Development of Ceramic/Metal Mutual Nanocomposites with Superior Strength and Toughness

众所周知，纳米复合材料技术即使在高温下也能将陶瓷材料的断裂强度提高2到4倍。高温蠕变速度也提高了3~4个数量级。本课题的目的是阐明纳米复合材料改善力学性能的机理，并应用该纳米复合材料技术开发各种多功能陶瓷材料(中间材料)。本课题的最终目标是在纳米复合材料技术的基础上，提出力学性能更好的纳米/团簇复合材料的概念。主要研究成果如下：1)在陶瓷/陶瓷和陶瓷/金属纳米复合材料中，开发了纳米第二相均匀分散的新工艺，阐明了纳米第二相分散改善力学性能的机理。2)在此基础上，利用陶瓷/陶瓷复合体系中的微纳米杂化概念和陶瓷/金属复合体系中的互纳米复合概念，开发出同时提高断裂强度和韧性的新型陶瓷材料，特别是氧化锆/钼纳米复合体系。3)提出了利用软弱第二相分散改善陶瓷材料力学性能的新材料设计。通过应用这一概念，大大提高了Si3N4/BN纳米复合材料的强度、韧性、热震断裂抗力和化学惰性，并与金属一样具有可加工性。在BaTi03/Ni纳米复合体系中，既获得了高强度，又提高了铁电性。例如，分散纳米镍颗粒可使复合材料的断裂强度提高2~3倍，介电常数也有相同程度的提高。

Nanocomposites technology is well known to improve 2 to 4 times the fracture strength of ceramic materials even at high temperatures. The high-temperature creep rate is also improved 3 to 4 orders by this technology. The purpose of this project are to clarify the mechanisms of mechanical property improvements and to develop various kinds of multi-functional ceramic materials (Intermaterials) by applying this nanocomposite technology. The final target of this project is to propose the nano/cluster composite concept with better mechanical properties, based on the nanocomposite technology.The main results obtained from this project is as follows : 1) In the ceramic/eramic and ceramic/metal nanocomposites, new processing to homogeneously disperse the nano-sized second phases were developed, and the mechanisms of mechanical property improvements by the nano-sized second phase dispersions were clarified. 2) Based on the above-mentioned informations, new ceramic materials, in which the fracture strength and toughness were simultaneously improved, were developed by the micro/nano hybrid concept in the ceramic/ceramic composite systems, and by the mutual nanocomposite concept in the ceramic/metal composite systems especially Zirconia/Mo nanocomposite system. 3) Furthermore, new material design to improve the mechanical properties of ceramic materials by the soft and week second phase dispersions was proposed. By applying this concept, significantly improved strength, toughness, thermal shock fracture resistance and chemical inertness were harmonized with the machinability like metals in the Si3N4/BN nanocomposite. In the BaTi03/Ni nanocomposite system, the high strength with the improved ferroelectricity was obtained. For example, the fracture strength was improved 2 to 3 times by dispersing the nano-sized Ni particulates, and the same level improvement was also observed for the dielectric constant.