Activation Energy in Hot Forming of Selected Fe-40at.%Al Type Intermetallic Compounds

Promising potential of the Fe-40at.%Al type alloys is used only in a limited way as yet, mainly due to their high brittleness. With regard to attraction of the given type material, the plastometric research at temperatures 800C to 1200C was carried out as a basic one, namely using the uniaxial compression tests at strain rates $10^{-2} s^{-1}$ to $10^1 s^{-1}$. Cylindrical samples were manufactured from laboratory castings, gained by means of the vacuum induction furnace. Two materials were tested - Fe-40Al and $Fe-40Al+TiB_2$. From the measured flow stress curves the values of maximum stress were obtained and used for determination of the activation energy in hot forming according to the classical equation of the hyperbolic sine type. Enumeration of its parameters led to a possibility to predict maximum deformation resistance values of the investigated alloys in dependence on temperature and strain rate. Pronounced effect of the added titanium diboride particles (< 10 μm) on the activation energy value and to a resistance to the formation of cracks was observed. Thanks to the obtained value of activation energy an equation sufficiently describing the initiation of dynamic recrystallization process in the $Fe-40Al+TiB_2$ material as a function of the Zener-Hollomon parameter could be derived.