Fretting wear of pure cobalt chromium and nickel to identify the distinct roles of HS25 alloying elements in high temperature glaze layer formation

HS25 cobalt-based superalloy was investigated between 100 and 600 °C under fretting wear (small amplitude reciprocating displacements) in a cross-cylinder contact. Tribological behavior was compared to pure cobalt, chromium and nickel tested under the same conditions and analyzed in terms of friction, wear, interface morphology and chemical composition by SEM-EDX and Raman spectroscopy. On HS25, the tribological tests resulted in the formation of a “glaze layer” of ground and compacted wear debris, which was protective against severe wear and high friction above 250 °C. Similar glaze layers were found for cobalt-cobalt (Co//Co) contacts, suggesting the determining role of cobalt in glaze layer formation whereas worn Cr//Cr and Ni//Ni interfaces exhibited poorly sintered debris and respectively adhesive and abrasive wear. To identify the role of alloying elements in glaze layer formation, the oxides formed in the interface were studied in terms of composition and thermal stability. As sintering appears to be a determining factor in glaze layer formation, the diffusion properties of cobalt and its oxides are emphasized. The strengthening and corrosion resistance properties of chromium and nickel in the alloy are also discussed.