Understanding the Role of a Cr Transition Layer in the Hot-Salt Corrosion Behavior of an AlSi Alloy Coating

The effect of a chromium (Cr) transition layer on the hot-salt corrosion behavior of an AlSi alloy coating was studied. Hot-salt corrosion experiments were performed at 650 °C and corrosion kinetic curves were plotted. The weight gain of the AlSi-coated samples increased to 0.89 mg/cm2 at 100 h and then decreased steadily to 0.77 mg/cm2 at 200 h. The weight of the AlSi-coated samples with the addition of a Cr transition layer increased immediately to 0.79 mg/cm2 at 20 h and then gradually increased to 0.85 mg/cm2 at 200 h. This Cr diffusion promoted the preferential creation of an Al2O3 layer, which effectively hindered the upward diffusion of Fe and also resulted in the production of a Cr2O3-SiO2 layer, which impeded the multi-scale salt mixture’s penetration. The Cr diffusion also caused a notable seal-healing effect, which healed the micro-pores. These oxidation and degradation reactions were considerably repressed by the high barrier properties of these oxide layers and the dense surface, resulting in the increased hot-salt corrosion resistance of the AlSi alloy coating. The current findings provide a feasible strategy for the design of a diffusion barrier layer of a thermal protective coating on martensitic stainless steel.