MSE Seminar: Matthew Bowers, Characterization of transformation-induced defects in nickel titanium shape memory alloys

Ph.D. Candidate advised by Dr. Michael Mills

All dates for this event occur in the past.

264 MacQuigg Labs
105 W. Woodruff Ave.
Columbus, OH 43210
United States

Abstract

Shape memory alloys have remarkable strain recovery properties that make them ideal candidates for many applications that include devices in the automotive, aerospace, medical, and MEMS industries.  Although these materials are widely used today, their performance is hindered by poor dimensional stability resulting from cyclic degradation of the martensitic transformation behavior.  This functional fatigue results in decreased work output and cyclic accumulation of permanent strain.  To date, few studies have taken a fundamental approach to investigating the interaction between plasticity and martensite growth and propagation, which is vitally important to mitigating functional fatigue in future alloy development.  The current work focuses on understanding the interplay of these deformation mechanisms in NiTi-based shape memory alloys under a variety of different thermomechanical test conditions.  Micron-scale compression testing of NiTi single crystals is undertaken to observe the defect content generated by a single martensite plate.  Scanning transmission electron microscopy (STEM) defect analysis is coupled with micromechanics-based modeling of local stresses to explain the observed defect substructure.  Thermal cycling of bulk polycrystalline NiTi is done for a mechanistic comparison between stress-induced and thermally-induced martensite.

 

Bio

Matthew graduated in 2009 from John Carroll University with a B.S. in Engineering Physics.  While at John Carroll, he performed research on the effect of temperature and hydrostatic pressure on the transport properties of dilute magnetic semiconductors with Dr. Jeff Dyck.  Since September 2009, he has been pursuing a Ph.D. in Materials Science and Engineering under the supervision of Dr. Mike Mills studying the mechanical behavior and underlying deformation mechanisms in shape memory alloys.  In the fall, he will start a post doctoral research position at the National Center for Electron Microscopy at Lawrence Berkeley National Lab.  When he's not piloting a TEM, Matthew enjoys playing guitar, brewing beer, and rock climbing.