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In-situ Observations of Martensitic Transformation in Pure Ti Thin Films using the Dynamical Transmission Electron Microscope (DTEM)

Published online by Cambridge University Press:  26 February 2011

Thomas Bradley LaGrange
Affiliation:
lagrange2@llnl.gov, Lawerence Livermore Natioan Laboratory, Chemistry and Materials Science, Materials Science and Technology Division, 7000 East Avenue, P.O. Box 808, Mail Stop, L-353, Livermore, CA, 94550, United States, (925) 454-0713
Geoffrey H. Campbell
Affiliation:
campbell7@llnl.gov
Jeffrey D. Colvin
Affiliation:
colvin5@llnl.gov
Wayne E. King
Affiliation:
weking@llnl.gov
Nigel D. Browning
Affiliation:
browning20@llnl.gov
Michael R. Armstrong
Affiliation:
armstrong30@llnl.gov
Bryan W. Reed
Affiliation:
reed12@llnl.gov
Judy S. Kim
Affiliation:
kim46@llnl.gov
Brent C. Stuart
Affiliation:
stuart3@llnl.gov
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Abstract

We have measured the transient events of the α-β martensitic transformation in nanocrystalline Ti films via single shot electron diffraction patterns with 1.5 ns temporal resolution. This was accomplished with a newly constructed dynamic transmission electron microscope (DTEM), which combines pulsed laser systems and pump-probe techniques with a conventional TEM. The DTEM thereby enables studies of transformations that are (1) far too fast to be captured by conventional bulk techniques, and (2) difficult to study with current ultrafast electron diffraction (UED) instruments (which typically require an accumulation of multiple shots for each diffraction pattern). Martensitic transformations in nanocrystalline materials meet both criteria, with their rapid nucleation, characteristic interface velocities ∼1 km/s, and significant irreversible microstructural changes. Free-standing 40-nm-thick Ti films were laser-heated at a rate of ∼1010 K/s to a temperature above the 1155 K transition point, then probed at various time intervals with a 1.5-ns-long intense electron pulse. Diffraction patterns show an almost complete transition to the β phase within 500 ns. Post-mortem analysis (after the sample is allowed to cool) shows a reversion to the α phase coupled with substantial grain growth, lath formation, and texture modification. The cooled material also shows a complete lack of apparent dislocations, suggesting the possible importance of a "massive" short-range diffusion mechanism.

Type
Research Article
Copyright
Copyright © Materials Research Society 2006

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