We are developing (and experimentally validating) a framework to create strong and tough joints between dissimilar materials. Currently, it is difficult to join different materials without forming weak and brittle phases between them. The current state of the art circumvents this issue by employing mechanical fasteners. However, this solution is not ideal for aerospace applications because nuts and bolts introduce excess weight and volume. By leveraging computational thermodynamics and robotic path planning algorithms, we design functionally graded interlayer foils that suppress deleterious phases when joining different classes of alloys.

Ultra-High Temperature Ceramics (UHTCs) are promising materials for use in extreme aerospace environments owing to their high melting points and excellent thermo-mechanical properties. However, oxidation and evaporative mass-loss in these materials at elevated temperatures limit their service lifetimes. To address this shortcoming, we are studying the synthesis and high-temperature oxidation behavior of nanoporous UHTCs infiltrated with either an ablative polymer or oxidation-resistant glasses. Our underlying hypothesis is that the morphology (porosity length scale and interfacial shape distribution) governs the resulting oxidation kinetics.

Tungsten is the leading plasma facing material (PFM) candidate for fusion reactors due to its attractive thermo-physical properties, resistance to sputtering, and chemical compatibility with tritium. As a PFM, tungsten will need to be fabricated into functional components with intricate geometric features, but its limited ductility at room temperature makes it challenging to forge/machine parts more complex than rods and sheets. Laser-based additive manufacturing (AM) techniques can reliably fabricate complex geometries without expensive tooling. However, it is challenging to fabricate crack-free AM tungsten due to high cooling rates and its low fracture toughness. We are utilizing a CALPHAD-based alloy design strategy to fabricate AM tungsten materials with little-to-no cracks and assess its thermo-physical and mechanical properties.

Collaborators: Professor Jason Trelewicz at Stony Brook University

Hard coatings deposited via thermal spray are widely used to enhance the corrosion, wear, and oxidation resistance of metal alloys. However, it is challenging to design for environments with multiple degradation mechanisms, such as corrosion fatigue. Coatings that perform excellent under static loading conditions can fail rapidly in dynamic environments either by delamination or developing deleterious cracks themselves. We hypothesize that the ideal coating is a multi-phase bicontinuous composite, where the constituent phases synergistically act to dampen surface pits and impart exceptional fracture toughness. We are studying the fabrication of these coatings, and their resulting fatigue/fracture properties.

Collaborators at Johns Hopkins University: Professors Jonah Erlebacher, Paulette Clancy, Somnath Ghosh, Mitra Taheri, Chao Wang. Collaborators at Northrop Grumman Corporation: Thomas Knight, Vivian Ryan, Eric Jones, Kevin Galiano

Unlike stainless steels, many other metals undergo severe corrosion in aqueous environments, which can impose significant human and financial losses. When corrosion resistant metallic alloys are exposed to corrosive agents occurring in water, they naturally evolve a thin protective surface oxide film. However, the necessary alloy composition to form a passivating film has remained elusive. We are developing analytical and numerical aqueous passivation models of binary alloys and validate them using multimodal experimentation, first-principles-based quantum mechanical models, and kinetic Monte Carlo simulations. This knowledge will be used to guide models that inform the design of the next generation of corrosion-resistant metallic alloys.

Collaborators: James Rondinelli (Northwestern University), Karl Sieradzki (Arizona State University)

Stress rupture strength and oxidation resistance are the initial screening criteria for developing high temperature alloys. Due to the success of environmental coatings, alloying strategies focus more on increasing high temperature mechanical strength rather than environmental resistance. However, coatings degrade over time and can expose the base material to an oxidizing environment during service. Thus, there is a growing need to understand the impact of alloying elements, which have different affinities for oxygen, bulk diffusivities, and oxide stoichiometries. Unfortunately, standard oxidation tests are low-throughput, probe one temperature and a one-material-at-a-time approach. We are developing a high-throughput test, which evaluates the oxidation behavior of multiple materials and temperatures in a single run.

Collaborators: Jian Cao and Wei Chen (Northwestern University); Scott Oppenheimer and Greg Natsui (General Electric).