New methods for controlling twin configurations and characterizing twin boundaries in 5M Ni-Mn-Ga for the development of applications
Smith, Aaron R. (2015-06-10)
Väitöskirja
Smith, Aaron R.
10.06.2015
Lappeenranta University of Technology
Acta Universitatis Lappeenrantaensis
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-265-808-1
https://urn.fi/URN:ISBN:978-952-265-808-1
Tiivistelmä
Traditional methods for studying the magnetic shape memory (MSM) alloys Ni-Mn-Ga
include subjecting the entire sample to a uniform magnetic field or completely actuating
the sample mechanically. These methods have produced significant results in
characterizing the MSM effect, the properties of Ni-Mn-Ga and have pioneered the
development of applications from this material.
Twin boundaries and their configuration within a Ni-Mn-Ga sample are a key
component in the magnetic shape memory effect. Applications that are developed
require an understanding of twin boundary characteristics and, more importantly, the
ability to predictably control them. Twins have such a critical role that the twinning
stress of a Ni-Mn-Ga crystal is the defining characteristic that indicates its quality and
significant research has been conducted to minimize this property.
This dissertation reports a decrease in the twinning stress, predictably controlling the
twin configuration and characterizing the dynamics of twin boundaries. A reduction of
the twinning stress is demonstrated by the discovery of Type II twins within Ni-Mn-Ga
which have as little as 10% of the twinning stress of traditional Type I twins.
Furthermore, new methods of actuating a Ni-Mn-Ga element using localized
unidirectional or bidirectional magnetic fields were developed that can predictably
control the twin configuration in a localized area of a Ni-Mn-Ga element.
This method of controlling the local twin configuration was used in the characterization
of twin boundary dynamics. Using a localized magnetic pulse, the velocity and
acceleration of a single twin boundary were measured to be 82.5 m/s and 2.9 × 107 m/s2,
and the time needed for the twin boundary to nucleate and begin moving was less than
2.8 μs. Using a bidirectional magnetic field from a diametrically magnetized cylindrical
magnet, a highly reproducible and controllable local twin configuration was created in a
Ni-Mn-Ga element which is the fundamental pumping mechanism in the MSM
micropump that has been co-invented and extensively characterized by the author.
include subjecting the entire sample to a uniform magnetic field or completely actuating
the sample mechanically. These methods have produced significant results in
characterizing the MSM effect, the properties of Ni-Mn-Ga and have pioneered the
development of applications from this material.
Twin boundaries and their configuration within a Ni-Mn-Ga sample are a key
component in the magnetic shape memory effect. Applications that are developed
require an understanding of twin boundary characteristics and, more importantly, the
ability to predictably control them. Twins have such a critical role that the twinning
stress of a Ni-Mn-Ga crystal is the defining characteristic that indicates its quality and
significant research has been conducted to minimize this property.
This dissertation reports a decrease in the twinning stress, predictably controlling the
twin configuration and characterizing the dynamics of twin boundaries. A reduction of
the twinning stress is demonstrated by the discovery of Type II twins within Ni-Mn-Ga
which have as little as 10% of the twinning stress of traditional Type I twins.
Furthermore, new methods of actuating a Ni-Mn-Ga element using localized
unidirectional or bidirectional magnetic fields were developed that can predictably
control the twin configuration in a localized area of a Ni-Mn-Ga element.
This method of controlling the local twin configuration was used in the characterization
of twin boundary dynamics. Using a localized magnetic pulse, the velocity and
acceleration of a single twin boundary were measured to be 82.5 m/s and 2.9 × 107 m/s2,
and the time needed for the twin boundary to nucleate and begin moving was less than
2.8 μs. Using a bidirectional magnetic field from a diametrically magnetized cylindrical
magnet, a highly reproducible and controllable local twin configuration was created in a
Ni-Mn-Ga element which is the fundamental pumping mechanism in the MSM
micropump that has been co-invented and extensively characterized by the author.
Kokoelmat
- Väitöskirjat [1036]