Preparation of Ti-Cu-Ni-Si-B amorphous alloys with a large supercooled liquid region

A large supercooled liquid region exceeding 60 K before crystallization was found in a wide composition range of 15 to 20 at%Cu and 25 to 30 at%Ni for the Ti94-x-yCuxNiySi4B2 amorphous alloys which satisfy the three criteria of multi-components, significant atomic size ratios and negative heats of mixing. The glass transition temperature (T-g) and the reduced glass transition temperature (T-g/T-m) of the Ti50Cu20Ni24Si4B2 alloy are 742 K and 0.63, respectively. The high thermal stability of the supercooled liquid as well as the high reduced glass transition temperature enabled us to produce bulk amorphous alloys with a diameter of 1 mm by copper mold casting. The crystallization of the Ti50Cu20Ni24Si4B2 amorphous alloy takes place through a single exothermic reaction and the four phases of Cu4Ti3, CuTi, NiTi and TiB precipitate almost simultaneously. The crystallization mode requires the long-range atomic rearrangements of the constituent elements and the necessity seems to cause the increase in thermal stability of the supercooled liquid. The success of forming the bulk amorphous alloys in the Ti-Cu-Ni-Si-B system with lower densities is important for the future development of bulk amorphous materials with a higher specific strength.