Thermal-spray coatings of austenitic materials are mainly used under corrosive conditions. The relatively poor wear resistance strongly limits their use. In comparative studies between ...nitrocarburized and untreated thermal-spray coatings, the influence of the nitrogen and carbon enrichment on the properties of the coatings and the microstructure was investigated. The cross-section micrograph of the nitrocarburized coating shows the S-phase formation in the surface layer region. The depth profile of the nitrogen and carbon concentration was determined by glow discharge optical emission spectroscopy (GDOS) analysis. A selective enrichment of the surface layer region with nitrogen and carbon by means of thermochemical heat treatment increases the wear resistance. The interstitially dissolved nitrogen and carbon causes the formation of strong compressive residual stresses and high surface hardness. Increases in the service life of existing applications or new material combinations with face-centred cubic friction partners are possible. In the absence of dimensional change, uniform as well as partial nitrogen enrichment of the thermal spray coating is possible. Nitrocarburized coatings demonstrate a significant improvement in adhesive wear resistance and extremely high surface hardness.
Enhancement stocking is a widespread but rarely evaluated practice in German vendace, Coregonus albula L. fisheries, which is precautionarily carried out to buffer yield fluctuations. However, it is ...assumed that stocking of larval vendace can elevate year‐class strength only in the presence of substantial reproductive deficits, which so far cannot be detected prior to the spring time period when stocking is conducted by fisheries managers. Simple measures for the early quantification of natural reproduction were tested, and the efficiency of larval enhancement stocking in a lake with strong reproduction deficits was analysed. Analysis in four lakes over 3 years revealed a significant positive correlation between standardised catches of vendace larvae caught with pump‐driven illuminated traps in spring and the abundance of young‐of‐year (YoY) vendace in the following autumn, whereas standardised catches of spawners were insufficient to forecast YoY recruitment. In a lake with low natural vendace reproduction, stocked vendace contributed 73–100% of year‐class strength and fisheries yield. Accordingly, enhancement stocking can efficiently compensate for reproduction deficits, and the simple larvae sampling method may facilitate early detection of these deficits, which would allow fisheries managers to respond accordingly through larvae stocking.
In the present study, the interfacial microstructure of dissimilar Al/Ti joints formed by a co-extrusion process has been investigated. The material combinations used for the experiments were ...commercially pure aluminium and titanium, respectively, in the alloys EN AW-6082 and TiAl6V4. X-ray diffraction, energy-dispersive X-ray spectroscopy, electron microscopy and electron backscatter diffraction revealed titanium aluminide formation in the interface, the development of deformation bands in the sleeve material, and the occurrence of grain size refinement and twinning in the core material. The results are discussed with respect to the concept of a hard core–soft sleeve co-extrusion comprising plastic deformation to promote solid-state diffusion. The study shows the phase distribution and the microstructural evolution in the bonding zone with the aim to improve the quality of the bonding by adequately adjusting the process parameters.
Abstract
Within this work, aluminum is oxidized via plasma-electrolytic oxidation (PEO) in the presence of organic substances, including reactive monomers. The aim of this approach is to generate ...polymers and simultaneously bind them to the surface of the freshly generated oxide layers. For this purpose, sheets of aluminum were immersed into electrolytes that comprised either 4 % of sodium acrylate or 10 % of sodium benzoate. The aluminum sheets were oxidized by anodic pulse current at 0.25 A/cm
2
for 30–90 s. By this process, predominantly oxidic conversion layers were produced. The presence of the monomers in the electrolyte influenced the passivation and discharge behavior and finally the microstructure of the layers. It further gave rise to organic material in the layer. In particular, infrared attenuated total reflection spectroscopy (ATR-IR) and X-ray photoemission spectroscopy (XPS) show that layers which were generated in the presence of acrylate or benzoate comprised -C-C-, -C=C-, -C-O, and C=O bonds.
Laser hardening provides significant advantages in processing time, and energy consumption compared to conventional hardening processes, especially for small batches. In addition, the functional ...characteristics can be adjusted locally for different applications. However, the differences of the microstructural states in the laser-treated areas and the surrounding untreated base material may result in corrosion issues. In this paper, the corrosion behavior of the high-alloyed, laser-treated steel X153CrMoV12 (1.2379) used in the meat-processing industry is investigated in Hanks' balanced salt solution, a simulated body fluid, globally by immersion tests and locally by microelectrochemical investigations, depending on the measured temperature in the laser spot. Differences of the susceptibility to pitting, as well as correlation to thermodynamic calculations were found. Thus, the application-related corrosion behavior can be estimated numerically.
