Search Results (10)

Copper and its alloys are widely used in marine environments due to their excellent corrosion resistance and thermal conductivity. Cold spray technology can avoid the thermal damage to the underlying material and is suitable for the manufacturing and repair of parts. In this study, Cu coatings were prepared on 304 stainless steel substrates by high-pressure cold spray technology, and the effects of cold spray parameters on the microstructure, mechanical properties, and cavitation resistance were investigated. The coatings (Cu-N₂1, Cu-N₂2, and Cu-He) were prepared using distinct cold spray parameters: Cu-N₂1 and Cu-N₂2 employed nitrogen gas at 5 MPa/800 °C with different nozzle geometries, while Cu-He utilized helium gas at 3 MPa/600 °C. The results show that the porosity of the Cu coating prepared by cold spray technology is less than 0.1%. The coating treated with helium gas exhibits a higher bonding strength (81.3 MPa), whereas the coating treated with nitrogen demonstrates greater strain hardening (130–136 HV_0.1). XRD results show that no phase change or oxidation occurred for coatings under all cold spraying conditions. After the cavitation test, the mass loss of the Cu coating is significantly less than that of the as-cast copper. The Cu coating surface first develops holes, and with the increase in cavitation time, the hole area begins to increase. However, with prolonged cavitation exposure, the surface of as-cast copper has a large area of holes, and with the increase in cavitation time, the hole growth rate is faster. These observations indicate the cavitation resistance of the Cu coating prepared by cold spray is more than 10 times higher than that of the as-cast copper. This study highlights the potential application of cold spray technology in the preparation of high-performance anti-cavitation copper coatings. Full article

Complex concrete elements are typically produced with lost formwork made out of timber or plastic. After usage, these timber or plastic panels are disposed of. This makes complex lost formwork a polluting and high-cost-inducing aspect of concrete construction. A possible solution for this problem could be 3D printing of concrete. This high degree of freedom construction process could easily be used to produce complex formwork. As the formwork stays in place, it has a function during and after the hardening of the inner concrete. Before hardening, the formwork keeps the fresh concrete in place. After hardening, the printed formwork takes the function of a concrete cover. The concrete cover protects the steel reinforcement against aggressive environmental substances such as chlorides and carbon dioxide. To properly execute this function, the printed material and the transition between printed material and inner concrete need to perform at least as well as the inner material. This experimental research investigates the usability of a 3D printed concrete mixture as a concrete cover in a combined concrete structure. The effect of the curing condition as well as two different surface finishing techniques of the printed formwork are taken into account. The effect of the different parameters is compared based on existing service life models. Results indicate that proper curing of the printed formwork is of key importance in order to obtain significant resistance against carbonation- and chloride-induced corrosion. Adjusting the nozzle with side trowels improves the resistance of the printed material against chloride intrusion and carbonation but has only a limited effect on the service life extension. Full article

Hard turning is an emerging machining technology that evolved as a substitute for grinding in the production of precision parts from hardened steel. It offers advantages such as reduced cycle times, lower costs, and environmental benefits over grinding. Hard turning is stated to be difficult because of the high hardness of the workpiece material, which causes higher tool wear, cutting temperature, surface roughness, and cutting force. In this work, a dual-nozzle minimum quantity lubrication (MQL) system’s performance assessment of ZnO nano-cutting fluid in the hard turning of AISI 52100 bearing steel is examined. The objective is to evaluate the ZnO nano-cutting fluid’s impacts on flank wear, surface roughness, cutting temperature, cutting power consumption, and cutting noise. The tool flank wear was traced to be very low (0.027 mm to 0.095 mm) as per the hard turning concern. Additionally, the data acquired are statistically analyzed using main effects plots, interaction plots, and analysis of variance (ANOVA). Moreover, a novel Weighted Aggregated Sum Product Assessment (WASPAS) optimization tool was implemented to select the optimal combination of input parameters. The following optimal input variables were found: depth of cut = 0.3 mm, feed = 0.05 mm/rev, cutting speed = 210 m/min, and flow rate = 50 mL/hr. Full article

