Corrosion resistance of plasma transferred arc (PTA) Inconel 625 deposits

Abstract

Although the industrial sector is very restrictive in terms of the amount of dilution of the substrate allowed in welded Inconel coatings (often below 10%), the real impact of small changes in dilution on corrosion resistance of Inconel deposits is not clear yet. To evaluate this, welding current, welding speed and powder feed rate were varied within narrow ranges during PTA deposition of Inconel 625 onto carbon steel substrates. The effects of welding parameters on dilution and convexity index of the beads were analyzed within the established operational envelope. Potentiodynamic corrosion tests were carried out using solutions with different corrosion aggressiveness for specimens with different dilutions. The current of 180 A appeared as a transient point for the effects of the welding current on dilution and convexity index, suggesting a complex interaction between welding current, welding speed and powder feed rate. XRD results showed that for the specimens with higher dilution, only the region very close to the interface with the substrate was affected, suppressing the formation of the M2C. Interdendritic corrosion with preferential dissolution of some phases was observed as the main corrosion mechanism for all the deposits. The specimens with higher dilution showed tendency for secondary passivation in NaCl and NaCl + FeCl3 solutions. Moreover, the corrosion potential and corrosion current density values obtained for the specimens with lower and higher dilution were very close, with negligible differences, regardless of the position in the bead. The presence of FeCl3 in the electrolyte shifted the corrosion potential to more positive values. In the NaCl + H2SO4 solution, the deposits showed significant differences only in terms of passivation current between higher and lower dilution specimens. However, in general the differences between the deposits were negligible, showing good overall aqueous corrosion resistance in a wide range of highly aggressive environments. Therefore, this work found a relatively wide operational envelope for Inconel 625 PTA deposits, showing that small changes in deposition conditions, and thus in dilution, do not affect the coating applicability.

Corrosion Behavior of CW6MC Nickel Cast Alloy (Inconel 625) Welded by Shielded Metal Arc Welding

“…From the EDS results, it can be noted that the intermetallic particles have a characteristic core-shell structure; where the shell is enriched with Nb, Mo and Si, while the core is composed mainly of Nb. The shell intermetallics, rich in Nb, Mo and Si, are Laves phases (points 1 and 3), whereas the core particles, rich in Nb (points 2 and 4), are NbC-type carbides, as reported in the literature [9,34,[42][43][44]. Additionally, in good agreement with the mentioned literature, the XRD patterns (Figure 5) of the BM and WM microstructure show the presence of NbC-type carbides and Laves phases in both regions.…”

“…Additionally, X-ray diffraction (XRD) analyses using a Bruker diffractometer model D8 Advance ECO operated with Cu Kα at 40 kV and 25 mA and the sweep angle range (2θ) from 30 • to 120 • with a scanning speed of 2 • /min were used to analyze the phases and intermetallics present in the material. The crystalline peaks of the XRD spectra were identified based on powder diffraction files (PDF) 330945, 893890 and 653574, and a literature survey [31][32][33][34]. The percentages of intermetallics in each one of the welding regions were quantified based on the ASTM E1245.…”

Durable Material Deposition via PTA upon Al-alloys

“…The methods used for surface treatment are around 1000 [2]. The most common metal reinforcement is the nickel-based layer deposited upon steel substrate via PTA [3,4], laser deposition [5,6] or comparison of both the above [7].…”

Corrosion resistance of thermal-pulsed Inconel 625 MIG/MAG weld overlays

“…However, as a deposition technique, MIG/ MAG produces weld beads with high dilution when compared with other methods such as TIG (Tungsten Inert Gas) [6], PTA (Plasma Transferred Arc) [7,8], laser cladding [9] and cold metal transfer [10]. High dilution is undesirable in weld overlays because it changes the chemical composition of the deposit, potentially reducing important properties such as wear and corrosion resistance [7,11]. The higher the dilution the greater the contamination of the overlay material from the less noble substrate.…”

“…When welded, Inconel 625 can present a very complex microstructure, often consisting of dendrites of γ phase rich in Ni and Cr, with precipitation of Nbrich intermetallic phases and Nb carbides [2,21]. The effects of microstructure on the corrosion resistance of Inconel 625 weld overlays are substantial and need to be carefully addressed and understood [11].…”