JSC “Kompozit”, Korolev, Russia:

I. A. Gvozdkov, Leading Engineer of the Institute of Beryllium, e-mail: gvozdick@inbox.ru
B. A. Belikov, Deputy Executive Officer of the Institute of Beryllium
V. S. Sizenev, Executive Officer of the Institute of Beryllium

National University of Science and Technology MISiS, Moscow, Russia:
P. Yu. Bryantsev, Assistant Professor, e-mail: p_bryant@rambler.ru

Requirements to materials for space-based optoelectronic devices (OED) are reviewed. There are shown the prospects of using beryllium-silicium alloys to develop thermal dimensional stable casting alloy (with composition close to the eutectic point providing the thermal dimensional agreement of parts in OED). The experimental alloys were made by investment casting, with beryllium content from 34 to 44% by weight. The microstructure was investigated by optical and scanning electron microscopy, and hardness was determined at room temperature and the linear coefficient of thermal expansion (CTE) in the temperature range from 20 to 500 ^oC. Eutectic alloy microstructure consists of eutectic and primary beryllium dendrites. The eutectic phase has both a columnar and plate structure. Primary dendrites are surrounded by pure silicon, formed by degenerate eutectic. Pores are detected in alloy microstructure. Pore distribution is diffuse in nature, and the shape is mainly spherical, which indicates the gas-shrinkage porosity. The presence of primary silicon crystals in hypereutectic alloy structure leads to embrittlement. The measured hardness of the alloys is between 450 and 550 HV, which are characterized as intractable alloys. The coefficient of linear thermal expansion of experimental alloys is reduced to 50% in the temperature range of 20–500 ^oC, compared with technical sintered beryllium. Weak CTE dependence on temperature was detected: the value of the CTE of the experimental alloys increases by only 12% in the temperature range of 100–500 ^oC, while the CTE of beryllium is changed to 48%. Reduced CTE of alloys provides thermal-dimensional agreement to optical glasses used in the OED.

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