The corrosion of Inconel X, Inconel 702, Rene 41, M-252, and WF-11 (Haynes 25) by potassium chloride and lithium fluoride at 1600 to 1900 F was studied. Thin coatings of the salts (1.5 mg/cm2) caused severe corrosion of the alloys in air, which resulted in accelerated failures of thin sheet specimens in creep-rupture testing. Rankings for the alloys based on creep-rupture tests were similar for uncoated and salt-coated materials: WF-11, Rene 41, and M-252 best, Inconel 702 poorer, and Inconel X poorest.
The corrosion products consist mainly of oxides and spinels, and also contain small amounts of chromates. Only very little corrosion, if any, occures without oxygen. The presence of the salt prevents the normal formation of a protective oxide film. X-ray diffraction studies showed differences between the normal oxidation products and the oxide corrosion products produced with salt present.
The types of corrosion include severe surface attack, intergranular penetration, and internal void formation. All of the alloys were susceptible to each of these types of corrosion. Grain boundary separation effects due to stress (2,500 to 10,000 psi) were also found.