Microstructural Engineering of Shape Memory Thin Films & Nanowires

Ainissa G. Ramirez, Yale University, DMR 0907090MotivationThin film shape memory alloys have garnered much attention as actuation materials for microelectromechanical systems (MEMS). Unfortunately, the as-deposited form of these films is amorphous and requires a high-temperature annealing step to create their actuating (crystalline) form. An understanding of the development of the microstructure during annealing enables researchers to make more informed decisions about processing conditions for specific properties. The aim of this work is to uncover the link between processing, properties, and structure for these materials.

Evolution of mechanical properties with crystallization in NiTi thin film metallic glasses X. Huang, J. San Juan, A. G. Ramirez; Scripta Materialia 63 (2010) pp. 16–19

Instrumented Indentation Approach for Elastic-Plastic Characterization of NiTi Thin Films Jiri Nohava, Xu Huang, Ainissa G. Ramirez, Bin Zhang, Thin Films 2010 Conference, Harbin, China (submitted)

Characterization and Prediction of Texture in Laser Annealed NiTi Shape Memory Thin Films G. Satoh, X. Huang, A.G. Ramirez, and Y.L. Yao, Journal of Manufacturing Science and Engineering (submitted)

Using nanoindentation on a film midway through crystallization allows us to examine the contribution of the amorphous and crystalline phases to the film’s mechanical properties. We find that structural relaxation is active and modifies the mechanical properties early in the crystallization process.

Broad Impact:

The aims of this research are to explore the impact of microstructure on properties. By using experimentally determined parameters for crystallization kinetics with TEM, we are able to tailor the microstructure (particularly the average grain size and the grain size distribution). By evaluating the properties of these tailored microstructures we can glean the impact of microstructure, in all of its subtleties, on properties. Such work extends our knowledge of the link between microstructure and properties by exploring the grain size character with greater precision. Our earliest work correlates microstructure with mechanical properties, and will be extended to other key properties.

Education:

•Revamped the Materials Science Laboratory by incorporating modern characterization techniques, such as AFM.

•Training: Dr. Xu Huang contributed largely to this work as did Henry Misas and Derek Zhao.

•Collaborations: Graduate students and their advisors at Columbia and NRL also contributed to this work.

Outreach:

•Directed and hosted the award-winning science lecture series for kids called Science Saturdays (www.sciencesaturdays.org ). Three science lectures with attendances of over 200 people occur each semester.

•Served as a science advisor for the American Film Institute (AFI), by helping screenwriters add more accurate science to their projects. (www.afi.com/education/conservatory/sloanprogram.aspx)

•Serves as an advisor to the NISE Network (Exploratorium /Boston/Minnesota); serves as an advisor NOVA/WGBH’s Making Stuff televison program.

28 Oct. 10

Microstructural Engineering of Shape Memory Thin Films & Nanowires

Ainissa G. Ramirez, Yale University, DMR 0907090