Microstructural Modification of NiTi Shape Memory Alloys and Biodegradable
By controlling the thermal evolution resulting
from laser irradiation, for both melt-mediated and solid phase processes,
spatial control over traditional properties such as mechanical, electrical
and thermal, in addition to so-called non-traditional material responses
such as biodegradability and shape memory responses may be realized.
Melt-mediated Laser Crystallization of NiTi
Shape Memory Alloys
This work proposes the use of pulsed,
melt-mediated laser crystallization techniques to control the spatial
distribution of crystalline zones within an amorphous matrix. Since shape
memory responses stem from crystallographic shifts, only the selectively
crystallized regions will exhibit these properties. This process provides
not only spatial control over the shape memory response, but through proper
use of operational parameters, has the potential for tailoring the shape
memory response itself, i.e. phase transformation temperature,
transformation strain, recovery stress etc.
The use of a melt-mediated process also provides
several advantages over homogenous furnace annealing as well as CW, solid
phase techniques. These include increased efficiency for large scale
fabrication due to single shot batch processing capabilities (i.e. no
rastering), increased control over the resulting microstructure, and
features with sharp boundaries due to low pulse duration to thermal
diffusivity time scales.