Macromechanical simulations provide excellent opportunities for rapid calculations of forming processes. Geometrical dimensions and residual stresses can be calculated with very good agreement. More ...complex forming simulations (e.g. crystal dynamic simulations or calculations with representative volume elements) are necessary if microstructural magnitudes, like crystallite sizes and microstrains, have to be included. Using the example of cold-rolling, this paper aims to describe a different approach for connecting macromechanical finite-element simulations with key parameters of the microstructure. By means of X-ray diffraction and confocal microscopy, crystallite sizes, microstrains, texture and roughness values are determined and correlated to the plastic strain. The plastic strain can be simulated easily and the microstructure after forming can be predicted. As a result of this calibration, more complex simulations can be avoided. Nonetheless, these calibrated macromechanical simulations can be used for the estimation of microstructure-related properties, like the corrosion behaviour.
– Complex interactions between fish predators and their prey have been found in structurally complex habitats built by submerged macrophytes. In contrast, the role of comparably structured littoral ...reed stands in shaping biotic interactions has not been investigated. We hypothesised that reed stands may be a valuable feeding habitat for juvenile fish, and that perch and roach may segregate along the spatial and dietary niche dimensions between reed and open water habitats. In contrast, the protection effect of reed against predators was assumed to be rather low because of the lower plant volume infested in reed when compared with submerged macrophytes. We analysed biomass and growth of juvenile (age 0 and age 1) perch and roach in littoral reed habitats and in open water habitats in front of the reed in the shallow Lake Müggelsee over 4 months in 2000. Sampling was conducted by point‐abundance electrofishing over the full diel cycle (day, dusk, night, dawn). Zooplankton and benthos biomasses were determined in both habitats as well, and habitat‐specific diet of fish was assessed during day and night. Roach were more frequent than perch in both habitats. Food of roach included a higher proportion of zooplankton, whereas perch fed more on macroinvertebrates. Overall, diet overlap between the fish groups was high. Diel distribution of fish did not follow the expectations of habitat segregation between perch and roach. Instead, the function of reed as refuge habitat against littoral piscivores (mainly birds) may have caused the strong daytime preference for reed in almost all fish groups, which was partly upset by roach at night. The higher behavioural plasticity of roach may explain their good performance even under the conditions of high structural complexity.
Resumen
1. Interacciones complejas entre peces predadores y sus presas han sido documentadas en hábitats estructuralmente complejos compuestos de macrófitas sumergidas. Por el contrario, el papel de la vegetación acuática emergente y más en particular el papel que juegan las manchas extendidas en la zona litoral de cañaverales de Phragmites spp. óTypha spp. sobre las interacciones biológicas ha sido poco investigado. Además, en lagos eutróficos decrece el nivel de cobertura de macrófitas sumergidas debido a una menor transparencia del agua y en consecuencia, la vegetación emergente llega a ser el hábitat complejo dominante en el litoral. A densidades similares la complejidad estructural es menor en las manchas de Typha que en las Phragmites debido a la falta de áreas extendidas de hojas. El efecto refugio para las presas es mayor a mayores complejidades vegetales mientras que la eficiencia alimenticia de los peces, en muchos casos, decrece al aumentar en nivel estructural. Estos patrones llegan a ser todavía más complejos si también se consideran diferentes especies de peces. Muchas de la interacciones entre Perca fluviatilis y Rutilus rutilus cambian si los peces se confinan en hábitats estructuralmente complejos. Planteamos como hipótesis que las manchas de cañaverales pueden ser un hábitat alimenticio de valor para los peces juveniles, particularmente para P. fluviatilis que son más eficientes que R. rutilus cuando se alimentan de macro‐invertebrados y de zooplancton en hábitats estructurados. Como consecuencia, esperamos que P. fluviatilis y R. rutilus deberían segregarse a lo largo dimensiones de nicho alimenticias y espaciales entre los hábitats de cañaverales y de aguas abiertas. Por el contrario, asumimos que el efecto de protección de los cañaverales contra los predadores es menor debido a un menor volumen de plantas infectadas en los cañaverales comparado con las macrófitas sumergidas.
