Evaluation of NiCrAlYSi overlay coating on Ni3Al based alloy IC-6 after an engine test

The second stage turbine vanes of a recently developed high performance jet aero-engine were cast using a Ni 3 Al based alloy IC-6, and then coated with NiCrAlYSi by vacuum arc deposition. After a 379 h engine test, the morphology, microstructure, phase structure and chemical composition of the coating were examined and analyzed by scanning electron microscopy with X-ray energy dispersion spectrometer, X-ray diffraction and electron probe microanalysis techniques. The analytical emphasis was placed on the effect of black spots which appeared on the coating surface after the test on the coating and base alloy IC-6. In addition, the origin of black spots was intensely investigated.The results indicated that the black spots were a kind of high-temperature hot corrosion caused by Na 2 SO 4 melt salt from the combusted gases of the engine, the existence of black spots accelerated the internal oxidation of the coating, but had not impaired the base alloy after 379 h engine operation. It may be summarized that NiCrAlYSi coating can provide an effective protection against oxidation and corrosion of base alloy IC-6 at elevated temperature of the present test.