The mechanism of reaction sintering of iron-iron boride cermets

Abstract

The process of reaction sintering of iron and boron in a vacuum has been analysed, as a result of which iron-iron boride cermets have been produced. They constitute a composite material in which iron boride, Fe2B, with a hardness of about 1800 HV plays the role of the reinforcement, while iron-iron boride, Fe-Fe2B, with a hardness of about 500 HV plays the role of the matrix. The eutectic filling the spaces between iron boride grains is composed of boron solid solution plates in iron with a hardness of around 250 HV, and iron boride, Fe2B, plates with a hardness of approximately 1800 HV. The combination of such different materials results in attractive properties of the cermet thus produced: high total hardness (1500 HV), constant over the whole section, and ductility. The properties mentioned, resulting from the cermet structure, depend (apart from the chemical composition) on the phenomena occurring while sintering: the boron diffusion in iron, the formation of the liquid phase and the processes of dissolving powder components in it, and finally upon the crystallization of the boride phase from the liquid. These all determine the unique character of the reaction sintering of iron and boron. The mechanism of this process is reported.