A Novel Processing Route for the Manufacture of Mg with Controlled Cellular Structure.
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
Cellular metals are a relatively new class of engineering materials that can be fabricated with either a random or controlled cellular structure. A controlled cellular structure allows the precise control of the pore geometry and hence subsequent material properties that can be important for some applications such as orthopathic implants. Recently the interest in using magnesium (Mg) as a biodegradable implant in the body has been growing rapidly. However, current methods for fabricating cellular magnesium typically results in a random arrangement of the cellular structure. A novel processing method is developed for the preparation of cellular metals with controlled open-cellular architectures. In particular, this process has been developed for magnesium due to the difficulties associated with powder processing. The fabrication routine utilises a multistage inverse templating technique implemented with assistance of a rapid prototyping (RP) technique. Rapid prototyped polymer performs of desired architectures were infiltrated using a specially designed slurry of NaCl. Removal of the polymer resulted in an accurate negative NaCl template that could be infiltrated with liquid metal using low pressure die casting. Subsequently, the template material is removed, resulting in a controlled cellular structure within Mg. Prior to metal infiltration, the compressive modulus, strength, grain growth and microstructure of the NaCl structure with and without sintering was examined using compression testing and electron backscattered diffraction (EBSD). For the EBSD analyses a new sample preparation technique for the micro porous samples had to be developed for use in the scanning electron microscopy (SEM). The NaCl and the cellular metal were evaluated using SEM and micro-computed tomography (µ-CT). Furthermore, the relationship between the original CAD model and the final NaCl pore morphology was investigated were the surfaces of the RP scaffold and the NaCl template were analysed and compared to the as-cast Mg.