2, University of Tennessee, Knoxville, Knoxville, Tennessee, United States
3, Barnard College, Columbia University, New York, New York, United States
Ultrasonic additive manufacturing (UAM) is a solid-state manufacturing technology for producing near-net shape metallic parts combining additive ultrasonic metal welding and CNC subtractive machining. Even though UAM has been demonstrated to produce robust metal structures in Al-Al, Al-Ti, Al-steel, Cu-Cu, Al-Cu, and Al-NiTi material systems, UAM welding of high strength steels presents challenges. In this study, current progress on steel to steel welding via UAM is discussed. The stainless steel 410 is selected for this study due to its wide range of applications and good heat treatment properties. The effect of pre-heat temperature as a process parameter along with the influence of hot isostatic pressing (HIP) as a post process treatment on the UAM steel samples are investigated. A custom shear test was designed to characterize the mechanical strength of unique laminated UAM steel samples. The results show that increasing the preheat temperature from 100°F to 400°F improves interfacial strength and structural homogeneity of the UAM steel samples, while the HIP process significantly improves the shear strength of UAM samples by over twice that of as-welded samples. Additionally, optical images, scanning electron microscope (SEM) analysis and electron backscatter diffraction (EBSD) measurements are presented. Specifically, the EBSD results indicate that plastic deformation and grain refinement happen at the welding interface during the UAM process compared with the as-received material and the HIP process mitigate the interfacial defects compared with the as-welded samples, which leads to the increased interfacial shear strength.