Formation of tough interlocking microstructures in silicon nitride ceramics by dynamic ripening

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Abstract
Ceramics based on Si3N4 have been comprehensively studied and are widely used in structural applications1,2. The development of an interlocking microstructure of elongated grains is vital to ensure that this family of ceramics have good damage tolerance3,4. Until now this has been accomplished by heating the appropriate powder compacts to temperatures above 1,700 °C for extended periods. This procedure involves a necessary step of controlling the size and population of seeds—added ex situ or formed in situ—to ensure selective grain growth5,6. Here we report the very fast (within minutes) in situ formation of a tough interlocking microstructure in Si3N4-based ceramics. The microstructures are obtained by a dynamic ripening mechanism, an anisotropic Ostwald ripening process that results from the rapid heating rate. The resulting microstructures are uniform and reproducible in terms of grain size distribution and mechanical properties, and are easily tailored by manipulating the kinetics. This process is very efficient and opens up new possibilities to optimize mechanical properties and cost-effectively manufacture ceramics.