Additive Manufacturing (AM) is an advanced manufacturing process in which an alloy component
can be made layer-by-layer using a range of techniques employing powder bed, blown powder or by
wire addition. In Arc Wire Directed Energy Deposition (AW-DED), welding arc is used as a heat source and wire as a feedstock. Due to the high deposition rates (in the order of 10- 25 Kg per hour) and increased process efficiency (up to 90 %), AW-DED is found to be attractive to build large volume components. Microstructural evolution in the components during AW-DED is strongly influenced by the multi-pass thermal cycles that prevail during melting and solidification of the feedstock wires. Among all the AW-DED AM processes, Gas Metal Arc (GMA-DED) based process is seen as an attractive to produce geometrically simple and large volume components. In this process, thermal cycles can be favourably modified by varying current and voltage waveforms. Moreover, solidification microstructures can also be altered by using a combination of pulsing and short-circuiting metal transfer strategies.
Ni-based super alloy, Inconel 625 is widely used for applications in aerospace, petrochemical
and marine environment due to excellent corrosion resistance, tensile and fatigue properties. In GMA-DED, current-voltage waveforms are carefully controlled to aid stable droplets transfer from molten feedstock wires in controlled dip short-circuiting or free flight modes. In this work, efforts were made to design new sets of current-voltage waveforms to generate directional solidified and equi-axed grains containing microstructures while depositing IN625 feedstocks wire in short-circuiting and short circuiting with pulse droplet transfer modes. The role of arcing current, short-circuiting current and current ramping rate at a short-circuiting instance on the microstructural evolution was analysed. Microstructural characterisation of components made by GMA-DED were studied by optical, scanning electron microscopy and electron back scattered diffraction imaging. Results showed that by carefully controlling the current-voltage waveforms during the metal transfer, it was possible to generate either directionally solidified or equi-axed grains containing microstructures in IN625
components deposited by GMA-DED. Corrosion resistance of Inconel 625 samples produced by GMA-DED were evaluated by potentiodynamic polarisation and electrochemical impedance spectroscopy analyses and the role grain morphologies on the corrosion behaviour was analysed. Mechanical properties were studied by Vickers micro-hardness measurements, room and elevated temperature tensile and compressive tests along the longitudinal and normal section of deposits to ascertain the role of grain morphologies on the mechanical behaviour of the Inconel 625 GMA-DED components.