Pressure-assisted thermal diffusion of iron–aluminum coating on laser selective melted 304L stainless steel

Selective laser melting (SLM) technology enables the direct fabrication of 304L austenitic stainless steel components with complex geometries and superior mechanical performance; however, limitations in surface hardness and general corrosion resistance restrict its broader industrial application. To address these challenges, this study investigates the formation of Fe–Al coatings on the surface of SLM-fabricated 304L and characterizes the interfacial microstructure under high-temperature and high-pressure conditions. The Fe–Al coating was synthesized via pressure-assisted high-temperature thermal diffusion—a method that is operationally straightforward, cost-effective, and imposes minimal equipment requirements. The microstructural evolution and elemental distribution within the coating were systematically analyzed under varying temperature and pressure conditions. Phase composition was determined using synchrotron radiation x-ray diffraction. The mechanisms by which temperature and pressure enhance the comprehensive properties of the coating are discussed, and the formation mechanism of the multi-physical-field-induced Fe–Al coating is elucidated. Results indicate that diffusion at 650 °C fails to achieve a reliable bond between the coating and substrate, while diffusion at 750 °C without applied pressure yields suboptimal results, characterized by numerous unmelted particles and an uneven coating surface. In contrast, when diffusion is conducted at 750 °C under a pressure of 80 Pa, a uniform coating ∼200 μm thick is obtained. The interface between the substrate and coating is planar and well-bonded, with a homogeneous and refined microstructure compared to the base material, indicating partial metallurgical bonding. Under pressure assistance, several new intermetallic phases form within the coating, including AlNi3, FeAl3, Al86Fe14, FeAl2, and AlCr2. The microhardness of certain regions reaches up to 745.8 HV0.2 ± 10%, representing a significant improvement in surface mechanical properties. These findings provide precise theoretical guidance and scientific principles for optimizing Fe–Al protective coatings on SLM-manufactured 304L surfaces.