C/C复合材料大气等离子喷涂mullite/ZrB2-MoSi2涂层抗烧蚀性能

采用大气等离子喷涂技术(APS)在C/C复合材料表面制备了mullite/ZrB₂-MoSi₂双层抗烧蚀涂层。借助XRD、SEM、EDS等分析手段对涂层的组织结构进行研究;基于氧丙烯焰烧蚀试验考察ZrB₂-MoSi₂/mullite复合涂层对C/C复合材料高温耐烧蚀性能的影响。结果表明,在1700 °C和1800 °C的氧丙烯焰下烧蚀60 s,ZrB₂-MoSi₂/mullite涂层试样的质量烧蚀率分别为3.49×10_-3 g/s与3.77×10_-3 g/s。其与单层ZrB₂-MoSi₂涂层试样相比,ZrB₂-MoSi₂/mullite涂层试样展现了出色的抗烧蚀性能。烧蚀过程中形成的硅酸盐玻璃可以作为热障层而减少氧气的进一步渗透,并且还具有自我封填缺陷的能力,使ZrB₂-MoSi₂/mullite涂层表现较好的抗烧蚀性。     

等离子喷涂制备ZrB2/SiC/Ta2O5涂层抗烧蚀性能研究

为了提高C/C复合材料的抗烧蚀性能,通过等离子喷涂法在C/C表面制备了SiC/Al₂O₃内层和ZrB₂/SiC/Ta₂O₅外层的双层涂层,通过XRD,SEM和EDS分析了涂层烧蚀前后的物相组成、微观结构和成分分布。烧蚀前涂层表面没有裂纹并且内层与基体、内层与外层之间结合良好。元素Zr、Si、Ta在涂层表面的分布相近,涂层表面成分分布均匀性良好。通过氧乙炔火焰在1800 ℃下对涂层的抗烧蚀性能进行考核。烧蚀过程中形成的镶嵌结构有利于阻挡氧气的渗入,Ta-Si-O玻璃层的形成封填了涂层孔隙,对基体有良好的保护效果,涂层表现出了较好的抗烧蚀性能。     

SiC/ZrB2-SiC-B4C涂层的抗氧化和耐烧蚀性能研究

碳/碳化硅复合材料(C/SiC)在使用时经常受到高温氧化和烧蚀作用。本文采用化学气相沉积(CVD)和浆料刷涂-烧结法制备了双层SiC/ZrB2-SiC-B4C涂层,对比研究了无涂层,单层SiC涂层和双层SiC/ZrB2-SiC-B4C涂层C/SiC复合材料在1500℃下的氧化和在4.2 MW/m2热流密度下的烧蚀性能。结果表明,制备态ZrB2-SiC-B4C涂层致密、完整,表面平均粗糙度约为1 μm,孔隙率约为4.2 %。在1500℃氧化30 h后,SiC/ZrB2-SiC-B4C涂层C/SiC复合材料的质量损失率约为10%,涂层表面氧化膜致密,无明显裂纹。高温烧蚀20 s后,SiC/ZrB2-SiC-B4C涂层的线烧蚀率和质量烧蚀率分别为1.0±0.3 μm/s和1.1±0.2 mg/s,与单层SiC涂层相比分别降低了75.0 %和50.0 %,SiC/ZrB2-SiC-B4C涂层烧蚀后形成的ZrO2-SiO2氧化膜可以减缓火焰对复合材料的机械剥蚀作用。     

