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Wire arc additive manufacturing (WAAM), also known as Arc-DED, possesses great potential for efficient production using various materials and wire types. This study utilized gas metal arc (GMA) and plasma transferred arc (PTA) variants of WAAM to deposit 2.25Cr-1Mo steel employing a metal-cored wire (MCW) and a solid wire counterpart having the same chemical composition for the comparative study. Initially, bead-on-plate trials were conducted with both WAAM processes and different shielding gas combinations in GMA-WAAM using the cored wire. The heat input versus deposition ratio was analysed to assess the heat input and the effects of shielding gases in GMA-WAAM. Arc behaviour was monitored with a process camera, and bead morphologies and dilutions were compared. Furthermore, test walls were deposited under the two WAAM processes and the shielding gas conditions, employing the cored and solid wire. Detailed microstructural study was conducted through optical microscopy, and hardness tests were performed to determine the mechanical properties. Energy dispersive X-ray spectroscopy (EDS) was used to examine the elemental composition and potential segregation in walls deposited with cored and solid wires. Results indicated a lower heat input when using cored wire and variable heat input due to shielding gases. A bainitic/martensitic microstructure was observed in test walls deposited with cored and solid wires with comparable microstructural features. The PTA process produced higher hardness than GMA, and solid wire exhibited slightly higher hardness than cored wire. Selection of shielding gas also influenced the hardness. Finally, the EDS maps and elemental study revealed comparable results for both wires. The results show good performance and outcome for cored wire.

In a sealed electromagnetic relay, the change in the surface roughness mainly depends on the collision wear between the contact and the moving reed and the ablation effect of the arc on the contact surface based on the strong correlation between the contact resistance and the surface roughness of the Ag-Mg-Ni contact. With a change in contact resistance, the contact temperature increase in a hermetically sealed electromagnetic relay (HSER) is greatly affected. Under extreme overload conditions, the contact surface is severely ablated by the arc, and the roughness increases rapidly with the number of cycles, which greatly affects the contact resistance of the contact surface and the reliability of the relay. A thermal model of a relay contact system based on the surface roughness of Ag-Mg-Ni contacts was established in this paper by analyzing the effect of an arc on the surface roughness of Ag-Mg-Ni contacts under heavy overload conditions. The arc image of the Ag-Mg-Ni contact was recorded using a double-axis arc photographing platform, and the moving track of the arc center under overload conditions was drawn. This paper explored the patterns of arc center movement on the contact surface and the effects of the arc on the surface roughness of the contacts by analyzing the probabilities of the arc center appearing in various locations. A mathematical model correlating the number of contact cycles with contact resistance was established. Subsequently, a finite element simulation model for the equivalent heat source of the contact was developed. The theoretical model error was less than 10%. The accuracy of the equivalent heat source model was verified by comparing the measured data with the simulation results.

Electric arcs are a necessary heat source in many industrial processes that take place in Submerged Arc Furnaces (SAFs). Arcs exhibit non-linear electrical characteristics and behave in a complex manner. Therefore, an improved understanding of their behavior enables better control of furnace operation. Modeling of industrial arcs is a multiphysics process that involves simultaneously solving several coupled physical phenomena, such as electromagnetics, fluid dynamics, and heat transfer, including a radiative heat transfer from the plasma arc. Coupling fluid dynamics and electromagnetics is known as Magnetohydrodynamics (MHD). For practical applications, however, there are also simpler approaches to arc modeling, either based on simplified physical principles or empirical behavior. In this paper, a combined Cassie–Mayr model (CMM) and a channel arc model (CAM) are implemented and coupled with a submerged arc furnace electrical circuit model. The complete circuit model parameters such as resistances and inductances are estimated using modeling of a full size furnace, and then, actual measurements from a SAF are used to validate the models by comparing current and voltage waveform. Both models are then used to estimate harmonic distortion in a SAF for different arc current ratios, which should help operators to estimate the arc current in real time thus be able to lower and raise the electrode to keep operating conditions constant.

