热管理用高导热碳化硅陶瓷基复合材料研究进展
Highly Thermal Conductive Silicon Carbide Ceramics Matrix Composites for Thermal Management: a Review
通讯作者: 白书欣, 教授. E-mail:shuxinde2021@163.com;叶益聪, 教授. E-mail:Yeyicognde2021@163.com
收稿日期: 2022-10-31 修回日期: 2023-01-18 网络出版日期: 2023-01-31
Corresponding authors: BAI Shuxin, professor. E-mail:shuxinde2021@163.com;YE Yicong, professor. E-mail:Yeyicognde2021@163.com
Received: 2022-10-31 Revised: 2023-01-18 Online: 2023-01-31
碳化硅陶瓷基复合材料以其高比强度、高比模量、高导热、良好的耐烧蚀性能、高温抗氧化性、抗热震性能等特性, 广泛应用于航空航天、摩擦制动、核聚变等领域, 成为先进的高温结构及功能材料。本文综述了高导热碳化硅陶瓷基复合材料制备及性能等方面的最新研究进展。引入高导热相, 如金刚石粉、中间相沥青基碳纤维等用以增强热输运能力; 优化热解炭炭与碳化硅基体界面用以降低界面热阻; 热处理用以获得结晶度更高、导热性能更好的碳化硅基体; 设计预制体结构用以建立连续导热通路等方法, 提高碳化硅陶瓷基复合材料的热导率。此外, 本文展望了高导热碳化硅陶瓷基复合材料后续研究方向, 即综合考虑影响碳化硅陶瓷基复合材料性能要素, 优化探索高效、低成本的制备工艺; 深入分析高导热碳化硅陶瓷基复合材料导热机理, 灵活运用复合材料结构与性能的构效关系, 以期制备尺寸稳定、具有优异热物理性能的各向同性高导热碳化硅陶瓷基复合材料。
关键词:
Silicon carbide ceramic matrix composites have been widely used in aerospace, friction brake, fusion fields and so on, and become advanced high-temperature structural and functional composites, due to their high specific strength and specific modulus, excellent ablation and oxidation resistance, and high conductivity and good thermal shock resistance. This paper reviews the latest research progress in preparation and property of silicon carbide ceramics matrix composites (CMCs) with high thermal conductivity. Researchers have improved the thermal conductivity of silicon carbide CMCs, including by introducing highly thermal conductive phases for reinforcing heat transport, such as diamond powders, and mesophase pitch-based carbon fibers (MPCF), by optimizing the interface between pyrolytic carbon (PyC) and silicon carbide matrix for reducing interfacial thermal resistance, by heat-treating for obtaining silicon carbide matrix with higher crystallinity and better thermal conductivity, and by designing preform structure for establishing continuous thermal conduction path. Meanwhile, research interests on silicon carbide CMCs are to explore new preparation with high efficiency and low cost through optimising their influencing factors, and to obtain isotropic highly thermal conductivity with dimensional stability and physical properties through deep understanding their thermal conductive mechanism, and flexible method based on the structure-activity relationship.
Keywords:
本文引用格式
陈强, 白书欣, 叶益聪.
CHEN Qiang, BAI Shuxin, YE Yicong.
