Features of polymorphic transformation during heating and cooling of cobalt

Differential scanning calorimetry was used to study the regularities of polymorphic $\alpha\leftrightarrow\beta$-transformation in polycrystalline cobalt. The value of the activation energy of the $\alpha\to\beta$-transformation during heating of cobalt (290–50 kJ/mol), enthalpy and entropy, depending on the thermal history of the metal, is determined. It is shown that the mechanisms of recrystallization under heating are closer to the first-order I phase transformations. When cooling under conditions of limited diffusion mobility of cobalt atoms, recrystallization is apparently carried out due to the passage of several diffusion-free mechanisms of phase transformation, implemented in close temperature ranges.