• Hutchinson, Christopher
• Gibson, Mark
• Kimpton, Justin
• Sun, W. W.
• Styles, Mark
• East, Daniel

Abstract

Glassy metals exhibit a range of interesting properties including high strength and corrosion resistance, but often have poor toughness and tensile ductility in the fully amorphous state. Recently it has been shown that desirable combinations of properties can be achieved by the partial crystallisation of glass-forming alloys, either during controlled solidification or by annealing a fully amorphous glass. The aim of this investigation is to understand the competition in phase formation during the crystallisation of metallic glasses in the Al-Ni-Y system. High-resolution, in situ synchrotron powder diffraction has been used to quantitatively follow the evolution of phases in 5 different alloys between Al87Ni9Y4 and Al75Ni15Y10, as they were continuously heated to melting and subsequently cooled. Upon heating, the first crystallisation product was found to vary from FCC Al to the intermetallic Al9Ni2 phase with increasing Ni concentration, while the crystallisation sequence also changed from a two-stage to a three-stage process. High number densities of crystallites (~1023 m-3) were observed initially for both phases. Upon cooling, the partially disordered Al9Ni3Y phase was found to form preferentially over the intermetallic phases observed during heating. The differences in phase formation during heating and cooling are discussed in terms of the nucleation barriers predicted by thermodynamic calculations. The role of possible compositional heterogeneities in the as-quenched glasses is also discussed.

Topics

• impedance spectroscopy
• amorphous
• corrosion
• phase
• glass
• glass
• strength
• forming
• annealing
• intermetallic
• ductility
• solidification