Comparative study on fretting wear behavior of micro-arc oxidation coatings formed in aluminate, phosphate, and silicate electrolytes on Ti6Al4V alloy

In this study, micro-arc oxidation (MAO) coatings were fabricated on Ti6Al4V alloy using silicate, aluminate, and phosphate-based electrolytes, and their fretting wear behaviors and underlying mechanisms were systematically compared. The results showed that the coatings' discharge behavior, microstructure, and chemical composition were tightly coupled to the electrolyte composition, which in turn significantly influenced their fretting wear behaviors. Abrasive wear was identified as a common fretting wear mechanism across all three coatings. In addition, the P-MAO coating exhibited severe fatigue wear and tribochemical reduction, corresponding to the poorest resistance to fretting wear. The Al-MAO coating underwent weaker fatigue wear than the P-MAO coating, yielding an intermediate level of fretting wear resistance. Benefiting from its densest and most uniform microstructure, the Si-MAO coating effectively suppressed fatigue damage, thereby achieving the best fretting wear performance. Meanwhile, against different coatings, the fretting wear characteristics of the ZTA counter body also varied. When fretting against the P-MAO coating, ZTA exhibited pronounced abrasive wear accompanied by adhesive transfer from the coating's substrate. When coupled with the Al-MAO coating, ZTA displayed discernible ploughing, indicative of a comparatively weaker abrasive wear response. By contrast, in fretting against the Si-MAO coating, the fretting damage on ZTA was minimal, manifesting only as faint surface scratches. Notably, unlike sliding wear, tribological performance depended more on coating compactness than on hardness in fretting wear. The Si-MAO coating-rather than the Al-MAO coating-demonstrated superior practical performance and application potential in fretting wear. The fretting damage evolution in the Al-MAO coating followed the pattern “crack initiation-pore compaction/crack propagation-wear removal/fatigue spallation,” whereas that in the Si-MAO coating proceeded via “pore compaction-wear removal.”