High-temperature Oxidation And Hot Corrosion Behaviors Of Several High-temperature Protective Coatings

Both as alone overlays and as a bond coating for TBCs, MCrAlY coatings are widely applied to blades and other hot gas turbine components. The cost of common technologies, such as APS, EB-PVD, used for the coating preparation is much higher than that of the aluminization, a traditional way to prepare aluminide coating. In the present study, a low-cost NiCr-CrAI coating was prepared by pack cementation compared with a simple aluminide coating, an Al-Si coating and a sputtered NiCrAlY coating. In addition, the sputtered NiCrAlY coating was aluminized using pack cementation process to make a further improvement in its oxidation and corrosion resistance. High temperature oxidation and corrosion behaviors of the coatings in comparison with the parent cast alloy have been investigated, by using thermogravimetry analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy with an energy-dispersive X-ray analysis attachment (SEM/EDS) and electron probe microanalysis (EPMA). The main results are summarized as following:1. Oxidation behaviors of simple aluminide coating, NiCr-CrAI coating and sputtered NiCrAlY coating at 1000-1100℃The simple aluminide coating possessed definite anti-oxidation ability at 1000 ℃; it degradated completely and lost protectiveness after oxidation at 1100℃. The NiCr-CrAI coating held an excellent oxidation resistance due to the formation of α— Al₂O₃ scale at 1000℃; Although the local degradation of the coating arose, it still had protective ability at 1100 ℃. The oxidation resistance of the sputtered coating was better than that of the simple aluminide coating at 1000℃; while it suffered from serious oxidation at 1100℃ due to the formation of Cr₂O₃ and TiO₂ mixed scales rather than α-Al₂O₃.2. Hot corrosion behaviors of simple aluminide coating, Al-Si coating, NiCr-CrAI coating and the sputtered coating in 25m.%K₂SO₄+ Na₂SO₄ at 900℃The results showed that the simple aluminide coating and the sputtered coating were damaged completely and lost the protectiveness after the hot corrosion test. In this case, nanocrystallization deteriorated corrosion resistance of the sputtered coating. NiCr-CrAI coating showed the excellent hot corrosion resistance in molten sulphate owing to the beneficial effect of Cr element. Because of the formation of protective Al₂O₃ scale and the existence of some Si-rich phases in the coating, Al-Si coating exhibited the best resistance to hot corrosion.3. Corrosion behaviors of the simple aluminide coating, Al-Si coating and...