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

SGER：利用多晶型转变处的反常扩散来实现元素的大量侵入和金属中更深的表面涂层

• 批准号: 0737883
• 负责人: K. S. Ravi Chandran
• 金额: $ 16.83万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-15 至 2009-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0737883&HistoricalAwards=false
• 关键词: SGER; Exploiting; Anomalous; Diffusion; Polymorphic

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).

技术支持：在这个高风险/高回报的变革性项目中，PI将探索通过利用多晶型转变处的异常扩散来“泵送”大量元素的有趣可能性，以实现金属的深层和富集的表面层/涂层。这个想法是由PI最近的观察引发的，在B在钛中的扩散过程中，发现了一个不寻常的和有趣的结果：纳米结构的硼化钛（Ti B）晶须表现出不寻常的更深的生长到钛基体中，当扩散发生接近多晶型转变温度。虽然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。在金属的多晶型转变附近发现了金属中的异常（快速）扩散，导致扩散系数的Arrhenius曲线弯曲。由于伴随相变的晶格不稳定性，推测这引发了巨大的原子通量，从表面到内部泵入大量物种（如C，B，N，O）。除了PI的初步证据，这些都没有得到最终证明。在本研究中将解决的广泛的智力问题是当间隙元素C、B、N、O扩散到金属中时会发生什么，接近或正好在多晶型转变温度，以及如何从原子/动力学的角度理解这个不寻常的过程。PI将在实验和理论上探索这方面，在两种候选材料，钛和铁在固态/气相扩散的B，C，N在多晶型转变。非技术性：如果在经历多晶型转变的主要金属类别（如Fe，Ti，Zr，Co）中证实了金属中物种的这种有害的更深扩散，那么这将对表面科学和工程产生巨大影响（高回报，转化元素）。然后可以利用这种现象进行元素（C、N、B、O）的固态扩散，以在金属上形成深的和富集的表面硬涂层（碳化物、硼化物和氮化物）。特别是，Fe和Ti是主要的候选者，因为这些金属通常被渗碳、氮化或硼化以增加表面硬度和耐磨性-在多晶型转变温度下的异常扩散可以在这里被利用，以更少的时间和能量成本产生更深和更富集的表面层。钛和铁中大量杂质的进入以及随之而来的更深涂层和硬化的实现将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，以增加硬度和耐磨性。在相变温度或接近相变温度下和在较短时间内执行这些过程应导致工业中的大量能量/成本节约。这项研究将雇用一名本科生和一名研究生（少数民族或代表性不足的群体候选人，如果有的话）。