Pressure metallurgy is a means of increasing the nitrogen content and thereby the resistance of stainless martensitic steels to pitting corrosion. The present study on their constitution and heat treatment reveals that even at normal pressure more nitrogen is dissolved in the melt if the carbon content increases, because the fraction of ferrite is reduced during solidification. Nitrogen is dissolved more readily during austenitisation than carbon which lowers the C/N ratio at hardening temperature and thus is likely to improve the corrosion resistance of martensite after quenching. As the stability of retained austenite is increased by nitrogen a strain induced transformation by ausforming is discussed.
The chromium content of standard martensitic stainless steel X65Cr14 is raised to 17 mass% to enhance the solubility of nitrogen. Up to 4 mass% of nickel are added to suppress a partially ferritic solidification. This combination increases the nitrogen content soluble at 1 bar pressure from 0.14 to 0.24 mass%, which allows to reduce the carbon content to about 0.4 mass% without a loss of hardening capacity. The lower carbon level prevents the precipitation of coarse eutectic carbides in segregated areas encountered in X65Cr14. Instead of nickel pressure is applied to raise the nitrogen content up to 0.45 mass%. Calculations are verified by melts. As the hardening temperature is increased the CrMoN solute content of austenite is raised and so is the pitting resistance after hardening. However, retained austenite reduces the hardness and ausforming at 200°C is applied to transform it during subsequent deep freezing and raise the hardness.
A blood clot needs to have the right degree of mechanical, chemical and biological properties to stem the flow of blood and yet to be suitable for lytic enzymes or mechanical thrombectomy so as not to form a thrombotic event. The origin and understanding of these mechanical properties are still not known in detail. Clots are made of a three-dimensional network of fibrin fibers stabilized through ligation with a transglutaminase, factor XIIIa. New methods to achieve information about mechanical properties were established in this work. We performed compressive strength experiments of aged human blood clots. Furthermore after the set up of a new test environment, it was possible to perform tensile strength measurements of aged animal blood clots. Stress strain curves of aged clots were measured and discussed. The viscoelastic properties of the clot material were quantitatively described. This work should make a contribution to a better understanding of the behaviour of aged blood thrombus bulk material and induced mechanical stress.
Keywords: blood clots / mechanical properties / aging conditions / viscoelastic behaviour /In der Behandlung ischämischer Schlaganfälle sind mechanische, chemische und biologische Eigenschaften von Blutgerinnseln von essentieller Bedeutung und entscheidend über den Erfolg einer Lyse-Therapie bzw. mechanischer Thrombektomie. Die Einflussfaktoren der Gerinnungsbedingungen auf die mechanischen Eigenschaften sind jedoch bisher noch nicht eingehend untersucht. Aus Schrifttum ist bekannt, dass auf mikrostruktureller Ebene die Blutgerinnsel aus Fibrinfasern, die untereinander in Knotenpunkten verbunden sind und in der Gesamtheit ein dreidimensionales Netzwerk bilden, bestehen. Dabei haben besonders die Faserdicke und die Knotenpunktendichte einen direkten Einfluss auf die mechanischen Eigenschaften eines Thrombus. Im Rahmen dieser Arbeit wurden Druck-und Zugversuche an Thrombus-Proben (hergestellt aus humanem bzw. tierischem Blut) durchgeführt und die Messergebnisse hinsichtlich der Gerinnungsbedingungen diskutiert.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.