Cubic γ-phase U–Mo alloys synthesized by splat-cooling

摘要

U–Mo alloys are the most promising materials fulfilling the requirements of using low enriched uranium (LEU) fuel in research reactors. From a fundamental standpoint, it is of interest to determine the basic thermodynamic properties of the cubic -phase U–Mo alloys. We focus our attention on the use of Mo doping together with ultrafast cooling (with high cooling rates ≥10 K s), which helps to maintain the cubic -phase in U–Mo system to low temperatures and on determination of the low-temperature properties of these -U alloys. Using a splat cooling method it has been possible to maintain some fraction of the high-temperature -phase at room temperature in pure uranium. U-13 at.% Mo splat clearly exhibits the pure -phase structure. All the splats become superconducting with in the range from 1.24 K (pure U splat) to 2.11 K (U-15 at.% Mo). The -phase in U–Mo alloys undergoes eutectoid decomposition to form equilibrium phases of orthorhombic -uranium and tetragonal '-phase upon annealing at 500 °C, while annealing at 800 °C has stabilized the initial phase. The -U easily absorbs a large amount of hydrogen (UH hydride), while the cubic phase does not absorb any detectable amount of hydrogen at pressures below 1 bar and at room temperature. At 80 bar, the U-15 at.% Mo splat becomes powder consisting of elongated particles of 1–2 mm, revealing amorphous state.