The effect of the raw materials and processing conditions on the properties of titanium foams

Metal foams possess a unique combination of properties, such as air and water permeability, impact energy absorption capacity, unusual acoustic properties, low thermal conductivity, good electrical insulating properties and high stiffness with very low specific weight. Titanium foams, in particular, have interesting properties in different industrial sectors such as aerospace as structural parts or in the biomedical field as implants. This work studies the manufacturing process of the foams using space holder technique (sodium chloride, NaCl)), as well as their characterisation. The effect of titanium powder characteristics and amount of space holder has been studied. It was found that for a constant NaCl amount, the powder characteristics greatly influence the final porosity of the foam, the pore interconnecting channel size as well as mechanical properties. It was also found that the amount of NaCl greatly influences the final porosity of the foam. It was observed that the pore geometry is directly linked to the space holder particle shape. Two types of porosity have been obtained: macroporosity (originated from the space holder) and micro-porosity (formed as a consequence of the sintering conditions). Finally, it has been concluded that by varying the titanium powder characteristics and space holder amount it is possible to tailor the properties of the foam to match the bone requirements: porosity, microstructure and mechanical properties, whilst also minimising the stress shielding produced by the Young's modulus mismatch between the bone and the implant.