Metal additive manufacturing (AM) has developed significantly since its invention. In this project, a laser-based directed energy deposition (DED) process will be utilized to fabricate metallic parts for nuclear reactor application. The top few layers will be further engineered using an ultrasonic impact peening treatment to enhance its wear resistance. Post printing, the samples will be analyzed using neutron diffraction to reveal the evolution of microstructure, residual stress, and phase fractions at different build height regions along the build direction of fabricated samples to correlate the microstructural details with process conditions. Friction and wear behavior of these additively manufactured samples will be conducted via both reciprocating sliding and fretting wear testing. Tribology is the science of friction, wear, and lubrication, making it inherently inseparable from surface engineering. AM offers unique capabilities that can be leveraged to enhance the reliability of various tribological contacts. This project will explore the symbiotic relationship between AM, surface engineering, and tribology with respect to sliding and fretting contact problems specifically connected to nuclear reactors. However, the major findings from this research will provide valuable insights to wide varieties of contacts in critical applications, such as biomedical, automotive, and aerospace sectors.

This Research Infrastructure Improvement Track-4 EPSCoR Research Fellows (RII Track-4) project would provide a fellowship to an Assistant professor and training for a graduate student at the University of North Dakota (UND). Tribology, a complex and highly interdisciplinary field, is the science of friction, wear, and lubrication. It is necessary to understand the differences in an AM part’s friction and wear mechanism compared to traditionally fabricated parts and in-depth material characterizations for proper commercialization. Surface engineering is connected to materials science since it pertains to the surface of solid matter. Additive manufacturing, surface engineering, and tribology have an interdependent relationship. Our research goal is to leverage this perspective to develop next-generation nuclear reactor components with enhanced reliability and customizability when encountering friction and wear at different temperatures. We will fabricate functionally graded metallic components made of Nitronic 60 stainless steel by leveraging customized laser-based directed energy deposition (DED) technique equipped with an ultrasonic impact peening (UIP) capability. Nitronic 60 is an inexpensive austenitic stainless steel widely used in the nuclear sector due to its galling-resistance properties. This material can present high-temperature wear and corrosion resistance, and widely used in valve seats, bushings, roller bearings, and rings. We believe that optimized process parameters during UIP treatment can result in a strain-induced FCC to HCP martensitic phase transformation (SIM) in the deposited near-surface layers of Nitronic 60, and enhanced materials states, such as residual stress with refined grains, can result in improved tribological behavior. Process-microstructure-property of deposited Nitronic 60 will be revealed by understanding phase fractions, residual stress evolution along build height through neutron diffraction and correlated that with reciprocating friction and wear testing as well as grid-to-rod fretting characteristics of fabricated samples.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.