Previous work has shown that the control of microstructure can be achieved during laser powder bed fusion (LPBF) through the control of heat input parameters or the heat distribution using the laser scanning strategies. By controlling the thermal gradient and the cooling rate, the columnar-to-equiaxed transition can help tailor the grain structure for creep-resistant or fatigue-resistant performance on demand. In this work, microstructural control using both heat input and scanning strategies was applied during LPBF of ATI 718Plus Ni-superalloy. The chemical composition of ATI 718Plus is relatively different from the widely used Inconel 718, allowing it to achieve a higher operating temperature while retaining the good processing characteristics of Inconel 718. Due to its higher maximum operating temperature, ATI 718Plus is a candidate for use in high-temperature components. The 718Plus alloy demonstrates a relatively wider processing window, where several parameters can be applied, resulting in different grain structures while achieving a fully dense build. Microstructural characterisation using X-ray diffraction and scanning electron microscopy, including electron backscattered diffraction, was performed to assess the impact of the investigated process parameters on grain structure and texture development in the builds. The investigated conditions displayed variations in grain structure morphology, texture strength, as well as the degree of micro-segregation caused by rapid solidification during the process. The solidification rate was estimated by correlating the solidification cell size with literature values for solidification rates in Ni-superalloys. The different scanning strategies resulted in noticeable changes in microstructure. Scanning strategies with a large island size and shift led to a more columnar microstructure, while small island size and shift led to a finer and more equiaxed microstructure.
After identifying the process parameters that could potentially achieve creep-resistant performance, the builds were exposed to post-LPBF heat treatments, using solution treatment and ageing with and without the application of additional hot isostatic pressing (HIPping) treatment to further grow the grain structure. The impact of post-processing on the microstructure was further explored and assessed.