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

The second stage turbine vanes of a recently developed high performance jet aero-engine were cast using a Ni3Al based alloy IC-6, and then coated with NiCrAlYSi by vacuum are deposition. After a 379 h engine test, the morphol ogy, microstructure, phase structure and chemical composition of the coatin g were examined and analyzed by scanning electron microscopy with X-ray ene rgy dispersion spectrometer, X-ray diffraction and electron probe microanal ysis techniques. The analytical emphasis was placed on the effect of black spots which appeared on the coating surface after the test on the coating a nd base alloy IC-6. In addition, the origin of black spots was intensely in vestigated. The results indicated that the black spots were a kind of high- temperature hot corrosion caused by Na2SO4 melt salt from the combusted gas es of the engine, the existence of black spots accelerated the internal oxi dation of the coating, but had not impaired the base alloy after 379 h engi ne operation. It may be summarized that NiCrAlYSi coating can provide an ef fective protection against oxidation and corrosion of base alloy IC-6 at el evated temperature of the present test. (C) 1999 Elsevier Science S.A. All rights reserved.