Two Birds with One Stone: Engineering Lead-free Oil-Containing Cu–FeS Composites with “Structure-Performance Regulation” Strategy for Dual Improvement of Mechanical and Tribological Properties

Despite the widespread use of lead-free metal-based liquid–solid self-lubricating materials in sliding bearings, the solid lubricating components in the material display inadequate wettability with the metal matrix. The poor pore connectivity and low effective porosity of materials severely restrict the liquid–solid self-lubricating performance of composites, and challenges remain in the development of lead-free, oil-containing Cu–FeS materials with enhanced mechanical and tribological properties through oil storage in internal pores. Here, a “structure-performance regulation” strategy is proposed to construct lead-free, oil-containing Cu–FeS composites with these attributes. A design system is constructed using Ni nitrate-coated FeS, and by adjusting the structure of internal pores and the bonding at heterophase interfaces, the material’s impact toughness and crushing strength increased by up to 120 and 58.3%, respectively. The ultimate bearing capacity increased by up to 51.2%, and the friction coefficient decreased by 37.5%. Notably, the improvement of mechanical and tribological properties is closely linked to the ratio of the Ni nitrate coating to FeS during preparation. When the Ni nitrate coating-to-FeS ratio is between 1:1 and 2:1, hierarchical pores are formed within the material, promoting strong interface bonding between solid lubricant FeS and the Cu matrix. This structure enhances the material’s oil storage capacity, improves the oil’s rapid response to external stimuli, and increases FeS retention on the worn surface. In addition, robust metallurgical bonding between FeS and Cu fosters uniform load transfer, enabling internal energy dissipation and mitigating local stress concentrations. Under these conditions, the combined improvement in mechanical and tribological properties is maximized.