Crystallization behavior and stability of ZrTiCuNiBe glasses

Bulk metallic glasses of the ZrTiCuNiBe type can be produced from the liquid melt at comparative low cooling rates. During solidification primary crystals in the glass can be formed. Their amount, size and morphology depends on the cooling rate, production parameters and on small variations of the composition of the alloy. In order to investigate the constitutional origin for the primary crystal formation and the crystallisation of these glasses the morphology, composition and structure of the crystalline equilibrium phases of two different alloys, Zr41Ti14Cu12.5Ni10Be22.5 (VI) and Zr46.8Ti8.2Cu7.5Ni10Be27.5 (V4), were investigated by means of SEM, energy dispersive X-ray analysis (EDX) in SEM and TEM, and the microdiffraction technique in TEM. Several phases were identified and characterized, including an orthorhombic phase of the Be2Zr type, a tetragonal phase of the CuZr2 type, and a Be rich complicated cubic phase. From the microstructure the crystallization sequence was deduced. The composition of all these phases differs' considerably from the nominal alloy composition. The equilibrium phases are compared with the crystalline phases formed during production and during annealing of the glass. The results are discussed using a description of the ZrTiCuNiBe alloy by a quasi-ternary (Zr,Ti)-(Cu,Ni)-Be system.