2. Analizamos la biomasa y el crecimiento de juveniles (edades 0 y 1) de P. fluviatilis y R. rutilus en hábitats litorales de cañas y en hábitats de aguas abiertas enfrente de los cañaverales en el lago somero Mëggelsee (Berlin, Alemania) sobre un período de cuatro meses del año 2000. Los muestreos se llevaron a cabo con pesca eléctrica aplicando el método de abundancias puntuales sobre un ciclo circadiano completo (amanecer, día, atardecer, y noche) Los puntos fueron elegidos al azar desde una lancha de 3 m de eslora, remando sistemáticamente a lo largo de transectos paralelos a la zona. Expresamos la densidad de cañas como el porcentaje de volumen vegetal infectado (PVI) siendo máximo en 15–20%. La biomasa de zooplancton y bentos fueron también determinadas en ambos hábitats a lo largo de los mismos transectos que los peces. La dieta específica del hábitat fue inspeccionada para los peces de día y de noche. Para evaluar la importancia de las categorías alimenticias, calculamos los índices de importancia relativa (IRI) y de similitud alimenticia (Sxy).
3. Desde Julio hasta Octubre, la biomasa de zoo‐bentos fue significativamente mayor en los cañaverales que en aguas abiertas mientras que la biomasa de zoo‐plancton (cladóceros y copépodos) no difirió entre ambos hábitats. R. rutilus fue más abundante que P. fluviatilis en los cañaverales que en aguas abiertas. El alimento de R. rutilus incluyó una mayor proporción de zoo‐plancton en ambos hábitats mientras que P. fluviatilis se alimentó de macro‐invertebrados. En general, el solapamiento alimenticio entre ambos grupos de peces fue alto. La distribución circadiana de los peces no siguió un patrón de segregación de hábitat entre P. fluviatilis y R. rutilus. En vez de ello, la función de los cañaverales como hábitat refugio contra piscívoros (esencialmente aves) pudo haber causado la fuerte preferencia por los cañaverales en la mayor parte de los grupos de peces que fue, al menos en parte, rechazado por R. rutilus durante la noche. La alta plasticidad comportamental de R. rutilus puede explicar su buen desarrollo incluso bajo condiciones de alta complejidad estructural.
Reliable information on fish stocks is given crucial importance in fisheries science and ecosystem management. Among others, the European Water Framework Directive calls for consistent sampling ...methods that provide comparable and reproducible results. However, the standardized sampling of fish in lakes by gillnets is conducted by low effort only in the pelagic areas, thus potentially not reflecting between-lake variability in fish density. Here, we compared two additional fishing methods, hydroacoustics and midwater trawl sampling, to estimate pelagic coregonid densities in two deep lakes. Night-time trawling was conducted in four different depth layers and compared with the simultaneously obtained abundance and biomass estimates from echo recordings. Overall areal fish biomass from both methods corresponded to each other (
R
2
=
0.40), with slope and intercept of major axis regression not differing from unity. However, we found differences in estimates for the deepest layers fished, and for very small and the largest coregonids, most likely to be explained by the specific technological details of either method. Our study supports that either hydroacoustics or trawl sampling should accompany gillnet fishing to monitor pelagic fish assemblages. Because both methods result in estimates of absolute fish densities per volume or area, their application may uncover subtle responses of fish assemblages to anthropogenic disturbance in deep lakes.
Among the advanced high-strength steels, quenching and partitioning (Q&P) steels provide excellent ultimate tensile strength in combination with good ductility. The mass fraction of martensite and ...austenite can be tailored by the Q&P treatment. In this study, the impact of the microstructure on the corrosion behaviour is investigated. For this, the microstructures of two Q&P processing routes and a quenched and tempered state are analysed using scanning electron microscopy and X-ray diffraction. Electrochemical impedance spectroscopy is conducted using two different media in order to determine the time evolution of corrosion rates during short-time corrosion. The results of this study demonstrate that correlations between Q&P microstructures and the corrosion behaviour can be analysed in detail with these experimental methods.
PDF