In recent years, hard turning has emerged as a burgeoning cutting technology for producing high-quality finishing of cylindrical-shaped hardened steel for a variety of industrial applications. Hard turning under dry cutting was not accepted because of the generation of higher cutting temperatures which accelerated tool wear and produced an inferior surface finish. Nowadays, minimum quantity lubrication (MQL) is widely accepted in hard turning to reduce the problems encountered in dry cutting. This research aimed to augment the MQL performance in the hard turning process of AISI D2 steel by applying a novel concept, namely, a dual jet nozzle MQL system that supplies the cutting fluid into the cutting zone from two different directions. The performances of hard turning are discussed using machinability indicator parameters, such as surface roughness, tool wear, cutting temperature, power consumption, noise emission, and chip morphology. The dual nozzle MQL greatly reduced the friction between contact surfaces in the cutting zone and provided improved surface quality (Ra = 0.448 to 1.265 µm). Furthermore, tool flank wear was found to be lower, in the range of 0.041 to 0.112 mm, with abrasion and adhesion being observed to be the main mode of wear mechanisms. The power consumption was greatly influenced by the depth of cut (46.69%), followed by cutting speed (40.76%) and feed (9.70%). The chip shapes were found to be helical, ribbon, and spiral c type, while the colors were a metallic, light blue, deep blue, and light golden. Full article

Electro-discharge drilling is a key technology for manufacturing sophisticated nozzles in a broad range of automotive and aerospace applications. The formation of debris in the working gap leads to arcs and short circuits on the lateral surface when state-of-the-art tool electrodes are used. As a result, limited drilling depth, increased linear tool wear, and the conicity of boreholes are still challenges. In this work, a new approach for the passivation of the lateral surface of copper tool electrodes by oxidation is shown. The comparison with state-of-the-art tool electrodes showed a reduction in the erosion duration by 48% for machining hardened steel. Promising improvements could be achieved by the thermal oxidation of the tool electrodes with the aim of increasing the electrical resistivity of the lateral surface of the tool electrode. However, due to the loss of strength, the high oxide layer thickness, and the partial delamination of the oxide layer, further comprehensive investigations on the influence of the oxidation temperature need to be conducted. Future adjustments with lower oxidation temperatures will be carried out. Full article

This study aimed to investigate if a thermal barrier coating (TBC) affected the energy efficiency of 3D printers. In accordance with this purpose, the used TBC technique is clearly explained and adapted to a nozzle in a simulation environment. Brass, copper, and hardened steel were selected to be the materials for the nozzles. The reason for the usage of a thermal barrier coating method is that the materials are made with low thermal conductivity, which reduces the thermal conductivity and energy losses. Yttria-stabilized zirconia was used to coat material on brass, copper, and hardened steel. To prevent temperature fluctuations, yttria-stabilized zirconia together with a NiCRAl bond layer was used and, thus, heat loss was prevented. Additionally, the paper addressed the effects of the coating on the average heat flux density and the average temperature of the nozzles. In addition, by means of the finite element method, steady-state thermal analyses of the coated and uncoated nozzles were compared, and the results show that the thermal barrier coating method dramatically reduced energy loss through the nozzle. It was found that the average heat flux was reduced by 89.4223% in the brass nozzle, 91.6678% in the copper nozzle, and 79.1361% in the hardened steel nozzle. Full article

