The irradiation of metallic glasses to induce nanocrystallization was studied in
two metallic glass compositions, Cu50Zr45Ti5 and Zr55Cu30Al10Ni5. Atomic mobility
was described using a model based on localized excess free volume due to displace-
ment cascades created by energetic particle irradiation. Due to the di erence in
cascade size among di erent masses of projectiles, a mass-dependent study was per-
formed. Metallic glass ribbon samples produced by melt-spinning were bombarded
with electron, He, Ar, and Cu particles. Electron irradiation and characterization
was performed "in-situ" by means of transmission electron microscopy. The di erent
metallic glasses showed dissimilar levels of radiation stability under electron irradi-
ation by Cu50Zr45Ti5 forming crystals 1-10 nm in diameter embedded in the amor-
phous matrix after about 30 minutes of irradiation, while Zr55Cu30Al10Ni5 showed no
such crystallization. Increasing projectile mass caused an increase in the maximum
nanocrystal diameter up to approximately 100 nm in Cu irradiated Zr55Cu30Al10Ni5.
Studies of di raction patterns of irradiated specimens showed nucleation of Cu10Zr7
phases in both specimens, as well as evidence of CuZr2 in Cu50Zr45Ti5 and both CuZr2
and NiZr2 in Zr55Cu30Al10Ni5. Crystal sizes in irradiated Zr55Cu30Al10Ni5 specimens
showed bimodal distribution with many large (50-100 nm) crystals and many small
(1-5 nm) crystals. The small crystals in irradiated Zr55Cu30Al10Ni5 were determined
to be NiZr2 phase because of the low abundance of Ni. After exposure to 2 keV Ar ions, areas of composition roughly Cu10Zr7 were found by energy-dispersive X-ray
spectroscopy but no crystallization was found. Further crystallization was achieved in
decomposed specimens after electron irradiation. This shows that atomic segregation
is a necessary step before nucleation in metallic glasses.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-08-7017 |
| Date | 14 January 2010 |
| Creators | Carter, Jesse |
| Contributors | Shao, Lin |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation |
| Format | application/pdf |
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