Friday, October 3rd.
Thesis Committee:
Prof. Kevin Hemker (MechE/MSE)
Prof. Jonah Erlebacher (MSE)
Prof. Jaafar El-Awady(MechE)
Dr. Michael Brupbacher (JHU/APL)
Dr. Melissa Terlaje (JHU/APL)
Alternates:
Prof. Ryan Hurley (MechE)
Prof. Regina Garcia-Mendez (MSE)
Zoom Information:
https://JHUBlueJays.zoom.us/j/97644837394?pwd=8XFNDfMyAa9bgyWADKNyVU2o970jks.1
Meeting ID: 976 4483 7394
Passcode: 101367
Abstract: Liquid Metal Dealloying of an Additively Manufactured Niobium-Titanium Alloy
Liquid metal dealloying (LMD) has emerged as a method of producing microporous metals, expanding the previously limited alloy systems that can be made by traditional dealloying techniques. The rise in additive manufacturing (AM) has enabled the creation of unique geometries previously unrealized via conventional processing methods. Laser powder bed fusion (LPBF), one of the most mature of the metal AM technologies, has become widely adopted in many industries from aerospace to biomedicine. This study focuses on the combination of these two processes to create structures with a macroporous LPBF Nb40Ti60 skeleton and a functional microporous surface created via LMD in a pure Cu bath.
To understand the fundamental differences between LMD of conventionally processed metals and LPBF alloys, several key elements were investigated: surface chemistry and topography, part geometry, and underlying microstructure. The increased surface roughness inherent to as-built LBPF surfaces, both normal and parallel to the build direction, were found to increase the dealloying thickness. However, widespread chemical contamination and oxidation from electrical discharge machining, a common method of removing parts from the AM build plate, was found to drastically slow the dealloying rate. The individual ligament and channel structures were unaffected by the starting surface topography but varied along the depth of the sample. The effects of part geometry were also investigated. Some features (e.g. curvature and through holes) had no effect on the dealloying behavior, while others (e.g. mass, concavity, and blind hole depth) changed the dealloying rate through different mechanisms. Finally, microstructural effects were studied. The high solidification rates of the LPBF process led to a small grain size, causing enhanced grain boundary effects and accelerated dealloying, but at the cost of structural stability. Many of these findings can be applied to conventionally processed metals, but taken as a whole, the lessons learned in this study serve to highlight the complexities of the liquid metal dealloying of additively manufactured alloys.