Formation Mechanism of Precursor Films at High Temperatures: A Review

The formation of a precursor film (PF) is always coupled with better wettability; thus, clarifying the formation mechanism is required to optimize the interfacial structures. However, recent research focuses on inert wetting systems at room temperature, which cannot guide practical material processing at high temperatures. In this review, PF formation mechanisms at high temperatures were reviewed. The mechanisms are surface diffusion, evaporation–condensation, subcutaneous infiltration, and rapid absorption and film overflow. In experimental metal/metal systems, the most probable mechanism is subcutaneous infiltration, related to the apparent contact angle, radius, and height of the gap between the substrate metal and the oxide film. The rapid absorption and film overflow mechanism usually occurs in metal/ceramic systems. The PF appearance for the adsorption mechanism must satisfy the paradox, that is, the relative inertial and high-affinity liquid/solid interface. Finally, another possible mechanism of PF appearance for the reactive wetting system at high temperatures was proposed, that is, the thin-surface transport mechanism. The PF formation is sensitive to external conditions. Therefore, it is necessary to develop thermodynamic and dynamic models for predicting and simulating PFs.