Phase transformations of ball-milled Nb50Zr10Al10Ni10Cu20 powders and the effect of annealing

A single amorphous phase of Nb50Zr10Al10Ni10Cu20 alloy owders was synthesized by milling the elemental alloying powders in an argon atmosphere, using a planetary ball mill operated at a rotation speed of 2.1 s(-1). During the early and intermediate stages of milling (43-360 ks) the atoms for alloying elements of Zr, Al, Ni and Cu migrated and diffused into the Nb (base material) lattice to form a supersaturated b.c.c. solid solution which transformed into an amorphous phase with the same composition upon post-annealing at 725 K for 7.2 ks in an argon atmosphere differential scanning calorimeter (DSC) (thermally enhanced solid-state amorphization, TESSA). As the milling time increases (360-540 ks), the powders are subjected to continuous defects and lattice imperfections that lead to a gradual change in the free energy so that the solid solution phase is transformed (mechanically enhanced solid-state amorphization, MESSA) to another metastable phase (amorphous). Towards the end of the milling processing time (720 ks), the b.c.c.-solid solution transformed completely into a single amorphous phase with the same composition. The crystallization temperature and the enthalpy change of crystallization for the obtained amorphous phase are 963 K and - 8.44 kJ mol(-1), respectively. (C) 2001 Elsevier Science BY All fights reserved.