Date of Award
Master of Science
Metallurgical and Materials Engineering
This research examined thin section prototypes having seven nominal thicknesses ranging from 0.1 to 2.0 mm, composing a series of geometric feature build plates manufactured by multiple laser powder bed fusion (L-PBF) machine configurations. The build plates and thin section feature prototypes underwent a full heat treatment cycle per established standards: anneal at 1066°C, SR+HIP at 1163°C, and fully treat-treated by combining SR+HIP+solution treatment at 1066°C and double aging treatment at 760°C and 680°C, respectively. The fully heat-treated (FHT) Inconel 718 wall specimens were sectioned from 16 distinct geometric feature build plates constructed on 15 different L-PBF machines. The thin wall specimens were analyzed using optical microscopy and Electron Backscatter Diffraction (EBSD) image mapping techniques. The microstructural findings for the FHT wall specimens show predominantly equiaxed grain structures with annealing twins. The grain size varies between ~ 21 microns to 93 microns, measured both parallel (YZ) and perpendicular (XY) to the direction of the build. It was perceived from most of the samples that the grain size grew larger as the wall thickness increased, attributed to slower rates of solidification in thicker walls. The fully heat-treated thin walls, which underwent a double aging process, also resulted in fully age-hardened grain structures with gamma double-prime precipitates. This precipitation led to a median Vickers (HV) hardness for nominal section thicknesses > 0.6 mm of ~ HV 472, aligning with commercially heat-treated and optimized Inconel 718 products. Furthermore, feature sizes exceeding 0.6 mm were consistently reproducible across all L-PBF machine configurations. This study also presented the evolution of microstructures starting from the As-built sample, through stages of SR, HIP, to the FHT wall specimens, specifically from the L-PBF machine ID M290. This evolution indicates the formation of equiaxed grain and annealing twins with the heat treatment cycles.
Recieved from ProQuest
Doris, Anannya, "Effect Of Multiple Machine Configurations And Wall Thickness On Microstructure And Microhardness Of Laser Powder Bed Fusion (l-Pbf) Additively Manufactured Heat-Treated Inconel 718 Products" (2023). Open Access Theses & Dissertations. 3966.