Additive Manufacturing and high-entropy alloys

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Two of the most exciting fields to emerge in materials science and engineering in recent years are additive manufacturing and high-entropy alloys. By building on its existing strengths, UVA is developing distinctive approaches in both areas to help realize their potential.

 

Susceptibility of 3-D printed materials

One obstacle to widespread use of 3-D printed metals is the effect on materials’ microstructure given the continuous welding inherent in the process. This is particularly an issue with aluminum alloys, but it is also a factor in austenitic stainless steels, which are subject to grain boundary sensitization and subsequent intergranular corrosion. Not all of the consequences of these welds can be determined through mechanical process testing that has been the focus of most work elsewhere, but are only revealed over time. Because of the department’s world-class research programs in time-dependent processes—corrosion, fatigue and oxidation—that the Office of Naval Research called on Professor Rob Kelly to evaluate the corrosion susceptibility of 3-D printed 316L and 625 corrosion resistant alloys, both mainstays of marine construction. Members of Kelly’s lab have already found evidence that parts printed with 316L exhibit sensitization in the as-printed condition, something that does not occur with material made using standard processes.

UVA faculty are also developing strategies to address these issues. Under the auspices of the Naval Surface Warfare Center, Dahlgren, Professor Sean Agnew and Associate Professor Jim Fitz-Gerald are determining whether laser surface treatment of 3-D printed metals can mitigate such time-dependent processes. In addition, Professor Haydn Wadley, in a collaboration with GE Additive Solutions, is exploring ways in which additive manufacturing can be used to significantly enhance the performance of cellular materials made from titanium alloys.

High-entropy Alloys

Another way in which the department is extending its expertise into new areas is high-entropy alloys. In the 13 years since these multiple principal element systems were first reported, researchers have developed a number of equiatomic alloys with heretofore irreconcilable properties, including alloys that are both strong and ductile. The major impediment to their systematic development is the absence of phase diagrams for such multicomponent systems, combined with the lack of fundamental modeling/simulation tools to predict microstructure evolution and the relationship of microstructure to specific properties.

To help solve this problem, the department is bringing to bear expertise in thermodynamics, metallurgy and simulation. Faculty members such as Wadley are collaborating with colleagues at other universities to secure funding to develop better simulation tools, and the department is actively reinforcing this expertise by recruiting faculty members specializing in relevant modeling methods. Professor John Scully, interim department chair, is designing improved corrosion-resistant alloys by using the tailored compositions and structures promised with high-entropy alloys as part of a prestigious DOE Energy Frontier Research Center where Scully leads the metals team. Ultimately, growing programs in additive manufacturing and high-entropy alloys will position the UVA Department of Materials Science & Engineering to help lead in the development of 21st century structural materials.