Dissertation Defense: Joy Morin

Title: Experimental Analysis of Oxidation Formation During Material Extrusion of Magnetostrictive Terbium-Iron-Dysprosium Films

Program: Materials Science and Engineering PhD

Committee Chair: Zhangxian Deng

Committee: Zhangxian Deng, Eric Jankowski, Dave Estrada, Bob Fox

Abstract: Magnetostrictive terbium–iron–dysprosium alloys, commonly known as Terfenol-D, deform in response to magnetic fields and exhibit changes in magnetization under mechanical stress. This instantaneous magneto-mechanical coupling enables the generation and detection of various acoustic waveforms for structural health monitoring. However, the use of Terfenol-D in acoustic transducers is limited by integration challenges and its susceptibility to oxidation during manufacturing.

The objective of this research is to develop a comprehensive additive manufacturing process for magnetostrictive Terfenol-D while minimizing material oxidization, and to gain an understanding of how the printed Terfenol-D oxidizes in neutron radiation. First, an ink composed of Terfenol-D nanoparticles with a predominant particle size of approximately 155 nm was synthesized via high-energy ball milling and printed onto metal substrates using a commercial material extrusion (MEX) system. The printed samples exhibited approximately 3 wt.% oxidation when stored in an inert environment, indicating that oxidation was negligible before sintering. Second, the as-printed samples were thermally sintered in a tube furnace under a forming-gas atmosphere, followed by neutron irradiation for up to 6 days in the Ohio State University Research Reactor. Significant oxidation occurred during sintering, with subsequent irradiation promoting further oxide formation and amorphization. Finally, oxidation during thermal sintering was investigated using vacuum, glovebox, and turbo vacuum furnaces, as well as electric field-assisted sintering (EFAS). EFAS achieved strong film–substrate bonding, while turbo vacuum sintering showed promise in reducing oxide formation.

This work demonstrates a MEX-based route for fabricating magnetostrictive thin films, expands the additive manufacturing material library, and provides insights into oxidation behavior and strategies for mitigating oxidation during Terfenol-D processing.