The gas tungsten constricted arc welding (GTCAW) process was used to join thin Su-718 alloy sheets to minimize alloying segregation and Laves phase precipitation in the fusion zone (FZ). The potentiodynamic corrosion behavior of GTCAW Su-718 alloy joints was studied and correlated to the microstructural features of welds. The potentiodynamic corrosion test was done in a 3.56 wt.-% NaCl solution to determine the corrosion rate of Su-718 alloy joints. The optical microscopy (OM) technique was used to analyze the microstructure of corroded weldments. The scanning electron microscopy (SEM) technique was used to study the Laves phase development in FZ. The SEM X-ray energy dispersive spectroscopy (EDS) technique was used to for elemental mapping of FZ. The corrosion resistance of Su-718 joints is inversely proportional to the precipitation of Laves phase in FZ. The GTCA welded Su-718 alloy joints disclosed superior corrosion resistance for the joints with lower Laves phase precipitation. It is correlated to the refining of FZ microstructure, which aids in minimizing the Laves phase precipitation. The joints with higher Laves phase precipitation revealed inferior corrosion resistance. It is attributed to coarsening of FZ microstructure, which raises the alloying segregation and leads to depletion of alloying elements in FZ. The dendritic core regions showed severe corrosion compared to the interdendritic regions. The corrosion resistance of GTCA welded Su-718 joints is better than that of CC-GTAW and PC-GTGAW joints and comparable to that of EBW and LBW joints. It refers to the arc constriction and high frequency current pulsation.

The work intends to study the microstructure, chemical and phase composition and homogeneity of chemical elements distribution in the Co-Cr-Fe-Mn-Ni high-entropy alloy produced via wire-arc additive manufacturing technology. The study has revealed three structure types in the alloy: (1) a smooth shagreen-type structure (an orange peel), which turns into a stripe-like structure (2) in some areas, and a grain structure (3) to appear as lengthy thin layers with the width of 50-80 μm and an average grain size of 12.5 μm, the most probable size of grains is detected to be in the range from 10 to 15 μm, a preferred number of such grains is 31%. The chemical composition of the produced alloy is assessed using X-ray microspectroscopy. The elements identified rank in descending order of concentration: Fe (38.88 wt. %), Co (26.08 wt. %), Ni (17.34 wt. %), Cr (14.33 wt. %), Mn (3.37 wt. %). The mapping of the alloy structure demonstrates the homogeneous and uniform distribution of chemical elements.

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