SGER: Exploiting Anomalous Diffusion at Polymorphic Transitions for Large Ingress of Elements and Deeper Surface Coatings in Metals

技术：在这个高风险/高回报的变革性项目中，PI将探索通过利用多态转变的异常扩散来“泵送”大量元素的有趣可能性，以实现金属中深层和富集的表面层/涂层。这个想法是由PI最近对钛中B扩散的观察引发的，在那里发现了一个不寻常而有趣的结果。纳米结构硼化钛（TiB）晶须在接近晶型转变温度时发生扩散，在钛基体中生长得更深。虽然一开始这可能看起来很奇怪，但有一些令人信服的间接证据支持这一现象。金属中的异常（快速）扩散在金属的多晶态转变附近被注意到，导致扩散系数的arrhenius图的曲率。由于伴随着相变的晶格不稳定性，推测这将触发巨大的原子通量，从表面向内部泵入大量物质（如C， B， N， O）。除了PI的初步证据外，这些都没有得到确凿的证明。在这项研究中要解决的广泛的知识问题是，当间隙元素，C， B， N， O扩散到金属中时，在多晶转变温度附近或正好在多晶转变温度下会发生什么，以及如何从原子/动力学的角度理解这一不寻常的过程。PI将在两种候选材料Ti和Fe中，在B， C， N的多晶态转变的固体/蒸气态扩散过程中，从实验和理论上探索这方面。非技术：如果在主要金属类别（如Fe， Ti, Zr, Co）中证实金属中物种的异常深层扩散，那么这将对表面科学和工程（高回报，转化元素）产生重大影响。然后，我们可以利用这一现象对元素（C、N、B、O）的固态扩散，在金属上形成深而丰富的表面硬涂层（碳化物、硼化物和氮化物）。特别是，铁和钛是主要的候选者，因为这些金属通常经过渗碳、氮化或渗硼以增加表面硬度和耐磨性——在多晶转变温度下的异常扩散可以在这里利用，以更少的时间和能量成本生产更深、更丰富的表面层。Ti和Fe中大量进入的间隙以及随之而来的更深的涂层和硬化的成就应该彻底改变表面处理行业-大量齿轮，轴承，工具，模具和其他部件通常进行表面硬化以提高硬度和耐磨性。在相变温度或接近相变温度下，在更短的时间内进行这些工艺，将为工业节省大量的能源/成本。本研究将雇用一名本科生和一名研究生（少数族裔或弱势群体候选人，如果有的话）。

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).