高音速或超高音速飞行器以其超高马赫数和长巡航机时, 其前缘机翼及前锥尖端与高速气流相互作用, 高速粒子剧烈烧蚀, 导致飞行器表面温度很高(>1800 ℃), 进而对热防护系统(Thermal Protection System, TPS)[1-2]和热结构材料(Thermostructural Composites, TSM)产生严重烧蚀。在核聚变领域, 包层材料需长期处于中子辐照、高温高压、粒子溅射等严苛的服役环境[3]。同样, 在民用领域, 摩擦制动系统产生的温度很高, 要求材料在具有较好的耐摩擦磨损性能的同时具有优异的热物理性质[4⇓-6]。高热导率(Thermal Conductivity, TC)的材料, 可将局部高热负荷转移到低温区域, 迅速减少局部结构热损伤, 延长材料服役寿命[7-8]。
碳化硅(Silicon Carbide, SiC)是由碳原子和硅原子形成强共价键组成的四面体, 具有高硬度、高强度、高导热(490 W/(m·K))[9]以及良好的热稳定性等特点, 被广泛应用于热交换部件和电子基板等[10]。但是, 碳化硅陶瓷材料质地较脆, 对裂纹敏感, 难以独立使用[11]。纤维增强碳化硅陶瓷基复合材料是以纤维为增强体, 碳化硅为基体的陶瓷基复合材料 (Ceramic Matrix Composites, CMCs), 除具有碳化硅的优异性能外, 还兼具增强纤维轻质高强、耐腐蚀、抗老化等优点[12-13], 如碳化硅纤维增强碳化硅陶瓷基复合材料(SiCf/SiC)[14⇓⇓-17]、碳纤维增强碳化硅陶瓷基复合材料(Cf/SiC, C/C-SiC)[18⇓-20]等。但是增强纤维石墨化程度较低, 石墨微晶尺寸较小, 热导率较低(碳化硅纤维热导率小于70 W/(m·K), 如表1所示[21]; 普通碳纤维热导率小于20 W/(m·K)[22]), 难以形成有效的导热通路。因此, 常见的碳化硅陶瓷基复合材料导热性能较差。
Producer | Brand | Modulus/GPa | Strength/MPa | Density/(g·cm-3) | Diameter/μm | TC/(W·m-1·K-1) |
---|---|---|---|---|---|---|
Nicalon | NL202 | 220 | 3000 | 2.55 | 14 | 2.97 |
Hi-Nicalon | 270 | 2800 | 2.74 | 12 | 7.77 | |
Hi-Nicalon-S | 420 | 2600 | 3.05 | 12 | 18.4 | |
Tyranno | Lox M | 187 | 3300 | 2.48 | 11 | 1.4 |
ZMI | 200 | 3400 | 2.48 | 11 | 2.5 | |
SA | 380 | 2800 | 3.10 | 10/7.5 | 65 | |
Sylramic | Sylramic | 400 | 2800 | 3.05 | 10 | 40-45 |
Sylramic-iBN | 400 | 3200 | 3.10 | 10 | >46 | |
KD[33] | KD-A | 170 | 2100 | 2.43 | 12.3 | - |
KD-B | 300 | 3000 | 2.76 | 11.2 | ||
KD-C | 320 | 2800 | 2.87 | 11.1 |
*Modulus is tensile modulus and TC is thermal conductivity of SiC-based fibers at room temperature
本文总结了热管理(Thermal Management, TM)用高导热碳化硅陶瓷基复合材料的制备工艺及其热物理性能相关研究工作, 结合目前研究现状, 展望了后续高性能碳化硅陶瓷基复合材料的发展方向。
1 引入高导热相提高热导率
1.1 高导热金刚石-碳化硅陶瓷基复合材料
金刚石(diamond)作为一种碳同素异形体, 碳-碳以强共价键结合, 非谐振动效应较弱, 声子散射的概率较低, 德拜温度较高(约2000 ℃), 在同样温度下, 具有超高的热导率(2000~2200 W/(m·K))[27]。
图1
图1
不同金刚石的硅-金刚石-碳化硅复合材料显微组织及热导率[31]
Fig. 1
Microstructures and thermal conductivities of Si-diamond-SiC composites with different diamond volume contents[31]
