The Research On Hot Corrosion Resistance Of Conicraly(Re) Alloy

The nickel-based alloy is required higher resistance of high temperaturecorrosion, owing to the rising temperature for improving the efficiency of gasturbine. MCrAlY coating provides a good protection against high temperatureoxidation. However, hot corrosion resistance of the coating has become asignificant issue for turbines using heavy oil or serving in marine environment.The degradation of coatings is accelerated by the molten salt. Based on theCoNiCrAlY alloy, pre-oxidation treatment and doping reactive elements foralloy are employed to explore their effectiveness of enhancing resistance.Pre-oxidation was performed on CoNiCrAlYRe alloy, which was subsequentlycorroded at900oC in molten Na₂SO₄for100h. Multi-layered oxide scale, whichexhibited good adhesion, was formed on the pre-oxidized specimen, while directcorrosion generated a non-protective oxide scale. Pre-formed oxide scale retarded thepenetration of sulfur to the substrate, and also benefited the repairing of Al₂O₃. Inaddition, the yttrium can trap the sulfur in the grain boundary.Palladium, cerium and dysprosium were doped respectively into theCoNiCrAlY alloy to explore the optimum doped-element for hot corrosionresistance. All the elements promoted the selective oxidation of aluminum andchromium in the initial stage of corrosion. The doping of0.2wt%dysprosiumbrought in best improvement in reducing the consumption of aluminum andenhancing the adhesion of scale, ahead of doping0.1wt%cerium. Palladiumaddition has less effect on the resistance of alloy.For CoNiCrAlYRe alloy, the effectiveness order of doping element wasthe same with that in CoNiCrAlY alloy. The rhenium promoted the formationof Cr₂O₃in the initial stage but has less cooperative effect with dopingelement on improving the resistance, since the benefits cannot overcame theadverse impact induced by the lower amount of aluminum.