Radiation Induced Nanocrystal Formation in Metallic Glasses

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Title: Radiation Induced Nanocrystal Formation in Metallic Glasses
Author: Carter, Jesse
Abstract: 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 .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2009 -08 -7017
Date: 2010-01-14


Radiation Induced Nanocrystal Formation in Metallic Glasses. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2009 -08 -7017 .

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