Fortschritte beim Rührreibschweißen von Aluminium,Magnesium und Stahl

Progresses on the friction stir welding of aluminium, magnesium and steel Friction Stir Welding (FSW) represents an innovative welding process for joining light metal, especially, aluminium and its alloys. Friction Stir Welding offers an attractive alternative to conventional fusion welding processes because of the excellent properties (particularly ductility), reproducibility, robustness, and surface finish obtained with the process. Within the scope of this work the Friction Stir Welding‐Process with its possible joint configurations is explained. The focus of this work concentrates on weldability studies concerning cladded aluminium alloys, aluminium cast alloys, aluminium tailored welded blanks both from similar and dissimilar joints produced in aluminium, magnesium and steel. The mechanical properties of the welded samples will be discussed.     

Vorhersage der Lebensdauer und Dauerfestigkeit von hochfesten,durchhärtenden Stählen

Fatigue Lifetime and Endurance Limit Prediction for High‐Strength Steels Smooth and notched specimens of the bearing steel 100Cr6 (SAE 52100) in a bainitic condition were used to determine the S‐N curves under tensile, torsional and combined in‐ and out‐of‐phase loading. In the area of high‐cycle fatigue, crack initiation was most likely caused by inclusions like Titanium Carbonnitrides or Aluminium Oxides. A micro mechanical model for the crack initiation by inclusions was developed. Another model was developed to describe the influence of these inclusions on the lifetime. A weakest‐link model, using the statistical distribution of inclusions and surface flaws, was used to describe the endurance limit.     

The impact of aging and drag-finishing on the surface integrity and corrosion behavior of the selective laser melted maraging steel samples

The maraging steel components fabricated using the selective laser melting process exhibit remarkable static strength. However, high pore density and large surface imperfections impede their overall mechanical and chemical performance. Thus, the components are often post-treated with mechanical- and thermal-based treatments to overcome their inherent imperfections and enhance their final mechanical properties. Although the post-processing treatments are useful in enhancing the selective laser melted components’ mechanical performance, their effect on corrosion behavior is not comprehensively evaluated. In this study, the selective laser melting prepared maraging steel samples’ corrosion behavior was examined in the as-built condition and compared with the post-processed samples subjected to aging and drag finishing operations. Compared to the as-built condition, both aging and drag-finishing post-processing treatments increased the selective laser melting samples’ corrosion even though the surface integrity was improved.     

Effects of chloride ions on electrochemical reaction of 316 stainless steel in mixtures of molten nitrate salts

Effects of chloride ion on decomposition of ternary nitrate and corrosion behaviors of 316 stainless steel (316 SS) were studied by electrochemical corrosion tests in molten salt. Chemical composition and morphology of the corrosion products were analyzed using x-ray diffraction and scanning electron microscopy equipped with energy disperse spectroscopy. Composition analysis for molten salt combined with morphology analyses of corrosion layer showed that presence of chlorine ions slowed down decomposition of ternary nitrate and increased corrosion rate of stainless steel markedly. The polarization curve obtained indicated that the corrosion current density increased from 3.02 mA ⋅ cm⁻² to 8.76 mA ⋅ cm⁻² with the addition of 10 % NaCl. Electrochemical impedance spectroscopy indicated a decrease in charge-transfer resistance of the double layer between 316 SS and ternary Nitrate containing 10 % NaCl, resulting in a decreased corrosion resistance of 316 SS.     

Microstructural characterization and mechanical integrity of stainless steel 316L clad layers deposited via wire arc additive manufacturing for nuclear applications

The potential applications of stainless steel 316L components using wire arc additive manufacturing offers many benefits such as improved part complexity, higher deposition rate and less material waste. Microstructural examination indicates the strong interlayer bonding between cladded layers and was mainly austenitic with columnar and equiaxed dendrites while equiaxed grains with annealing twins were observed in the stainless steel 316L substrate. In the current study, we report that stainless steel 316L additively cladded via wire arc additive manufacturing exhibits a 11 % and 14 % increase in the yield strength and tensile strength, correspondingly in contrast to the stainless steel 316L substrate. The enhanced mechanical properties are attributed to the columnar structure and interlayer remelted peritectic growth. Hardness values were higher at the cladded layers compared to the interface and substrate. Interface sample failed in the substrate side and all samples exhibited ductile mode of fracture with fine dimples and micro voids. Wire arc additive manufacturing process can be employed for producing or repairing components with better mechanical properties and corrosion performance for elevated temperature environments including nuclear reactor applications.     

Determination of the s-phase formation coefficient of plasma nitrided austenitic steel

Plasma nitriding is an effective surface hardening treatment for austenitic stainless steels. During plasma nitriding, s-phase formation takes place which is not only responsible for high hardness and wear resistance but also for good corrosion resistance. In order to estimate the thickness of the s-phase for austenitic stainless steel in a plasma nitriding process, an empirical model is devised. A number of plasma nitriding processes of austenitic stainless steel (304 L) were carried out with varying treatment temperature from 360 °C to 450 °C and process duration ranging from 10 hours to 24 hours with constant pressure, voltage, pulse-to-pause-ratio and gas mixture. A time-temperature dependent s-phase formation coefficient is determined by measuring the thickness of the s-phase using a scanning electron microscope (SEM) and glow discharge optical emission spectroscopy (GDOES). The developed model is verified by three controlled experiments. This model fits the thickness of the s-phase with an error of less than 6 %.