Microstructure and mechanical properties of two tool steels with ultrahigh boron content

[ES] En el presente trabajo se han modificado dos aceros para herramientas convencionales por la presencia de un contenido de boro entre 0,5 y 1 % en masa. Ambos aceros se procesaron por la ruta pulvimetalúrgica, incluyendo atomización por argón y compactación isostática en caliente. El material compactado presentó una microestructura caracterizada por una distribución de partículas de borocarburos M23(C,B)6 fma y homogénea en una matriz de ferrita-martensita. Esta microestructura permanece prácticamente inalterada tras los ensayos de cambios en la velocidad de deformación durante el ensayo de compresión a temperaturas entre 750 y 1.000 °C. En el caso del acero Fe-lB-lC se obtuvo un valor para el exponente de la tensión de 4,5, que sugiere que la deformación plástica está controlada por un mecanismo de fluencia por movimiento de dislocaciones. Por otro lado, para el acero Fe-0,5B-l,5C, se obtuvieron valores para el exponente de la tensión comprendidos entre 2 y 3, que sugieren que la deformación plástica está controlada por un mecanismo de deslizamiento de fronteras de granos. En ambos casos, se encontró un valor de la energía de activación para la deformación plástica que se asoció con la energía de autodifusión del hierro a través de la red.[EN] In the present work, two selected tool steels have been modified by a boron addition of 0.5 and 1 mass %. Both steels were processed by powder metallurgy methods, including argón atomization and hot isostatic pressing. The Consolidated materials presented a microstructure consisting of a fine and homogeneous distribution borocarbides M23(C,B)6 in a ferrite-martensite matrix. No changes are observed in the microstructure after deformation by compression-strain-rate-change tests at temperatures ranging from 700 to 1,100 °C. For the Fe-lB-lC steel, a stress exponent of 4.5 was obtained, that suggests that slip creep is the controlling deformation mechanism. On the other hand, a stress exponent between 2 and 3 was obtained for the Fe-0.5B~1.5C steel that suggests that grain boundary sliding is the controlling deformation mechanism. In both cases, the activation energy for creep was related to the activation energy for iron self-diffusion.Peer reviewe

Development of a high strength Al-Mg2Si-Mg-Zn based alloy for high pressure die casting

A high strength Al-Mg2Si-Mg-Zn based alloy has been developed for the application in high pressure die casting to provide improved mechanical properties. The effect of various alloying elements on the microstructure and mechanical properties including yield strength, ultimate tensile strength and elongation of the alloy was investigated under the as-cast and heat-treated conditions. The typical composition of the high strength alloy has been optimised to be Al-8.0wt%Mg2Si-6.0wt%Mg-3.5wt%Zn-0.6wt%Mn (Al-11.0wt%Mg-2.9wt%Si-3.5wt%Zn-0.6wt%Mn) with unavoidable trace impurities. The mechanical properties of the alloy were enhanced by a quick solution treatment followed by ageing treatment. The improved tensile properties were at a level of yield strength over 300MPa, the ultimate tensile strength over 420MPa and the elongation over 3% assessed using international standard tensile samples made by high pressure die casting. The microstructure of the die-cast alloy consisted of the primary α-Al phase, Al-Mg2Si eutectics, AlMgZn intermetallics and α-AlFeMnSi intermetallics under the as-cast condition. The AlMgZn intermetallic compound was dissolved into the Al-matrix during solution treatment and subsequently precipitated during ageing treatment for providing the effective improvement of the mechanical properties.The financial support is gratefully acknowledged for the Engineering and Physical Sciences Research Council (EPSRC) (Project number: EP/I038616/1), Technology Strategy Board (TSB) (Project number: 101172) and Jaguar Land Rover (JLR), United Kingdom

Intraoperative Defibrillation Testing of Subcutaneous Implantable Cardioverter‐Defibrillator Systems—A Simple Issue?

