Nikhil Kumar

This investigation focuses on the development of dual‐layer coating of AlN and TiAlN by Chemical vapor deposition (CVD) to improve surface protection for advanced engineering applications. The Aluminium nitride (AlN) interlayer was first deposited on p ‐type c‐Si (100) substrates over a temperature range of 200°C to 800°C, followed by the TiAlN top layer. The effect of deposition temperature on the structural, morphological, mechanical, and electrochemical properties of the coatings was systematically investigated. Surface morphology and microstructure were examined using Field emission scanning electron microscope (FESEM), while phase composition was studied by X‐ray diffraction (XRD). Atomic force microscope (AFM) provided insights into nanoscale surface roughness, and Raman spectroscopy confirmed the vibrational modes of the coating phases. The X‐ray photoelectron spectroscopy (XPS) analysis confirmed the formation of strong Titanium‐Nitride (Ti─N), Aluminium nitride (Al─N), and Aluminium Titanium nitride (Al─Ti─N) bonds, indicating successful synthesis of a chemically stable dual‐layer structure. Nanoindentation revealed that the dual‐layer coating deposited at 700°C exhibited superior hardness and Young's modulus values of 29.64 and 209.69 GPa, respectively, indicating improved mechanical integrity. Electrochemical corrosion testing demonstrated excellent corrosion resistance, with the lowest corrosion current density observed for the coating formed at 700°C. Collectively, the results confirm that CVD‐deposited AlN/TiAlN dual‐layer coating offer a promising route for surface engineering applications that requires high hardness, better tribological property, and corrosion resistance in aggressive environments.

The High Velocity Oxyfuel (HVOF) system has established itself as a leading process for depositing NiCoCrAlY and MCoCrAlX coatings, which serve as a crucial bond coat in the Thermal Barrier Coating system (TBC) for high temperature applications. By providing exceptional protection against hot corrosion, oxidation and wear, these coating have become ideally suited for aerospace components and gas turbine applications. Recent advancements have primarily focused on enhancing coating performance through strategies such as pre-oxidation, implementation of multilayers and graded structures, vacuum heat treatment, rare earth doping and oxide dispersion strengthening. These modifications ultimately result in improved grain refinement, adhesion, superior thermal stability and enhanced mechanical properties. This article will provide significant development in HVOF-sprayed MCrAlX/NiCoCrAlY coatings with particular focus on microstructural evolution, durability and process optimization under extreme environmental conditions.

Laser welding of plastics has developed into a significant area of research, encompassing a range of complex methods. This process finds extensive applications across various sectors of modern society, such as science, medicine, and electronics. Despite substantial progress made in this field, there remains considerable potential for research to better understand how process parameters – like weld speed, laser power, frequency, and stand-off distance – affect outcomes like weld strength and geometry. Dongxia et al. (2012) applied the Taguchi method to optimize weld bead width in laser welding, considering factors such as laser power, welding speed, and wire feed rate. They concluded that higher welding speed, wire feed rate, and laser power tend to reduce weld quality. Shanmugarajan et al. (2016) used grey relational analysis (GRA) for multi-objective optimization in laser welding of P92 steel, with input parameters including laser power, welding power, welding speed, and focal position. Their measured outcomes included depth of penetration, weld width (WW), and the heat-affected zone (HAZ) width. Tilekar and Kamble (2017) conducted a review of the effects of various input parameters, such as laser power, weld speed, focal length, fiber diameter, and shielding gas, on the outcomes of laser welding for different materials. They observed that laser power and welding speed are closely associated as far as their impact on the weld is concerned. Solati et al. (2019) explored how beam pulse energy, travel speed, and focal position affect the fusion zone in laser welding of stainless steel. They conducted multi-objective optimization using Taguchi-based GRA to assess the depth of penetration and WW. Kumar et al. (2014) examined the influence of current, stand-off distance, and clamping pressure on joint strength and WW through transmission laser welding of thermoplastics in a lap joint configuration. Shin and Choi (2014) investigated how scanning speed impacts laser-welded joints between acrylonitrile butadiene styrene (ABS) plastic and polycarbonate (PC)-based polymers, focusing on how energy inputs affect the fusion zone, the HAZ, and the mechanical properties of the weld. Nakhaei et al. (2013) used the Taguchi method to optimize the joint strength of polypropylene–clay nanocomposite sheets by considering clay content, power, scan speed, and focal position as input parameters. Dawood et al. (2013) reported that increasing laser power results in a wider weld due to higher energy input, which increases the melt pool size. Chen et al. (2017) observed a linear relationship between laser power and WW up to a certain threshold, beyond which the WW stabilized. In a study by Haupt et al. (2015), it was found that reducing the laser speed during welding could increase the energy deposition in the welding zone, which ultimately leads to a weld. Nonetheless, if the speed is decreased much, it may cause damage to the material. Hsu and He (2014) showed that there exists a speed range where the WW is maximized without sacrificing the integrity of the material. Kim and Shin (2016) in their study demonstrated that infrared lasers are better at creating welds, in specific types of plastics compared to visible or ultraviolet lasers. This is because they are absorbed efficiently and reflect less at wavelengths. White et al. (2018) studied how carbon black impacts polyamide, thereby discovering that adding amounts leads to broader and more consistent welds by improving the material’s absorption capacity. Kumar et al. (2017) concluded that thicker material can lead to tighter welds because of the larger thermal mass, hence absorbing heat more effectively. On the contrary, darker materials have higher absorption, thus resulting in a wider weld, a finding also backed up by Nguyen et al. (2019). Zhang and Li (2017) found that higher clamping pressures lead to narrower welds by restricting the flow of molten plastic. Conversely, low clamping pressures can cause gaps, resulting in inconsistent welds. Wu et al. (2016) highlighted those higher ambient temperatures preheat the material, resulting in wider welds due to the reduced thermal gradient.

