The uraniumrhenium alloy system

Abstract

The phase diagram of the uraniumrhenium alloy system is presented along with a discussion on transformation kinetics of the uranium solid solutions. The phase diagram is of the double eutectic type with the intermediate phase having the composition URe 2. This phase exhibits allotropy at 180°C and melts congruently at 2200°C. URe 2 reacts sluggishly with the uranium solid solutions below 750°C to form the peritectoid compound U 2Re. Eutectic reactions occur at 1105° and 2105°C at respective compositions of 10.5 and 65.5 wt. % Re. Eutectoid reactions occur at 643° and 681°C at compositions of 1.4 and 6 wt. % Re, respectively. The maximum solubility of rhenium in α uranium is about 0.4 wt. % at 643°C and in β uranium is 1.9 wt. % at 681°C. The solubility of rhenium in γ uranium is 6 wt. % at 681°C and increases to about 7 wt. % at 975°C. The solubility of uranium in rhenium is 0.6 wt. % at room temperature with little variation up to 2000°C. Alloys of β and γ uranium containing more than about 1.2 and 7 wt. % Re respectively, can be readily supercooled to room temperature. Rapid cooling of γ alloys containing less than about 7 wt. % Re resulted in a direct γ → α′ transformation, the α′ state being a supersaturated α phase having a banded microstructure. Evidence is presented for the existence of two transition states, one involving the γ phase decomposition and the other the β → α transformation. The sequence of phase changes involved in cooling the uranium solid solutions is discussed.