Zr-Rich Zr-Al-Ni-Ag Metallic Glass Composites with High Strength and Plastic Strain

The glass-forming ability (GFA), thermal stability and mechanical properties of new Zr-rich Zr70-76Al7-7.5Ni15-20Ag2-2.5 alloys are assessed. Melt-spinning gives a glass (G) for 70-74 at%Zr and [G + beta-Zr + omega-Zr] phases for 76 at%Zr. Crystallization occurs in stages: G -> [G + icosahedral quasicrystal (IQ)] -> [Zr2Ni + Zr2Ag + Zr5Al3] for 70Zr, G -> [G + IQ + beta-Zr + omega-Zr] -> [alpha-Zr + Zr2Ni + Zr2Ag + Zr5Al3] for 72Zr, and G -> [G + beta-Zr + omega-Zr] -> [beta-Zr + omega-Zr + Zr2Ni + Zr2Ag] -> [alpha-Zr + Zr2Ni + Zr2Ag + Zr5Al3] for 74-76Zr. Annealed ribbons with G, [G + IQ] or [G + beta-Zr + omega-Zr] phases have good bending plasticity. The IQ and [beta-Zr + omega-Zr] phases are spheroidal with diameters 15-28 and 20-35 nm, respectively. As-cast 1.5-mm-diameter rods contain a single glassy phase for 70-72Zr and [G + beta-Zr + omega-Zr] phases for 74-76Zr. The rods exhibit high strength and plastic strain: 1499 MPa & 6.3% for 70Zr, 1475 MPa & 9.2% for 72Zr, 1458 MPa & 3.8% for 74Zr, and 1610 MPa & 2.7% for annealed 70Zr with [G + IQ] phases, respectively. These plastic strains exceeding 2% are unprecedented for [G + IQ] and [G + beta-Zr + omega-Zr], indicating strengthening by precipitate dispersions. The formation of plastic [G + IQ] and [G + beta-Zr + omega-Zr] bulk composites is expected to increase the engineering importance of Zr-based BMGs.