A battery pack consists of several Li-ion cells connected, with laser welding being the preferred method for creating strong and durable joints. This paper investigates laser overlap welding for producing tab-to-terminal interconnects for battery packs. A 1.5 kW QCW YLR fiber laser with a wobble head was used to weld 0.3 mm copper (Cu), nickel-plated copper (Cu[Ni]) and nickel (Ni) tabs to a 0.3 mm nickel-plated steel (Hilumin) terminal. The weldability and joint suitability analyses were conducted by evaluating joint strength, weld micrographs, joint resistance and temperature rise with the aim of developing a better and safer battery pack. It was observed that a maximum joint strength of 1125 N was obtained from the Ni tab-to-Hilumin joints which were approximately 39 and 48% more than the strength obtained for Cu[Ni] (804.79 N) and Cu (753.44 N) tab-to-Hilumin joints, respectively. The fractography analysis indicated ductile fracture with failure in base metal for Cu-based welds and brittle fracture with failure in the joint interface for Ni-based joints. This was in consistence with the microhardness results, which illustrated the hardest weld pool in Ni-to-Hilumin joint. In addition, the change in contact resistance and joint temperature rise was measured simultaneously for 180 s at 50 A amplitudes of current passed through the joints and showed higher resistance in Ni-to-Hilumin joint (0.54 mΩ) compared to Cu[Ni] (0.337 mΩ) and Cu (0.353 mΩ)-to-Hilumin joints.

This work compared different machine learning models such as linear regression, polynomial regression and XG-Boost for the prediction of laser welding qualities in aluminum alloys. The key weld quality parameters are ultimate load, weld width and penetration depth. Each model was trained and validated based on data experimentally collected by varying laser power, scanning speed and offset distance to compare them. Quantitative results are shown to prove that XG-Boost produces a better predictive accuracy, as it gives a root mean square error (RMSE) of 0.05 for ultimate load, 0.03 for penetration depth, and 0.02 for weld width. On the other hand, its linear regression counterpart has higher values of 0.08, 0.06, and 0.05, while polynomial regression-clearly outperforming its linear variant-averaged about 0.04 in these metrics. While this is so, high R-squared values, predicted by the XG-Boost model across ultimate loads, are indicative of its better competency in the capturing of complicated patterns, especially with regard to data outliers. These findings confirm the capability of XG-Boost to perform precise parameter optimization in laser welding by significantly reducing experimental trial needs and helping manufacturing efficiency with reliable data-driven predictions.

