Influence of droplet transfer behaviour on the microstructure, mechanical properties and corrosion resistance of wire arc additively manufactured Inconel (IN) 625 components

A Ni-based superalloy, Inconel 625, is widely used for aerospace, petrochemical and marine applications due to its excellent corrosion and elevated temperature mechanical properties. In this study, efforts were made to identify optimum deposition parameters to produce directionally solidified Inconel 625 components using wire arc additive manufacturing (WAAM). Components were deposited by short-circuiting and short-circuiting with pulse mode of droplet transfers using a commercial cold metal transfer gas metal arc welding (CMT-GMAW) power source. For a given arc energy, metal droplet transfer behaviour was studied using a high-speed camera. Microstructural analysis and corrosion resistance of Inconel 625 samples produced by WAAM and samples made by conventional casting process were compared by advanced characterisation methods. Inconel 625 samples produced using a combination of short-circuiting with pulsing free flight transfers showed improved mechanical properties than as-cast samples and samples made only by short-circuiting transfer due to the formation of directionally solidified coarse-grained columnar microstructure. Moreover, corrosion resistance of WAAM samples was found to better than that of as-cast samples. Based on the results, an optimised current-voltage waveform and droplet transfer modes were identified to produce defect-free Inconel 625 deposits with desired microstructure, and mechanical and corrosion-resistance properties.