|
         |
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.
Laser surface modification of semi-crystalline polymers Crystallinity of semi-crystalline polymers affects their degradation and physical properties. Laser surface treatment at varying fluences can be used to spatially control the generation of a polymer surface with an altered degree of crystallinity. These structures structure have applications for time released drug delivery. Rapid surface melting due to high laser quench rates contribute to an overall reduction in crystallinity. Partial melting may be an important contributory factor. Laser surface treatment can potentially allow for an automated process that can spatially control the surface morphology and hence degradation associated with a different crystallinity at the surface.
|