The Crystallization of Niti Shape Memory Thin Films
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Date: 04-20-2006
Start Time:
10:00am
End Time: 11:00am
Speaker: Ainissa G. Ramirez
From:
Yale University
Location: 233 Mudd
Hosted by:
Center for Integrated Science
Abstract:
Shape memory alloys (such as NiTi) have fascinated scientists for their
ability to “remember” their original shape when heated. This change is
base on a martensitic phase transformation from one crystal structure
to another. Their thin-film embodiment has drawn much attention because
of their potential use as actuation materials in microelectromechanical
systems (MEMS). NiTi thin films are commonly sputtered in an amorphous
form and require a high-temperature crystallization step to create
their crystalline (actuating) form. The crystallization process is
driven by nucleation and growth and is highly dependant on temperature.
We have studied the crystallization process using in situ heating
transmission electron microscopy methods. This talk will present our
observations and a quantitative description of the crystallization
kinetics using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory. Our
approach of coupling our experimental observations with the JMAK theory
has rendered us able to predict the microstructure (particularly, the
average grain size) over a broad range of temperatures. It has been
found that the resulting microstructures control the martensitic
transformation behavior and the films associated actuation properties.
Such insights can contribute to the development of materials with
optimal (actuation) properties.
Ainissa G. Ramirez, Ph.D. is an Assistant Professor of Mechanical
Engineering at Yale University. Her work focuses on the development of
thin film NiTi shape memory alloys for microelectromechanical systems
(MEMS). Dr. Ramirez received her training in materials science and
engineering at Brown University (Sc.B.) and Stanford University
(Ph.D.). She worked as a member of technical staff at Bell
Laboratories, Lucent Technologies in Murray Hill, NJ for 4 years before
joining the faculty at Yale in 2003. She has been awarded MIT’s TR100
Young Innovators Award, the Sloan Research Fellowship, and the NSF
CAREER award. She has written over 25 technical articles and holds 6
patents. Dr. Ramirez is also a leader in science education and serves
as an advisor to the Liberty Science Center (Jersey City, NJ) and the
Exploratorium (San Francisco, CA). At Yale, she is the director of the
award-winning science lecture series for children called, Science
Saturdays. She sits on the board of directors for the Connecticut
Academy for Education.