Defect and Diffusion Forum Vol. 439

Abstract: Since their early investigations, TiN coatings have sparked considerable interest because of their remarkable mechanical properties, especially their prominent hardness (30–60 GPa) and oxidation resistance. They are mainly used to harden and protect cutting or sliding tools and occasionally for decoration. Small quantities of different ligands, including Ni, Cu, or Co, are added to improve the smooth performance of cutting tools. These alloying elements lead to the formation of nanocomposites, potentially altering their mechanical characteristics and imparting notable flexibility. In this context, this study focuses on the production of pure TiN and Cu-doped TiN thin films. Magnetron sputtering was used as a deposition technique, simultaneously sputtering Ti and Cu-targets, both with high purity (99.99%), and in a gas mixture of Ar and N₂. X-ray diffraction, SEM, profilometry, nanohardness, and scratch test analyses were employed to characterize the TiN and TiN/Cu films. The results reveal that 3–4% of Cu content led to a slight decrease in hardness, while surface adhesion increased with the addition of copper. Furthermore, the elasticity of the doped films improved the strength and wear resistance of coatings with Cu compared to TiN films without added Cu.

Abstract: The application of microfluidic technology within the field of additive manufacturing is investigated, with a specific focus on devices designed for precise material dosing. An in-depth examination is conducted to explore how microfluidic technology can be integrated into Cartesian 3D printing systems, enabling precise and controlled material dispensing throughout the manufacturing process. A novel methodology was developed to assess these devices, evaluating their feasibility and effectiveness in improving the quality and efficiency of manufactured products. Experimental analysis was performed to examine various microfluidic device configurations and their impacts on material dosing precision, along with their potential for reducing waste. Promising advancements in additive manufacturing were demonstrated by the findings, which offer new insights and opportunities in fields such as medicine, electronics, and engineering. The foundation for enhancing material dosing control in additive manufacturing was laid by this study. Keywords: Microfluidic technology, additive manufacturing, precise material dosing, Synthetic material.

Abstract: Microfluidics is an efficient technology for controlling fluid movement in microchannels at extremely low speeds. The main advantage lies in the significant reduction of samples and reagents, thereby reducing costs and analysis times. Three devices with retention systems are introduced that are manufactured through 3D printing (SLA) incorporating microchannels with variations in levels and dimensions. Fluid velocity is studied, considering factors such as channel width, length, rounding, height, and shape. The analysis of velocity along the channel reveals liquid retention at the devices' maximum point, ensuring more precise results in microdevices.

Abstract: Wire arc additive manufacturing (WAAM) stands out as a highly promising direct energy deposition (DED) technology for producing large-scale metallic parts, primarily due to its efficiency, high deposition rate, and low production costs. WAAM can be exploited with many advantages to a wide range of metallic materials, including aluminum, copper, and magnesium. This paper deals with the examination of thermal cycles and temperature fields developed during additive manufacturing of an AA5087 aluminum alloy part using conventional Cold Metal Transfer (CMT) with variable deposition parameters. The thermal cycles were experimentally measured by an Ahlborn Almemo 5690-2 measuring station equipped with K-type thermocouples. A simulation model of the deposition process was developed to perform a more detailed study of the impact of the travel speed on the temperature distribution and geometrical characteristics of single weld beads, using ANSYS software. The measured and computed thermal cycles and peak temperatures reached during the 1^st and 2^nd deposition cycle were compared. The maximum measured temperatures at a travel speed of 25 cm/min were 503.4 °C (1^st cycle) and 419.6 °C (2^nd cycle), while the calculated temperatures were 502.5 °C and 417.4 °C, respectively. At a higher travel speed of 35 cm/min, the peak temperatures were lower, with experimental values of 459.6 °C (1^st cycle) and 417.5 °C (2^nd cycle), and calculated values of 459.0 °C and 391.2 °C.

Abstract: Demands for ultra-low temperature refrigeration systems have been increasing in various fields such as recent LNG (Liquefied Natural Gas) ship BOG (Boil-off Gas) re-liquefaction processes. For the criteria of LNG tankers, the system is essential for mitigating the pressure increase of LNG storage tanks due to BOG. Therefore, this paper optimized the refrigerant charge level of an ultra-low temperature refrigeration system using the Cascade MR-Joule-Thomson. The novelty of this study stems from introducing the dimensionless number called Charge level to optimize the refrigerant charge amount of ultra-low temperature refrigerators using the Cascade MR-Joule-Thomson refrigeration cycle. Experimental results showed that as the refrigerant charge amount increased, the absolute amount of refrigerant within the limited volume increased, leading to an increase in both the suction and discharge pressures of the system. Additionally, the cooling capacity also showed an increasing trend. In contrast, the discharge temperature and cooling time exhibited a decreasing trend. Based on these results, the optimal refrigerant charge amount was determined.

Abstract: The drying process that is responsible for ensuring the coffee quality, reduces the moisture of the coffee bean thus avoiding unwanted microorganisms. Traditional drying methods take between 16 and 45 hours to dry coffee beans, which results in high operational costs. Therefore, the application of the microwave drying technique is a possible alternative, as it can reduce drying periods by four times. In this study, the main goal was to evaluate the heating kinetics and distribution of a single coffee bean due to microwaves to verify its heterogeneity. Initially, a single coffee bean was designed and inserted into a monomode microwave cavity. The geometry of the coffee bean was simplified as a semi-ellipsoid with its diameters measured experimentally and with four different curvatures at the edges. As a result of the numerical simulations, the temperature distribution on the coffee bean over time was obtained as well as the average temperature and temperature at its center. The heating kinetics plot described a linear curve for every geometry, having a higher inclination in the sharp edge and decreasing as the curvature increases. Also, when comparing the average and center temperatures, the temperature in the center is 107.58 °C and the average temperature of the coffee bean is 96.09 °C, which corroborates the fact that the microwave heating occurs from inside out. In conclusion, the microwave heating in coffee beans is heterogeneous, starting in its center, favoring the mass transfer phenomenon during drying and can be influenced by the sharpness of the coffee beans edges.

Abstract: In this study, we proposed a moved-view analysis, a method for obtaining the Soret coefficient S_T by analyzing the interference fringe change during field-of-view movement in the steady state. This analysis was designed to solve the problem that the sign of the concentration gradient could also be reversed if the plot of the concentration distribution was only slightly shifted owing to the narrow field of view. The data obtained from the experiment conducted to measure S_T at the International Space Station were analyzed using moved-view analysis. For the moved-view analysis, the linearity of the concentration distribution induced by the Soret effect is larger than that for the method without field-of-view movement, and a more reliable S_T can be obtained. The analysis error that sometimes occurred when the laser wavelength switched led to the underestimation of the phase change Δϕ, resulting in generating the data with low linearity. This unreliable data should be removed.