The effects of surface oxidation and segregation on the adhesional wear behavior of aluminum—bronze alloys

Abstract

The worn surfaces of selected Cu-A1 alloys, resulting from sliding contact with a sapphire right cylinder, along with unworn surfaces and wear debris, were characterized using an appropriate combination of scanning electron microscopy (SEM), optical stereomicroscopy, X-ray diffraction (XRD), and X-ray photoelectmn spectroscopy (XPS). XPS, angle-resolved XPS (ARXPS) and ion sputter profiling techniques were employed to characterize surface compositional changes occurring in the unworn and worn surfaces as a function of increasing aluminum content. The transfer of Cu_—A1 alloy to the sapphire counterface (adhesional wear of the Al-bronze) increased with increasing aluminum content, which corresponded to increased wear and damage to the alloy surfaces. XPS and SEM analyses of pure copper and a Cu-1 weight percent (w/o) A1 alloy showed the worn surfaces to consist of a smooth and continuous Cu₂O layer. ARXPS analysis of as-polished and worn surfaces of Cu-4 w/o A1 and Cu-6 w/o A1 alloys showed significant surface enrichment by aluminum. The preferential formation of Al,₂O₃ on the surface decreases the mechanical stability and adherence of the surface oxide layer to the A_l-bronze. Disruption of the Al₂O₃ oxide layer combined with an increase in surface energy (increased aluminum content) greatly increases the probability of forming an interfacial bond at the sapphire_—Al-bronze interface which is stronger in shear than the cohesive strength of the alloy. When these conditions prevail, transfer of Al-bmnze to the sapphire occurs and adhesional wear and galling are observed.

Keywords:

• X-ray photoelectron spectroscopy (XPS or ESCA)
• adhesion
• galling
• wear
• Cu—Al alloys
• aluminum-bronze
• surface oxidation