**1. Introduction**

Superalloy Alloy 718 (NiCr19NbMo, EN 2.4668) is a Ni-Cr-Fe-Mo alloy for service conditions up to 650°C, where hardening is achieved by additions of Nb, Ti, and Al resulting in controlled precipitation of mainly γ" (Ni3Nb) and to a small extent γ' (Ni3(Al, Ti) [1]. Due to this, this alloy is widely used for static and rotating components in stationary gas turbines, rocket drives and spacecraft, motor vehicle

turbo chargers, high-strength screws, springs and mounting elements, and for heatresistant tools in forgeries, extruders, and separating shearers [2].

Ni-alloys have a high cost and are difficult to machine, with main reasons being their high temperature resistance, high initial work hardening rate, and presence of carbides in the microstructure [3]. Therefore, additive manufacturing (AM) techniques could result in cost, weight, and machining savings for a wide range of applications using Alloy 718 [4]. The AM with wire-based arc processes (WAAM®) offers the possibility of producing small and large-volume components of low and medium complexity at high deposition rates. A disadvantage is the poorer surface quality and accuracy and thus the need for mechanical finishing of functional surfaces [5–7]. A typical process for WAAM® is the energy-reduced Cold Metal Transfer (CMT) process, a variant of GMAW, which is widely used industrially for cladding with Ni-base solid wires [8–11]. This is due to the very low dilution with substrate, high deposition rate, very low heat input, less spatter, and low susceptibility to hot cracking [12], factors that are also advantageous for AM.

Recently, the number of publications on AM of Alloy 718 with the GMAW is increasing [13] published a study as early as 2007 on the use of the MIG process for AM of an internal flange of combustor outer casing of Alloy 718. The present study has highlighted the presence of deleterious Laves- and δ phases in the weld deposition structures encouraged by extended time at high temperature during either deposition or subsequent post-deposition heat treatment. In addition, associated discontinuities in the form of hot cracks and shrinkage porosity have been identified [14, 15] evaluated the effect of oxide, wire source, and heat treatment on the mechanical properties of additive plasma arc welding with cold wire feed of Alloy 718 with oscillating torch in inert shielding gas atmosphere. Results showed that oxides formed during deposition had no effect on the mechanical properties. Wires from different suppliers resulted in around 50 MPa difference in UTS. Standard heat treatment improved the strength from 824 MPa to 1110 MPa, but the average strength was lower than the wrought alloy and laser powder-based AM IN718. The microstructure of the WAAM material showed large columnar grains and numerous Laves phase [16] identified an aging effect in deposits of Alloy 718, which produced with CMT-WAAM® process. Deposits consisting of 10 layers were manufactured, where interpass time (0, 30 s, and 60 s) was the only process parameter varied. An aging effect was observed, which caused precipitation of the <sup>γ</sup>″ and <sup>γ</sup><sup>0</sup> strengthening phases and the <sup>δ</sup> phase. The highest hardness value was measured in the middle section of each deposit due to precipitation of the strengthening phases [4] investigates the effects of processing parameters and heat treatments employed on CMT-WAAM® of Alloy 718. The process stability was analyzed by electrical transients and melt pool imaging, showing an opposite trend to the measured heat inputs. Laves length and carbide diameter decreased with travel speed, while the as-deposited hardness increased. These observations permitted a linear wall to be fabricated with a minimal heat input per layer of 181 J–185 J/mm. Compared with powder-based AM, the CMT welds exhibit a larger melt pool size and lower as-deposited hardness, but has been found to show satisfactory aging response and similar Laves phase area fraction.

In the present work, the influence of different heat inputs and shielding gases in CMT-WAAM with S Ni 7718 on the macrostructure, seam defects, chemical composition, mechanical properties, and hardness was investigated. The investigations were carried out with two different wire batches on two component geometries (wall and block). These different geometries generate different welding situations (single- or multi-bead welding) and stress conditions.

*Properties of Additively Manufactured Deposits of Alloy 718 Using CMT Process Depending… DOI: http://dx.doi.org/10.5772/intechopen.102455*