NiCr-Cr3C2-ZrO2-BaF2·CaF2涂层高温摩擦磨损性能*

为提高 NiCr-Cr₃C₂-BaF₂·CaF₂ 涂层高温耐摩擦磨损性能,减少热喷涂过程中润滑相 BaF₂·CaF₂ 火焰烧蚀,采用溶胶凝胶方法将 BaF₂·CaF₂ 粉体以弥散形式包覆于抗烧蚀陶瓷相 ZrO₂ 内,形成 ZrO₂-BaF₂·CaF₂ 抗烧蚀包覆型粉体,将粉体与 NiCr-Cr₃C₂ 混合后爆炸喷涂以提高涂层内 BaF₂·CaF₂含量,并表征涂层微观组织和高温耐磨损性能。结果表明：ZrO₂包覆型粉体中 BaF₂·CaF₂呈弥散式分布,制备的 NiCr-Cr₃C₂-ZrO₂-BaF₂·CaF₂涂层相比传统 NiCr-Cr₃C₂-BaF₂·CaF₂涂层,Ca、Ba 元素含量均提升 1 倍以上,两涂层显微硬度分别为 1 041 HV 和 690 HV,这说明 ZrO₂陶瓷包覆能有效减少 BaF₂·CaF₂在喷涂过程中的高温烧蚀,且大幅提升了涂层硬度。高温摩擦磨损试验结果显示,NiCr-Cr₃C₂-ZrO₂-BaF₂·CaF₂ 涂层在 600 ℃、 700 ℃和 800 ℃时的平均摩擦因数分别为 0.25、0.17 和 0.18,与 NiCr-Cr₃C₂-BaF₂·CaF₂涂层相比分别降低了 16.7%、39.3% 和 5.3%;NiCr-Cr₃C₂-ZrO₂-BaF₂·CaF₂涂层磨损率为 5.47×10^-6 mm³ ·N^?1 ·m^?1 ,较 NiCr-Cr₃C₂-BaF₂·CaF₂涂层降低了 38.6%。 对磨球表面的微观表征显示,涂层中润滑相含量提升使 NiCr-Cr₃C₂-ZrO₂-BaF₂·CaF₂ 涂层在对磨球表面形成更为完整的润滑转移膜,这将有利于涂层的高温润滑性、稳定性和耐磨损性能。研究结果对热喷涂粉体中易烧蚀物相的热防护和高温自润滑耐磨涂层性能的提升具有借鉴意义。     

坯体密度对C/C-SiC复合材料烧蚀性能的影响

以纳米SiC粉为惰性填料,采用先驱体浸渍裂解法制备C/C-SiC复合材料,研究了不同密度C/C坯体对复合材料烧蚀性能的影响。结果表明,不同密度C/C坯体对制得的复合材料性能有很大的影响,其中C/C预制体密度为1.24g/cm~3试样制得的复合材料性能最优,其最终密度为1.80g/cm~3,开孔率为7.32%,线烧蚀率和质量烧蚀率分别为0.0040mm/s和0.0012g/s。     

LPVCS改性制备Cf/SiC复合材料及其耐高温性能

以液态聚碳硅烷(LPVCS)、聚碳硅烷(PCS)为先驱体,采用PIP工艺制备了连续碳纤维增强碳化硅(C_f/SiC)复合材料。LPVCS是一种新型先驱体,具有室温下为液态、浸渍效率高的优点,同时由LPVCS裂解得到的SiC基体具有能够与T300碳纤维形成合适界面力的优点。相比于全周期采用PCS浸渍制备的C_f/SiC复合材料,第一周期使用LPVCS浸渍,第二至八周期使用PCS浸渍,第八周期之后使用LPVCS浸渍制备的C_f/SiC复合材料具有更优异的力学性能,其三点弯曲强度由301MPa提高到442MPa,断裂韧性由11.2MPa.m_1/2提高到26.1MPa.m_1/2。力学性能提高的原因为两个方面,第一周期使用LPVCS浸渍得到了合适的界面结合强度,第八周期之后使用LPVCS浸渍提高了SiC基体的致密化程度。     

PREPARATION AND ANTI–OXIDATION PROPERTY OF SiC/SiC–MoSi2 COATING ON C/C COMPOSITE

采用包埋法和涂刷法在C/C复合材料表面依次制备了SiC内涂层和SiC--MoSi₂外涂层, 借助XRD与SEM对涂层的微观结构进行了分析, 研究了涂覆后的C/C复合材料在高温静态空气中的防氧化性能. 结果表明: SiC/SiC--MoSi₂复合涂层有效缓解了MoSi₂与C/C热膨胀不匹配问题, 涂层无裂纹; 复合涂层在900和1500℃静态空气环境下均可对C/C复合材料有效保护100 h以上; 涂层的多层、多相结构以及在高温氧化后表面生成的SiO₂薄膜是其具有优异防氧化性能的原因.     

