Quasicrystal formation in Zr-Cu-Ni-Al-Ta metallic glasses and composites

Abstract

We have examined the crystallisation behaviour of Zr-Cu-Ni-Al-Ta metallic glasses and metallic-glass-matrix composites. Monolithic and composite alloys were prepared by varying the amount of Ta added to a Zr-based glass-forming alloy. We find that additions as low as 2 at.% Ta promotes the formation of the icosahedral phase during devitrification, which in turn has a significant effect on the subsequent crystallisation behaviour. The DSC and time-resolved X-ray scattering results show that following the nucleation of the quasicrystals the alloys exhibit an exothermic event that does not correspond to any discernible structural change. We discuss the possible mechanisms for the second exotherm.

Acknowledgments

This work was supported by the U.S. Department of Energy through the following contracts: The in situ high-energy XRD work and data analysis were supported under Contract No. W-7405-ENG-82 at Iowa State University. The high-energy XRD work was performed at the MUCAT sector of the Advanced Photon Source (Contract No. W-31-109-ENG-38). The ex situ diffraction and calorimetry work at Johns Hopkins University were supported under grant DE-FG02-98ER45699.