Under a $500,000 grant from the National Science Foundation, engineers at the University of Pittsburgh will use the Dynamic Transmission Electron Microscope (DTEM) at Lawrence Livermore National Laboratory (LNLL) to observe rapid phase transitions in aluminum alloys under laser and electron-beam processing. The study is expected to deliver valuable data and computer-modelling capabilities to the metal-additive manufacturing industry.
Characteristic to transmission electron microscopes (TEMs), the DTEM allows scientists to observe objects to near atomic level, down to the order of a few angstroms. Synonymous to the way light microscopes observe scales limited by the wavelength of the photons in that particular light spectrum, a person can use a TEM to view objects as small as the wavelength of an electron. (The De Broglie wavelength of an electron at 1-eV kinetic energy is about 1.23 nm, while a photon's wavelength in the visible-light spectrum is much bigger, ranging between 400 and 700 nm.)
Perhaps the most outstanding feature of the DTEM, though, is its high temporal resolution. While scientists are better inclined to determine the beginning and end products of catalytic and multistep reactions, they often remain ambivalent about the state of reactants during intermediate steps. With nanosecond and microsecond temporal resolution, the DTEM will enable the university’s engineering students to observe various rapid transitions of aluminum alloys during welding, joining, and other processes.
Joe McKeown, LLNL materials scientist, explains, "DTEM allows you to see the interface between the solid and liquid during rapid solidification, which is extremely hard to do."
Students will begin to use the DTEM at LLNL this fall. "Prior to the advent of the DTEM, we could only simulate these transformations on a computer," Wiezorek said in a news release. "We hope to discover the mechanisms of how alloy microstructures evolve during solidification after laser melting by direct and locally resolved observation."
For more information about LLNL’s DTEM, download the article “A Bright Idea for Microscopy” (PDF file).
