Fabrication, morphologie et proprietes mecaniques des mousses metalliques a base de titane et d'alliages de titane metastables pour des applications biomedicales =FABRICATION, MORPHOLOGY AND MECHANICAL PROPERTIES OF TI AND METASTABLE TI BASED FOAMS FOR BI

摘要

This study is about manufacturing, morphological and mechanical characterization of Titanium (TiCp), metastable Ti based alloy Ti-Nb-Zr (TNZ) and Ti-Nb-Ta (TNT) foams. This new kind of biomaterials has been created to be used as orthopedic implants. The conventional titanium implants are much more rigid than human bone. This rigidity mismatch between the implant and bone generates the "stress shielding" phenomenon, which causes bone resorption, implant loosening and, ultimately, the implant failure. A solution to this problem is to produce porous titanium implants, named metallic foams. These porous implants are less rigid and come close, even mimic, the mechanical properties of bone, which prevent stress shielding. Furthermore, the porous structure of foams is composed of pores open to surface and interconnected. This characteristic allows body fluid circulation and bone ingrowth, resulting in an adequate implant/bone connexion.;Metallic foams with porosity ranging from 0.25 to 0.65 have been produced from the different materials using a powder metallurgy based method, the space-holder technique. The morphology characterization show that for all the foams, the 0.35 ... 0.45 porosity range appears to be the most suitable for bone ingrowth, since these porosities lead to a pore size globally encompassed in the recommended 100...600 &mgr;m range.;From the mechanical behavior point of view, all as-sintered foams demonstrate similar compression behaviour in terms of their apparent Young's modulus and critical stresses. In the recommended 0.35...0.45 porosity range, their Young's modulus varies from 15 to 8 GPa, while their yield stress varies from 300 to 150 MPa. The first characteristic comes close to that of cortical bone, while the second exceeds significantly bone resistance. These results meet the foams' mechanical properties established for their use as orthopedic implants. Compared to Ti foams, mechanical properties of metastable TNZ and TNT alloys' foams can additionally be regulated within +/-20% range, by selecting an appropriate post-sintering thermal treatment. This effect, which is initiated by activating reversible stress-induced beta to &agr;&feet;&feet; martensitic transformation, is strongly perceptible for TNZ foams, while being much less pronounced for TNT foams.