This Small Business Technology Transfer Phase I project seeks to develop biomimetic structures in engineering ceramics based on the damage-tolerant sea shell micro-architecture. Poor damage tolerance of engineering ceramics leads to catastrophic failure modes under stress, which restricts their structural utility. In extreme conditions, ceramics generally function only as a thermal or chemical barrier. Gains in damage tolerance have been made in select ceramics via transformation toughening, acicular grains, and engineered architectures such as Fibrous Monoliths (FMs). Significant further gains can be achieved by mimicking the micro-architecture of the Strombus Gigas (sea shell). The multiscale architecture of the sea shell will be replicated in a model engineering ceramic system comprised of silicon nitride and boron nitride by borrowing and significantly building on the techniques used in making FMs, including thermoplastic deformation and assembly. Modeling of crack propagation through these complex architectures will be performed to help guide the development of the process. The microstructural, mechanical, and thermal properties of the engineered ceramics will be characterized. This research will establish the viability of the proposed thermoplastic deformation/assembly techniques to engineer a third-order biomimetic ceramic material which is expected to have a work-of-fracture more than twice as large as a comparable FM.
The broader impact/commercial potential of this project will be the development of highly damage-tolerant ceramics that will increase their utility in engineering applications and validate bio-inspired materials engineering. The biomimetic ceramics will improve on the damage tolerance of existing ceramic systems by a significant margin and therefore will be of great interest to many industries: manufacturing, military/aerospace, and medical. No comparable technology exists which combines the benefits of ceramics (low density, thermal stability, high hardness) without their disadvantages (poor damage tolerance). Ceramic- and metal-matrix composites offer better reliability than bulk ceramics, but are expensive and often fall short of design requirements. Ultra tough ceramics will produce better performance in medical implants, maintain American manufacturing leadership, and promote advanced vehicle technology. By creating materials which can meet both thermal and structural requirements, this technology will create more multi-functional ceramics. Additionally, this project will lead to a better understanding of crack propagation through damage-tolerant hierarchical structures. Finally, the project will involve undergraduate and graduate students at Villanova University, and key results of the research will be disseminated in multidisciplinary conferences and journals.
The overall objective of this Phase I STTR project was to demonstrate a method to fabricate biomimetic ceramics with ultra-high toughness and damage tolerance. The availability of biomimetic, tough ceramics will enable their use in many applications. The architecture of the Conch (Strombus Gigas) shell provided the inspiration for the biomimetic ceramics. These shells have a multiscale, multilayered, crossed-lamellar architecture built with two natural materials, calcium carbonate and protein. The goal was to replicate this structure in an artificial ceramic material with silicon nitride and boron nitride as the principal components. The specific technical objectives for Phase I were to develop processing methods to make artificial crossed lamellar structures, produce features in these structures that were in the millimeter to micron scale, and to exceed the damage tolerance of comparable monolithic ceramics. Each of the technical objectives was met during this effort. A thermoplastic deformation and assembly methodology was developed that proved to be very effective in constructing biomimetic ceramics whose architecture mimics the crossed lamellar structure of the Strombus Gigas shell. Multiscale structures have been built in the biomimetic ceramics that resemble the Strombus Gigas. These structures have been built to the scales set as targets for Phase I. The damage tolerance metrics of the biomimetic ceramics are very promising and exceed those of comparable monolithic ceramics. Moreover, they are relatively inexpensive to fabricate. Near term potential applications are multi-hit armor and high temperature aerospace applications. Current armor ceramics suffer from limited damage tolerance and consequently have poor multi-hit capabilities unless significant secondary materials are used. Ceramic matrix composites have desirable properties for high temperature applications but are very expensive to fabricate. Based on both cost and performance, these biomimetic ceramics could be revolutionary. These ceramics will contribute to maintaining American manufacturing leadership and promote advanced vehicle technology. Undergraduate and graduate students have been involved in this project, thus providing interdisciplinary research experience for the next generation of engineers.
