High temperature corrosion behavior of an AIP NiCoCrAlY coating modified by aluminizing

NiCoCrAlY coatings were prepared on superalloy K417G using arc ion plating (AIP), then some specimens coated with NiCoCrAlY were aluminized using a pack cementation method. The high temperature oxidation and hot corrosion behavior of the ordinary and the aluminized NiCoCrAlY coatings were studied. The results indicated that α-Al2O3 scales grew on both coatings during oxidation at 1000 °C and 1100 °C in air, and the aluminized NiCoCrAlY coating always showed lower oxidation rates and lower degradation rates. The hot corrosion tests were carried out by applying salt films of 25 wt.% K2SO4 + 75 wt.% Na2SO4 mixture on the specimens and exposing in air at 900 °C. The aluminized NiCoCrAlY coating showed a longer lifetime by forming a continuous Al2O3 scale. But, cracks and spallation of the oxide scales occurred on the ordinary NiCoCrAlY coating after 80 h.