Powder bed fusion of Ni-based superalloys has seen rapid development and improvements over recent years, both at academic and industrial levels. The high-temperature strength and oxidation resistance of Ni-based superalloys, together with the design flexibility inherent to additive manufacturing, enable the production of optimized components for gas and aircraft turbines. There are, however, certain challenges related to the fabrication and post-processing of 𝛾’-strengthened alloys by PBF-LB/M.

This thesis investigates PBF-LB/M fabrication of IN939, focusing on understanding the interplay between processing and post-processing parameters, microstructure, and the resulting properties of printed parts using a wide range of experimental techniques. An appropriate processability window for IN939 using a pulsed wave laser is identified, yielding defect-free parts (>99.5 % relative density) with minimal crack formation. The influence of the energy input on microstructural features such as grain morphology and crystallographic texture is examined. The fabrication of thin-walled IN939 parts is also investigated. The incorporation of a pre-contour scan before hatch scanning effectively enhances thermal diffusivity at a subsurface level, leading to reduced melt pool depth and mitigating keyhole porosity, particularly for walls thinner than 1 mm.

The influence of the as-built microstructure on the recrystallization kinetics is also explored. The presence of MC carbides in the as-built state retards the onset of recrystallization via Smith-Zener pinning. Additionally, as-built samples with a smaller initial grain size, coupled with a weaker crystallographic texture, recrystallize at lower temperatures. A modified solution treatment consisting of 8 h at 1200ºC is proposed to induce recrystallization of PBF-LB/M irrespective of the initial microstructure. Mechanical testing from room temperature to 950ºC is performed for samples following the standard and modified thermal treatments. The latter hinders diffusion-related deformation mechanisms, and thus results in superior yield and ultimate tensile strengths along the full temperature range. Finally, the possibility of locally tailoring the microstructure in-situ via scanning parameter modifications is tested. The horizontal melt pool overlap is identified as a useful variable to control and predict the degree of epitaxial growth, and therefore the final microstructure.