Key Engineering Materials Vol. 943

Abstract: The present research shows the possibility of using an ytterbium nanosecond pulsed fiber laser for wear resistance improvement of carbon and alloy steels. The wear test was performed in accordance with the block-on-ring scheme with dry sliding friction on a friction machine. Surface dispersing/alloying was carried out from a boron carbide paste. This leads to a significant wear resistance improvement of steels. It was revealed that the mass loss during wear test reduced by several times after laser treatment compared to the non-treated samples. The wear mechanism differs depending on the type of steel and largely refers to their microstructure and composition. The tribo-oxide layer forms during the wear test.

Abstract: The effects of rare earth element Y addition on the structure, elastic modulus and hardness of Ti₈₀Nb_20-xY_x (x =0, 1, 2) alloys were investigated experimentally. The results showed that the structure of Ti-Nb-Y ternary alloys consist of the Ti-Nb matrix and Y-rich precipitates. Increasing the Y content can significantly improve the hardness and elastic modulus decreases with of Ti-Nb-Y alloys.

Abstract: In the electroless nickel-boron coating process, surfactant helps to minimize the surface tension between the substrate and the electrolyte in the bath. Despite, its high cost and the formation of micelles from monomeric surfactant molecules at its critical micelle concentration (CMC), it is essential to optimize the concentration while using in the bath. In this study, to solve this problem, mathematical models are developed using regression and artificial neural network (ANN) techniques to relate the concentration of amphoteric surfactant (0-0.162 g/L) as an independent variable and microhardness as a dependent variable. Then, the developed model was used to optimize microhardness at CMC using a genetic algorithm (GA). The goodness of fit of the models was evaluated using the coefficient of determination (R²). The ANN model was found to be the best fit with R² = 0.99. The maximum microhardness of 852 HV was achieved at the CMC of 0.064 g/L, from the GA using the validated model as a fitness function.

Abstract: FSW is a welding process which done by movement of tool against the workpiece. Tool is an important part in FSW process because tool generates most of the heat in the FSW process, so the tool material and geometry are important because they receive high stress and temperature. This research was conducted to decide the best pin geometry for tool from the 4-pin geometry that has been decided, which is straight cylindrical, tapered cylindrical, hexagonal, and tapered square. The optimization process is done with Taguchi method using 4 factors where each factor has 4 levels, factors that used in this research are tool rotation speed, welding speed, tool shoulder angle, and tool tilt angle with the respond is temperature at welding joint. The optimization process will be done in all of the pin geometries that has been decided and the best pin geometry out of 4 geometries will be chosen. The best pin out of 4 geometries is the hexagonal pin with the optimized parameters are the rotational speed of 1208 rpm, welding speed of 65 mm/min, tilt angle of 2.5° and concave angle of 2° with max. temperature of 322.48°C. The significant factor obtained was the tool rotational speed and concave angle with significance level of 95%.

Abstract: Efficiency energy is an importance goal in transportation device development. Reducing weight of device is a way to reduce fuel consumption from transportation device, using thin plat in a device or construction could reduce the weight. The originality of this study was Micro Dissimilar Friction Stir Spot welding used to join Cu and Al plate with copper sheet on top the aluminum sheet. Micro welding is a joining thin plat less than 1 mm welded by Friction Stir Spot welding which has been called a Micro Friction Stir Spot welding, using a Pin on the Shoulder. Peak load average, macrostructure and shear strength of a copper and aluminum sheet joint welded by Micro Friction Stir Spot welding were discussed in this study. Copper and Aluminum 0.5 mm could be successfully joined. Shoulder diameter 6 mm effected to the highest peak load, and welding force 50 kgf significantly increased the peak load. Mixing Cu and Al formed in a weld joint. Friction was not complete occurred in shoulder interface and deflection copper sheet formed in around weld nugget because of Pin and Shoulder. A Pin on Shoulder affect to form a joint only around Pin, shear strength could not conclude because the weld joint areas developing tend to an incomplete joining.

Abstract: This research was conducted to investigate the effect of variations in tool rotation and surface roughness towards shear strength on the newly developed friction lap welding (FLW) for dissimilar joints between stainless steel (SS) 304 and Nylon 6 plates. Under constant welding traverse speed at 30 mm/min, the variation of tool rotation used were 1100 and 2200 rpm and surface roughness of 0.32; 1.25; and 1.88 μm initially obtained from different surface modification methods. The shear test was conducted at FLW dissimilar joint based on AWS D8.9-97 standard. The results showed that the shear stress increased along with the higher tool rotation and at the greater surface roughness. The highest shear strength value was found at the tool rotation of 2200 rpm and surface roughness of 1.88 μm with 9.447 MPa. The tool rotation may produce a higher heat input as well as an effect on the value of nylon hardness. On the other hand, rougher SS surfaces provide a larger area for the interfacial adhesive bond between nylon and metal; therefore, they can act as an interlocking site when the shear loading was applied. These phenomena were also confirmed by fracture morphology and microscopic image analysis.

Abstract: This study aims to determine the effect of the concave shoulder angle of the FSW tool on heat generation rate and temperature simulation results. The FSW tool used in this study is the FSW tool with straight cylindrical geometry, tapered cylinder, hexagonal, and tapered square. Calculation of heat generation rate is carried out for all FSW tools, then the optimal one is selected and then simulated. The process of calculating heat generation rate and simulation using the Taguchi method has 4 factors, each of which has 4 levels. The factors used in this study are tool rotation speed, welding speed, concave shoulder angle, and tool tilt angle with temperature response. on the weld joint. The results of this study indicate that the influence of the concave shoulder angle on the heat generation rate and temperature simulation is very influential. Based on the results of the heat generation rate calculation, the FSW tool with hexagonal pin geometry was chosen to be simulated. The simulation results show that the selected process parameters are tool rotation speed of 1208 rpm, welding speed of 90 mm/s, concave shoulder angle of 5°, and tool tilt angle of 3°. From the selected parameters, it was experimented with to produce a fairly good connection even though there were still surface defects.

Abstract: Duplex stainless steels (DSSs) are being increasingly employed in the oil and gas and chemical industries, which, despite their high alloying degree and high resistance to general corrosion, are subject to pitting and crevice corrosion. According to their resistance to pitting and crevice corrosion, steels are ranked according to the PREN. However, nowadays there are many grades of DSSs, in which the content of Cr, Mo and N varies in different quantities, therefore the selection of the grade must be carried out with great care, considering not only PREN, but also the production technology, operating conditions, and the geometry of products. The crevice corrosion behaviors of three grades of duplex stainless steels quenched from 1050, 1100 and 1200 °C were studied in FeCl₃ solution at 50°C. It is shown that PREN allows to rank only different grades in terms of corrosion resistance. With a constant PREN value, but with different contents of ferrite and austenite in steel, completely different values of the corrosion rate can be obtained, therefore, PREN must be used with great care. It was found that in the studied steels, the optimal ferrite content, at which the lowest crevice corrosion rate is achieved, is at 65 vol.%.

Abstract: Heat exchangers are widely used in the industry for processing natural gas. The article discusses the causes of corrosion damage to the internal surface of the stainless steel tubes for the heat exchanger coil. Chemical composition of tubes was obtained for provided damaged batch. Results of metallographic studies, as well as results of scanning electron microscopy of individual parts of pipes are presented. Tests for resistance to intergranular corrosion were carried out. The study revealed that the main reason of corrosion damage on the inner wall of the tubes is the formation of carbides along the boundaries of austenitic grains, and as a result, the chromium-depleted grain was subjected to corrosion.