The Mechanical Mixed Layer and Its Role in Cu-15Ni-8Sn/Graphite Composites

ABSTRACT

This article provides an in-depth investigation into the formation of the mechanical mixed layer (MML) and its role in Cu-15Ni-8Sn/graphite composites. Wear tests were conducted at room temperature using a ring–block configuration with an applied load of 50 N and sliding speed of 0.42 m/s. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were performed to analyze the worn surfaces and subsurfaces. Results indicated that high graphite content contributed to the formation of a protective MML. When the MML formed on the tribosurface as the graphite content increased, both the friction coefficient and wear rate greatly decreased. The friction coefficient with a stable value of 0.075 and wear rate of 6.10 × 10⁻¹⁶ (m³/N· m) were the lowest when an apparent tribolayer appeared at the graphite content of 38 vol%. The characteristics of the MML and its influence on wear mechanisms of the composites are discussed. The MML existing on the worn surface protected the materials from severe adhesion and abrasion and the predominant wear mechanisms changed to delamination, which resulted in the drastic changes in wear resistance and friction coefficient.

KEYWORDS:

• Self-lubricating composites
• tribological properties
• delamination
• mechanical mixed layer