B4C-BNNTs/TiB2-B4C层状陶瓷复合材料组分与结构设计及增韧机理研究

The application of boron carbide(B4C) as a kind of important light super-hardness and high-temperature structural ceramic materials has been restricted mainly due to its poor sinterability and poor fracture toughness. Borron nitride nanotubes (BNNTs) has high strength and good toughness. In our subject, the B4C-BNNTs/TiB2-B4C laminar ceramic composites with good facture toughness and high flexure strength will be fabricated by tape casting-laminated-hot pressing or SPS sintering using BNNTs reinforcing and toughening B4C ceramic matrix composites as matrix layers and TiB2-B4C ceramic matrix composites as interface layers. The Poisson ratio, thermal expansion coefficient, elastic modulus and strength of the interface layers and the bonding strength between the matrix layer and the interface layer will be controlled by regulating the components and the microstructure of the interface layer.The interfacial residual stress will be calculated by means of finite element method and then its calculation will be applied to design of composition and structure for interface layers. The influence of the phase composition on the microstructure of the bonding interface between matrix layer and interface layer will be investigated. The effect of the geometric parameters including layer thickness, layer thickness ratio and layer number on the flexure strength and the fracture toughness will also be studied. Additionally, the relationship between the components, the technological parameters and the microstructure, the mechanical properties will be researched. Moreover, the secondary phase toughening mechanism, the laminated compound toughening mechanism,and their synergic toughening mechanism will be made clear .

碳化硼陶瓷是一种重要的轻质超硬高温结构陶瓷材料，因其难烧结、韧性差，使其应用受到限制。氮化硼纳米管具有高强度和高韧性。本研究以B4C-BNNTs为基体层，以TiB2-B4C 为夹层，通过改变夹层的组分、结构调控夹层材料的泊松比、热膨胀系数、弹性膜量、强度及其与基体层的界面结合强度，通过采用有限元法计算分析界面残余应力，对夹层组分、结构进行设计，采用流延－叠层－热压或SPS烧结工艺，制备出高断裂韧性、高强度的B4C-BNNTs/TiB2-B4C层状复合材料。研究不同相组成对BNNTs/B4C基体层的显微结构、力学性能以及对基体层与夹层结合界面显微结构的影响；研究强界面的层状复合几何参数，包括层厚、层数、层厚比对BNNTs/B4C陶瓷基层状复合材料的强度和断裂韧性的影响；建立成分、制备工艺、显微结构与力学性能之间的关系，探讨第二相增韧与层状复合增韧以及两者协同增韧作用机理。

碳化硼作为一种重要的轻质超硬高温结构陶瓷材料，在航空航天、核能和军事等领域有着广泛的应用前景，但因其难烧结、韧性差使它的进一步应用受到限制。本研究采用有限元分析软件ANSYS，设定B4C-BNNTs层厚度为hb，TiB2-B4C层厚度为ht，参数n为基体层和夹层层厚之比即hb/ht，主要研究了不同B4C-BNNTs层厚、不同层厚比、不同层数和在TiB2层中不同B4C含量对B4C-BNNTs/TiB2-B4C层状复合材料层间残余应力的影响。结果表明：当B4C- BNNTs层厚为150-200μm，层厚比n为0.5-2，层数为15-80层，在TiB2层中B4C含量为20wt%,B4C- BNNTs/TiB2-B4C层状复合材料层间残余应力处于较为适宜的状态。.基于有限元ANSYS分析结果，采用水基流延成型和热压烧结工艺制备了B4C-BNNTs/TiB2-B4C层状陶瓷复合材料。主要研究了不同B4C-BNNTs厚度、不同B4C-BNNTs和TiB2-B4C层厚比n、B4C-BNNTs层中不同BNNTs含量和TiB2-B4C层中不同B4C含量对B4C-BNNTs/TiB2-B4C层状陶瓷复合材料残余应力和力学性能的影响。采用X射线衍射法进行了层间残余应力的测量，通过万用试验机等仪器进行了抗弯强度、断裂韧性和硬度的测试。实验结果表明：当B4C-BNNTs层厚为175μm，层数为69层，B4C-BNNTs和TiB2-B4C层厚比为1，B4C-BNNTs层中BNNTs含量为1.5wt.%，TiB2-B4C层中B4C含量为20wt%，烧结温度为2050℃，压力为30MPa，保温1h可获得性能最优的B4C-BNNTs/TiB2-B4C层状陶瓷复合材料，此时B4C-BNNTs/TiB2-B4C层状陶瓷复合材料的相对密度、抗弯强度、断裂韧性和维氏硬度分别为99.1%、570.5MPa、7.7 MPa·m1/2和38.6GPa。.B4C-BNNTs/TiB2-B4C2层状陶瓷复合材料的增韧机理主要是热胀系数失配造成的预加应力，提升复合材料断裂阻抗；基体层与硬夹层界面较强的结合力消耗断裂能，裂纹偏转、脱层；BNNTs在断裂过程中起到拔出、桥连及偏转裂纹的作用。