Ti/Zr/Hf Quasicrystals and Crystal Approximants
Quasicrystals are highly ordered, yet nonperiodic, metallic phases.
First discovered in 1984, this novel phase has been reported in a wide
range of aluminum and titanium - 3d transition metal (TM), and aluminum-rare
earth (RE) alloys. Early studies in this group established the similarity
between the local atomic structures of Al-based quasicrystals and corresponding
amorphous phases, and demonstrated that the different periodicities of
the decagonal phases could be explained by an interpenetrating stacking
of fundamental icosahedral clusters.Since 1988, attention has increasingly
focused on the Ti/Zr-based quasicrystals, which, while similar in many
ways to the Al-based ones, show some important differences. The Ti-TM-Si
quasicrystals are metastable, produced only by rapid quenching, are extremely
disordered, and require large amounts of oxygen to form. In contrast,
Ti-Zr-Ni phases are well ordered and stable, produced by relatively low
temperature annealing, nearly 300oC below the melting temperature.
Notable accomplishments in this research group include:
-
The first quantitative estimates of the interfacial energy between a quasicrystal
and a metallic glass, demonstrating the strong similarities in the local
structures of quasicrystals and undercooled liquids and glasses.
-
The discovery of all known Ti-3d transition metal-Si-O (Ti-TM-Si-O) quasicrystals
and a demonstration of the critical role played by oxygen on the formation
of the quasicrystals and related complex crystal phases, called crystal
approximants.
-
The first determination of the atomic structure of the 1/1 approximant
in Ti-Cr-Si-O, a(TiCrSiO), showing that it is
a bcc packing of MacKay icosahedra.
-
The discovery of the only stable non-aluminum-based quasicrystal, Ti41.5Zr41.5Ni17,
and the demonstration that is currently the only viable candidate for a
ground-state quasiperiodic phase.
-
The first realistic determination of the structure for any Ti/Zr-based
quasicrystal for Ti41.5Zr41.5Ni17.
-
The discovery of the growth of the icosahedral phase from the liquid phase
in Ti/Zr-Ni21 alloys.
-
The discovery of a nearly pure 3/2 rational approximant phase in a rapidly
quenched Ti-Hf-Ni alloy.
List of recent publications:
Coming soon...
Back to Materials Physics
Research Home
webpage created by: Van T. Huett email:
vthuett@artsci.wustl.edu
Last Updated: 11/7/01