(a) Si-20% diamond (sintered at 1523 K); (b) Si-60% diamond (sintered at 1643 K); (c) Fracture surface of (b); (d) EDX of(c); (e) XRD patterns of (a, b); (f) Experimental and theoretical thermal conductivity of Si-diamond-SiC composites
借助反应熔渗(Reactive Metal Infiltration, RMI)工艺, Zhang等[32]制备了金刚石体积分数为12%(RBSD1)、17%(RBSD2)、27%(RBSD3)、39%(RBSD4)的致密金刚石-碳化硅陶瓷基复合材料, 如图2所示。复合材料热导率与金刚石体积分数密切相关, 当金刚石体积分数从12%增加到39%时, 复合材料室温热导率从249 W/(m·K)提高到329 W/(m·K)。Thommy等[34]采用液相渗硅(Liquid Silicon Infiltration, LSI)或者硅合金工艺制备了高体积分数硅-金刚石-碳化硅复合材料(金刚石体积分数55%~79%, 碳化硅体积分数3%~36%, 硅或者硅合金体积分数4%~23%), 热导率在336~432 W/(m·K)范围。
图2
图2
不同体积分数的金刚石-碳化硅复合材料显微组织及热导率[32]
Fig. 2
Microstructures and thermal conductivities of diamond/SiC composites with different diamond volume contents[32]
(a) RBSD1; (b) RBSD2; (c) RBSD3; (d) RBSD4; (e) Diamond/SiC interface; (f) Graphite interlayer in diamond/SiC interfacial region; (g) TEM image of diamond/SiC interfacial region in post-annealing RBSD; (h) Thermal conductivities of RBSDs before and after high temperature annealing
Yang等[35]利用1600 ℃气相渗硅工艺(Vapor Silicon Infiltration, VSI) 制备了金刚石-碳化硅复合材料, 当金刚石体积分数为46%时, 复合材料热导率最高为562 W/(m·K); Zheng等[36]经1650 ℃气相渗硅, 制备了热导率为518 W/(m·K)的金刚石-碳化硅复合材料, 其热导率随着金刚石、碳化硅体积分数的增加而增大, 较大尺寸且表面粗糙的金刚石颗粒有利于硅蒸汽的附着沉积进而形成碳化硅; Yang等[37]研究了金刚石-碳化硅复合材料的反应熔渗机制, 认为熔融硅的爆炸蒸发, 固体体积膨胀以及反应过程中的热量释放是导致复合材料致密的关键因素, 制备的金刚石-碳化硅复合材料密度为3.33 g/cm3, 热导率为580 W/(m·K)。Matthey等[38]分别利用酚醛树脂(Phenol Formaldehyde Resin, PF)和纤维素(Cellulose)作为黏合剂, 与不同粒径的金刚石以及碳化硅粉混合后压制成坯, 最后经无压渗硅(Pressureless Silicon Infiltration)制备出热导率为500 W/(m·K)的高导热金刚石-碳化硅散热件。
1.2 高导热中间相沥青基碳纤维增强碳化硅陶瓷基复合材料
近年来, 国产高导热石墨纤维制备技术日臻成熟, 性能逐渐完善[40], 赋予高导热碳化硅陶瓷基复合材料更优的热物理性能以及更广阔的应用前景。
作为一种热塑性材料, 沥青是一种结构和化学组成非常复杂的物质, 通常由带有烷基侧链的稠环芳烃和杂环化合物混合而成[41]。原料沥青, 如石油沥青、煤沥青和萘系沥青等, 经调制改性处理可得到各向同性沥青或各向异性沥青, 再经熔融纺丝、均质预氧化、碳化、高温石墨化后得到沥青基碳纤维。按照原料, 沥青基碳纤维可分为各向同性沥青基碳纤维和中间相沥青基碳纤维(高性能沥青基碳纤维)[43]。其中, 中间相沥青基碳纤维(Mesophase Pitch-based Carbon Fiber, MPCF) 中含有大量向列型液晶相的芳烃平面大分子, 在纺丝时受剪切作用力或炭化过程中热作用下生成的碳质微晶, 可沿纤维轴向取向生长, 使中间相沥青基碳纤维较聚丙烯腈基碳纤维(Polyacrylonitrile Based Carbon Fiber)具有良好的热物理性质[42-43], 如表2所示。
