Session: 03-15-01: Composites Design for Automated Fiber Placement and Additive Manufacturing

Paper Number: 137935

137935 - Influence of Post-Processing and Intra-Build Design Parameters on the Fracture Toughness Variation of Electron Beam Melted Ti6al4v 

Metal Additive Manufacturing (AM) has attracted a growing interest in engineering applications, where mechanical properties can be optimized for the desired application using post-processing treatments. Therefore, a thorough understanding of the post-processing effects on the material is integral for the safe utilization of AM metals and for ensuring the structural integrity of engineered components. This study investigates the effect of a low-temperature, high-pressure Hot Isostatic Process (HIP) on the fracture toughness of Electron Beam Melted (EBM) Ti6Al4V. Additionally, the intra-build design parameters, including part size, orientation, and location within the build chamber (radial distance and height) are evaluated using a design of experiments to account for the sources of variation in fracture behavior. One hundred (100) compact tension (CT) samples were investigated systematically in three different orientations and reported an approximate fracture toughness K_Q of 75MPaÖm after post-processing. ANOVA statistics of the influence and interaction of intra-build design parameters and orientation on the HIP samples showed orientation to be the largest source of variation, followed by the intra-build design parameters. Build orientation accounted for roughly 10% of overall fracture toughness variation due to microstructure anisotropy. The ZX orientation noted the most significant increase in fracture toughness after HIP, with a 26% increase compared to the untreated condition due to the slight increase in α-lath thickness and removal of internal defects. The specimen location within the build chamber and thickness contributed to the remaining fracture toughness variation observed, with an increase in fracture toughness with the increase in build height and thickness. The low-temperature, high-pressure HIP process successfully reduced internal defects with limited microstructure coarsening, making it a promising treatment for structural applications. While larger specimens are recommended in the future to obtain plain-strain fracture toughness values necessary for qualification, the reported post-processed EBM Ti6Al4V fracture toughness values reported less than 10% variation in overall properties, making it promising for use in load-bearing applications.

Presenting Author: Melody Mojib University of Washington

Presenting Author Biography: Melody is a PhD candidate at the University of Washington pursuing PhD in mechanical engineering. She comes to UW after working in the 3D printing industry to contribute further to metal additive manufacturing research. Her research concentrates on characterizing the fracture-critical properties of Electron Beam Melted titanium alloys.