In this paper, the influence of various laser wobbling patterns, such as circle, ellipse, figure eight, bowtie, Celtic, flower, atomic, hexagon, triangle and star, on grain refinement mechanisms during welding of Inconel 625 sheets is evaluated. An in-depth analysis of molten pool stirring mechanisim during welding was addressed to understand the effectiveness of wobble patterns in grain refinement and fusion zone (FZ) strengthening. The dynamic stirring effect of the laser beam’s wobble motion significantly influences the solidification process and resulting microstructure. Laser spot trajectories and temporal energy deposition were analyzed to elucidate their impact on the FZ. Electron backscatter diffraction (EBSD) micrographs showed significant grain refinement during the welding. However, the wobbling patterns with elliptical and flower-type paths resulted in coarse equiaxed grains with an average grain size of ~ 52 µm. Furthermore, the optimal patterns for refining the grain structure of Inconel 625 superalloy during laser welding are circular and atomic-type wobble patterns with grain refinement of ~ 35%. These findings highlight the potential of tailored laser wobble patterns for optimizing weld quality through controlled grain nucleation and refinement.

This study explores through transmission laser welding of dissimilar, optically transparent polymers, acrylic and polycarbonates using a novel hybrid approach that integrates Response Surface Methodology (RSM) and Finite Element Method (FEM). Quantitative analysis involved a 3 factor, 3 level central composite design with process inputs of laser power, frequency and scanning speed. The resulting weld qualities, such as weld width, Heat Affected Zone (HAZ), ware measured, showing weld width ranges from 112.65 μm to 302.64 μm and HAZ between 20.85 μm to 105 μm. The thermal modelling provided predictions for depth of penetration, with values spanning from 106.25 μm to 228.65 μm. validated against experimental data, demonstrating an average error of 8.09%. Qualitatively, the investigation indicatees that laser power and scanning speed substantially effect the weld quality, with higher power leading to broader weld widths and greater HAZ. The FEM simulations confirmed these trends and provided insights into temperature distributions. The investigation contributes to the existing knowledge pool that would be beneficial to the academia and industries.

The escalating necessity for more efficient and defect-free joining of ‘ultra-thin foil collectors-to-tabs’ in electric vehicle (EV) Li-ion pouch cells motivates this study. The prevalent ultrasonic welding (USW) method for these joint types, faces limitations such as design constraints and access requirements, laser welding (LW) emerges as a promising alternative offering flexibility, one-side access and faster speeds with efficient heat input. This study aims to investigate the feasibility of LW as a viable alternative to USW for joining current collectors-to-tab joints. It compares the mechanical, metallurgical, electrical and thermal analysis of the joints to evaluate both welding techniques for joint defects. The comparison of solid-state material mixing during USW and the intermixing of aluminium (Al) and copper (Cu) during fusion LW using EDX analysis presents interesting observations in the study. The USW generates a thin transition layer with intermetallic compounds (IMCs) attributed to the diffusion of Cu into the Al matrix during joining, which is comparatively lower as in the case of LW with higher material mixing with brittle IMCs like Al₂Cu and Al₄Cu₉. However, the joint strength of LW is comparatively lower than the USW joint attributed to the reduced fusion zone area. Furthermore, from the electrical contact resistance and the joint temperature analysis, it was found that the resistance and temperature vary by as much as 13% and 6%, respectively, for the 50 A and 75 A passing currents when the USW is replaced with the LW process.

The inspection of the quality of welds in battery packs plays an important role in ensuring safety during the manufacturing and operation of energy-storage devices in automotive vehicles during service. This research investigated the novel application of laser Doppler vibrometry, a widely used non-destructive optical technique for modal analysis, to the post-weld evaluation of micro-TIG-welded interconnections in lithium-ion supercells. The experimental modal analysis showed features in the modal models of the supercells that were unique to their welding conditions. The comparisons between the supercells showed an absence of linear correlations between the modal parameters and the welding current, as well as differences in the welding parameters obtained from the negative and positive terminals of the cylindrical cells. These findings suggested that the modal parameters of the supercells were more strongly influenced by the rigidity of the structural materials than by the localized compliance of the welded interconnections. While this investigation demonstrated a method for using laser Doppler vibrometry to distinguish between different welding conditions in lithium-ion supercells at a structural level, further development is needed to identify the weld quality of individual interconnections.