Ermüdung und Mikrostruktur von koronaren Stents

Fatigue and Microstructure of Coronary Artery Stents During implantation the structure of coronary artery stents is subjected to distinct plastic deformation. Subsequently the implant has to sustain up to 700 million cycles induced by the cyclic diameter change of coronary arteries. Regions of high deformation show characteristic deformation structures like slip traces or extrusions and intrusions of grains on the surface without failure of the material. In order to gain information about the microstructural and microtextural evolution during deformation microstructure characterisation by means of scanning electron microscopy as well as transmission electron microscopy and single grain orientation determination were carried out. The analysis of cyclic deformation with different frequencies is of special interest. Several correlations between microstructure and deformation state are observed. Few deformation characteristics occur in the solution annealed stents and increase after dilation. Inhomogeneous deformation behaviour depending on the deformation of individual grains is observed. After cyclic deformation further changes in the microstructure can be observed. These changes caused by cyclic deformation are sensitive to load frequency and generate the formation of a completely different microstructure. Knowledge of microstructure evolution caused by distinct plastic deformation and fatigue in so called oligocrystalline structures is basis for ongoing development in stent optimization.