新型轻量超硬AlMgB14陶瓷的自强韧及构效关系研究

Lighweight and ultrahard AlMgB14 ceramic becomes a armor candidate, which possibly plays an important role in the future. There is an unexpected increase in the hardness when Si is added into AlMgB14. The behavior is much different from common ceramic materials like B4C and SiC. But the AlMgB14-Si material still faces problems such as low toughness and unstable mechanical properties..Both Carbon and silicon will be introduced to give the material high toughness as well as ultrahigh hardness. A reaction between the C and the Si is expected to happen and produces an elongated shaped SiC, which will enhance fracture toughness in situ. The SiC growing behavior, and its grain boundary structure and composition will be controlled to tailor the property. The crack paths and fracture behaviors will be analyzed for clarifying the mechanism of the high toughness. Meanwhile, the carbon also acts as reductant to modify microstructure and enhances the stability of the mechanical properties. The carbon takes the effect by removing impurities from the ceramic and improving its densification. The densification behavior, the dynamic process of sintering, and microstructural evolution will be studied using electronic microscopes, an advanced real-time observation sintering system and other characterization methods. The factors promoting sinterability and refining microstructure are likely to be revealed. In addition, the cause of the ultrahigh hardness in the AlMgB14-Si is still unclear. The mechanism is to be uncovered in terms of bonding nature, electronic structure, grain size, nanotwins, grain boundary, and hardness testing. As a result, a homogenous, dense, ultrahard AlMgB14 ceramic coupled with high facture toughness will be obtained. This will provide theoretical supports for the lightweight and high-performance AlMgB14 material in the application of ceramic armors.

AlMgB14轻质、超硬是面向未来的新型硬质防弹材料。与常规陶瓷不同，AlMgB14掺杂Si后，硬度反常地升高，但其仍有韧性低、性能不稳定的问题。本研究拟共掺Si和C解决上述问题，以赋予材料硬韧兼备的特性。C与Si反应可形成柱状SiC晶粒。本研究拟研究柱状SiC晶粒形成条件和生长规律、SiC晶界形态、材料裂纹扩展和断裂行为，以显著提升AlMgB14的断裂韧性，并阐明增韧的机制。AlMgB14性能不稳定的根源是微结构杂质含量高、不致密。本研究拟结合独有的实时观察烧结技术，研究C对微结构、烧结动力学及烧结行为影响，探明C促进致密化，改善微结构的机制。此外，Si提升AlMgB14硬度机制仍模糊不清。本研究拟研究Si对电子能带结构、价键结构、晶粒尺寸、晶粒内纳米孪晶、晶界的影响，结合微观和宏观硬度表征，揭示引起材料硬度突升的机制。本项目的实施有望为轻质高性能AlMgB14陶瓷的应用提供理论指导。

超硬材料和工具为高科技材料和各种制成品的开发提供了有力的支撑。一种新型超硬材料AlMgB14因具有优良的力学性能以及较好的化学稳定性，较低的规模化生产成本而受到广泛的关注。现阶段，制备高纯度的AlMgB14粉体制备工艺繁杂，设备要求较高，大大提高了其制备成本。本课题通过原料选择、制备工艺、煅烧工艺的优化，可制备纯度为95.2 wt.% 的AlMgB14粉体。AlMgB14晶粒接近等轴状，大小约3-5 μm。本课题探究了添加金属Al以获得高韧性、高强度AlMgB14-Al复合材料。通过优化的工艺，AlMgB14-15%Al复合材料抗弯强度可达600 MPa，断裂韧性可达6.8 MPa·m1/2。为进一步提高力学性能，本课题以金属Ti以及TiB2掺杂的方式，以期望获得高性能的AlMgB14-TiB2复合陶瓷材料。当TiB2含量达到70 wt.%时，复合材料的抗弯强强度最高可达到873 MPa。AlMgB14-TiB2复合陶瓷硬度，随着TiB2含量的增加，其硬度在31-33 GPa附近波动。采用Ti粉为第二相添加剂时，当Ti的含量为2 mol时，AlMgB14-TiB2复合材料的断裂韧性最高约为6.1±0.7 MPa·m1/2。复合材料的抗弯强度随着Ti含量的增加而增加，其中Ti的含量为1.5 mol时抗弯强度最大，最大值为786 MPa。