Amorphous–nanocrystalline alloys: fabrication, properties, and applications

Owing to their unique mechanical and functional properties, both amorphous and nanocrystalline alloys have attracted extensive research interest over the past decades. However, in spite of the tremendous efforts dedicated to both kinds of alloys, their engineering applications are still hindered today because some fundamental issues, such as low thermal stability and poor ductility, are yet to be solved. To overcome these issues, one recent strategy proposed is to combine both amorphous and nanocrystalline structures in a single alloy through the use of either an amorphous or a nanocrystalline alloy as a "template". On the one hand, the derived amorphous–nanocrystalline alloys may inherit the unique properties from either the amorphous or the nanocrystalline "template", such as outstanding magnetic properties, extraordinary wear/corrosion resistance, and superior hardness and strength. On the other hand, these amorphous–nanocrystalline alloys also exhibit enhanced thermal stability and ductility, which are difficult to achieve for either the amorphous or the nanocrystalline alloy template. In this review article, we would like to first discuss a number of experimental methods developed to fabricate amorphous–nanocrystalline alloys, including partial crystallization in amorphous precursors, grain boundary amorphization, and physical vapor deposition. After that, we will give an overview of the mechanical and functional properties of the amorphous–nanocrystalline alloys. Finally, we will have a discussion on the existing applications of the amorphous–nanocrystalline alloys in various areas such as renewable and green energy, catalysis, and surface protection.