RESISTANCE TO FRACTURE AND FATIGUE IN ADDITIVELY MANUFACTURED ALLOYS [Keynote]
Punit KumarGrand Ballroom E
Ti-6Al-4V fabricated by the laser powder bed-fusion (LPBF) process consists of metastable α' microstructure and columnar prior β grain (PBGs) mesostructures. These micro-and mesostructures adversely affect fracture toughness (KIc) in as-built conditions. After an optimized post-processing heat-treatment, the KIc of LPBF Ti-6Al-4V improves by ⁓104%; however, the anisotropy in KIc persists due to preferential crack growth along the columnar PBGs. In another LPBF fabricated β Ti-alloy, Ti41Nb, the crack tortuosity from the mesostructures formed by compositional segregation improves the KIc by ⁓80%. These results demonstrate extrinsic toughening in AM alloys. While such toughening from mesostructures enhances AM alloys' reliability, the processing-induced defects present in them, i.e., porosity, significantly reduce their high cycle fatigue (HCF) resistance. Therefore, in the second part of the present study, the HCF life of 316L and 17-4 PH steels produced by the binder jet printing process was investigated. The hot isostatic pressing (HIP) was employed on these steels to improve their HCF life. The HCF life of HIPed 17-4 PH steel is comparable to their conventionally manufactured counterparts; however, in 316L, HIP fails to improve fatigue life. Based on these findings, the microstructural origin for fracture and fatigue resistance in AM alloys are discussed.