Research progress in U-based amorphous alloys

Abstract

Uranium-based amorphous alloys are a unique family of amorphous materials, which have so far been less studied due to the high chemical activity and radioactivity of uranium metal. In this paper, we review the compositions, preparations and thermal stability characteristics of U-based amorphous alloys obtained in the early experimental studies, and summarizes our recent results of the preparations and material properties of stable U-based amorphous alloys. The latest progress in our study of U-based amorphous alloys is presented in the three aspects. Firstly, the preparation methods, alloy systems and compositions, formation and crystallization behaviors of the new U-based amorphous alloys, along with the preliminary mechanisms for their formation and structure stabilization are reviewed. A number of new uranium-based amorphous alloy systems have been established based on eutectic law and structural packing model. These alloys show high ability to form glass, and the reduction of glass transition temperatures of some alloys to those of conventional amorphous alloys. The formation rules of binary (U-Fe/U-Co/U-Cr), ternary (U-Co-Al/U-Fe-Sn) and multicomponent alloy system have been investigated. It was found that the ability to form glass is strongly related to some physical parameters such as the local cluster structure, the electron concentration, the enthalpy of mixing, the electronegativity of the alloy component as well as the atomic size. The fragilities of U-based amorphous alloys indicate that they belong to a class of strong glass forming system, which means that the critical dimensions of such amorphous alloys can be further enhanced, and bulk amorphous samples are expected to be prepared. The crystallization activation of this kind of amorphous alloy is higher, and the crystallization process is dominated by nucleation. Then, the microstructures especially the first high-resolution electron microscopic results of the unique amorphous materials are reviewed. Finally, the micro-mechanical and anti-corrosion properties are reported in great detail. It is found that U-based amorphous materials show excellent mechanical properties and corrosion resistance, and the strength and hardness are much higher than those of conventional crystalline uranium alloys, and the corrosion resistance is also superior to the latter, which may be caused by its disorderly amorphous structural characteristics. Amorphous alloys have been the subject of intense fundamental and application research in recent years. Stable U-based amorphous alloys appear to cover all physical phenomena displayed by amorphous alloys. The discovery of outstanding properties in these new alloys therefore would stimulate both the fundamental studies including structure, electronic, glass transition, crystallization, etc., and the application-orientated studies of the thermal stability, mechanical and corrosion properties.