# Mechanical and Metallurgical Properties of CO\({}_{2}\) Laser Beam INCONEL 625 Welded Joints
###### Abstract  
In the frame of the circular economy, welding of Ni-based superalloys has gained increasing importance when applied, for instance, to repairing highly expensive components widely used in strategical sectors, such as the defense and aerospace industries. However, correct process parameters avoiding metallurgical defects and premature failures need to be known. To reach this goal, Inconel 625 butt-welded joints were produced by CO\({}_{2}\) laser beam welding and different combinations of process parameters. The experimental investigation was carried out with three parameters in two levels with an L\({}_{4}\) orthogonal array. Laser power, welding speed, and shielding gas flow rate were varied, and the results were reported in terms of mechanical properties, such as microhardness, tensile strength, distortion, residual stress, and weld bead geometry, and metallurgy. At a lower welding speed of 1 m/min, the full penetration was observed for 3.0 kW and 3.3 kW laser powers. However, sound welds (porosity-free) were produced with a laser power of 3.3 kW. Overall, the obtained full-penetration specimens showed a tensile strength comparable with that of the parent material with residual stresses and distortions increasing with the increase in heat input. laser beam welding; radiography; tensile strength; residual stress; microstructure +
Footnote †: journal: Applied Sciences  
these mentioned changes in the welded joint also have a negative impact on components' performances when working at elevated temperatures. The gas tungsten arc welding (GTAW) process is widely employed to join high-strength alloys with suitable filler materials with both constant and pulsed current processes [2; 3; 4]. As per the earlier research, the microstructures were observed to have satisfactory solid solubility with parent and filler metals but a wide fusion zone. Hot cracking is one of the major problems observed during single-pass welding, resulting in unacceptable permanent damage to the structure. As an alternative, this was overcome by employing a multipass welding procedure with the foresight to maintain appropriate inter-pass temperature [5; 6; 7; 8]. However, the mechanical and metallurgical properties can be improved by employing advanced welding techniques such as electron beam welding (EBW) and laser beam welding (LBW). Their high-power density allows for reducing the heat input and therefore the FZ and HAZ dimensions together with a higher welding speed. This results in improved metallurgical and mechanical properties and productivity. Moreover, these processes can be easily automated compared to conventional welding techniques. The full-penetration welding is carried out in a key-hole regime, which results in quality welds with a narrow heat-affected zone (HAZ), as mentioned above. Excess penetrations are eliminated, and no further machining process for finishing in LBW welds compared to the arc welding process is needed. Microstructural changes are limited because of the low heat input with faster cooling rates [9; 10; 11; 12; 13; 14; 15]. In references [16; 17], authors carried out a comparative study using both arc and electron beam welding process applied to 316L stainless steels; they found that metastable phases formed during solidification of fusion zone in EBW joints compared to that obtained with the GTAW process. [PERSON] et al. [18] focused on the joining of SMO 254 stainless steel by means of autogenous CO\({}_{2}\) laser beam welding (LBW) and pulsed current gas tungsten arc welding (PCGTAW). They found that for a 5 mm thick plate, the LBW heat input was only 120 J/mm, compared to a value of 3032 J/mm required by the PCGTAW process. Surprisingly, tensile residual stress was observed in the weld region and heat-affected zone of PCGTAW joints, while pure compressive residual stresses were induced in the case of laser-welded joints due to lower heat input value.