Static and Dynamic Corrosion Behaviors of HVOF-Sprayed TiAl-Nb Coating in Molten Zinc

The static and dynamic corrosion of TiAl-Nb coating in molten zinc could be divided into incubation period and rapid corrosion period. It has a long incubation period during which no corrosion occurs in molten zinc. After the incubation period, the corrosion occurs rapidly and rapid corrosion period is controlled by reaction–diffusion and dissolution mechanisms. The lifetime of TiAl-Nb coating primarily depends on the incubation period, which is not available for other materials. This type of corrosion has not been reported in other literature; we first refer to it as “incubation style” corrosion. The lifetime of TiAl-Nb coating in static corrosion was 41 days, and the lifetime was prolonged in dynamic corrosion. Compared with the static corrosion, the contact probability between the flowing molten zinc and the coating was reduced, the molten zinc was difficult to wet the coating, and the incubation period of dynamic corrosion was prolonged. After the incubation period, the mechanical scouring effect of flowing molten zinc accelerated the loss of corrosion product and spalled TiAl-Nb splats, which shortened the rapid corrosion period. As the erosion speed increased from 100 to 500 r/min, the micromechanical scouring effect of flowing molten zinc was intensified, the incubation period was increased by 27%, and the rapid corrosion period was shortened by 25%.