Effect of MoS2 on the Microstructural Evolution and Tribological Behavior of the Self-lubricating Composite NiCrBSiFe/MoS2 Produced by Spark-Plasma Sintering

Abstract

Solid lubricants offer a promising approach for the targeted reduction in friction and wear. Additional to the external optimization of friction pairings, solid lubricants can be structurally incorporated into metallic matrix by designing self-lubricating composite materials. Microstructural characteristics of these composites such as the amount, chemical composition and distribution of solid lubricants distinct influence the property profile, especially the tribological behavior of bulk materials. Besides the bulk material composition, the lubrication effect is related to the contact condition during wear testing. Molybdenum disulfide (MoS₂) was investigated as promising solid lubricant for the Ni-based alloy NiCrBSiFe. Microstructure, hardness and wear behavior of the spark-plasma sintered composites with MoS₂ contents up to 10 wt.% were determined in this study. The best friction behavior was observed for the composite containing 7.5 wt.% MoS₂. The coefficient of friction for this composite is more than halved compared to the NiCrBSiFe reference. Simultaneously, the wear rate is reduced from 0.41 to 0.15 × 10⁻⁴ mm³/Nm due to MoS₂ incorporation at higher wear loads of 26 N. Based on the overall tribological results, the composite with 10 wt.% MoS₂ was laser surface hardened using a high-power 10 kW diode-pumped solid-state laser. An adherent Fe/Ni sulfide top-coat and CrS precipitates were formed. Compared to the unfused condition, the laser hardened composite exhibited 200 HV0.5 higher hardness and a similarly high wear resistance. Hence, the incorporation of MoS₂ and implementation of laser surface hardening for self-lubricating composites is a promising concept for improving the surface properties.