Investigation on the Microstructure and Mechanical Properties of FeGa₃ Surface Film on SKD11 Substrate

Gallium-based liquid metal is corrosive to steel alloys, forming FeGa3 surface film, which can potentially be applied as a solid lubricant for enhancing wear resistance and mitigating liquid metal-induced corrosion. However, the characteristics of the surface film remain insufficiently explored. In this study, a liquid metal of Ga-In-Sn was ultrasonically soldered onto annealed or decarburised SKD11, then heated in a vacuum chamber to form a 30 μm-thick FeGa3 reaction layer. The surface film on the annealed specimen with alpha-ferrite microstructure exhibits high porosity with a surface roughness of 1.97 Ra. In contrast, the film on the decarburised specimen with ferritic microstructure showed minimal porosity with a surface roughness of 1.29 Ra. Nanoindentation tests showed that the surface films on annealed and decarburised substrates had Young’s Modulus of 231 GPa and 242 GPa, and nanohardness values of 11.4 GPa and 12.7 GPa, respectively. The high porosity is attributed to the suppression of FeGa3 formation in regions containing chromium carbides. Shear stress for fracture was measured using microcantilever tests at the interface between the substrate and inner matrix of the surface films, revealing lower fracture shear stress in the annealed specimen, attributed to the presence of larger pores within its microstructure.