Pushing property limits of structural materials with additive manufacturing

Atieh Moridi, Assistant Professor, Sibley School of Mechanical and Aerospace Engineering, Cornell University

Hopeman 224

Designing materials with high strength and ductility has been a longstanding challenge in materials science. The potential for property enhancement to further push the strength-ductility envelope of metallic materials is either exhausted or incremental. Therefore, drastic new strategies are needed to meet the global demand of making high performance materials. Exploiting the intrinsic properties and flexibility of additive manufacturing (AM) offers ample opportunities for integrated materials and manufacturing innovation. In this talk, I will highlight different examples of how AM enables us to access new microstructures and properties.

In the first example, I show that by deliberately introducing a high density of lack of fusion (LoF) defects, a processing regime that has been avoided so far, followed by pressure assisted heat treatment, we can print titanium alloys with reduced texture and exceptional properties. Such improvement is achieved through the formation of low aspect ratio α-grains around LoF defects upon healing, surrounded by α-laths. This occurrence is attributed to surface energy reduction and recrystallization events taking place during healing of the defects.

In the second example, I show how modifying the solidification pathway can be used to change the morphology of grains. To study the solidification pathway during AM process, my group has integrated a custom printer at the Cornell High Energy Synchrotron Source (CHESS). Conducting operando AM experiments at high temporal resolution reveals that existence of metastable phases during solidification contributes to formation of rough and convoluted grain boundaries resembling a fractal object. The fractal grain boundaries are expected to enhance mechanical properties such as fracture toughness and high-temperature fatigue properties opening a new avenue of alloy design to improve mechanical properties.