Krystalizace slitin stribro-germanium v podminkach mikrogravitace

In presented work the influence of melt convection on crystallization of silver - germanium alloys was studied. In the first part of work literature sources on this field were treated. In this chapter the general information on primary and eutectic crystallization are given. Another chapter focuses on examined system silver - germanium. The last chapter deals with the influence of microgravity on transport processes as well as on crystallization processes. Literature research showed that the transport of components within a melt is the most important parameter affecting all stages of solidification process. The effect of transport is rather complex and has not been so well understood. The conditions of distinct convection rates were obtained by processing the samples on Earth and under space environment. In experiment a number of parameters of crystallized samples was examined. This made possible to approximately estimate the mechanism of crystallization process under distinct convection conditions. The main result of experimental part is the fact that the absence of convection significantly enhances the departure of crystallization process from the equilibrium phase diagram of the system. Regarding the non-equilibrium level of the process, the most interesting alloy is that enriched in silver with respect to eutectic point. Even at relatively low cooling rate (only 10 K/min), the non-equilibrium level (undercooling of eutectic crystallization) under limited convection is significant in this sample. Therefore the microgravity can become a valuable environment to prepare extremely non-equilibrium structures or amorphous metallic structures unavailable under common conditionsAvailable from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi