Search Results (7)

In order to improve the performances of metal containers, furnace bodies and agricultural tools manufactured by mild steels, Ni/W-SiC nanocomposites are prefabricated on mild steel substrate by the pulse electrodeposition (PED) method. The morphology, texture, microstructure, microhardness, and wear performances of Ni/W-SiC nanocomposites are examined by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), dispersive X-ray spectroscopy (EDX), hardness tester, and friction wear testing. The results indicate that the SiC size in nanocomposites is ~32.4 nm when its concentration in electrolytes is 7 g/L. The S1 and S4 nanocomposites’ microstructures (the S1 composite was prefabricated at 4 g/L, and the S4 composite was deposited at 13 g/L) reveal many large cauliflower-shaped grains. However, the S2 nanocomposite (the S2 composite was obtained at 7 g/L) demonstrates the homogeneous, finest and smoothest surface morphology. The diffraction angles of S1 nanocomposite are 41.2°, 51.7°, and 71.2° depicting the sharpest diffraction peaks, corresponding to the (1 1 1), (2 0 0), and (2 2 0) crystal planes of Ni-W grains, respectively. Moreover, the S2 nanocomposite exhibits the lowest wear depth and width of 34.2 μm and 5.5 mm, respectively. Some shallow and fine scratches on the as-described nanocomposites’ surface indicate its excellent tribological performance. However, the S4 nanocomposite exhibits a wear depth of 86.3 μm and a width of 11.9 mm. Full article

This paper is a study of the microstructure and other selected properties of solid-state, high-speed, rotary friction-welded tungsten and mild steel (S355) joints. Due to the high affinity of tungsten for oxygen, the welding process was carried out in a chamber with an argon protective atmosphere. Joints of suitable quality were obtained without any macroscopic defects and discontinuities. Scanning electron microscopy (SEM) was used to investigate the phase transformations taking place during the friction welding process. Chemical compositions in the interfaces of the welded joints were determined by using energy dispersive spectroscopy (EDS). The microstructure of friction welds consisted of a few zones, fine equiaxed grains (formed due to dynamic recrystallization) and ultrafine grains in the region on the steel side. A plastic deformation in the direction of the flash was visible mainly on the steel side. EDS-SEM scan line analyses across the interface did not confirm the diffusion of tungsten to iron. The nature of the friction welding dissimilar joint is non-equilibrium based on deep plastic deformation without visible diffusive processes in the interface zone. The absence of intermetallic phases was found in the weld interface during SEM observations. Mechanical properties of the friction-welded joint were defined using the Vickers hardness test and the instrumented indentation test (IIT). The results are presented in the form of a distribution in the longitudinal plane of the welded joint. The fracture during strength tests occurred mainly through the cleavage planes at the interface of the tungsten grain close to the friction surface. Full article

Wire arc additive manufacturing (WAAM) involves the deposition of weld beads layer by layer using an electric arc energy source. However, during this procedure, the properties of each layer may differ because of unequal thermal distribution, resulting in a difference in microstructure and, therefore, mechanical properties in between the layers. This negative effect can be compensated for by combining WAAM with a subsequent forming process to introduce dynamic recrystallization, which allows a more homogeneous microstructure distribution within the material. This paper investigates numerically and experimentally the hybrid process of combined WAAM and forming of fine-grained mild steel (FGMS) SG3/G4Si (1.5130) to achieve a high degree of recrystallization in all layers of the WAAM-deposited material. Three different possible combinations of WAAM and forming are considered regarding the sequence and setup of the processes to show their influences on the recrystallization behavior. It was found that combining welding and forming allows recrystallization of up to two layers; however, the top layer is not recrystallized. Preliminary simulation results show that this can be resolved by adding a top roller to induce plastic strain after welding, leading to recrystallization in the top layer. The found results promise a certain controllability of the recrystallization behavior. Full article

In the current work, mild steel used in shipbuilding applications was friction-stir-welded (FSWed) with the aim of investigating the microstructure and mechanical properties of the FSWed joints. Mild steel of 5 mm thickness was friction-stir-welded at a constant tool rotation rate of 500 rpm and two different welding speeds of 20 mm/min and 50 mm/min and 3° tool tilt angle. The microstructure of the joints was investigated using optical and scanning electron microscopes. Additionally, the grain structure and crystallographic texture of the nugget (NG) zone of the FSWed joints was investigated using electron backscattering diffraction (EBSD). Furthermore, the mechanical properties were investigated using both tensile testing and hardness testing. The microstructure of the low-welding-speed joint was found to consist of fine-grain ferrite and bainite (acicular ferrite) with an average grain size of 3 µm, which indicates that the temperature experienced above A1, where a ferrite and austenite mixture is formed, and upon cooling, the austenite transformed into bainite. The joint produced using high welding speed resulted in a microstructure consisting mainly of polygonal ferrite and pearlite. This could be due to the temperature far below A1 experienced during FSW. In terms of joint efficiency expressed in terms of relative ultimate tensile, the stress of the joint to the base material was found to be around 92% for the low-speed joint and 83% for the high-welding-speed joint. A reduction in welding was attributed to the microstructure, as well as the microtunnel defect formed near the advancing side of the joint. The tensile strain was preserved at 18% for low welding speed and increased to 24% for the high welding speed. This can be attributed to the NG zone microstructural constituents. In terms of crystallographic texture, it is dominated by a simple shear texture, with increased intensity achieved by increasing the welding speed. In both joints, the hardness was found to be significantly increased in the NG zone of the joints, with a greater increase in the case of the low-welding-speed joint. This hardness increase is mainly attributed to the fine-grained structure formed after FSW. Full article

