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Posted: Feb 05, 2018
Bone-inspired self-crack-healing ceramics capable of quick full strength recovery
(Nanowerk News) A NIMS-YNU research group discovered that self-healing ceramics undergo three healing stages analogous to bone healing processes: inflammation, repair and remodeling. Using clues provided by bone healing mechanisms, the group added a healing activator to crystalline grain boundaries, enabling the ceramic to fully heal cracks in as little as one minute at 1,000°C, the operating temperature of an aircraft engine (Scientific Reports, "A Novel Design Approach for Self-Crack-Healing Structural Ceramics with 3D Networks of Healing Activator").
(Left and middle) Self-healing process in ceramics, which completes in as little as one minute. (Right) A network of manganese oxide (green) facilitates self-healing (Image: NIMS)
Self-healing ceramics were discovered by an YNU research group in 1995. Lightweight and heat-resistant, they have been drawing global attention for their potential use as turbine materials in aircraft engines.
However, their self-healing mechanisms had been poorly understood, and cracks only fully healed within a limited temperature range between 1,200 and 1,300°C. Therefore, identification of the mechanism and development of ceramics capable of rapid self-healing within a larger temperature range have long been sought.
The present research group found that self-healing processes occur in three stages: when a ceramic cracks, oxygen enters though the crack and reacts with silicon carbide—a ceramic component—to form silicon dioxide (the inflammation stage). Alumina—a base ceramic material—and silicon dioxide then react to form a gap filling material, sealing the crack (the repair stage).
Finally, the filler crystallizes to restore the original strength in the cracked part (the remodeling stage). In addition, based on the insight that the bodily fluid network in humans promotes the healing of damaged bones, the research group added a trace amount of a healing activator – manganese oxide – to alumina grain boundaries as a 3D network structure.
As a result, newly developed ceramics healed cracks in as little as approximately one minute at 1,000°C, compared to conventional ceramics, which heal cracks in 1,000 hours at 1,000°C.
Based on these results, the research group plans to develop innovative, heat-resistant ceramics which will never break even when cracked by selecting effective healing activator phases and thereby precisely manipulating the self-healing capability of ceramics.
This project was carried out by a research team led by Senior Researcher Toshio Osada (Research Center for Structural Materials (RCSM), NIMS), Group Leader Toru Hara (RCSM, NIMS), Principal Researcher Taichi Abe (RCSM, NIMS), Takahito Ohmura (Deputy Director of the RCSM, NIMS), Chief Researcher Masanori Mitome (International Center for Materials Nanoarchitectonics, NIMS) and Professor Wataru Nakao (Faculty of Engineering, YNU).