Producer | Brand | Modulus/GPa | Strength/MPa | Density/(g·cm-3) | Diameter/μm | TC/(W·m-1·K-1) | |
---|---|---|---|---|---|---|---|
UCC | P75 | 517 | 2100 | 2.00 | 10 | 185 | |
P100 | 759 | 2410 | 2.15 | 10 | 520 | ||
P-120 | 828 | 2410 | 2.18 | 10 | 640 | ||
Mitsubishi | K-1100 | 931 | 3100 | 2.2 | 10 | 1000 | |
K13D2U | 935 | 3700 | 2.21 | 10 | 800 | ||
K13C2U | 900 | 3800 | 2.2 | 10 | 620 | ||
K63B12 | 860 | 2600 | 2.15 | 10 | 400 | ||
Nippon | Granoc | 920 | 3530 | 2.19 | 7 | 600 | |
YS-95A | |||||||
Granoc | 880 | 3530 | 2.18 | 7 | 500 | ||
YS-90A | |||||||
NOCVARB | NM6030-15 | ≥550 | ≥1500 | ≥2.1 | - | ≥250 | |
NM9050-20 | ≥850 | ≥2000 | ≥2.15 | - | ≥450 | ||
NM9080-20 | ≥850 | ≥2000 | ≥2.15 | - | ≥750 | ||
NMA080-25 | ≥950 | ≥2500 | ≥2.15 | - | ≥750 | ||
TIANCE-TECH | TC-HC-600-S | 750 | 2300 | 2.20 | 13 | 600 | |
ECO | - | 500-900 | 2500-3500 | 2.2 | 8-12 | 500-800 | |
TOYI-CARBEN | TYG-1 | 800 | 2300 | 2.2 | 12 | 600 | |
TYG-2 | 900 | 2500 | 2.2 | 12 | 800 |
*Modulus is tensile modulus and TC is thermal conductivity of MPCF
纺丝过程中的纤维预氧化制度以及喷丝板结构造成了中间相沥青基碳纤维横截面不同[44]。Edie等[45]认为中间相沥青基碳纤维横截面主要有辐射状、洋葱皮状、乱层状、叠层状、放射褶皱结构、线型结构以及混合结构。其中, 辐射状结构具有良好的导热性能, 但皮部收缩程度比芯部剧烈, 容易产生裂纹, 力学性能降低; 洋葱皮状以及乱层状结构在热处理过程中收缩较均匀, 缺陷较少, 具有较高的拉伸强度; 放射褶皱状结构在具有较好力学性能的同时还兼具优良的导热性能; 而对于线型结构, 沥青熔体在更为充分的剪切力作用下, 具有更好的取向, 可避免热处理过程中的热应力集中和开裂现象, 使得纤维拉伸强度提高[46]。 因此, 可根据实际需要, 调控中间相沥青基碳纤维的横截面结构。
如图3所示, Huang等[25]利用自研热导率800 W/(m·K)的中间相沥青基碳纤维(TYC-1, Toyi-Carbon)与高模量聚丙烯腈基碳纤维(M40J)编制成三维连续预制体, 经化学气相渗透(Chemical Vapor Infiltration, CVI)和高温石墨化处理, 再经聚合物浸渍裂解工艺(Polymer Impregnation Pyrolysis, PIP)制备得到热导率为221.1 W/(m·K)的三维高导热碳化硅陶瓷基复合材料(3D-C/C-SiC), 得益于其优异的高导热特性, 3D-C/C-SiC表现出较小的温度梯度以及优良的耐烧蚀性能(线烧蚀率为0.11 μm/s, 质量烧蚀率为0.56 mg/(cm2·s))。
图3
图3
3D HTC C/C-SiC制备工艺及微观组织[25]
Fig. 3
Diagram of fabrication and microstructure of the 3D HTC C/C-SiC composite[25]
