Formation, microstructure and mechanical properties of ductile Zr-rich Zr–Cu–Al bulk metallic glass composites

We examined the microstructure, phase stability, mechanical properties and deformation behaviors of cast (Zr0.58Cu0.42)100-xAlx (x = 0, 3, 5, 7, 10) bulk metallic glass composites (BMGCs). With increasing Al content, the glass-forming ability of the new Zr-rich Zr–Cu–Al alloys gradually increases, enabling the fabrication of BMGCs for the alloys containing more than 3 at.% Al. The as-cast structure changes from Cu10Zr7 + CuZr2 for the Al-free base alloy to glass + crystal for the Al-added alloys. The new Zr-rich Zr–Cu–Al BMGCs exhibit a large fracture strain of ∼3.4–7.8% and a high fracture strength of ∼1731–1984 MPa under compression. The compressive fracture strain of Zr-rich Zr–Cu–Al alloys can be explained by the percolation theory. The (Zr0.58Cu0.42)95Al5 composite containing ∼70 vol.% crystalline phase possesses the largest plastic strain of ∼6%, and fracture strength of over 1900 MPa under compressive condition. The superior plastic deformation capability under compression is related to the following factors: (1) The formation of three types of shear bands with distinct morphological characteristics, (2) the plastic deformation of B2–CuZr phase itself, together with stress-induced martensitic transformation from B2–CuZr phase to B19’ phase, and (3) the interaction between crystals and shear bands. The present results have implications for better understanding the deformation mechanisms of the Zr-rich Zr–Cu–Al BMGCs and for designing high-performance BMGCs with enhanced plasticity.