Silicon nitride for lightweight stiff structures for optical instruments

摘要

Due to their very specific set of material properties, silicon nitride and silicon carbide have gained a lot of interest in the last 20 years. Moreover, many new approaches in technical equipment and processes were enabled with corresponding research and production activities.rnAlso large efforts were made at FCT during the last years, to get able to supply even very large and complex shaped components made of sintered silicon carbide (SSiC) and of gas pressure sintered silicon nitride (GPSN) ceramics. This approach has opened new applications and markets for such ceramic materials. On the other side, designers and engineers are now allowed to think much more complex in designing of ceramic components. In this paper, a new rapid prototyping routine for very complex components as well as the corresponding materials will be presented. Components for optical equipment in innovative avionic and space applications, and more conventional technologies are described.rnNot only their unique key intrinsic properties, like high Youngs Modulus, very low CTE, very high strength and fracture toughness for a ceramic but also newly developed and adopted shaping, sintering and machining technologies in both green and sintered state have let to highly valued products. This enabled FCT to offer Carl Zeiss Optronics using silicon nitride for a newly designed, very complex housing structure of an avionic pod camera. Due to a very low CTE, high stiffness and less weight, an improved performance was reached.rnAlso Thales Alenia Space is engaged since some years in activities to develop and qualify Silicon nitride ceramics for space projects. Extremely stiff, very lightweight and large truss space structures with a very low CTE, high rigidity and no outgasing for satellites can now be realized. Deep tests sequence has been performed to qualify truss beams and end fittings made in the same material.rnAlso advanced dynamic testing equipment for avionic turbine blades requires new approaches. In cooperation with TIRA a series of shaker heads were developed which can operate at much higher frequencies and so reduce fatigue testing time and costs. Last but not least, highly precise and thin walled disc structures with diameters up to 380 mm are produced for wafer handling and testing equipment.