Tribo-Corrosion Behaviors of Single-Phase CoCrFeNi and Two-Phase AlCoCrFeNi High Entropy Alloys in 3.5% NaCl Solution

The tribo-corrosion behavior in a seawater environment represents a significant challenge in the marine engineering and marine equipment field. The interaction of wear and corrosion can result in the premature failure of moving parts in a seawater environment. It is therefore imperative to enhance the tribo-corrosion resistance of moving parts in seawater. High-entropy alloys with their distinctive multi-major element solid solution structure exhibit remarkable corrosion and wear resistance, offering significant potential for application in marine engineering. The development of high-entropy alloys with excellent corrosion and wear resistance must address the following issues: (1) the composition, organization, structure of the alloy and their impact on corrosion and wear resistance. Typical high-entropy alloy matrix organization includes single-phase solid solution and two-phase composite structure, with the matrix structure comprising Face-Centered Cubic (FCC) phase and Body-Centered Cubic (BCC) phase. (2) Providing a detailed account of the tribo-corrosion behavior of the alloy, including the role of wear on corrosion behavior and the role of corrosion on wear behavior. Considering the considerations, this paper presented a comprehensive investigation into the tribo-corrosion performance of CoCrFeNi and AlCoCrFeNi high-entropy alloys in a 3.5% NaCl solution. To provide a point of comparison, 304 stainless steel was selected for analysis. The corrosion and wear interaction was then quantified through a systematic approach. It was determined that the CoCrFeNi alloy possessed an FCC phase structure, whereas the AlCoCrFeNi alloy exhibited a BCC/ Body-Centered Cubic Ordering Phase 2 (B2) phase coupled two-phase structure. The inferior corrosion resistance of the AlCoCrFeNi alloy in comparison to the CoCrFeNi alloy could be attributed to two factors: firstly, the formation of a microscopic corrosion cell within the two-phase structure; secondly, Aluminum (Al) and chromium (Cr) elements competed for oxygen atoms during the corrosion process. Moreover, the chemical property of aluminum itself was more reactive, which reduced the content of the passive layer Cr₂O₃. The dynamic frictional corrosion conditions resulted in more pronounced corrosion behavior of the CoCrFeNi and AlCoCrFeNi high-entropy alloys in comparison to the static pure conditions. In pure wear conditions with cathodic protection, both CoCrFeNi and AlCoCrFeNi high-entropy alloys demonstrated superior hardness and wear resistance compared to 304 stainless steel, attributable to solid-solution strengthening. The BCC/B2 coupled AlCoCrFeNi alloy exhibited the highest hardness and excellent wear resistance. Under tribo-corrosion conditions, corrosion exacerbated the wear behavior of the alloys. The CoCrFeNi alloy, with the best corrosion resistance and moderate hardness, showed the lowest ΔW_C (increase in friction rate due to corrosion). While the AlCoCrFeNi alloy with poorer corrosion resistance, and the 304 stainless steel with lower hardness, exhibiting higher ΔW_C values. The ΔW_C/W₀ (Pure wear rate） ratios of CoCrFeNi, AlCoCrFeNi high-entropy alloys and 304 stainless steel were all below 1, indicating that material loss during the tribo-corrosion process was primarily influenced by wear.