High-Temperature Hot Corrosion Resistance of CrAl/NiCoCrAlY/AlSiY Gradient Composite Coating on TiAl Alloy

TiAl alloys are used in high-temperature components such as the turbine blades of aeroengines because of their excellent properties. However, TiAl alloys are prone to thermal corrosion when in near-ocean service. In order to solve this problem, a hot-corrosion-resistant CrAl/NiCoCrAlY/AlSiY gradient composite coating was prepared on the surface of the TiAl alloy. The phase composition and morphology of the coating were analyzed. Hot corrosion tests of the traditional NiCoCrAlY coating and CrAl/NiCoCrAlY/AlSiY gradient composite coating on a TiAl substrate were performed. The samples were coated with 75%Na2SO4 + 25%NaCl salt film and treated at 950 °C for 100 h, and the corrosion products were analyzed. The results indicate that compared with the TiAl substrate and traditional NiCoCrAlY-coated samples, the composite coating showed better hot corrosion resistance, only slightly cracking, and no corrosion loss occurred. This is mainly because the continuous Al2O3 layer can effectively resist the damage caused by the melting reaction in salt, and the Cr-rich layer can not only slow the mutual diffusion of elements but also generate a good corrosion resistance chromium oxide protective layer under serious corrosion. Moreover, the corrosion mechanism of the TiAl substrate, traditional NiCoCrAlY coating, and experimental composite coating was analyzed in detail.