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The use of magnesium alloys as degradable metals for biomedical applications is topic of ongoing research. As a further aspect, the demand for multifunctional materials is increasing. Hence, binary Mg-Ag alloys were designed to combine the favourable properties of magnesium with the wellknown antibacterial property of silver. In this study, three Mg-Ag alloys, Mg2Ag, Mg4Ag and Mg6Ag which contain 1.87%, 3.82% and 6.00% silver by weight respectively were casted and processed with solution and aging heat treatment. Afterwards, the samples were investigated in vitro for metallographic, mechanical, corrosive, cytocompatible and antibacterial properties. The metallurgical analysis and phase identification showed that all alloys contained Mg4Ag as the dominant second phase. The mechanical properties of the Mg-Ag alloys were dramatically improved in several parameters especially after heat treatment. Corrosion tests revealed that after heat treatment, content of silver reduced the corrosion rate and exhibited less susceptibility to pitting corrosion than pure magnesium. Mg(OH)2 and MgO presented as main magnesium corrosion products while AgCl was found as the primary silver corrosion product. Immersion tests demonstrated that content of silver did not significantly shift the pH, osmolality and magnesium ion release in the environment. Cultivation and cytotoxicity tests with both primary cells and cell lines revealed that Mg-Ag alloys induce no negative effect on cells and show minor cytotoxicity. Antibacterial testing in a dynamic bioreactor system proved the alloys to reduce the viability of two common pathogenic bacteria, Staphylococcus aureus and Staphylococcus epidermidis. In summary, biodegradable Mg-Ag alloys are cytocompatible biomaterials with adjustable mechanical and corrosion properties while having sound antibacterial ability.

Die Kriecheigenschaften von zwei Magnesium-Zink-Legierungen, bezeichnet mit MEZ (Mg-2.6wt%RE-0.4Zn-0.13Mn-0.12Zr) und ZECa (Mg-2.8Zn-1.9Ca-0.32RE-0.08Sr), wurden im thixo-gegossenen Zustand im Temperaturbereich von 135 to 200°C untersucht. Die beiden Legierungen zeigten nach 100 h bei 175°C und 80 MPa weniger Kriechen als die Standardlegierung AE42. Die Verbesserung der Kriecheigenschaften wurde auf die bimodale Korngrößenverteilung nach dem Thixo-Guss und auf die Gussqualität zurückgeführt., The creep properties of two magnesium-zinc alloys, designated as MEZ (Mg-2.6wt%RE-0.4Zn-0.13Mn-0.12Zr) and ZECa (Mg-2.8Zn-1.9Ca-0.32RE-0.08Sr), have been studied in the thixocast state at temperatures of 135 to 200°C. The two alloys showed less creep than the state of the art AE42 alloy after 100 h of creep exposure up to 175°C and 80 MPa. The improvement on the creep resistance has been related to the bimodal microstructure obtained after thixocasting and to the quality of the castings.

Es wurden beta-annealed Zustände mit großer und kleiner Korngröße sowie bi-modale Zustände mit kleiner Korngröße der hochfesten metastabilen beta-Titanlegierung Ti-5Al-5V-5Mo-3Cr mit je mindestens drei Festigkeitsniveaus hergestellt. Es wurden mechanische Kennwerte (u.a. sigma(0.2), A_5, sigma(HCF) und K(IC)), deren Mikrostruktur und Bruchflächen dieser Zustände bis zu sehr hohen Dehngrenzen von bis zu 1900 MPa miteinander verglichen. Durch Variation von Umformung und Glühtemperatur der Rekristallisation kann einerseits die Korngröße und dadurch die Brucheigenschaften beeinflusst werden. Andererseits ist es davon unabhängig möglich Anteil und Größe der alpha-Titanausscheidungen durch die Auslagerung zu definieren, was die Festigkeit bestimmt. Die Relationen der mechanischen Eigenschaften ändern sich bei Dehngrenzen über ca. 1400 MPa, da hier der Festigkeitsunterschied von dem Korninneren zu den ausscheidungsfreien Zonen der Korngrenzen einen großen Einfluss hat., beta-annealed conditions with small and big grainsizes and bi-modal conditions with a small grainsize were made of the metastable beta-titanium alloy Ti-5Al-5V-5Mo-3Cr, each with three or more strengthlevels. Mechanical properties (like sigma(0.2), A_5, sigma(HCF) and K(IC)), microstructures and fractured surfaces of conditions with yield strength up to 1900 MPa were compared. Grainsize and fracture properties could be affected by a variation of deformation and annealing temperatures. Independently from that, volume and size of alpha-titanium-precipitates are defined by aging, which sets the strength. The relations between mechanical properties are changing at strengthlevels above 1350 - 1400 MPa, caused by a great influence of the difference in strength between grain and precipitation-free-zone.

What happens to a metal when its size is reduced? What changes are expected, what has to be taken into account? By taking the metal-hydrogen system (M-H-system) as model system this book tries to give some answers to these questions. A large variety of material physics experiments on thin films, multi layers and clusters of only several nanometers size is presented. The results are discussed with regard to mechanical stress and micro structure of the samples (including surfaces). The important impact of the stabiliser on the physical properties of the nano-size system is proved by first measuring huge mechanical stress and large strains. Stress and strain are in accordance with stress and strain calculated by using linear elastic theory. However, most systems avoid very huge stress by deforming plastically or by detaching from the stabiliser. Second, the micro structural contribution (grain boundaries, dislocations, surfaces, interfaces) on phase boundaries is estimated. It will be shown, that the measured nano-sized M-H phase boundaries can not be explained by micro structural contributions, only. To explain the experimental data, stress has to be taken into account. For small clusters, new structures have to be considered - cluster "phase diagrams" change completely compared to those of the bulk system. With respect to micro structure and mechanical stress published data will be re-discussed, offering solutions for conflicting results. Thus, this book gives an inside view on changes of material physical properties of M-H systems by nano-sizing.

The Fokker-Planck equation describing a beam of charged particles entering a homogeneous medium is solved here for a stationary case. Interactions are taken into account through Coulomb cross-section. Starting from the charged-particle distribution as a function of velocity and penetration depth, some important kinetic quantities are calculated, like mean velocity, range and the loss of energy per unit space. In such quantities the energy straggling is taken into account. This phenomenon is not considered in the continuous slowing-down approximation that is commonly used to obtain the range and the stopping power. Finally the well-known Bohr or Bethe formula is found as a first-order approximation of the Fokker-Planck equation. © 1996 Società Italiana di Fisica.