# Synthesis and Tribological Characteristics of High-Performance Self-Lubricating CoCrFeNiMox-Ni/MoS2-Ag-Cr2O3 Composites

## TL;DR

This study creates self-lubricating composites that work well at high temperatures by adjusting the Mo content in a high-entropy alloy matrix.

## Contribution

The novel contribution is the development of Mo-doped high-entropy alloy composites with stable lubrication across a wide temperature range.

## Key findings

- Increasing Mo content enhances hardness and yield strength due to σ-phase formation.
- Composites show low friction and wear rates from 25–800 °C due to synergistic lubrication mechanisms.
- Tribochemical reactions at high temperatures form lubricating oxide films, maintaining performance.

## Abstract

High-temperature self-lubricating materials with stable tribological performance across a wide temperature range are essential for advanced mechanical systems under extreme conditions. However, balancing mechanical strength and lubrication efficiency remains a key challenge. This study fabricated CoCrFeNiMox-Ni/MoS2-Ag-Cr2O3 composites (x = 0.2, 0.5, 1) via spark plasma sintering, aiming to investigate the effect of Mo content on their microstructure, mechanical properties, and tribological behavior. Microstructural analysis showed that the as-sintered composites mainly consist of FCC phase, Cr2O3, Ag, and Ni/MoS2. Increasing Mo content from 0.2 to 1 wt.% significantly promoted the formation of hard σ-phase intermetallics, leading to increased hardness (up to 546 HV) and yield strength (peaking at 502 MPa). Tribological tests at 25–800 °C indicated continuous lubrication behavior in all composites. The minimum friction coefficient was 0.23, and wear rates remained below 10−6 mm3/N·m. In the low-to-medium temperature range, lubrication was dominated by the synergistic effect of Ni/MoS2 and Ag: Ni/MoS2 formed low-shear-strength films, while Ag reduced surface adhesion. Meanwhile, the Mo solid solution strengthened and the σ-phase enhanced wear resistance by improving hardness and inhibiting plastic deformation. At high temperatures, tribochemical reactions generated lubricating films composed of oxides and molybdates, which maintained tribological performance by reducing direct contact between friction pairs. This study demonstrates that Mo-doped high-entropy alloy composites can serve as high-performance wide-temperature self-lubricating materials, providing a basis for designing “matrix-lubricant” systems for extreme-temperature applications.