泡沫铝三明治结构粉末冶金法制备工艺及泡孔结构优化

粉末冶金法可实现泡沫铝三明治结构面板/芯层的冶金结合,并在制备近终型泡沫铝异型件上优势突出。基于国内研究现状,本文完善了粉末冶金法制备工艺,并优化了泡孔结构。研究发现,芯层采用AlMg4Si8铝合金成分组成,钢质面板经边缘焊接密封处理后,当芯层粉末松装密度为1.12 g/cm_³时,在1500 kN轧制压力、0.06 m/s轧制速度及55％轧制压下率下,对灌满芯层粉末的包覆面板进行450 °C热轧,获得了面板/芯层冶金结合、致密度高的发泡前驱体。另外,当发泡剂TiH₂被低熔点Sn包覆预处理后,在发泡初期分解出的H₂被液态Sn包裹,避免了在固态基体空隙间的扩散,减少了裂纹的产生,发泡前驱体在720 °C发泡300 s后可获得泡孔结构相对均匀、72.7%孔隙率的泡沫铝三明治结构。     

CuxSiy改性C/C-SiC复合材料的制备及其性能

以针刺整体炭毡为预制体,采用化学气相渗透法(CVI)增密制备C/C多孔体,然后采用反应熔体浸渗法(RMI),将Cu与Si同时熔渗进C/C坯体中制备CuxSiy改性C/C-SiC复合材料.研究CuxSiy改性C/C-SiC复合材料的组织结构、力学性能和摩擦磨损性能,并与C/C-SiC复合材料进行对比.结果表明:CuxSiy改性C/C-SiC复合材料的弯曲强度和冲击韧性略低于C/C-SiC复合材料的;采用30Cr钢作对偶时,CuxSiy改性C/C-SiC复合材料的摩擦因数约为0.24,线磨损率小于4 μm·side-1·cycle-1,均与C/C-SiC复合材料的相近,但其摩擦表面温度降低约50 ℃;以自身材料作对偶时,CuxSiy改性C/C-SiC复合材料的摩擦磨损性能略低于C/C-SiC复合材料的.     

激光辅助热喷涂NiCoCrAlYTa/ZrO2/BaF2·CaF2涂层的组织及性能∗

高温耐磨涂层是航空发动机关键摩擦副可靠使用的重要保障,鉴于其服役环境日益严苛复杂,进一步提高涂层的高温耐磨性能是十分必要的。利用激光辅助热喷涂技术制备 NiCoCrAlYTa / ZrO₂ / BaF₂·CaF₂ 高温耐磨涂层,利用 SEM、EDS 分析高温耐磨涂层的横截面微观组织及化学成分,研究 ZrO₂ / BaF₂·CaF₂质量分数、激光功率及扫描速度对耐磨涂层微观组织、力学性能及高温耐磨性能的影响。结果表明：激光辅助处理可以诱导耐磨涂层表面形成具有树枝状结构的 ZrO₂陶瓷层; 当激光功率为 80 W,扫描速度为 8 mm / s,喷涂粉末为 75 wt.% NiCoCrAlYTa+25 wt.% ZrO₂ / BaF₂·CaF₂时,制备涂层的微观组织、综合力学性能及高温耐磨性能达到最好;在此工艺参数下,涂层顶部的 ZrO₂ 陶瓷层最为致密均匀,其平均纳米硬度为 13.6 GPa,平均弹性模量为 182.5 GPa,800 ℃时的磨损率为 2.7×10^?5 mm³ ·N^?1 ·m^?1 。将高温耐磨涂层的组分设计与激光辅助热喷涂工艺相结合,可为提高涂层综合性能的提供解决途径。     

