Thermodynamic functions of Fe3B borides

Abstract

In this work we study the structural properties of hypoeutectic and hypereutectic Fe-B alloys, depending on the temperature of heating above the liquidus line and the cooling rate. Experiments were carried out for the Fe-B system alloys with boron content of 2.0–4.5% (wt.), the rest is iron. To determine physical properties of the alloys microstructural and X-ray diffraction analysis were used. It is shown that overheating of the molten alloy to 150 K above the liquidus line and aftercooling leads to complete suppression of the formation of primary iron crystals in the hypoeutectic alloys and partially to suppression of Fe2B formation in the hypereutectic alloys of the Fe-B system. For the first time it is shown that heating of Fe-B hypoeutectic alloys to 150 K above the liquidus line and cooling with a rate of 103 K/s lead to formation of Fe3B boride in as-cast state, which was present in the eutectic colony. Taking into account the contribution of the first degree approximation of the high-temperature expansion of the thermodynamic potential for Fe3B iron boride in the binary Fe-B alloy, we obtain for the first time temperature dependences for the thermodynamic functions such as Gibbs energy, chemical potentials of boron and iron in Fe3B boride, entropy, enthalpy and heat capacity Cp. In addition, the method suggested enables to determine the temperature of the formation of Fe3B iron boride, which is in agreement with the data of other authors.

Keywords

• розплав
• перегрів сплаву вище лінії ліквідусу
• сплави системи fe-в
• термодинамічні функції
• борид заліза fe3в