Microstructure, Mechanical Properties and Dry Sliding Wear Behavior of Cu-Al₂O₃-Graphite Solid-Lubricating Coatings Deposited by Low-Pressure Cold Spraying

In this study, Cu-Al₂O₃-graphite solid-lubricating coatings were deposited on the 304 stainless steel substrate by low-pressure cold spray technique. The influences of Cu-coated graphite content on the microstructure, mechanical properties and dry sliding wear behavior of the Cu-based solid-lubricating coatings were investigated. The results showed that the mixture addition of Al₂O₃ and Cu-coated graphite is an effective strategy to improve the solid lubricity of Cu-based coatings while simultaneously retaining favorable mechanical properties and bonding strength. When the Cu-coated graphite content increased from 0 to 20 wt.% in the spray powder, the Brinell hardness and the interface bonding strength of the Cu-based coatings declined, but the solid-lubricating property improved obviously. The Cu-based solid-lubricating coating with 10 wt.% Al₂O₃ and 10 wt.% Cu-coated graphite exhibited the lowest friction coefficient of 0.29, which was attributed to the formation of a lubricating tribo-layer and the reduction in cracks on the worn subsurface. Additionally, the wear mechanism changed from adhesive wear to abrasive wear and delamination with the increase in graphite content.