Background: The results of the recently published randomized SIMPLE trial question the role of routine intraoperative defibrillation testing. However, testing is still recommended during implantation of the entirely subcutaneous implantable cardioverter‐defibrillator (S‐ICD) system. To address the question of whether defibrillation testing in S‐ICD systems is still necessary, we analyzed the data of a large, standard‐of‐care prospective single‐center S‐ICD registry. // Methods and Results: In the present study, 102 consecutive patients received an S‐ICD for primary (n=50) or secondary prevention (n=52). Defibrillation testing was performed in all except 4 patients. In 74 (75%; 95% CI 0.66–0.83) of 98 patients, ventricular fibrillation was effectively terminated by the first programmed internal shock. In 24 (25%; 95% CI 0.22–0.44) of 98 patients, the first internal shock was ineffective and further internal or external shock deliveries were required. In these patients, programming to reversed shock polarity (n=14) or repositioning of the sensing lead (n=1) or the pulse generator (n=5) led to successful defibrillation. In 4 patients, a safety margin of <10 J was not attained. Nevertheless, in these 4 patients, ventricular arrhythmias were effectively terminated with an internal 80‐J shock. // Conclusions: Although it has been shown that defibrillation testing is not necessary in transvenous ICD systems, it seems particular important for S‐ICD systems, because in nearly 25% of the cases the primary intraoperative test was not successful. In most cases, a successful defibrillation could be achieved by changing shock polarity or by optimizing the shock vector caused by the pulse generator or lead repositioning.<br

Rethinking Rural Homelessness: A Comparison of the Causes, Solutions, and Services for Persons Experiencing Homelessness in Appalachia Versus Urban Areas in the United States

Although homelessness in urban areas has been analyzed extensively, there is little research and data on homelessness in rural areas, specifically in Appalachia. The goal of this research is to shed some light on rural homeless experiences by comparing them to their urban counterparts. Four people from organizations that work with persons experiencing homelessness were interviewed using a snowball sample and asked questions which compare the causes, services, and solutions for homelessness in rural and urban areas. Based on these interviews, it can be concluded that the issues people experiencing homelessness go through, such as mental health problems and stigma, are similar throughout rural and urban locations, but the causes, services, and solutions for homelessness in Appalachia are distinct to the region and vary from those in urban areas. Some key differences include the visibility of persons experiencing homelessness, the impact of poverty and the opioid epidemic, and the types of barriers on rural and urban care centers. Acknowledging what makes homelessness in Appalachia unique can guide programs and services in their pursuits of preventing and ending homelessness

Essays in Economic Theory

This thesis studies information aggregation and reputation management in three microeconomic environments. In the first chapter, I consider a committee voting setup with two rounds of voting where committee members who possess private information about the state of the world have to make a binary decision. I investigate incentives for truthful revelation of their information in the first voting period. Coughlan (2000) shows that members reveal their information in a straw poll only if their preferences are homogeneous. By taking costs of time into account, I demonstrate that committees have strictly higher incentives to reveal information if a decision with high levels of consensus can already be made in the straw poll. In such scenarios, members of all homogeneous and some heterogeneous juries are strictly better off when the requirement for early decisions is chosen carefully. The second chapter studies a seller whose reputation is determined by the types of her customers. In the model, a monopolist repeatedly sells a good to heterogeneous customers who, depending on their type, increase or decrease the seller's reputation. First, I study a trade-off between realizing current-period profits and building reputation for future periods. Second, I analyze reputation dynamics. Over time, reputation always converges to a stable level. Convergence behavior, however, depends strongly on the good's durability. While the reputation of less durable goods fluctuates around the long-run reputation, the reputation of more durable goods converges monotonically. In the third chapter, I examine a dynamic reputation model in which a long-lived online seller of unknown logistical ability competes against an offline retailer. In order to deliver goods to her short-lived buyers, the online seller has to employ one of two shippers which differ in their expected delivery time. Her buyers, in turn, update their beliefs about the seller's logistical ability based on their experienced waiting time for the good. I find that incentives to assign a fast shipper depend significantly on the information about the delivery process that buyers can observe. I compare the equilibrium outcomes of four specifications where buyers can or cannot observe the shipper's quality upon delivery of the good, and can or cannot track and trace the delivery process in detail. The ability to track the delivery proves harmful to the buyers' welfare in most cases, whereas the ability to observe the shipper's quality can be beneficial or harmful depending on the exact setup and parameter specification

