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Controlling the grain size and morphology during fusion-based additive manufacturing remains a challenge for many alloys. This work investigates Titanium diboride (TiB 2 ) nucleant particle addition to the high strength Aluminium 2319 alloy produced during wire arc additive manufacturing (WAAM). Two Cold Metal Transfer (CMT) processing conditions are explored (low heat input CMT and high heat input CMT) and the effectiveness of the grain refiner is studied. The addition of TiB 2 is found to refine the average equiaxed grain size by up to 22% compared to the non-inoculated alloy. The Interdependence Model is applied to understand the grain refinement mechanisms occurring in low heat input AM technologies in alloys containing powerful growth restricting solutes such as Al 2319.

Duplex stainless steels are increasingly used for offshore subsea components as the technology allows for deeper recovery of oil & gas reserves. Alloy UNS S31803 (EN 1.4462 / UNS S32205) combines high strength with good resistance to pitting and crevice corrosion. This grade is alloyed with nitrogen and has good weldability. For heavy-walled process piping intended for subsea sour service, the properties of the root pass are of high importance. For this reason, the effect of using nitrogen in the backing gas was investigated. Test pieces were manually welded with the gas tungsten arc welding (GTAW) process using ER2209 filler wire. Tensile, bending and hardness testing was carried out and showed acceptable results across all specimens. Higher contents of nitrogen in the backing gas showed more austenite formation and a significant increase in pitting corrosion resistance when compared with pure argon. With Ar + 2% N 2 , there was no pitting, but a small weight loss of 1.7 g/m 2 was measured. 10% N 2 was required to pass both the corrosion tests ASTM G48 Method A (4 g/m 2 ) and ASTM A923 (1 g/m 2 ). The highest average impact toughness was achieved with pure nitrogen as the backing gas.Heavy-walled pipe used for the collection of hydrocarbons subsea are increasingly exposed to harsh conditions and the internal root welds are exposed to high levels of H 2 , H 2 S, and CO 2. The expectation for a lengthy service

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