Osaka University Achieves High-Strength Nickel-Based Superalloys through 3D Printing

Professor Hiroyuki Yasuda, Associate Professor Yanzhun Zhao, and graduate student Aoi Yamashita, along with other researchers at Osaka University, announced on the 11th that they have discovered a method to manufacture nickel-based superalloys with higher strength than traditional materials using Laser Powder Bed Fusion (L-PBF) technology, and have identified its control methods. This research reveals the deformation behavior of this special high-strength hierarchical structure. With the new mechanical function control method, it is expected to significantly enhance the performance of metal components in various fields such as aerospace, energy, transportation equipment, and medical devices.

The nickel-based superalloys produced using the metal 3D printing L-PBF technology exhibit a “crystal orientation layered structure” with two different crystal orientation regions arranged in layers, as well as a nanoscale (nano is one billionth) “cellular structure.” Together, these form a high-strength hierarchical structure. The research team analyzed the deformation behavior of the crystal orientation layered structure using “in-situ neutron diffraction” and conducted a detailed study of the cellular structure.

The study shows that in the crystal orientation layered structure, the initiation stress for plastic deformation in the narrow sub-layers is higher than that in the main layer, which determines the overall strength of the formed body. The cellular structure in the sub-layers contains enriched regions of specific elements such as niobium and densely packed low-angle grain boundaries (the relative orientation difference between adjacent crystal grains is less than 15 degrees). These enriched regions are a result of the elemental distribution phenomenon caused by the rapid solidification of the molten pool formed during the L-PBF process; while the dislocation cells are introduced during the ultra-rapid cooling process after solidification, causing plastic relaxation.

Based on these results, the research team developed a technique to artificially differentiate the cellular structure by controlling the laser energy density during the forming process. They also found that low-angle grain boundaries can undergo refinement strengthening. By overlaying the new strengthening mechanism derived from the cellular structure onto the unique deformation behavior of the crystal orientation layered structure, the effectiveness of metal 3D printing in controlling the microstructure and mechanical functions of metal components is demonstrated.