Gas-Phase Nitridation under Kinetic Control -- A New Concept for Surface Hardening of Ti-Base Alloys

技术支持：钛基合金由于其高的比强度和在氧化环境中的耐腐蚀性而在技术上是重要的。然而，在许多应用（航空航天工程、生物医学、体育、珠宝、建筑）中，这种合金的性能受到其众所周知的差的表面硬度和耐刮擦性、非常高的摩擦系数和快速磨损以及在还原介质中差的耐腐蚀性的严重限制。解决这些缺陷的有效方法是在钛合金零件形成最终形状后优先硬化其表面。这种"表面"硬化最有效地通过间隙溶质（例如氮）的向内扩散来实现。然而，钛与所有相关的间隙溶质形成非常稳定的化合物。因此，用间隙溶质对Ti基合金进行表面硬化的常规方法不可避免地产生沉淀物（氧化物、碳化物或氮化物），这严重降低了耐磨性、疲劳性和耐腐蚀性。PI团队的开创性实验产生了一种新概念，使氮从气相向内扩散到钛基合金中，而不会沉淀有害的氮化物颗粒。这一新概念被称为"动力学控制下的氮化"，并已在两种不同的工艺方案中成功实施，产生了氮浓度高达20原子%的无沉淀情况，并极大地提高了表面硬度。在这项研究中，PI建议研究这些新的和不寻常的材料的表面，微观结构和基本特性。非技术：这项工作的更广泛的影响包括钛基合金制成的零件和组件的新工程应用，与这些新应用相关的新工作，与这些新应用中的一些钛基合金的高比强度相关的初级能源的节省，通过提供更好的医疗植入物材料来对抗疾病的进步，以及飞机安全性的改善。G.通过减少直升机中钛基合金液压管路的灾难性故障。拟议项目的结果也将深刻影响CWRU的材料科学课程。这两个PI都有支持代表性不足的少数民族的记录，并且在他们的研究小组中有很大一部分女学生。Co-PI继续努力向中学生介绍材料科学和显微镜。

Technical: Ti-base alloys are technologically important because of their high specific strength and resistance against corrosion in oxidizing environments. However, in many applications (aerospace engineering, biomedicine, sports, jewelry, architecture) the performance of such alloys is severely limited by their notoriously poor surface hardness and scratch resistance, very high friction coefficients and rapid wear, as well as poor corrosion resistance in reducing media. A powerful approach to counter these deficiencies is to harden the surface of Ti-alloy parts preferentially after they have been formed into their final shape. Such "case" hardening is most effectively achieved by Inward diffusion of interstitial solutes, for example nitrogen. However, titanium forms very stable compounds with all relevant interstitial solutes. Consequently, conventional methods to case-harden Ti-base alloys with interstitial solutes inevitably produce precipitates (oxides, carbides, or nitrides), which severely degrade the wear-, fatigue-, and corrosion resistance. Pioneering experiments by the PI's group have resulted in a new concept enabling inward diffusion of nitrogen into titanium base alloys from a gas phase without precipitating detrimental nitride particles. This new concept is denoted as "Nitridation under kinetic control" and has been successfully implemented in two different processing schemes, yielding precipitation-free cases with nitrogen concentrations of up to 20 at% and a tremendous increase in surface hardness. In this investigation, the PIs propose to study the surface, microstructure, and fundamental properties of these new and unusual materials. Non-Technical: The broader impacts of this work include new engineering applications of parts and components made from Ti-base alloys, new jobs related to these new applications, savings of primary energy related to the high specific strength of Ti-base alloys in some of these new applications, advances in fighting diseases by making available better materials for medicalimplants, and improvements in aircraft safety - e. g. by reducing catastrophic failureof Ti-base alloy hydraulic lines in helicopters. The results of the proposed project will also profoundly impact materials science courses at CWRU. Both PIs have a record of supporting underrepresented minorities and have had a substantial fraction of women students in their research groups. The Co-PI has a continuing effort of introducing middle school students to materials science and microscopy.