Surface Processes in Tribocorrosion of Highly Alloyed Metallic Materials

高合金耐腐蚀金属材料用于一系列应用，包括生物医学、石油和天然气以及航空航天应用。作为一个具体实例，钴-铬（CoCr）合金由于其机械性能（高硬度）以及良好的耐磨性而通常用于摩擦学应用中。此外，由于其优异的耐腐蚀性，CoCr合金已被广泛用作暴露于腐蚀性环境的组件的关键材料，例如关节植入物，化工厂的阀门，核工业中的夹持器闩锁臂。已被广泛研究的CoCr合金的耐腐蚀性已被证明是由于形成了保护性的铬氧化物表面膜，这也阻止了金属离子的释放。氧化膜的组成取决于环境，强烈影响保护程度。尽管CoCr合金取得了成功，但由于腐蚀和磨损（也称为摩擦腐蚀）的耦合导致的降解现象，在某些应用中观察到由这些材料制成的部件的早期失效。作为一个具体示例，在由CoCr合金制成的金属对金属（MoM）轴承的情况下，其目前占美国每年进行的超过200，000次初次全髋关节置换手术的约35%，已经表明，退化主要由摩擦腐蚀现象引起。尽管主题的相关性，非常少的是已知的钴铬合金的摩擦腐蚀行为。之前已经确定，CoCrMo髋关节轴承表面形成摩擦膜，包括基础合金的原始化学成分和变性蛋白质的残留物，此外，在关节连接期间，可能发生微观结构变化和与关节环境的化学反应，产生纳米晶体金属和有机成分的机械混合区，称为生物摩擦层。这一层似乎对减少磨损和腐蚀至关重要。尽管有这些结果，关于表面和亚表面金属的微观结构改性、表面化学变化（即，拟议的研究项目旨在从根本上了解生物相容性对摩擦腐蚀引起的表面化学和材料结构变化的依赖性。这将通过调查的动态表面化学和冶金过程中发生的近表面区域的钴铬作为摩擦学和电化学条件的函数。摩擦腐蚀测量、高级表面化学表征和表面/次表面区域的冶金分析与所得蛋白质吸附行为的相关性将提供一系列应用中（包括作为关节植入物材料）CoCr降解的基础机制的全貌。

Highly alloyed corrosion-resistant metallic materials are used in a range of applications, including biomedical, oil and gas, and aerospace applications. As one particular example, cobalt-chromium (CoCr) alloys are commonly employed in tribological applications because of their mechanical properties (high hardness) as well as good wear resistance. Additionally, thanks to their excellent corrosion resistance, CoCr alloys have widely been used as lynchpin materials for components exposed to aggressive environments, such as joint implants, valves in chemical plants, gripper latch arms in nuclear industries. The corrosion resistance of CoCr alloys, which has been extensively investigated, has been shown to be due to the formation of a protective Cr oxide surface film, which also prevents the release of metal ions. The composition of the oxide film, which depends on the environment, strongly affects the degree of protection. In spite of the success of CoCr alloys, early failures of components made of these materials have been observed in some applications due to degradation phenomena resulting from the coupling of corrosion and wear (also called tribocorrosion). As one particular example, in the case of metal-on-metal (MoM) bearings made of CoCr alloys, which currently constitute ~35% of over 200,000 primary total hip replacement procedures performed annually in the U.S., the degradation has been shown to be mainly induced by tribocorrosion phenomena. In spite to the relevance of the topic, remarkably little is known about the tribocorrosion behavior of CoCr alloys. It has previously been determined that CoCrMo hip bearing surfaces form tribofilms comprising the original chemical constituents of the base alloy and the remnants of denatured proteins and in addition can undergo microstructural changes and chemical reactions with the joint environment during articulation that produce a mechanically mixed zone of nanocrystalline metal and organic constituents, referred to as a biotribolayer. This layer appears to be critical to reducing wear and corrosion. Despite these results, significant ambiguity still remains concerning the correlation between microstructural modifications of the surface and subsurface metals, surface chemical changes (i.e., composition and thickness of the oxide layer), and biocompatibility.The proposed research project aims to develop a fundamental understanding of dependence of biocompatibility on tribocorrosion-induced variations in surface chemistry and materials structure. This will be achieved through the investigation of the dynamic surface chemical and metallurgical processes occurring in the near-surface region of CoCr as a function of tribological and electrochemical conditions. The correlation of tribocorrosion measurements, advanced surface chemical characterization and metallurgical analysis of the surface/subsurface regions with the resulting protein adsorption behaviour will provide a full picture of the mechanism(s) underpinning the degradation of CoCr in a range of applications, including as materials for joint implants.