Effect of pre-oxidation on the hot corrosion of CoNiCrAlYRe alloy

The effect of pre-oxidation on the resistance to hot corrosion was examined by corroding the CoNiCrAlYRe alloy at 900 °C in molten Na2SO4. Preoxidized specimens featured strong adhesion of oxide scale with uniform multi-layered structure. The time of pre-oxidation was crucial for controlling Al content sufficient for subsequent hot corrosion. However, direct corrosion yielded a defective and non-protective oxide scale, which allowed detrimental penetration of sulfur into substrate. Sulfur migrating along phase boundary was trapped by yttrium to diminish slightly sulphidation. Thus, two advantages of proper pre-oxidation treatment were presented, as keeping repairing for Al2O3 scale and inhibiting sulfur penetration.

Research highlights
► The preoxidized specimen produces a uniform and protective oxide scale with good adhesion in hot corrosion.
► The time of pre-oxidation is crucial for subsequent performance of alloy in corrosion.
► Sulfur penetrating to substrate is trapped by Ni5Y phase to form stable yttrium sulfide.