TECHNICAL: In this high risk/high payoff, transformative project, PI will explore the interesting possibility of "pumping" a large amount of elements by exploiting the anomalous diffusion at polymorphic transitions, to achieve deep and enriched surface layers/coatings in metals. This idea has been triggered by PI's recent observations during B diffusion in titanium where an unusual and interesting result was found. Nanostructured titanium boride (TiB) whiskers exhibited an unusually deeper growth into titanium substrate, when diffusion occurred close to the polymorphic transition temperature. Although this might appear strange at first, there is some convincing and indirect evidence supporting this phenomenon. Anomalous (fast) diffusion in metals has been noted near polymorphic transitions of metals leading to a curvature in Arrhenius-plot of diffusion coefficient. Due to the lattice instability accompanying the phase transition, this is speculated to trigger huge atomic flux, pumping-in lot of species (such as C, B, N, O) from surface to interior. Except for PI's preliminary evidence, none of these have been demonstrated conclusively. The broad intellectual question that will be resolved in this research is what happens when interstitial elements, C, B, N, O are diffused into metals, near or exactly at the polymorphic transition temperatures, and how this unusual process can be understood from atomic/kinetic point of view. PI will explore this aspect, both experimentally and theoretically, in two candidate materials, Ti and Fe during solid/vapor state diffusion of B, C, N at polymorphic transitions. NON-TECHNICAL: If this anomalously deeper diffusion of species in metals is confirmed across major classes of metals (such as Fe, Ti, Zr, Co) that undergo polymorphic transitions, then this would have a great impact in surface science and engineering (high payoff, transformative elements). One can then exploit this phenomenon for solid state diffusion of elements (C, N, B, O) to form deep and enriched surface hard coatings (carbides, borides and nitrides) on metals. In particular, Fe and Ti are prime candidates as these metals are commonly carburized, nitrided or borided to increase surface hardness and wear resistance--the anomalous diffusion at the polymorphic transition temperature can be taken advantage of here, in producing deeper and more enriched surface layers at much less time and energy cost. Demonstration of large ingress of interstitials in Ti and Fe and the attendant achievement of deeper coating and hardening should revolutionize the surface treatment industry - a large number of gears, bearings, tools, dies and other components are routinely surface hardened to increase hardness and wear resistance. Performing these processes at or near phase transition temperatures and at shorter times should lead to large energy/cost savings in industry. This research will employ one undergraduate student and one graduate student (minority or under-represented-group candidate if available).
