Structural and tribological properties of sulfonitrocarburizing layers prepared by plasma nitrocarburizing and low temperature ion sulfurizing

The reduction in the friction coefficient and minimizing wear are fundamental characteristics of friction components. Sulfurization effectively enhances the self-lubricating properties of metallic surfaces, while nitriding/carburizing can enhance the resistance to wear. This study explored two methods to create a sulfonitrocarburizing layer on 38CrMoAl. One method involved a simultaneous treatment of ammonia, carbon dioxide, and hydrogen sulfide, while the other employed a two-step process of initial nitrocarburizing, polishing, and sulfurization. The single-step treatment resulted in erratic COF and poor wear resistance. In contrast, the two-step treatment produced a composite structure of FeS polycrystals, sulfur-containing nanocrystals, and a nitrocarburizing layer. Further optimization made the composited structure achieve equilibrium between self-lubrication and binding force, resulting in a significant friction reduction effect exceeding 800 s and good occlusion resistance. This study presents a paradigm for successfully integrating treatments for strengthening metal surfaces, demonstrating the potential to enhance the efficacy of friction components.