Fabrication, morphology and mechanical properties of Ti and metastable Ti-based alloy foams for biomedical applications

Metallic foams with porosity ranging from 0.25 to 0.65 have been produced from TiCp, Ti–Nb–Zr and Ti–Nb–Ta prealloyed powder by using the space-holder technique, and analysed from both the pore morphology and mechanical propertiesʹ points of view. For all the foams, the most suitable porosity range for bone ingrowth appears to be 0.35 to 0.45, since these porosities lead to a pore size that is globally encompassed in the recommended 100–600 μm range. From the mechanical behavior point of view, all of the as-sintered foams demonstrate similar compression behavior in terms of their apparent Youngʹs modulus and critical stresses. In the recommended 0.3–0.45 porosity range, their Youngʹs modulus varies from 15 to 8 GPa, whilst their yield stress varies from 300 to 150 MPa. The first characteristic comes close to that of cortical bone, whilst the second significantly exceeds bone resistance. Compared to Ti foams, the mechanical properties of metastable TNZ and TNT alloy foams can also be regulated within a ± 20% range, by selecting an appropriate post-sintering thermal treatment. This effect, which is initiated by activating reversible stress-induced β to α″ martensitic transformation, is strongly perceptible for TNZ foams, whilst much less pronounced for TNT foams.