Wire arc additive manufacturing of functionally graded material for marine risers

Functionally graded materials (FGM), whose structural properties are varied along their volume to perform an intended function, have a full application in the marine industry. Under the corrosive marine environment, a corrosion-resistant alloy of duplex stainless steel, functionally graded with carbon-manganese steel along with the inner layer, is proposed here for the risers. The interface strength of FGM, fabricated using Cold Metal Transfer - gas metal arc welding, based on Wire Arc Additive Manufacturing (WAAM) in the lab-scale, is compared with an X-52 Carbon Manganese steel to highlight the superiority of the proposed FGM. The role of metal transfer characteristics on the microstructure formation at the layers adjacent to the interface is analyzed and correlated with the voltage-current waveform those obtained during the deposition process. Based on the experimental studies carried out, it is seen that the yield strength of the FGM interface is very close to that of X52 steel, with a marginal increase of about 6% in the ultimate strength. Based on the energy dispersive X-ray analysis, it is observed that there is no enrichment of chromium across the interface towards the carbon-manganese steel side. It is vital for the corrosion-resistance of duplex stainless steel. Proposed FGM shows advantages both in strength and durability and hence seen as a promising candidate for marine riser applications.