(a) Fabrication process of 3D HTC C/C-SiC; (b-f) Microstructures of the 3D HTC C/C-SiC composite; (g) Interface energy spectrum diagram of the 3D HTC C/C-SiC; (h) Ablation tests and (i) temperature curves of the C/C-SiC
图4
图5
2 界面优化降低界面热阻
固体和界面热传输的多尺度模拟表明, 声子输运主导的传热是多尺度的, 声子将与不同特征尺寸的结构相互作用而发生声子散射, 削弱材料的热输运能力, 如点缺陷、位错、层错、孪晶边界、孔隙以及各种微结构等[53]。
Li等[54]采用化学气相沉积(Chemical Vapor Deposition, CVD)工艺在热解炭(Pyrolytic Carbon, PyC)表面沉积碳纳米管(Carbon Nanotubes, CNTs)用于改善热解炭基体与碳化硅的界面结合, 结果表明, 800 ℃沉积20 min, 使用体积分数为15%的乙烯气体沉积的碳纳米管增强碳化硅陶瓷基复合材料的性能最好(抗弯强度466 MPa, 热导率17.2 W/(m·K))。
Cui等[55]通过化学气相渗透工艺在热解炭表面原位生长碳化硅纳米线(Silicon Carbide Nanowires, SiCNWS)用于改善聚合物浸渍裂解(Polymer Impregnation Pyrolysis, PIP)制备的三维碳化硅纤维增强碳化硅陶瓷基复合材料的力学特性和热导率, 结果表明沉积碳化硅纳米线的复合材料抗弯强度和热导率(最高4.46 W/(m·K))分别提高了46%和43%。
Li等[56]研究了酚醛树脂含量对化学气相渗透(Chemical Vapor Infiltration, CVI)和反应熔渗制备碳纤维增强金刚石-碳化硅复合材料的微观结构和导热性能的影响, 结果表明, 酚醛树脂含量显著影响反应熔体渗透前复合材料孔隙结构以及反应熔渗后基体的相组成和密度, 酚醛树脂含量较高时, 无定形碳(Amorphous Carbon, a-C)的含量增加, 金刚石与无定形碳的非晶态界面区域增加, 界面结合较差, 导致复合材料的界面热阻增加, 从而降低复合材料热导率。
图6
图6
碳化硅纤维表面电泳沉积碳纳米管微观组织及复合材料热物理性能[57]
Fig. 6
Microstructures of SiC fiber with electrodeposited CNTs and thermophysical properties of SiCf/SiC compersites[57]
(a) Surface of SiC fibers with CNTs; (b) Surface of SiC fibers without CNTs; (c) Interface between CNTs and PyC; (d) TEM image of PyC deposited on CNTs; (e, f) HRTEM images of PyC deposited on (e) SiC fibers and (f) CNTs; (g) Bending strength and (h) thermal conductivity of SiC/SiC composites with different interfaces
3 高温热处理影响热导率
改善碳化硅陶瓷基复合材料的密度和晶粒尺寸可以进一步提高复合材料的性能。具有较高密度的碳化硅陶瓷基复合材料往往具有较高的热导率, 而细化碳化硅晶粒将降低其热导率[4]。一方面, 可通过热处理促进碳化硅晶粒长大, 获得更高结晶度的碳化硅, 进而提高复合材料的热导率; 另一方面, 随着热处理的进行, 碳化硅基体与热解炭的非晶态界面区域增加, 进而降低复合材料的热导率。
图7
图8
图8
金刚石/SiC复合材料界面区域表征[58]
Fig. 8
Characterization of diamond/SiC interfacial zone[58]
(a) TEM image of diamond and SiC separated by a layer of graphite with lighter contrast; (b) HRTEM image of the rectangular region in (a) showing the graphite (G) and diamond (D) zones; (c-e) TEM and HRTEM images of (c, d) graphite layer and (e) reaction formed nano-crystalline SiC with stacking faults; (f) TEM image of Al4C3 formed adjacent to the interface; (g) HRTEM image from the rectangular region in (f); (h) ADF STEM of diamond/SiC interfacial area in (f)
