Formation of Cu-Zr-Al bulk metallic glass composites with improved tensile properties

The dependence of microstructure on the alloy composition and cooling rate of a series of (Zr_0.5Cu_0.5)_100-xAl_x (x = 1, 2, 3 , ... , 10 at.%) alloys was investigated in detail and explained in the framework of time-temperature-transformation diagrams. The relationship between the microstructures of bulk metallic glass (BMG) composites and their mechanical properties was characterized systematically. It was found that the addition of aluminum can promote the formation of the metastable austenitic CuZr phase, and composite structures with B2-CuZr particles can be formed in alloys containing 3-8% Al. Both the volume fraction and distribution of the reinforced B2 phase could greatly affect the deformation behavior, and the BMG composites with homogeneously distributed single B2-CuZr phase exhibited stable tensile ductility. Analysis indicates that the B2-CuZr austenite transformed into the B19′ martensite during deformation (i.e., stress-induced martensitic transformation), which accounts for the observed superior mechanical properties of the current BMG composites.