Manufacturing of Hybrid Surface Composites Cu/(B4C + MoS2) Via Friction Stir Processing

Abstract Copper's limited tribological characteristics often constrain its use in industrial applications like bushings, bearings, automotive parts, etc. To address this, copper-based surface composites have gained significant interest in recent years. Incorporating a combination of solid lubricant and hard ceramic reinforcements has proven effective in improving their wear resistance and overall tribological behavior. In this study, friction stir processing (FSP), a solid-state fabrication technique, was employed to develop both monoreinforced (B4C) and hybrid-reinforced (B4C + MoS2) surface composites on a copper substrate. Hybrid composites were produced by changing the reinforcing ratios of B4C and MoS2 inside the copper matrix, specifically 10%, 15%, and 25% MoS2 (with the remainder being B4C). A single-pass FSP approach with different tool traverse directions was used during the capping and stirring stages to ensure uniform mixing of the reinforcement particles within the copper matrix. Microstructural evaluation revealed a homogeneous distribution of reinforcement particles within the stir zone; however, clustering was observed at higher MoS2 concentrations (15% and 25%). Both microhardness and wear resistance were significantly enhanced in the reinforced composites compared to pure copper. The mono B4C composite demonstrated higher hardness around 120 HV with minimal variation, while the hybrid composite containing 75% B4C and 25% MoS2 exhibited the lowest material loss (0.0014 g), indicating superior wear resistance, largely due to the lubricating effect of MoS2.