Wire feed rate plays a vital role in determining the weld characteristics in gas metal arc welding (GMAW). The wire feed rate is affected by any change in welding current in the case of steady current GMA welding and by any change in frequency, peak current, base current and duration of peak and base currents in the case of pulsed GMA welding. To predict the wire feed rate for any set of these parameters, a mathematical model was developed from the results obtained by conducting experiments. Electrode resistance heating constant and arc resistance heating constant were also determined by fitting a regression model. The above parametric constants have been used to simulate the wire feed rates for pulsed GMA welding for different pulse parameters using MATLAB. The effects of pulse parameters on the burnoff factor and burnoff rates were also analysed. The investigation was carried out using AWS 5.22–95 filler wire of size 1.2 mm diameter and the base metal used was IS:2062 structural steel plate of 20 mm thickness. An argon and 5% CO2 gas mixture at a flow rate of 16 l/min was used for shielding throughout the welding.

This paper summarizes the status of various external energy-assisted friction stir welding techniques developed till date. Preheating the workpiece material through an external energy source helps overcome the drawbacks of conventional Friction stir welding (FSW) processes while welding hard and high melting point materials. External energy is provided in the form of induction heat, laser heat, resistance heat, arc heat, radiation and ultrasonic vibrations. Significant advantages have been observed while using energy-assisted FSW such as extended process window, improved process parameters and mechanical properties, reduced load and tool wear. The current work reviews the experimental setup developed, dominant process parameters involved, enhanced heating obtained in the process, force reductions achieved, mechanical properties and microstructural characterisations of the joints produced in the various attempts taken in this direction. However, the extent of research done on these variants of thermal heating is still in initial phase. Therefore, the challenges faced in the various processes have also been explained.

The heat resistance of carbon fiber-reinforced ultra-high-temperature ceramic matrix composites (C/UHTCMCs) was characterized by arc-wind tunnel testing with heat fluxes of 2, 4.54, and 6.68 MW/m2. C/UHTCMCs were fabricated via Zr-Ti binary alloy (Zr-20at%Ti, Zr-64at%Ti, Zr-80at%Ti) melt infiltration. The thickness and weight changes of the specimen were dependent on the composition of the infiltrated Zr-Ti alloy. Microstructural and thermodynamic analyses revealed that formed oxides on the surface of composites are composed of ZrO2 solid solution, ZrTiO4 solid solution, and TiO2 solid solution. The composition of oxides also depends on the composition of infiltrated alloys. The difference originates from the formation and composition of oxide scales and the dynamic pressure. Especially, formation of liquid oxides accelerates the recession of composites because liquid oxides are disappeared from the surface owing to the dynamic pressure during arc-wind tunnel testing. To withstand aerodynamic heating above 2000 °C, formation of a solid (and liquid) oxide on the exposed surface is required to reduce recession.

In this study, an Inconel 625 component was fabricated by gas tungsten arc welding-based additive manufacturing and the as-deposited specimens were heat treated at 980 and 1100 °C for 1.0 h, respectively. The effects of heat treatment on the corrosion resistance and microstructure were investigated. Potentiodynamic polarization tests showed that the as-deposited Inconel 625 alloy had disparities in corrosion resistance compared with wrought Inconel 625 alloy. The corrosion resistance deteriorated after heat treatment at 980 °C due to needle-like δ phases provided more sites to pitting initiation. While the corrosion potential (E corr ) increased by 32%, passivation current density (I corr ) decreased by 52% after heat treatment at 1100 °C, which was comparable with that of wrought Inconel 625 alloy. Detailed microstructural examination demonstrated the recrystallization occurred with the dissolution of Laves and δ phases, weakening of 〈001〉 orientation, decrease of low angle grain boundaries and formation of large numbers of stable twin grain boundaries. All the evolution of the crystal and microstructure contributed to the striking corrosion resistance of the 1100 °C heat-treated Inconel 625 alloy.