This paper presents a tool wear monitoring methodology on the abrasive belt grinding process using vibration and force signatures on a convolutional neural network (CNN). A belt tool typically has a random orientation of abrasive grains and grit size variation for coarse or fine material removal. Degradation of the belt condition is a critical phenomenon that affects the workpiece quality during grinding. This work focuses on the identifation and the study of force and vibrational signals taken from sensors along an axis or combination of axes that carry important information of the contact conditions, i.e., belt wear. Three axes of the two sensors are aligned and labelled as X-axis (parallel to the direction of the tool during the abrasive process), Y-axis (perpendicular to the direction of the tool during the abrasive process) and Z-axis (parallel to the direction of the tool during the retract movement). The grinding process was performed using a customized abrasive belt grinder attached to a multi-axis robot on a mild-steel workpiece. The vibration and force signals along three axes (X, Y and Z) were acquired for four discrete sequential belt wear conditions: brand-new, 5-min cycle time, 15-min cycle time, and worn-out. The raw signals that correspond to the sensor measurement along the different axes were used to supervisedly train a 10-Layer CNN architecture to distinguish the belt wear states. Different possible combinations within the three axes of the sensors (X, Y, Z, XY, XZ, YZ and XYZ) were fed as inputs to the CNN model to sort the axis (or combination of axes) in the order of distinct representation of the belt wear state. The CNN classification results revealed that the combination of the XZ-axes and YZ-axes of the accelerometer sensor provides more accurate predictions than other combinations, indicating that the information from the Z-axis of the accelerometer is significant compared to the other two axes. In addition, the CNN accuracy of the XY-axes combination of dynamometer outperformed that of other combinations. Full article

The paper presents the assessment of the possibility and reliability of the digital image correlation (DIC) system for engineering and scientific purposes. The studies were performed with the use of samples made of the three different materials—mild S235JR + N steel, microalloyed fine-grain S355MC steel, and high strength 41Cr4 steel subjected to different heat-treatment. The DIC studies were focused on determinations of dangerous zones with large stress concentrations, plastic deformation growth, and prediction of the failure zone. Experimental tests were carried out for samples with different notches (circular, square, and triangular openings). With the use of the DIC system and microstructure analyses, the influence of different factors (laser cutting, heat treatment, material type, notch shape, and manufacturing quality) on the material behavior were studied. For all studied cases, the stress concentration factors (SCF) were estimated with the use of the analytical formulation and the finite element analysis. It was observed that the theoretical models for calculations of the influence of the typical notches may result in not proper values of SCFs. Finally, the selected results of the total strain distributions were compared with FEM results, and good agreement was observed. All these allow the authors to conclude that the application of DIC with a common digital camera can be effectively applied for the analysis of the evolution of plastic zones and the damage detection for mild high-strength steels, as well as those normalized and quenched and tempered at higher temperatures. Full article

The micro ablation characteristics of steel inflicted by the lightning currents and the influence of anti-corrosion coating on these characteristics are seldom investigated, even though fundamental to applications of steel. In this work, ablation tests on uncoated and coated mild steel plates were conducted with the 2 ms rectangular current simulating the component B of lightning currents. The macro-morphology, microstructure, and Vickers hardness of ablation zones were investigated systematically. The ablation characteristics and mechanisms of coated and uncoated steel were analyzed comparatively. It was found that the energy density of the 2 kA 2 ms rectangular current arc exceeded 10⁶ W/cm² causing the steel near the arc root melted within 2 ms and ablation formed. The width-depth-ratio of the ablated zone was 43.7 for uncoated plate, and only 7.5 for coated plate, since coating constricted the splashing effect of steel melt occurring on uncoated plate and confined the arc root. The metallographic microstructure and EBSD results showed the ablated zones of uncoated and coated steel both consisted of quenched martensite mixed with a handful of ferrite. There were fined equiaxed grains both in the fusion zone (FZ) and heat affected zone (HAZ) of uncoated plates whereas coarser columnar grains and fined equiaxed grains in the FZ and HAZ of coated plates, respectively. In the HAZ of uncoated plate, the average Vickers hardness of steel increased by 113%, while, in the HAZ and FZ of the coated plate, it increased by 209% and 136%, respectively. Full article