In-situ Studies of the Martensitic Transformation in Ti Thin Films using the Dynamic Transmission Microscope (DTEM)

Conference · Mon Nov 21 04:00:00 EST 2005

OSTI ID:928203

LaGrange, T B; Campbell, G H; Colvin, J D; King, W E; Browning, N D; Armstrong, M R; Reed, B W; Kim, J S; Stuart, B C

The {alpha} to {beta} transition in pure Ti occurs mainly by a 'martensitic type' phase transformation. In such transformations, growth rates and interface velocities tend to be very large, on the order of 10{sup 3} m/s, making it difficult to observe the transformation experimentally. With thin films, it becomes even more difficult to observe, since the large surface augments the nucleation and transformation rates to levels that require nanosecond temporal resolution for experimental observations. The elucidation of the transformational mechanisms in these materials yearns for an apparatus that has both high spatial and temporal resolution. We have constructed such an instrument at LLNL (the dynamical transmission electron microscope or DTEM) that combines pulsed lasers systems and optical pump-probe techniques with a conventional TEM. We have used the DTEM to observe the transient events of the {alpha}-{beta} transformation in nanocrystalline Ti films via single shot diffraction patterns with 1.5 ns resolution. With pulsed, nanosecond laser irradiation (pump laser), the films were heated at an extreme rate of 10{sup 10} K/s. was observed At 500 ns after the initial pump laser hit, the HCP, alpha phase was almost completely transformed to the BCC, beta phase. Post-mortem investigations of the laser treated films revealed that substantial grain growth occurred and lath microstructure, containing no apparent dislocations. The lack of dislocations may indicate that the {alpha} to {beta} transformation may also proceed by a 'massive' type mechanism (short range diffusion).

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 928203
• Report Number(s): UCRL-PROC-217255
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
DIFFRACTION
DIFFUSION
DISLOCATIONS
ELECTRON MICROSCOPES
GRAIN GROWTH
IRRADIATION
LASERS
LAWRENCE LIVERMORE NATIONAL LABORATORY
MICROSCOPES
MICROSTRUCTURE
NUCLEATION
PHASE TRANSFORMATIONS
RESOLUTION
THIN FILMS
TRANSFORMATIONS
TRANSIENTS