Structures and properties of a Zr-based bulk glass alloy after annealing

A bulk glass Zr52.5Ni14.6Al10Cu17.9Ti5 alloy with 6 mm diameter is prepared by pre-melting sponge zirconium together with other pure metal elements and followed by injecting cast. In the samples, the content of oxygen is chemically analyzed in the level of 706 ppm (atomic concentration), which significantly affects the crystallization and the microstructure. When the bulk glass samples are annealed at the temperature far below the crystallization temperature(Tx), the predominant phases of Zr2Ni0.67O0.33 and Zr2Ni compounds crystallize and uniformly distribute on glass matrix. These predominant phases will grow and join together to form net-shape phase when the annealed temperature is in the range of Tx to above Tx. The glass matrix phase separated by the net-shape phase into the size of about 25 μm at 703 K to 15 μm at 823 K almost fully transforms into Zr2Ni and a small amount of Zr2Cu and Zr4Al3. At annealing temperatures far above Tx, Zr2Cu and Zr4Al3 compounds crystallize by phase separation to form nanostructure with nano-scale phases of Zr2Cu and Zr4Al3 compounds distributed on the matrix of Zr2Ni. The micro-compressive tests by Nanoindenter II reveal that the bulk glass phase has a lower elastic modulus and lower microhardness. Increasing the annealing temperature, the modulus and microhardness for the crystallized microstructure increase. With the phase separation taking place, the modulus and microhardness for the nanostructure are improved slightly. But the different deformational mechanism between micro-scale and bulk specimens is unknown.