Ashley Paz y Puente, assistant professor of mechanical and materials engineering at the University of Cincinnati (UC) College of Engineering and Applied Science (CEAS), has been awarded a three-year, $400,741 grant from the National Science Foundation (NSF). Beginning September 1, 2017 through August 31, 2020 (estimated), Paz y Puente will lead as the Principal Investigator of her project, “Gas-Phase Alloying and Sintering Kinetics of 3D Printed Ni Scaffolds.”
Garnering the increasing attention of several industries is the fabrication of metallic scaffolds, or lattice structures, with progressively complex geometries. Thanks to their open porosity, these structures possess a rare coupling of low density and high surface area, making them the ideal candidates for a wide array of applications ranging from batteries to commercial airplanes to biomedical implants.
Yet, the challenge remains in fabricating these technologically important alloys that house such useful geometries. The ever-beneficial increase in porosity often compromises the mechanical properties that are important in maintaining the structural stability of the scaffold. Thus, traditional manufacturing and newer additive manufacturing techniques (commonly referred to as 3D printing) often fall short in successfully creating these open-structure materials.
Paz y Puente explains, “While the ability to create near-net-shape metallic parts with high geometric complexity has made powder-bed additive manufacturing techniques attractive, many engineering relevant alloys are difficult to fabricate with high quality due to poor sintering, internal porosity, and cracking.”
Paz y Puente and her team of UC CEAS graduate students—Safa Khodabakhsh, Arun Bhattacharjee, Haozhi Zhang, Ajith Achuthankutty, and Aditya Patibandla—have been awarded the prestigious NSF grant to conduct further research aimed at providing fundamental knowledge required for the development of an alternative process for successfully making these metal scaffolds.
The main material system of interest in this research is the basis for Nickel (Ni)-based superalloys, which are most well-known for their use in jet engines. By creating this material in an open structure, the weight can be significantly reduced. Additionally, the increased surface area and permeability of a scaffold allow for highly efficient active cooling of the material resulting in the ability to operate at higher temperatures.
Paz y Puente and her group theorize a new process for producing these metal scaffolds using a two-step approach controlled by thermodynamics and kinetics.
She describes, “One alternative approach is to decouple the printing and alloying by using particle-based ink printing to create the desired geometry from a pure metal or simple alloy that is known to print successfully, and then further alloy the part in a separate step using a deposition process and homogenization to reach the target composition. This process will enable an assortment of different materials to be produced from the same precursor printed metal part."
To accomplish this, Paz y Puente’s team will work with different characterization techniques to investigate the relationships between the processing, structure, and properties of these materials. They will focus on developing ways to combine additive manufacturing and coating deposition processes to fabricate metallic scaffolds while studying the governing diffusion and phase transformation kinetics.
Paz y Puente addresses their hypothesis, “Our new two-step approach is ideal for creating metallic scaffolds, taking advantage of the open porosity and small diffusion distances. The overall aim of this project is to study the fundamental sintering and alloying kinetics of such scaffolds using a combination of conventional metallography and in situ X-ray tomographic microscopy. The phase and pore evolution will be systematically studied as a function of geometry, composition, powder and strut size, and anneal time and temperature and the mechanical behavior will be computationally predicted and experimentally determined.”