Failure Analysis on a Compaction Roll made of Silicon Nitride

Owing to its excellent mechanical and thermal properties such as high strength, high hardness, and good thermal shock resistance, silicon nitride is a material suitable for forming tools. This work analyses the failure of a compaction roll made of Si3N4. One of the two ceramic rings broke during the compaction rolls' operation. Fractographic examinations have shown that very high tensile stresses occurred in the ceramic material during operation. These stresses first led to the formation of cracks and then to the total failure of the roll ring. Failure analysis has shown that roll design and clamping are of major importance. Causes for the generation of tensile stresses are shown and suggestions are made on how to ensure a safe operation of the rolls.