid water in crystal defects leads to a decrease of the surface tension, and therefore of the friction coefficients of the sintered BN at room temperature; at high temperature the water vapor can react with hNB to form B2O3 and the B2O3 can further react with water vapor to form H3BO3 which has a lamellar structure, leading to a decrease of the sintered BN. (2) The NiCr/Cr3C2-BN composite coatings with different contents of BN were fabricated by atmospheric plasma-spray technology with the Granular BN as a solid lubricat, it was found that the porosity of the composite coatings increased, and the microhardness and tensile strength of the NiCr/Cr3C2-BN composite coatings gradually decrease with increase of the BN in the composite powders. The microhardness and tensile strength of the NiCr/Cr3C2-BN composite coatings were 570~857 and 15~30MPa, respectively. The main bonding mechanism of the NiCr/Cr3C2-BN composite coatings is mechanical bonding, and also maybe partically metallurgical and physical bonding. The thermal shock resistances of the NiCr/Cr3C2-BN composite coatings with different contents of BN are very well. The oxidation kinetics curves of the NiCr/Cr3C2-BN composite coatings basically follow parabola law. The main oxidation mechanism of the NiCr/Cr3C2-BN composite coatings is that the oxidation occurs inside and outside of the coatings at the same time, therefore the coatings can be used in the environment under 800℃. With increase of the temperature, the friction coefficients of the NiCr/Cr3C2-BN composite coating without BN gradually decrease and the minimum is about 0.56 at 800℃,but the wear rates of the coatings gradually increase and the values are all between 10-5~10-4 mm3/Nm magnitude level. The friction coefficients and wear rates of the NiCr/Cr3C2-BN composite coating with different contents of BN gradually increase and then decrease. The friction coefficients of the NiCr/Cr3C2-BN composite coating with different contents of BN gradually decrease with increase of the BN in the composite powders under the same testing condition, which reveals that the addition of BN is benefit to the friction coefficient of the atmospheric plasma-sprayed NiCr/Cr3C2-BN composite coatings. The NiCr/Cr3C2-BN composite coating with 10%BN in the composite powder has the optimum properties. (3) The NiCoCrAlY/Al2O3 composite coatings were fabricated by atmospheric plasma-spray and high velocity oxygen fuel technologies. It was found that the main phases of the NiCoCrAlY/Al2O3 composite coatings are NiCoCrAlY alloy phase and Al2O3 phase. The phases of the APS sprayed NiCoCrAlY/Al2O3 composite coatings are also include a little of Cr2O3 and CoCr2O4, which reveals that the oxidation of the alloy occurs in the process of thermal spraying. Compared with the APS sprayed coating, The HVOF sprayed coating has much smooth surface, dense microstructure and low porosity. The porosity of the HVOF sprayed coating is about 0.41%, which is only 1/7 of the APS sprayed composite coatings; The microhardness of the HVOF sprayed coating is about 550, which is 25% more than that of the APS sprayed composite coatings; The tensile strength of the coating is 48MPa, which is 70% more than that of the APS sprayed composite coatings. The brittle fracture is the main fracture mechanism of the APS sprayed coating and the cracks extend along the hole between two layers. Meanwhile, the cracks of the HVOF sprayed coating extend along the interface between NiCoCrAlY alloy and Al2O3. The mian bonding mechanisms of the APS and HVOF sprayed NiCoCrAlY/Al2O3 composite coatings are mechanical bonding, and also maybe partically metallurgical bonding. The thermal shock resistances of the APS and HVOF sprayed NiCoCrAlY/Al2O3 composite coatings are very well at 700~850℃ and the oxidation kinetics curves of the coatings can be divided into three stages: severely slopeing line, parabolic and slightly slopeing line. The oxidation resisitance of the HOVF sprayed coating is better than that of the APS sprayed coating. The friction coefficients of the APS sprayed composite coating are close to those of the HVOF sprayed composite coating, but the wear rates of the HOVF sprayed coating are much lower than that of the APS sprayed composite coatings. The abrasive mechanism of the NiCoCrAlY/Al2O3 composite coatings is dominated by mixed brittle crack and abrasive at low temperature, and it was characterized by oxidation, adhensive wear, abrasive, plastic deformation and as well as coating transfer to the coupled pin. (4) The NiCoCrAlY/Cr2O3 composite coatings were fabricated by atmospheric plasma-spray and high velocity oxygen fuel technologies, it was found that the HOVF sprayed coating has smooth surface, dense microstructure, high microhardness, high tensile strength, good thermal shock resistances and oxidation resisitance compared with the APS sprayed coating. The oxidation kinetics curves of the NiCoCrAlY/Cr2O3 composite coatings are similar to the NiCoCrAlY/Al2O3 composite coatings, but the oxidation resisitance of the NiCoCrAlY/Cr2O3 composite coatings are much better than that of the NiCoCrAlY/Al2O3 composite coatings prepared by the same method. The friction coefficients of the APS and HVOF sprayed NiCoCrAlY/Cr2O3composite coating decrease with the increase of the temperature and the lowest value are 0.27 (APS) and 0.3 (HVOF) at 800℃, respectively, which are significantly lower than those of the APS and HVOF sprayed NiCoCrAlY/Al2O3 composite coatings. The abrasive mechanism of the NiCoCrAlY/Cr2O3 composite coatings is dominated by mixed brittle crack and abrasive at low temperature, and it was characterized by oxidation, plastic deformation and as well as coating transfer to the coupled pin. |
| 语种 | 中文 |
| 公开日期 | 2013-09-25 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1800]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 曹玉霞. 航空发动机高温固体润滑耐磨涂层的制备与性能研究[D]. 中国科学院研究生院. 2012. |
入库方式： OAI收割
来源：过程工程研究所
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