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Ceramic materials of the quasi-binary LaB6-MoB2 system

Kysla Galyna (National Technical University “KPI”, Prospect Peremohy, Kyiv, Ukraine)
Loboda Petro (National Technical University “KPI”, Prospect Peremohy, Kyiv, Ukraine)

Alloys of the quasi-binary LaB6-MoB2 system synthesized by melting in an atmosphere of helium have been studied. It has been established that the phase diagram of the system is eutectic and the phases do not interact. The eutectic colony crystallizes in form of the platelike eutectic on the basis of the LaB6 crystal of a cubic structure. It has been also shown that the crystallization from melt under conditions of crusibleless zone melting is accompanied by the MoB2 phase decomposes during cooling with precipitation of the submicron Mo2B5 and α-MoB crystallites. This results in an increase of hardness. According to the Mo - B phase diagram, the decomposition temperature of the MoB2 increases with increasing the boron content. In addition, the degree of the decomposition is higher if the melting point of alloy is higher, since the intensity of diffusion process increases at high temperatures.

Keywords: ceramics, eutectic alloy, crusibleless zone melting, metal boride