Collaborative Research: Making nanostructured ceramics from micrometer-sized starting powders

Project Summary Nanostructured materials (grain size < 100 nm) exhibit unique and often superior properties as compared to their microstructured counterparts, including high yield stress, high superplasticity, and significantly improved radiation damage tolerance. However, the fabrication of dense nanostructured bulk ceramics represents a tremendous technical challenge because of grain growth during sintering. To date, several techniques have been developed to synthesize nanostructured ceramics, such as two-step processing and high-pressure consolidation. All these techniques are based on the philosophy of tailoring processing conditions to mitigate grain growth during sintering, and require starting with ultrafine nanometer-sized powders, which are difficult to be processed and mass-produced in an economic and reproducible way. This collaborative research aims to develop a unique processing technique, based on a fieldactivated sintering process (also known as Spark Plasma Sintering, SPS), to make bulk nanostructured ceramics from micrometer-sized starting powders. In order to establish necessary knowledge base for successful development and applications of the proposed technique, the following research are proposed: (i) experimentally investigate the effect of processing conditions on the development of microstructures, (ii) perform numerical modeling on electrothermal-mechanical interactions in the SPS processing, and (iii) establish the processing-microstructure-property relationships. The proposed project is inspired by the preliminary results, in which we have demonstrated that nanostructured PMN-PT ceramics with the grain size of 20-100 nm and AIN ceramics with the grain size of less 100 nm can be synthesized from starting powders of a few micrometers using the SPS process. The proposed work will be carried out by an interdisciplinary team consisting of experts from the University of Central Florida (UCF) and the University of Kentucky (UK). The PI, Dr. An of UCF has extensive experience in material processing, and microstructural and property characterization. The Co-PI, Dr. Yang of UK, is an expert of theoretical modeling and mechanical property characterization. Thereby, the Pis have sufficient and complementary experiences to ensure the success of the project. Intellectual Merit: The proposed project will carry out fundamental studies for the development and application of a unique processing technology to make bulk nanostructured ceramics from micrometer-sized starting powders. The successful delivery of proposed work will advance our technology and fundamental science beyond their current state in the following areas: (i) develop a novel and rather convenient processing technique for making bulk nanostructured ceramics, (ii) achieve an in-depth understanding of the field-activated sintering process for the formation of nanostructured ceramics, (iii) promote and broaden the use of nanostructured materials and the SPS technique in engineering applications, and (iv) advance fundamental science in the processing-structure-property relationships of nanostructured materials. Broader Impacts: The proposed project will maintain and enhance U.S. competitiveness and leadership in materials, aerospace, military and transportation industries. The broader impact to education and training will include: (i) integrating research findings into graduate/undergraduate courses to improve curriculums in nanostructured material processing, properties and applications; (ii) training graduate and undergraduate students on advanced material processing, nanostructured materials, material characterization and numerical modeling, to prepare next-generation work force; (iii) enhancing the participation of underrepresented groups in scientific research and education through a well-designed aggressive plan; and (iv) educating science and engineering to K-12 students, high school science teachers and public at large.