The use of cutting fluid is crucial in the grinding process due to the elevated heat generated during the process which typically flows to the workpiece and can adversely affect its integrity. Considering the conventional technique for cutting fluid application in grinding (flood), its efficiency is related to certain factors such as the type of fluid, nozzle geometry/positioning, flow rate and coolant concentration. Another parameter, one which is usually neglected, is the cutting fluid temperature. Since the heat exchange between the cutting fluid and workpiece increases with the temperature difference, controlling the cutting fluid temperature before its application could improve its cooling capability. In this context, this work aimed to analyze the surface integrity of bearing steel (hardened SAE 52100 steel) after grinding with an Al₂O₃ grinding wheel with the cutting fluid delivered via flood technique at different temperatures: 5 °C, 10 °C, 15 °C as well as room temperature (28 ± 1 °C). The surface integrity of the workpiece was analyzed in terms of surface roughness (Ra parameter), images of the ground surface, and the microhardness and microstructure beneath the machined surface. The results show that the surface roughness values reduced with the cutting fluid temperature. Furthermore, the application of a cutting fluid at low temperatures enabled the minimization of thermal damages regarding visible grinding burns, hardness variation, and microstructure changes. Full article

The main purpose of this study is to perform shaking table tests to validate the inelastic seismic analysis method applicable to pressure-retaining metal components in nuclear power plants (NPPs). To do this, the test mockup was designed and fabricated to be able to describe the hot leg surge line nozzle with a piping system, which is known to be one of the seismically fragile components in nuclear steam supply systems (NSSS). The used input motions are the displacement time histories corresponding to the design floor response spectrum at an elevation of 136 ft in the in-structure building in NPPs. Two earthquake levels are used in this study. One is the design-basis safe shutdown earthquake level (SSE, PGA = 0.3 g) and the other is the beyond-design-basis earthquake level (BDBE, PGA = 0.6 g), which is linearly scaled from the SSE level. To measure the inelastic strain responses, five strain gauges were attached at the expected critical locations in the target nozzle, and three accelerometers were installed at the shaking table and piping system to measure the dynamic responses. From the results of the shaking table tests, it was found that the plastic strain response at the target nozzle and the acceleration response at the piping system were not amplified by as much as two times the input earthquake level because the plastic behavior in the piping system significantly contributed to energy dissipation during the seismic events. To simulate the test results, elastoplastic seismic analyses with the well-known Chaboche kinematic hardening model and the Voce isotropic hardening model for Type 316 stainless steel were carried out, and the results of the principal strain and the acceleration responses were compared with the test results. From the comparison, it was found that the inelastic seismic analysis method can give very reasonable results when the earthquake level is large enough to invoke plastic behavior in nuclear metal components. Full article

Miniature products and components must be surface treated to improve their wear resistance and corrosion toughness. Among various processes, low-temperature plasma nitriding was employed to harden the outer and inner surfaces of micro-nozzles and to strengthen the micro-springs. A table-top nitriding system was developed even for simultaneous treatment of nozzles and springs. A single AISI316 micro-nozzle was nitrided at 673 K for 7.2 ks to have a surface hardness of 2000 HV0.02 and nitrogen solute content up to 10 mass%. In particular, the inner and outer surfaces of a micro-nozzle outlet were uniformly nitrided. In addition, the surface contact angle increased from 40° for bare stainless steels to 104° only by low-temperature plasma nitriding. A stack of micro-nozzles was simultaneously nitrided for mass production. Micro-springs were also nitrided to improve their stiffness for medical application. Full article

Cold-spray techniques have been a significant development for depositing metal coatings in recent years. In cold-spray processes, inexpensive nitrogen gas is widely used as the propellant gas in many industries. However, it is difficult to produce austenitic stainless steel coatings with dense microstructures with cold-spray techniques when using nitrogen propellant gas because of work hardening. In this study, the effects of cold-spray conditions using a nitrogen propellant gas on AISI 316L stainless steel coatings were examined. It was found that a higher nitrogen propellant gas temperature and pressure produce coatings with dense microstructures. The measured AISI 316L coating hardness values suggest that AISI 316L particles sprayed at temperatures of 700 and 800 °C soften due to the heat, allowing uniform deformation on the substrate and consequently forming dense coating microstructures. In addition, AISI 316L powder with particle diameters of 5–20 µm resulted in a denser coating microstructure than powder with particle diameters of 10–45 and 20–53 µm. Finally, the standoff distance between the nozzle and the substrate also affected the AISI 316L coating microstructures; a standoff distance of 40 mm produced the densest microstructure. Full article