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A novel ceramic tool concept allows near-isothermal steel thixoextrusion experiments. Thermal shock impacts are successfully eliminated from the load profile of conventional semi-solid processing technologies of high melting point alloys. Thus, the application of thermal shock sensitive oxide ceramics exhibiting excellent corrosion resistance as forming dies is feasible. Extruded steel parts show high shape accuracy at very low extrusion forces.

The design and performance of silicon nitride (Si3N4) dies for the semi-solid processing of steels is studied by the example of a punch and a lower swage in upset forging. The observed failure mechanisms and degradation effects are related to short-term effects resulting from mechanical and thermal loads and long-term effects owing to chemical and tribological attack. Results show that well-defined process conditions (cycle time, solidification time in the die) and a ceramic-suitable design are a pre-requisite for reliability and sufficient service life of ceramic dies.

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