Wear analysis of glassy carbon in the fused silica molding process depending on the surface quality of the glassy carbon

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Precision glass molding of fused silica is an alternative and promising method for the production of optical components made of fused silica in medium and large quantities. At present glassy carbon is the most promising mold material for fused silica molding. But even glassy carbon fits the mechanical, thermal and chemical requirements for the molds this material also shows wear behavior in the form of glass adhesions with increasing molding time. This makes a remachining of the molds necessary and leads to an inefficiency of the whole process. Investigations in the previous project have shown that even on the surface of the polished glassy carbon molds micro- and nano-defects exist which play an important role in the development of wear. In these defects, which appear like notches, high compressive stresses and especially high tensile stresses occur during the molding process with increasing molding time. This leads to a gradual spalling of material, which again lead to an increase of defects and therefore to damaging of the optical functional surface. In addition, glass is deposited in these defects, which also impair or destroy the function of the optical surface. The phenomenon of the glass deposit is favored by adhesion processes between the glass and the mold. Due to the relatively long contact times, especially on the lower mold, bindings between the SiO2 molecules of the fused silica and the glassy carbon network are generated. These bindings can be strong enough that during the molding process glass material is dissolved from the glass compound and remains on the mold surface. The overall goal of the follow-up project is therefore to describe the wear mechanisms of glassy carbon while molding fused silica in detail to understand their root causes and based on this to develop prevention strategies. The focus of the research is the manufacturing and processing methods of the material and possible wear protective layers.