# Comparative Study of Surface-Coated MoS2 on the Multiscale Tribological Performance of Cu-Based Composites

## TL;DR

This study compares how different coatings on MoS2 affect the friction and wear performance of copper-based composites under various braking conditions.

## Contribution

The study introduces a comparative analysis of Ni and Cu coatings on MoS2 for improving tribological performance in Cu-based composites.

## Key findings

- Ni coating suppresses MoS2 decomposition and forms a strong diffusion-bonded interface.
- Cu coating leads to unstable friction and interface failure due to poor-strength diffusion.
- Cu-BC-MoS2@Ni shows lower wear rates under high braking energy density.

## Abstract

The Ni coating suppresses MoS2 decomposition during sintering.MoS2@Ni forms a diffusion-bonded interface with higher load-bearing capacity.Cu coating promotes interfacial reaction and defect formation.Cu-BC-MoS2@Ni exhibits lower wear rate under high braking energy density.

The Ni coating suppresses MoS2 decomposition during sintering.

MoS2@Ni forms a diffusion-bonded interface with higher load-bearing capacity.

Cu coating promotes interfacial reaction and defect formation.

Cu-BC-MoS2@Ni exhibits lower wear rate under high braking energy density.

MoS2 acts as a high-performance lubricant, enhancing friction material stability, reducing wear and noise under extreme conditions, and preserving friction pair performance. However, its tendency to decompose and poor matrix wettability make surface modification essential for effective use in Cu-based composites. In this study, comprehensive investigations combining macro-scale and micro-scale friction experiments were conducted to examine the interfacial friction behavior of MoS2 with different coatings and its tribological effects on copper-based composites under varying braking energy densities. The results indicate that the nickel coating suppressed MoS2 decomposition, forming a high-strength diffusion interface with the matrix. This enhances the frictional stability and suppresses interfacial defect formation during micro-friction tests. However, the copper coating formed a poor-strength diffusion-reacting interface with matrix, leading to unstable friction at the interface and interface failure. Coating-dependent interfacial properties and micro-friction behaviors lead to varying tribological performance in Cu-based composites with MoS2 during macro-friction tests. Nickel-plated MoS2 (MoS2@Ni) exhibits superior lubrication and frictional stability. The friction coefficients of Cu-based composites with MoS2@Ni under low, medium and high working conditions are 0.36, 0.3 and 0.24, respectively, which are 6%, 12% and 13% lower than those of copper-plated MoS2 (MoS2@Cu). Meanwhile, its friction stability is 0.8, 0.6 and 0.58, respectively. With rising braking energy density, wear in Cu-based composites transitions from ploughing to oxidation and then to delamination. Defective MoS2@Cu/matrix interfaces intensify delamination wear caused by the unstable fracture of subsurface plastic deformation layer cracks at higher energy density.