Theoretical and Experimental Investigations of Gum Metal

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TECHNICAL: PIs will pursue a transformative research program to study in detail the mechanical properties of the recently discovered class of Ti-Nb alloys known as Gum Metals. Gum Metals display super-elasticity, high strength, and significant ductility all in the absence of traditional, dislocation mediated plasticity. In an effort previously funded (in part) through an NSF NIRT, PIs have conducted a rudimentary analysis of the mechanical properties of these materials. Specifically, PIs have demonstrated that Gum Metals are deforming near their ideal strength limit. Further, PIs demonstrated that the dislocations may be pinned easily, even at stresses approaching the ideal strength. Using nanoindentation experiments, PIs showed that the material deforms through (apparently) continuous rotations of nanoscale volume elements. All of these properties have been linked to an electron-filling-induced transition from a body-centered cubic to a hexagonal close packed structure. PIs will expand substantially their prior investigations of Gum Metal behavior in two directions. First, PIs will develop a more detailed understanding of the mechanical properties of Gum Metals. These studies will expand to include the study of dislocation cores, as well as more detailed mapping of the nanoscale deformation patterns associated with nanoindentation. PIs will use theory to identify new alloys that are candidates for Gum Metal behavior. PIs will synthesize the alloys in thin film form and explore directly their mechanical properties. NON-TECHNICAL: Gum Metal behavior presents several exciting opportunities for materials theorists and metallurgists. Since the mechanical properties of these materials are linked to quantities that can be computed directly using the best available quantum mechanical based total energy methods, there is a genuine opportunity for rapid, computer aided, advanced engineering of these alloys. Further, theory will be used to identify other candidates for Gum Metal behavior. PIs' work is aimed at exploiting these opportunities, and it will advance the understanding of Gum Metal behavior and, more generally, an understanding of metallurgical possibilities. The project will have a broad impact in a number of ways. First, there will be two graduate students working directly on the project, and their research conducted within this program will advance their Ph.D. studies. Each student will be encouraged to write papers and to attend meetings of professional societies in order to disseminate their research results. Second, the research results will be incorporated directly into the graduate level Computational Materials Science course taught at Berkeley. Third, the PIs will recruit undergraduates to work on the project using programs at Berkeley aimed at engaging students from underrepresented groups in research. Within a much broader perspective, the existence of alloys with mechanical properties that conflict with 80 years of metallurgical wisdom is truly exciting. The potential for the engineering of advanced materials is clear. The research program may lead to a broad new class of alloys with "super" properties and numerous technological applications.