Relaxation and crystallization behavior of the Zr50Cu40Al10 metallic glass

We examined relaxation and crystallization behavior of the ternary Zr50Cu40Al10 metallic glass by using positron annihilation and transmission electron microscopy (TEM). Observed changes in positron annihilation lifetime of the alloy annealed isothermally at 673 K, which is below the glass transition temperature, correlate well with observed density changes; while coincidence Doppler broadening (CDB) spectra exhibit no significant change. These observations demonstrate that free volume decreases without a rearrangement of atoms during structural relaxation. On the other hand, CDB spectrum has exhibited considerable changes when the same alloy was annealed at 773 K. TEM observations suggested that crystallization occurs via growth of spherulites of several hundred urn in diameter, which themselves are composed of radially grown grains. Chemical analysis revealed that Cu atoms are partitioned out during the growth of the spherulites. Diffraction study indicated that the unit cell of the crystalline phase belong to an orthorhombic system with a = 0.892, b = 0.550, and c = 1.060 nm; while remaining interspherulite regions are found to crystallize into an fcc phase with a = 1.28 nm, which is probably isostructural to the T3 phase.