Hot corrosion behaviour of a laser beam irradiated nickel base superalloy

Abstract

The structure and the hot corrosion resistance of cast nickel‐base superalloy M 38 irradiated by CO2 laser beam of 1.3 KW output have been examined by means of optical microscopy, XRD, SEM and EPMA in comparison with un‐irradiated specimens. The hot corrosion tests were carried out in a crucible filled with a mixture of 75 Na2SO4 + 25 NaCl at 900°C for 15, 35, 55, 80 and 100 hrs, respectively. The results showed that the corrosion resistance of the irradiated alloy is by a factor 2–3 higher than that of the cast alloy. In contrast to significant internal oxidation/sulfidation along the grain boundaries in the cast alloy, under a dense protective oxide scale mainly consisting of Cr2O3, there was no sign of internal oxidation/sulfidation in the irradiated alloy. The irradiated surface layer may be regarded as an effective barrier forming part of the superalloy itself.