A calorimetric study of high temperature phase stability in Fe–U alloys

Abstract A differential scanning calorimetry study of high temperature phase equilibria and phase transformation kinetics in Fe 100− x U x binary alloys, with x varying from 0 to 95 mass% U is undertaken. Accurate measurement of transformation temperatures pertaining to: (i) α-Fe → γ-Fe → δ-Fe polymorphic phase change, (ii) UFe 2 + γ-Fe → L and U 6 Fe + UFe 2 → L transformations and (iii) melting has been made as a function of uranium concentration. The measured transformation temperatures are used to construct the binary Fe−U phase diagram, which showed general agreement with the latest assessment. The L → UFe 2 + γ-Fe eutectic reaction is found to occur at 1357 ± 5 K, with the eutectic composition of 47 mass%. The heat of transformation associated with this invariant reaction is estimated to be 19,969 ± 1736 J mol of atoms −1 . The L → U 6 Fe + UFe 2 reaction occurs at 89 mass%, and at 1001 ± 5 K, with a heat of transformation 20,250 ± 2113 J mol of atoms −1 . The heat of melting of stoichiometric UFe 2 is estimated to be 20,983 ± 2098 J mol of atoms −1 , which is higher than the currently assessed value by 30%. A non-faceted microstructural morphology is found to accompany the eutectic solidification process of all the alloy compositions.