Effects of the Shielding Gas and Substrate Thickness on Dilution and Microstructure of Inconel® 625 MIG/MAG Welded Coatings

Abstract

Inconel® 625 alloy is a corrosion-resistant nickel-based superalloy, often deposited onto cheaper substrates due to its high cost. In this research, deposition of Inconel 625 was carried out by MIG/MAG (Metal Inert Gas/Metal Active Gas) welding process due to its ease of operation, automation and productivity. The main purpose of this work is to evaluate the shielding gas and substrate thickness on the cooling rate, dilution and microstructure of Inconel® 625 coatings welded by the MIG/MAG process. The cooling rate during deposition was measured using thermocouples. Dilution was evaluated from macrographs of cross section of the welded coatings using Image J software. The microstructure of the coatings was assessed via SEM/EDS (Scanning Electron Microscope/Energy Dispersive Spectroscopy) and X-ray diffraction (XRD). The results showed that cooling rates were higher for plates welded with Ar + 25% He, leading to lower dilution. In the microstructure, a γ-Ni matrix with precipitated phases of Mo and Nb was identified.

Effect of the Shielding Gas and Heat Treatment in Inconel 625 Coatings Deposited by GMAW Process

“…Further magnification (D) evidences the presence of small white precipitates. The microstructure observed in Figure 2 agrees with the literature for welded Inconel 625 [3,14,16,18]. The dendrites appear darker in color, while the interdendritic regions appear lighter, suggesting that the interdendritic regions are rich in elements with a higher atomic number.…”

“…However, there was a variation in the mass percentage of the element Fe in the samples welded with CO 2 , and the HE samples were compared. This greater amount of Fe results from the greater dilution induced by CO 2 compared with He, as also observed by Macedo and Celente [18]. CO 2 presents a higher ionization potential and thermal conductivity than He; thus, the energy transferred to the melting pool is higher [23], increasing the diffusion of iron from the substrate to the top of the coating.…”

“…Moreover, the surface tension of the molten pool is higher with pure Ar, producing more convex beads. This may lead to discontinuities (welding defects) in the coatings produced by GMAW [18]. Alternatively, mixtures of Ar with active gases (e.g., CO 2 ) can potentially lead to a more stable arc and reduce the convexity index of the beads, thus reducing defects in the coatings at the expense of even higher dilutions.…”

“…Alternatively, mixtures of Ar with active gases (e.g., CO 2 ) can potentially lead to a more stable arc and reduce the convexity index of the beads, thus reducing defects in the coatings at the expense of even higher dilutions. In previous works, our groups have deposited Inconel 625 coatings using GMAW under Ar+25%He and Ar+25%CO 2 shielding gases with interpass temperature control [6,14,18]. The microstructures of the coatings, verified via scanning electron microscopy (SEM) coupled to energy-dispersive X-ray spectroscopy (EDS), were composed of γ (Ni,Cr-CFC) dendrites surrounded by an interdendritic phase rich in Nb-Mo precipitates and carbides (Nb,Mo MC type and Cr 23 C 6 ).…”

“…The microstructures of the coatings, verified via scanning electron microscopy (SEM) coupled to energy-dispersive X-ray spectroscopy (EDS), were composed of γ (Ni,Cr-CFC) dendrites surrounded by an interdendritic phase rich in Nb-Mo precipitates and carbides (Nb,Mo MC type and Cr 23 C 6 ). The use of Ar+25%CO 2 shielding gas led to greater dilution when compared to Ar+25%He [18].…”