A phase-field method coupled with CALPHAD for the simulation of ordered κ-carbide precipitates in both disordered γ and α phases in low density steel

In order to simulate multi-component diffusion controlled precipitation of ordered phases in low density steels using the phase-field method, the Gibbs free energy of the γ,α and κ phases in the quaternary Fe-Mn-Al-C system was linked to the CALPHAD method using a three-sublattice model which is based on the accumulation of considerable thermodynamic data in multi-component systems and the assurance of continuous variation of the interface area. This model includes the coherent precipitation of κ phase from a disordered FCC γ phase and semi-coherent precipitation of the same κ phase from a disordered BCC α structure. The microstructure evolution of κ-carbide was simulated with three-dimensional phase-field model. The simulation was first performed for a single particle in both γ and α phases to investigate the evolution of interfacial and elastic strain energy during the precipitation process. The simulation results show that κ has a cuboidal morphology in γ and elongated plate-like morphology in α which is in agreement with the morphologies reported in the literature. The multi-particle simulations were also performed for the precipitation of κ phase from both disordered γ and α. The results also demonstrate that the size of κ precipitates in γ is remarkably smaller than that in α phase

Studien zur Physiologie und Pathologie der Hämostase bei Schmuckschildkröten und grünen Leguanen

Plasmatic clotting times and number of thrombocytes were established in clinically healthy slider turtles and green iguanas as well as in animals with clinically conspicious symptoms. The used commercial reagents for prothrombin time, activated partial thromboplastin time and thrombin time proved reliable for the analysis of reptilian blood. The steel ball coagulo-meter as well as the coagulometer according to Schnitger and Gross can be used for meassuring. Altogether 239 blood samples of clinically healthy slider turtles were analysed and evaluated for genus, species, gender, age and season. Furthermore 67 clinically incon-spicuous green iguanas were available for the coagulation analysis. For the evaluation of the results the influence of age and gender were taken into consideration. For slider turtles as well as for green iguanas reference values for the three clotting parameters could be established because of the relatively close correspondence of the values determined twice in each sample and in repetition. In order to receive correct results it is of great importance to intermeadiatly analyse citrate plasma samples. Reference factors for the number of thrombocytes of green iguanas and slider turtles, which were manually counted, could also be defined. Apart from the coagulation diagnostics the examination of clinical blood chemistry and haematological blood parameters in animals with pathological changes gave important clues for the aetiology of hemostatic disorders, which were proved by the histological results of dissected patients. Serious hepatic dysfunctions mostly lead to a reduced synthesis of coagu-lation factors and therefore to coagulopathies. It is important to take into consideration that clinically evident symptoms do not always have to be connected with prolonged plasmatic clotting times. Hypovitaminosis k, disseminated intravascular coagulation, thrombocytopenia and vasopathies can also cause bleeding disorders. The results of the verification of the success of therapy of green iguanas, which were clinical-ly as well as laboratory diagnostically conspicous, coincide with the empirical experiences and show, that Phytomenadion for treatment of hypovitaminosis k is also suitable in reptile medicine. The control of the clotting time after application of Konakion ® (orally or intra-muscular) in slider turtles with increased parameters, which in most cases could be attributed to a reduced liver function, showed, that Phytomenadion has an at least temporary positive impact on the regeneration of the liver and in many cases lead to an improvement of values. In comparison to untreated animals the effect was especially apparent in the activated partial thromboplastin time