Research Summary
Evidence of Mechanical Mixing During Ultrasonic Consolidation Utilizing Focused Ion Beam Milling and Transmission Electron Microscopy
Authors: Jennifer M. Sietins, John W. Gillespie, Jr., and Suresh G. Advani
What is ultrasonic consolidation?
• Ultrasonic Consolidation (UC) is a solid-state processing technique that can be used to weld metal foils together.
• Using a foil-fiber-foil method or prepreg tapes, metal matrix composite (MMC) structures can be fabricated through a layered build-up process.
• Metal foils are placed on top of a stationary anvil and a rotating horn travels the length of the foils.
• Three machine variables:
•• Applied normal force or load
•• Oscillation amplitude
•• Welding speed

Motivation
• Atomistic level microscopy has not been explored for ultrasonically consolidated samples and can provide more information regarding the UC bonding mechanisms.
• Diffusion in particular is a widely debated bonding mechanism due to the short weld times (<1 s) and low temperatures (< 0.5 Tmelting).
• Previous work has shown that x-ray energy dispersive spectroscopy (XEDS) in the Scanning Electron Microscopy (SEM) is not a valid technique to measure the short-scale diffusion during UC due to the interaction volume interference.
• Transmission electron microscopy (TEM) samples should provide more insight for diffusion and other potential bonding mechanisms since the weld zone is of the order of a few microns.
Procedure

Mechanical Mixing Evidence


Conclusions
Microstructural evidence of mechanical mixing has shown the dispersion of copper-rich fragments, subgrain formation at the interface, and phase transformations
Intermetallic compounds were identified through TEM XEDS
Acknowledgements
This work is supported by the Army Research Laboratory through the Composite Materials Research program.