Materialwissenschaft und Werkstofftechnik最新文献

The fatigue behavior of a fully processed, non-oriented electrical steel sheet is investigated for different shear cutting parameters. Therefore, three cutting clearances (15 μm, 35 μm and 50 μm) in combination with two different punching tool wear states (sharp and worn) are compared regarding their mechanical properties. For this purpose, surface measurements, nanoindentation tests and stress-controlled fatigue tests with a positive load ratio are performed for all six parameter sets. During shear cutting the material gets locally strain-hardened and a deformed surface with micro-notches is created. Compared to a polished reference condition, the fatigue strength of the shear-cut sheets is severely deteriorated. However, the intensity of deterioration varies depending on the shear cutting parameters. For small cutting clearances, the highest fatigue life is observed for a sharp cutting tool. In contrast, for medium and high cutting clearances, samples that are cut with a worn tool achieve higher fatigue lives. Surface characteristics in the fracture zone, which act as a failure-critical crack location, are considered as the main influencing factor.

The galvanic corrosion of AISI 304 stainless steel/B30 copper-nickel alloy (304SS/B30 Cu−Ni) was investigated in neutral and acidic solutions with and without fluoride ion (F⁻) by wire beam electrode techniques, macro-electrochemical methods and scanning electron microscope. The results show that the passivation film was eroded by the synergistic effect of the proton (H⁺) and fluoride ion on the coupled sample surfaces, leading to changes significantly in the surface electrochemical activity and corrosion rate. The surface morphology after being immersed for 48 h in different solutions was observed by scanning electron microscope. However, 304 stainless steel is used as an anode relative to B30 copper-nickel alloy, with a typical polarity reversal, when fluoride ion is added to an acidic solution with pH=2.0.

The rapid expansion of global infrastructure growth has caused a substantial rise in construction and demolition waste. This study introduces an innovative approach for investigating mixed recycled aggregate in concrete generated from construction and demolition waste by treating it with cement and nano-silica slurry wrapping techniques. A central composite design experimental methodology was used to optimise the slurry for treatment, considering cement content, nano-silica content, and water-to-aggregate ratio as independent variables. At the same time, water absorption and Los Angeles abrasion with visual inspection were response-targeted values. Multi-objective response optimisation and desirability analysis determined optimal levels. Scanning electron microscopy, x-ray diffraction, and x-ray fluorescence were used to analyse mixed recycled aggregate facade changes after treatment. In addition, concrete with untreated and optimised treated mixed recycled aggregate at 0 %, 25 %, 50 %, 75 %, and 100 % as a replacement for natural aggregate was tested for workability and mechanical properties. The findings showed that 50 % replacement improved concrete characteristics at the optimal percentage due to the coating process-filled fracture holes and densified mixed recycled material, improving concrete matrix bonding.

Flux cored arc welding has emerged as a vital welding technology in the realm of pipes and petrochemical pipelines, addressing the severe weld quality, material compatibility, and safety criteria in these essential applications. The paper begins with a brief description of the flux cored arc welding process, explaining its procedural complexities, the necessary tools used, and the variety of consumables used. The review then describes the complexities of flux cored arc welding's applicability in joining pipes due to the unique welding demands imposed by petrochemical pipelines. A thorough examination of flux cored arc welding characteristics and processes follows, identifying the critical welding parameters that have a significant impact on the structural strength and durability of flux cored arc welded joints. The review goes further to highlight key applications of flux cored arc welding through case studies by illustrating the adaptability of the welding procedure to different scenarios. An in-depth analysis of flux cored arc welding technological advancements that highlights the current developments in electrode composition, shielding gases, and automation is also considered. In conclusion, this study offers a thorough overview of flux cored arc welding uses in pipes and petrochemical pipelines, fusing technical clarification with real-world applications.

The permeability, solubility, and diffusion of hydrogen in alloy 718 were examined through both, experimental results and data from existing literature. There is a notable difference between hydrogen solubilities calculated from concentration measurements and those derived from permeation measurements. Consequently, based on a synthesis of experimental and literature data, the following coefficients for hydrogen are proposed: K₀=186 mol/(m³ * MPa^0.5) and H_S=8140 J/mol for solubility, P₀=1.68 * 10⁻⁴ mol/(m³ * MPa^0,5) and H_P=57974 J/mol for permeability as well as D₀=9.01 * 10⁻⁷ m²/s and H_D=49834 J/mol for diffusivity. It is shown that these coefficients can largely be applied independently of the heat treatment of alloy 718.

Continuous casting of steel is widely used to manufacture semi-finished long or flat products. Various stresses are present during slab casting: stresses arise from friction between the mold wall and the solidified shell, thermal stresses on the strand surface, and stresses from bending and straightening operations. Steels present a minimum ductility point during continuous casting in the solid-state condition. This work aims to answer the metallurgical reasons for the occurrence of the ductility minimum in a micro-alloyed steel by investigating the microstructural evolution. The samples are in situ melted via induction heating in the BETA250-5^® thermomechanical simulator machine, followed by hot tensile tests conducted at different temperatures and strain rates. The ductility drop is analyzed in the range of 650 °C–1100 °C at different strain rates, 10⁻² s⁻¹ to 10⁻³ s⁻¹. Furthermore, the study investigated the development of the ferrite phase at the prior austenite grain boundaries, the thickness of ferrite, dynamic phase transformation, and the influence of the test conditions on these parameters. The fracture mechanism and ferrite phase thickness are determined from metallography investigations using light optical microscopy and scanning electron microscopy. Finally, the microstructural changes are correlated to the ductility minimum using the measured results.

In the present investigation two smart prediction tools, namely the multiple regression analysis and general regression neural network models were developed to predict average grain size and shape factor of the semi-solid AZ91D magnesium alloy microstructure prepared by mechanical stirring. The process parameters (stirring temperature, stirring rate, stirring time) were considered as input variables to establish predictive models. The models were developed using the multiple regression analysis was employed to determine the significance of process parameters on microstructure. In the general regression neural network models, the k-fold cross validation method is used to optimize the smoothing factor. The neural network models were trained, validated and tested. The results show the general regression neural network models achieve higher prediction accuracy for predicted error within 5 % compared with regression models within 10 %, which suggests that the model is more reliable. Finally, the accuracy of models was demonstrated based on experimental verification, asserting that they can provide a foundation for developing a comprehensive prediction system to optimize the structural and processing of semi-solid magnesium alloys.