Scientific Events

This presentation provides an overview of recent developmental efforts at Oak Ridge National Laboratory (ORNL) on heat-resistant ferrous materials with Laves-phase strengthening for fossil-fired energy conversion systems. Laves phases are attractive as second-phase strengtheners in Fe-base alloys, including ferritic and austenitic stainless steels, since most of the Fe-rich Laves phases (Fe₂M intermetallic compounds, M: Nb, Mo, W, Zr, Ti, etc.) are thermodynamically equilibrated with BCC- or FCC-Fe solid solution. Because of the characteristics, relatively easy control of second-phase dispersion is expected through a traditional “solution-and-annealing” process combined with proper alloying additions. The thermal stability of the Laves phase precipitates at elevated temperature was found to be controlled and improved through combinations of multiple Laves-phase forming elements, which guides the alloy design and provides effective strengthening of high-temperature structural materials for the extended periods of time. Laves-phase precipitation in Fe-base matrix can be expected in relatively large composition/temperature ranges, which also allows designing the alloys with proper surface protections, such as chromia- or alumina-scale formation on the surface. This leads to proposing and designing new high-temperature structural materials to be used in extreme environments such as Advanced USC or supercritical CO₂ cycle applications. The presentation will also introduce various developmental efforts in Fe-base, Cr-base, and Cu-base alloys with Laves-phase strengthening at ORNL in the last decades. Research supported by the U.S. Department of Energy, Office of Fossil Energy, the Crosscutting Research Program. [more]

Advances in 3D additive manufacturing techniques have enabled the fabrication of nanostructures with remarkable mechanical properties. Using the latest 3D printing techniques, novel material structures with specific architectures, often referred to as metamaterials, can be produced. They can exhibit superior mechanical and physical properties at extremely low mass densities and, thus, expand the current limits of the yet stiff and strong architectures, architectures with high mechanical resilience or with negative Poisson’s ratio. Mechanical size effects were shown to result in extraordinary strength values of different specific architectures. Understanding the underlying characteristics of these complex new materials, such as the deformation and failure mechanisms, and how they impact behavior of the structure, is critical and increasingly challenging. In this presentation, the principles underlying ultra-strong yet light 3D nano-architected metamaterials as well as strategies to tailor their properties will be discussed. [more]