Phase change and heat treatment of U-Mn alloys

Behaviors of the transformations and grain refinement were studied using a series of uranium alloys varying in manganese content from 0.25 to 1.0 a/0. The tendency of the retention of β or γ uranium phase by quenching was examined as a function of manganese content. The β phase can be retained, while the retained γ phase could not be detected at all. TTT diagrams were determined and the existence of two modes in the β-to-α transformation is cleared. The M_s temperature increases with decreasing manganese content and activation energy of U-1.0 a/0 Mn alloy is calculated as 43.5 kcal/g-atom from the β-to-α TTT diagram in nucleation and growth mechanism. Grain refinement is attained by the β-to-α transformation of nucleation and growth mode in the temperature region below the nose of the TTT diagram. (author)