Mechanical Behavior of 316L Stainless Steel after Strain Hardening

The effects of strain hardening on the mechanical behavior of 316L stainless steel were studied in the paper. The original and different strain hardening materials were compared to investigate the mechanical behavior. The results demonstrate that the yield strengths increase with the magnitude of strain hardening significantly, but the ultimate strengths of the original and different strain hardening materials are closed. In addition, the plastic parameters of 316L stainless steel including fracture elongation and fracture surface shrinkage decrease with the magnitude of strain hardening. Finally, the Ramberg-Osgood equation is used to predict the stress-strain curves after strain hardening, and the results indicate that the predicted values agree with the experimental values

Microstructural evolution in solution heat treatment of gas- atomised Al alloy (7075) powder for cold spray

Cold gas dynamic spray is being explored as a repair technique for high-value metallic components, given its potential to produce pore and oxide-free deposits of between several micrometers and several millimeters thick with good levels of adhesion and mechanical strength. However, feedstock powders for cold spray experience rapid solidification if manufactured by gas atomization and hence can exhibit non-equilibrium microstructures and localized segregation of alloying elements. Here, we used sealed quartz tube solution heat treatment of a precipitation hardenable 7075 aluminum alloy feedstock to yield a consistent and homogeneous powder phase composition and microstructure prior to cold spraying, aiming for a more controllable heat treatment response of the cold spray deposits. It was shown that the dendritic microstructure and solute segregation in the gas-atomized powders were altered, such that the heat-treated powder exhibits a homogeneous distribution of solute atoms. Micro-indentation testing revealed that the heat-treated powder exhibited a mean hardness decrease of nearly 25% compared to the as received powder. Deformation of the powder particles was enhanced by heat treatment, resulting in an improved coating with higher thickness (* 300 lm compared to * 40 um for untreated feedstock). Improved particle–substrate bonding was evidenced by formation of jets at the particle boundaries

Redes epóxi/amina alifáticas com perspectivas para aplicações cardiovasculares. Propriedades biológicas in vitro

Este trabalho descreve as propriedades biológicas in vitro de três redes epoxídicas à base do éter diglicidílico do glicerol (DGEG) curadas com poli(oxipropileno) diamina (D230), isoforona diamina (IPD) e 4,4'-diamino-3,3'-dimetil-diciclohexilmetano (3DCM). As interações biológicas entre os polímeros e o sangue foram estudadas por ensaios biológicos in vitro. Estudos de adsorção de proteínas, adesão de plaquetas, atividade do lactato desidrogenase (LDH) e propriedades de tromboresistência estão apresentados. Os ensaios de adsorção de proteínas na superfície dos polímeros mostrou que as redes epoxídicas adsorvem mais albumina do que fibrinogênio. Os resultados relacionados à adesão de plaquetas, atividade do lactato hidrogenase e propriedades de tromboresistência indicaram que as redes DGEG/IPD e DGEG/3DCM exibem comportamento hemocompatível. Desta maneira, assumimos que estes polímeros epoxídicos são materiais compatíveis com o sangue

The use of cold sprayed alloys for metallic stents

With the invention of the coronary stent, which is a wire metal mesh tube designed to keep the arteries open in the treatment of heart diseases, promising clinical outcomes were generated. However, the long term successes of stents have been delayed by significant in-stent restenosis (blockages) and stent fracture. In this research work, it has been proposed to use Cold Gas Dynamic Spraying (CGDS) coating material as an alternative choice to manufacture metallic stent. In CGDS, fine particles are accelerated to a high velocity and undergo solid-state plastic deformation upon impact on the substrate, which leads to particle-particle bonding. The feature of CGDS distinct from other thermal spray techniques is that the processing gas temperature is below the melting point of the feedstock. Therefore, unwanted effects of high temperatures, such as oxidation, grain growth and thermal stresses, are absent. In response to the fact that the majority of stents are made from stainless steel (316L) or Co-Cr alloy (L605), this study specifically addresses the development and characterization of 316L and 316L mixed with L605 coatings produced by the CGDS process. Scanning electron microscopy and electron backscatter diffraction were used to investigate the microstructural changes of these coatings before and after annealing. The effect of gas type on the microstructure of 316L coatings and the role of post-heat treatment in the microstructure and properties are also studied. Of particular interest are grain refinement, heat treatment, mechanical properties and corrosion behavior of the cold sprayed material.L'invention du stent coronaire, est un tube en treillis métallique conçu pour maintenir les artères ouvertes dans le traitement des maladies cardiovasculaires. Des résultats cliniques prometteurs ont été rapportés. Cependant, le succès à long terme des stents est problématique à cause des resténoses intra-stent et des fractures de stent par fatigue. Dans ce travail de recherche, il est proposé d'utiliser la technologie de pulvérisation dynamique des gaz à froid (CGDS) comme une alternative pour la fabrication de stents métalliques. En CGDS, de fines particules sont accélérées avec une vitesse élevée et subissent une déformation plastique à l'impact sur un substrat. La particularité du CGDS parmi les autres techniques de pulvérisation thermique est que la température des gaz dans le processus est bien en dessous du point de fusion de la matière. Par conséquent, les effets indésirables des températures élevées, telles que l'oxydation, la croissance du grain et les contraintes thermiques, sont absents. Comme la majorité des stents sont faits en acier inoxydable 316L et en alliage Co-Cr, cette étude porte spécifiquement sur le développement et la caractérisation de l'acier inoxydable et l'acier inoxydable 316L mélangé avec revêtements d'alliages Co-Cr produite par le procédé CGDS. Les techniques de microscopie électronique à balayage et à diffraction d'électrons rétrodiffusés ont été utilisées pour étudier les changements de microstructures de ces revêtements avant et après recuit. L'effet du type de gaz sur la microstructure des revêtements 316L et le rôle du post-traitement thermique à froid par pulvérisation dans la microstructure et les propriétés mécaniques et électrochimiques ont été également étudiées