<p>This study proposes a “friction-induced synchronous precipitation” mechanism for film formation in FeS/Cu–Bi self-lubricating composites, advancing beyond the traditional view that lubricant precipitation and surface wear are independent processes. A stress field calculation model was established by integrating Hertz contact theory and Coulomb friction law. Ring/block sliding friction simulations, combined with experimental characterizations, revealed the precipitation and film formation behavior of FeS lubricating phase particles during friction for the first time. The results show that differences in material properties between lubricating phase particles and the matrix, interactions between particles and the matrix, and the distribution of internal stresses collectively drive lubricant precipitation. This process enables the migration and enrichment of internal lubricants at the material wear surface. The findings elucidate the complete mechanism of solid lubricant behavior from debonding and transfer to surface enrichment and film formation, and provide essential theoretical support and technical guidance for the development of new self-lubricating composites.</p>