C／C坯体对RMI C／C—SiC复合材料组织的影响

以PAN基炭纤维（Cf）针刺整体毡为预制体，用化学气相渗透（CVI）、浸渍炭化（IC）方法制备了不同炭纤维增强炭基体的多孔C／C坯体，采用反应熔渗（RMI）法制备C／C—SiC复合材料，研究了渗Si前后坯体的密度和组织结构。结果表明：不同C／C坯体反应溶渗硅后复合材料的物相组成为SiC相、C相及单质Si相；密度低的坯体熔融渗硅后密度增加较多；密度的增加与开口孔隙度并不是单调增加的关系，IC处理的坯体开口孔隙度低，但渗硅后复合材料的密度增加较多；IC坯体中分布分散的树脂C易与熔渗Si反应，CVI坯体中的热解C仅表层与熔渗Si反应，在Cf和SiC之间有热解C存在；坯体密度相同时，IC处理的坯体中SiC量较多，单质Si相含量少且分散较好，而CVI坯体中SiC量较少，单质Si相的量较多；制备方法相同时，高密度的C／C坯体，渗硅后C相较多。     

高密度预制体制备炭/炭复合材料的弯曲力学性能与断裂机制

以丙烯作为碳源,氮气作为载气,采用初始密度为0.94g/cm3三维正交PAN基12K炭纤维预制体,利用自制的快速CVI炉制备基体热解炭结构为带状结构的C/C复合材料。力学性能测试结果表明,材料的弯曲断裂特征与制备过程中受到的高温热处理次数有关。从载荷-位移曲线来看,当C/C复合材料经过两次热处理时,C/C复合材料呈明显假塑性断裂特征。当C/C复合材料经过三次热处理时,载荷-位移曲线趋于稳定平滑,抗弯强度降低。从C/C复合材料断面的SEM图可以观察到材料断裂可以分为层间断裂和层内断裂,而层内断裂又因热解炭填充密度变化呈明显的分区断裂。由于热解炭和纤维含量在C/C复合材料中分布的差异,材料在不同的区域表现出不同的断裂特征,从而使得材料具备良好的弯曲强度同时具有一定的韧性特征。     

Microstructures and Ablation Resistance of ZrC Coating for SiC-Coated Carbon/Carbon Composites Prepared by Supersonic Plasma Spraying

To improve ablation resistance of silicon carbide (SiC)-coated carbon/carbon (C/C) composites, in this study, zirconium carbide (ZrC) coating was prepared on the surface of SiC-coated C/C composites by supersonic plasma spraying. The coating exhibits dense structure, and a good bonding with substrate. The oxyacetylene ablation results show that the ZrC coating greatly improved the ablation resistance of SiC-coated C/C composites. After ablation for 30 s in oxyacetylene flame, the linear ablation rate is only 0.9 × 10⁻³ mm/s, and the weight is increased by 2.0 × 10⁻³ g/s. The excellent ablation resistance is mainly attributed to the formation of a dense and continuous zirconia (ZrO₂) layer during the oxidation of the ZrC coating.     

Comparison of morphology and microstructure of ablation centre of C/SiC composites by oxy-acetylene torch at 2900 and 3550 °C

High-temperature application above 1600 °C of C/SiC composites requires evaluation of the ablation properties. The C/SiC composites were prepared by low pressure chemical vapor infiltration using CH₃SiCl₃ as precursor. As-prepared C/SiC composites were ablated by oxy-acetylene flame with the temperature of 2900 and 3550 °C. Above 3550 °C, subliming of carbon fiber and silicon carbide matrix was the main ablation behaviour. At 2900 °C, thermal decomposition and oxidation of SiC matrix were the main ablation behaviour. A carbon coating resulted from the pyrolysis of the acetylene prevented the C/SiC from oxidizing dramatically.     

