石墨烯/氧化铝起伏界面网络的强韧化机理研究

The small volume fraction of graphene could effectively strengthen and toughen ceramics, which is one of hot topics on developing new ceramic matrix composites. Although graphene nanoplatelets could improve the mechanical properties to some extent, the mechanism of the graphene/ceramic interface on stress transfer and crack propagation is not thoroughly interpreted. In this study, the graphene/alumina wavy interface network is obtained by combination of directional solidification, atomic layer deposition，vacuum infiltration and spark plasma sintering techniques etc. The stress transfer mechanism on the interfaces is studied by use of the stress triggered specific peak shift in in-situ Raman bending test. Further, a modified Shear-Lag model is developed to calculate the shear stress by considering effects of multilayer carbon and wavy interfaces. For the statistic of crack deflection angle and capturing of the crack propagation, the in-situ scanning electron microscope coupled with single edge v-notch beam bending test is conducted. Micro digital image correlation (DIC) technique is also employed to analyze the local stress and strain field at the tip of crack, rendering the calculation of energy dissipating rate. The influence of the wavy graphene/alumina interface network on the strength and toughness is discussed through quantitatively illustrating how this interface network impacts the deformation behavior of grapheme/alumina composites. Hopefully, the detailed experiment and the considerate models could provide some perspective to explore new graphene/ceramic composites with excellent strength and reliability.

通过添加少量的石墨烯来提高陶瓷材料的强度和韧性，是开发新型陶瓷基复合材料的研究热点之一。纳米石墨烯片虽在一定程度上强韧了陶瓷，但石墨烯/陶瓷界面上应力传递与裂纹扩展规律尚未得到系统的研究。本项目拟结合定向凝固、原子层沉积、真空浸渍和放电等离子烧结技术获得石墨烯/氧化铝起伏界面网络的复合材料；利用石墨烯与氧化铝的拉曼锋位的应力敏感性，采用原位拉曼弯曲实验研究石墨烯/氧化铝界面上应力传递机制，并构建考虑多层碳原子、起伏界面的Shear-Lag模型计算剪切应力；结合电镜下单边开口梁的四点弯曲实验和显微DIC（Micro Digital Image Correlation）技术，统计裂纹偏转角度并计算裂纹前端的应力与应变场及能量释放率等，定量分析石墨烯/氧化铝起伏界面网络对裂纹扩展的影响以阐明强韧化机理，为进一步开发高强、高韧的石墨烯/陶瓷复合材料提供理论依据和实验参考。

纳米石墨烯增强陶瓷基复合材料中界面应力传递与裂纹扩展规律尚未得到系统的研究。本项目着重研究了以还原氧化石墨烯气凝胶（rGO）为多层石墨烯片的载体，通过真空浸渍法将其与两亲嵌段聚合物P123改性氧化铝浆料复合，干燥焙烧后的前驱粉体经放电等离子烧结得到石墨烯/氧化铝复合块体。从平行于电场方向和垂直于电场两个方向，对Al2O3、P123/Al2O3、rGO/P123/Al2O3样品的晶粒形貌、晶粒度，织构，杨氏模量、显微硬度以及断裂韧性进行表征与分析。结果表明，三种样品在晶粒形貌、杨氏模量和纤维硬度上各向异性特征不明显。低浓度、偏聚在氧化铝晶粒周围的热解炭不仅因钉扎作用显著细化氧化铝晶粒（~6倍），而且通过微裂纹增韧了氧化铝基体。Al2O3单边开口梁的断裂韧性在两个方向具有显著的各向异性，因其经SPS烧结形成了强{0001}纤维织构。P123/Al2O3断裂韧性的各向异性因纤维织构强度减弱而减弱。微米片径的多层氧化石墨烯片的添加脆化了rGO/P123/Al2O3样品，原因是裂纹易沿着石墨烯片层间直接扩展而不发生复杂路径偏转。但是，当裂纹沿着垂直于电场方向偏转，石墨烯片的拔出可补偿该方向上的断裂韧性损失。因此，通过热解炭和多层石墨烯片的添加，rGO/P123/Al2O3样品的断裂韧性趋于各向同性。以上结果为开发高强高韧的石墨烯陶瓷复合材料提供实验和理论参考。