Stability of Colossally Supersaturated Alloys

我们的研究小组对合金进行了低温渗碳和氮化处理，发现Fe-Cr-Ni合金（奥氏体不锈钢）中可以溶解高浓度的碳和氮。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。这使得形成一种均匀的、无沉淀的、超硬的“s相”，由碳或氮浓度超过平衡溶解度极限约十万倍组成！到目前为止，我们的工作主要集中在这种“巨大过饱和”（CSS）的潜在物理原理，以及由表面下的间隙溶质（“case”）提供的25-50微米厚硬化层的机械性能和耐腐蚀性上。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机械应力下的可靠性和寿命，并通过回火（即热处理）进一步处理它。此外，我们建议将研究扩展到Ni-Cr和Co-Cr合金，对这些合金来说，巨过饱和硬化具有重要的技术意义。具有大量过饱和的间隙溶质（碳、氮）的合金构成了特殊条件下金属分解和沉淀现象基础研究的独特模型系统。特别是，它将有助于了解碳化物和氮化物在极高过饱和条件下成核、生长和成熟的物理原理，以及分解如何影响CSS最初提供的卓越的力学性能和出色的耐腐蚀性。这为“变革性”发现提供了巨大的潜力。两个相关研究小组的专业知识、经验和仪器的很大程度上互补，将使这一重要的表面工程领域取得重大进展。该项目将为双方在表面工程领域的长期合作奠定基础。我们想要获得的对css硬化合金在外加温度和应力下分解的物理理解对于许多结构合金的应用非常重要，例如轴承、食品加工刀片、阀门、轴套、模具、核反应堆部件、医疗植入物以及外科和牙科器械。我们希望通过了解其物理基础来提高可靠性和使用寿命，从而通过避免不必要的合金零件生产和回收来节省主要能源资源和保护战略原材料。超硬耐磨和耐腐蚀合金的可用性将使新产品的设计成为可能，从而加强美国和英国的工业，这有助于创造新的就业机会。长寿命人体植入物可以提高患者的生活质量，降低英国/美国的医疗服务成本。拟议研究的结果极有可能产生新的知识产权。该项目将对CWRU和大华银行的学生教育和培训产生重大影响。研究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，该项目将使本科生能够大量参与实践，从而有助于吸引优秀的本科生到我们的院校学习。这些学院在招收本科生和女学生以及交换研究生和博士后研究助理参与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.