Multiple layers of C250 maraging steel were deposited into a single-wall structure by using wire arc additive manufacturing (WAAM). The microstructural characteristics of the as-deposited C250 steel, in terms of solidification structures and phases, were investigated by using optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The results show that lath martensite and austenite phases are formed in the as-deposited C250 steel. Apart from these two phases, Laves phase Fe₂Ti particles, which have not been reported in C250 steel, are also observed in the C250 steel produced by the WAAM process. TEM analysis does not reveal the formation of strengthening precipitates in the as-built C250 steel, which is further confirmed by hardness measurement. GRAPHICAL ABSTRACT

A Gleeble-based test method has been developed to study the change in the ductility signature of Haynes^® 282^® during isothermal exposure from 5 s to 1800 s. A temperature range of 750 to 950 °C has been used to investigate the effect of age-hardening reactions. Microstructural constituents have been analyzed and quantified using scanning and transmission electron microscopy. Carbides present in the material are identified as primary MC-type TiC carbides, Mo-rich M₆C secondary carbides, and Cr-rich M₂₃C₆ secondary carbides. Gamma prime (γ′) precipitates are present in all the material conditions with particle sizes ranging from 2.5 nm to 58 nm. Isothermal exposure causes the growth of γ′ and development of a grain boundary carbide network. A ductility minimum is observed at 800–850 °C. The fracture mode is found to be dependent on the stroke rate, where a transition toward intergranular fracture is observed for stroke rates below 0.055 mm/s. Intergranular fracture is characterized by microvoids present on grain facets, while ductility did not change during ongoing age-hardening reactions for intergranularly fractured Haynes^® 282^®.

The weldability of additive manufactured Alloy 718 was investigated in various heat-treated conditions. The microstructure of the base metal was examined in detail in order to understand the effect of different pre-weld heat treatments; i.e., solution, solution and aging, and hot isostatic pressing. After welding, the variation in total crack lengths, maximum crack length and the total number of cracks in the heat affected zone (HAZ) were used as criteria for the cracking susceptibility of each material condition where wrought Alloy 718 was used as the reference material. Selective laser melting (SLM) manufactured Alloy 718 was susceptible to HAZ cracking in all material conditions. Total crack lengths in HAZ were highest in the SLM as-built condition and lowest in the SLM hot isostatic pressed condition. The cracks that were found in the HAZ of the welded materials consisted of liquation cracks, with eutectic product surrounding the cracks, as well as cracks from which liquation products were absent.