Infrared Transparent Ceramic Windows 2 for High-Speed Vehicles

摘要

The project has created new technical approaches to manufacture large size transparent ceramic windows (transparency 85% and higher in the IR part of spectrum) using advanced consolidation techniques such as 3D printing (binder jet printing of green prototypes up to 120 mm in diameter) and spark plasma sintering (enable to form domes of 70 mm in diameter). The proposed approach has required the development of ceramic nanopowders specifically formulated by internal structure to be applied in 3D binder-jet technology of meniscus-shape domes. The technologies for the synthesis of nanopowders of magnesium fluoride (MgF_2) and magnesium-aluminum spinel (MgA_2O_4) have been developed, and batches of 3 kg of the both powders have been manufactured. According to the results of the analysis, it was found that the powders are thermally, mechanically and optically-suitable for the manufacture of IR-transparent windows. The specific surface of MgF_2 powder is 38-40 m~2/g, for MgAl_2O_4 powder it is 27 m~2/g. Shaping technologies by slip casting and 3D-printing suitable for sintering under pressure have been developed. Granules from KPI powders and Baikovsky powders have been prepared. Based on the granules a printing process has been developed using CJP 360 printer. Before sintering stage, the FEM calculations of the press instrument design and shape were carried out and optimal construction providing uniform temperature and strain rate distributions were defined. FEM simulation of the sample under pressure consolidation conditions (spark-plasma sintering and hot pressing) resulted in manufacturing of molds valid for the pilot production of dome-shaped windows. Optimization of the graphite press mold using FEM allows five times shortening of operation regime. The developed technologies of spark-plasma sintering (SPS) and hot pressing (HP) are key-enable technologies to produce transparent (88% and above) in the IR range. It has been shown that rapid sintering conditions (heatin