Élaboration d’alliages Fe-Mn-Zn par frittage pour l’application d’implants bio-résorbables
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- With the increasing incidence of cardiovascular disease, which is the leading cause of death in the world, the search for materials for coronary implants has gained considerable importance in the medical world. It has been discovered that the stent is only needed as a mechanical support during the healing time of the vessel. Therefore, the category of biomaterials can be reconsidered. These materials must meet many constraints, in terms of their mechanical properties, bio-compatibility, bio-degradation and radio-opacity. In particular, the Fe-Mn system has interesting mechanical properties, but an insufficient corrosion rate. The addition of zinc could mitigate this problem. The Fe-Mn-Zn system is therefore investigated in this thesis. Fe20Mn12Zn and Fe25Mn5Zn composition alloys were shaped by powder metallurgy. Pre-alloys were first created by a compression step followed by a heat treatment. Then, a spark plasma sintering process was performed on these milled materials. The alloys obtained are dense and homogeneous, entirely of face cubic centered crystalline phases and contain numerous precipitates at the grain boundaries. The measured mechanical properties encourage the realisation of more advanced experiments. However, the presence of zinc does not appear to have accelerated corrosion, but further tests are needed to confirm the results. A reaction mechanism has also been proposed in two steps. During the first 30 minutes of heat treatment, the zinc becomes liquid and diffuses rapidly into the particles of manganese and surrounding iron. The shrinkage during its solidification causes the appearance of large porosity. The diffusion of zinc causes a change in crystalline structure, which imply a slowing of the diffusion. A long period is then needed to homogenize the material.