Stability of Colossally Supersaturated Alloys

我们的团队对暴露在最近开发的低温渗碳和氮化工艺下的合金进行的工作表明，极高浓度的碳和氮可以溶解在Fe-Cr-Ni合金(奥氏体不锈钢)中。在这个过程中，碳或氮在足够低的温度下从表面扩散到合金中，以抑制碳化物或氮化物的析出。这使得能够形成均匀的、无沉淀的、超硬的“S相”，其碳或氮浓度超过平衡溶解度极限约10万倍！到目前为止，我们的工作主要集中在这种“巨大过饱和”的基本物理原理以及由表面下的间隙溶质(“壳”)提供的加工后的25-50微米厚的硬化层的机械性能和耐蚀性上。我们在这里提出的工作是第一次努力研究这种不寻常的材料在高温和施加机械应力下的可靠性和寿命，并通过回火-即暴露于热处理-进一步处理它。此外，我们建议将研究扩展到镍铬和钴铬合金，对这些合金来说，超饱和硬化具有重要的技术意义。具有巨大过饱和间隙溶质(碳、氮)的合金构成了独特的模型系统，用于在特殊条件下对金属中的分解和沉淀现象进行基础研究。特别是，它将使理解碳化物和氮化物在极高过饱和度下形核、生长和成熟的物理原理，以及分解如何影响由CS最初提供的显著机械性能和出色的耐腐蚀性。这为“变革性”的发现提供了很高的潜力。两个相关研究小组的专业知识、经验和仪器设备在很大程度上具有互补性，这将使这一重要的表面工程领域取得重大进展。该项目将为两个领导小组在表面工程领域的长期合作奠定基础。对于结构合金的许多应用，例如轴承、食品加工刀片、阀门、衬套、模具、核反应堆部件、医疗植入物以及外科和牙科器械，物理上了解表面硬化合金在施加温度和应力下的分解情况是非常重要的。我们希望通过了解它们的物理基础来提高可靠性和寿命，从而通过避免不必要的合金部件生产和回收，大幅节省一次能源资源和节约战略原材料。超硬耐磨和耐腐蚀合金的供应将使新产品的设计成为可能，从而加强美国和英国的工业，这可能有助于创造新的就业机会。长寿命的身体植入物可以提高患者的生活质量，降低英美医疗服务成本。拟议的研究结果极有可能产生新的知识产权。该项目将对CWRU和UOB的学生教育和培训产生重大影响。其结果将直接影响两所大学材料科学课程的理论和实践部分。此外，该项目将使本科生有大量的实践参与，因此将有助于吸引优秀的本科生进入我们的院校。私人投资机构在吸引本科生和女学生以及交流研究学生和博士后研究助理参与其研究活动方面有着良好的记录。

The work our groups have carried out on alloys exposed to recently developed processes for low-temperature carburising and nitriding revealed that extraordinarily high concentrations of carbon and nitrogen can be dissolved in Fe-Cr-Ni alloys (austenitic stainless steel). In this process, carbon or nitrogen diffuses into the alloy from the surface at a temperature sufficiently low to suppress the precipitation of carbides or nitrides. This enables the formation of a homogeneous, precipitate-free, superhard " S-phase" consisting with carbon or nitrogen concentrations that exceed the equilibrium solubility limit by about one-hundred-thousand times!To date, our work has focused on the underlying physical principles of this "colossal supersaturation" (CSS) and the mechanical properties and corrosion resistance of the as-processed 25-50 micron -thick hardened layer provided by the interstitial solute ("case") below the surface. The work we propose here constitutes a first effort to investigate the reliability and lifetime of this unusual material at elevated temperature and under applied mechanical stress and to further process it by tempering - i. e. exposure to heat treatments. Moreover, we propose to extend the research to Ni-Cr and Co-Cr alloys, for which hardening by colossal supersaturation has great technological importance.Alloys with a colossal supersaturation of interstitial solute (carbon, nitrogen) constitute unique model systems for fundamental studies of decomposition and precipitation phenomena in metals under unusual conditions. In particular, it will enable understanding the physical principles of carbide and nitride nucleation, growth, and ripening under extremely high supersaturation and how the decomposition affects the remarkable mechanical properties and outstanding corrosion resistance initially provided by CSS. This provides a high potential for "transformative" discoveries. The largely complementary expertise, experience, and instrumentation of the two involved research group will enable significant progress in this important field of surface engineering.This project will lay the foundation for long-term cooperation of two leading groups in the field of surface engineering. The physical understanding of the decomposition of CSS-hardened alloys under applied temperature and stress we intend to obtain is of great importance for many applications of structural alloys, e. g. bearings, food processing blades, valves, bushings, dies, nuclear reactor components, medical implants and surgical and dental instruments. The increase of reliability and lifetime we hope to enable by understanding their physical foundations will lead to major savings of primary energy resources and conservation of strategic raw materials by avoiding unnecessary production and recycling of alloy parts. The availability of super-hard wear-and corrosion-resistant alloys will strengthen US and UK industry by enabling the design of new products, which can contribute to the creation of new jobs. The long-life body implants can improve the quality of life of patients and reduce UK/US health service costs. The results of the proposed research are highly likely to generate new intellectual property. The project will have significant impact on student education and training at CWRU and UoB. The results will directly impact the theoretical and practical parts of materials science courses at both universities. Further, the project will enable significant practical participation of undergraduate students and will therefore help to attract excellent undergraduate students to our institutions. The PIs have a record in engaging undergraduate students and women students and in exchanging research students and postdoctoral research associates in their research activities.