Dissimilar metal joints are critical areas of aerospace engineering as they demands the joining of materials with diverse properties to meet the requirements of aircrafts and spacecraft. Dissimilar metal joints enables the integration of materials with different mechanical, thermal and corrosive resistant properties and achieve light weight structures with less fuel consumption and enhance the overall performance of aircraft and spacecraft. But creating such a dissimilar joint is very challenging and require advanced welding techniques to ensure improved reliability and efficiency of these joints. During dissimilar metal joints an intermetallic alloy is formed which has to be free from oxides. Copper and Stainless steel joints have a wide range of application in aerospace industry specifically in heat exchangers and electrical connectors. In this paper, a comparative analysis of the dissimilar metal joints of Copper and Stainless Steel 304 made with a conventional Gas Tungsten Arc Welding (GTAW) and Electron Beam Welding (EBW). GTAW is performed with and without filler in an open atmospheric environment whereas Electron Beam Welding is performed inside a vacuum chamber. The presence of fatigue cracks, voids and pores are analyzed using Optical and Scanning Electron Microscope. EDX analysis is also performed to analyze the elemental composition in the intermetallic alloy formed during both welding methods.

Wear and corrosion of boiler tubes in coal-based boilers are one of the serious problems. Trying to solve this issue, FeCr alloy with 45%Cr-content coating and Fe-based coating with 13%Cr-content were arc sprayed onto carbon steel substrates to enhance both the wear and corrosion resistance of boiler heat exchanger pipelines. The microstructure, chemical compositions, and phases of the coatings were analyzed using a scanning electron microscopy, energy-dispersive spectrometer, and x-ray diffraction, respectively. The wear resistance of the coatings was assessed at 25 and 300 °C using a ball-on-disk wear tester. The corrosion resistance of the coatings was evaluated based on seawater immersion, electrochemical impedance, and polarization tests. The porosities of FeCr alloy and Fe-based coatings were 4.05 and 5.75%, respectively. The microhardness values of FeCr alloy and Fe-based coatings were 377.50 ± 46.88 HV 0.5 and 666.69 ± 57.64 HV 0.5 , respectively. FeCr alloy coating with lamellar structure was mainly composed of FeCr solid solution phase and a small amount of Cr oxide and Fe 3 O 4 phases, and Fe-based coating was composed of a mixture phase of amorphous and crystalline, and a small amount of Fe 3 O 4 phase. FeCr alloy coating had better wear resistance than Fe-based coating at both 25 and 300 °C. The wear mechanisms of the coatings were also studied. The corrosion resistance of FeCr alloy coating was better than that of Fe-based coating in corrosive solutions. Therefore, FeCr alloy coating can provide better high-temperature wear resistance and anticorrosion performance for boiler heat exchanger piping, compared with Fe-based coating.

Ceramic based coating is one of the surface engineering techniques for improving surface properties of material. SiC ceramic and Co based cermet coating material has high hardness, strength, superior wear and corrosion resistance for raising the surface features of low carbon steel. In this investigation, a cost-effective Tungsten Inert Gas (TIG) heat source was utilised efficiently to form SiC-Co coating on low carbon steel. The examination of coated samples' morphology is conducted through Scanning Electron Microscopy (SEM), revealing the presence of various Fe-rich dendritic structures within them. Furthermore, x-ray Diffraction (XRD) analysis of these coated samples has identified the presence of different intermetallic hard phases, including FeSi, Fe 2 Si, CoSi 2 , CoSi. Hardness of SiC-Co coated surface is improved by around 1064 HV 0.1 , which is more than 4 times that of the untreated low carbon steel (~ 230 HV 0.1 ). High hardness and different intermediate phases improve the wear resistance of SiC-Co coated surface more than 20 times that of untreated low carbon steel. SEM analysis of wear tested SiC-Co coated surface noticed minor ploughing, scratches, debris, and delaminated layers. In contrast, large delaminated layers, severe scratches, and ploughing is noticed on untreated low carbon steel.