图9
图9
不同温度热处理的SiCf/SiC复合材料微观组织及热导率[59]
Fig. 9
Microstructures and thermal conductivities of SiCf/SiC composites with different heat-treatment[59]
(a) SiC matrix without heat-treatment; (b) SiC matrix with 1700 ℃-2 h heat-treatment; (c) SiC matrix with 1900 ℃-2 h heat-treatment; (d-f) TEM images of SiC matrix corresponding to (a-c); (g) Thermal conductivity of 2D SiCf/SiC after different heat-treatments; (h) Full width at half maximum of (111) diffraction crystal plane after different heat-treatments
高温热处理可促进碳化硅晶体发育, 提高结晶度, 减少晶体缺陷带来的声子散射, 从而提高复合材料的热导率。同时, 随着热处理温度升高, 复合材料界面区域增大, 尤其是碳化硅与含无定形碳的界面区域发生石墨化转变, 将增大界面热阻, 降低复合材料热导率。
4 结构设计提高热导率
由于纤维预制体的结构特点, 纤维增强碳化硅陶瓷基复合材料沿厚度方向, 碳纤维与基体之间结合较弱, 热输运能力较面内方向弱, 面内热导率约是沿厚度热导率的10~100倍[60], 热导率各向异性。
研究者围绕高导热填料的均匀分散以及如何构建连续有效的导热通路, 进行了诸多探索。
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Zhang等[64]为了提高化学气相渗透工艺制备碳纤维增强碳化硅陶瓷基复合材料的厚度热导率, 利用激光加工微孔技术, 使中间相沥青基碳纤维束沿厚度方向均匀排列以构建连续的导热通路。结果表明, 经结构设计的复合材料热导率约为初始结构的340%。
综上所述, 借助巧妙的辅助工艺, 可有效改善连续纤维增强复合材料厚度方向的热输运能力, 明显减少因纤维预制体几何结构特点造成的高导热碳化硅陶瓷基复合材料应用瓶颈。值得注意的是, 连续纤维增强碳化硅陶瓷基复合材料的厚度热导率较面内热导率仍然存在数量级的差异。这可能是在结构设计过程中, 厚度方向的增强体纤维与基体之间的界面结合较差难以形成贯穿的导热通路, 孔隙等结构缺陷引起的界面热阻较高等原因造成的。
5 总结与展望
高效传热和高温耐热相结合是高导热碳化硅陶瓷基复合材料在热管理领域应用的关键。本文综述了高导热碳化硅陶瓷基复合材料的最新研究成果, 详细分析了高导热碳化硅陶瓷基复合材料制备工艺及导热作用机理。围绕目前的研究内容, 后续可持续关注以下几个方面:
1)适当引入高导热相以期制备各向同性碳化硅陶瓷基复合材料。综合考虑增强体形态、尺寸、含量、分布等对碳化硅陶瓷基复合材料性能的影响, 探索制备高致密、低孔隙、各向同性高导热碳化硅陶瓷基复合材料是实现高效传热的基础。
2)合理调控碳化硅基体与增强体界面。非晶态界面区域、均匀性以及结构影响声子热输运能力。设计、优化碳化硅基体与增强体界面相容性是降低边界声子散射效应, 提高碳化硅陶瓷基复合材料热导率的途径。
3)深入分析碳化硅陶瓷基复合材料高温热处理机理。一方面, 高温热处理可促进碳化硅晶体发育, 提高热导率; 另一方面, 碳化硅陶瓷基复合材料非晶体界面区域的石墨化转变, 碳的饱和及溶解过程是工艺优化、组织调控、制备高导热碳化硅陶瓷基复合材料的核心。
4)结构设计构筑三维贯穿有效导热通路。增强纤维沿厚度方向与基体结合较弱, 导致纤维增强复合材料热物理性能各向异性。因此, 探索高导热碳化硅陶瓷基复合材料构效关系, 构筑三维贯穿导热通路是设计、制备、加工结构-功能一体化先进陶瓷基复合材料的关键。
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