LaB6改性C/C-ZrC-SiC复合材料的制备及其抗烧蚀性能

采用料浆浸渍结合树脂浸渍裂解法制备了含9.73 wt.% LaB6的LaB6-C/C预制体,再利用反应熔体浸渍法（RMI）制备了LaB6改性C/C-ZrC-SiC复合材料,考察了材料的微观结构和烧蚀行为,探究LaB6对材料抗烧蚀性能的作用机理。结果表明：在热流密度为2380 kw/m2的氧乙炔焰烧蚀120 s后,LaB6改性C/C-ZrC-SiC复合材料的质量烧蚀率和线烧蚀率分别为1.05×10-3 g/s和2.17×10-3 mm/s,较未改性C/C-ZrC-SiC复合材料分别降低了74.8 %和61.9 %。烧蚀过程中,LaB6发生氧化反应生成La2O3和B2O3,La2O3与ZrO2之间的固溶作用以及化学反应,再加之液态B2O3具有促进固相反应传质的作用,使得材料表面形成大面积连续稳定的ZrO2-La2Zr2O7-La0.1Zr0.9O1.95熔融态保护层,这是材料优异抗烧蚀性能的主要原因。     

Microstructure of carbon fiber preform and distribution of pyrolytic carbon by chemical vapor infiltration

The carbon/carbon composites were made by chemical vapor infiltration(CVI) with needled felt preform. The distribution of the pyrolytic carbon in the carbon fiber preform was studied by polarized light microscope (PLM) and scanning electronic microscope(SEM). The experimental results indicate that the amount of pyrolytic carbon deposited on the surface of chopped carbon fiber is more than that on the surface of long carbon fiber. The reason is the different porosity between the layer of chopped carbon fiber and long carbon fiber. The carbon precursor gas which passes through the part of chopped carbon fibers decomposes and deposits on the surface of chopped carbon fiber. The pyrolytic carbon on the surface of long carbon fibers is produced by the carbon precursor gas diffusing from the chopped fiber and the Z-d fiber. Uniform pore distribution and porosity in preform are necessary for producing C/C composites with high properties.     

Formation mechanism and oxidation behavior of MoSi2–SiC protective coating prepared by chemical vapor infiltration/reaction

In order to protect C/C composites from oxidation, SiC-MoSi₂ composite coating was synthesized by chemical vapor infiltration /reaction (CVI/CVR) technology. A porous Mo layer was prefabricated on SiC coated C/C composites, and then MoSi₂ and SiC were subsequently prepared in a CVI /CVR process using methyltrichlorosilane (MTS) as precursor. The deposition and reaction mechanism of the MoSi₂-SiC composite coating was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The oxidation behavior of SiC-MoSi₂ coated specimens was tested. The results show that the porous Mo layer can be densified with SiC phase decomposed from MTS, and transformed into SiC-MoSi₂ by reacting with MTS as well. A dense composite coating was prepared with optimized deposition parameters. The coated specimen exhibits a good oxidation resistance with a little mass loss of 1.25% after oxidation at 1500 °C for 80 h.     

Effect of stress level on fatigue behavior of 2D C/C composites

Laminated carbon fiber clothes were infiltrated to prepare carbon fiber reinforced pyrolytic carbon (C/C) using isothermal chemical vapor infiltration (CVI). The bending fatigue behavior of the infiltrated C/C composites was tested under two different stress levels. The residual strength and modulus of all fatigued samples were tested to investigate the effect of maximum stress level on fatigue behavior of C/C composites. The microstructure and damage mechanism were also investigated. The results showed that the residual strength and modulus of fatigued samples were improved. High stress level is more effective to increase the modulus. And for the increase of flexural strength, high stress level is more effective only in low cycles. The fatigue loading weakens the bonding between the matrix and fiber, and then affects the damage propagation pathway, and increases the energy consumption. So the properties of C/C composites are improved.     

Preparation and mechanical properties of carbon/carbon composites with high textured pyrolytic carbon matrix

Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon (C/C) composites was 1.89 g/cm³ after depositing for 150 h. The microstructure and mechanical properties of the C/C composites were studied by polarized light microscopy, X-ray diffraction, scanning electron microscopy and three-point bending test. The results reveal that high textured pyrolytic carbon is deposited as the matrix of the composites, whose crystalline thickness and graphitization degree highly increase after heat treatment. A distinct decrease of the flexural strength and modulus accompanied by the increase of the toughness of the C/C composites is found to be correlated with the structural changes in the composites during the heat treatment process.