Corrosion resistance of alloy 600 surface-alloyed by laser beam

Abstract

In order to increase corrosion resistance of Alloy 600 used as steam generator tubing of nuclear power plants, the surface of alloy 600 was modified by melting or alloying with a continuous CO2 laser beam. In case of laser-surface-melting (LSM), rapidly solidified surface layer of about 200μm in thickness was obtained. For laser-surface-alloying (LSA), before laser beam irradiation the specimen surface was coated with 50Cr+50Ni (in wt. %) mixed powder by plasma spray in order to add alloying elements. The corrosion properties of the laser-surface-melted and the laser-surface-alloyed specimens was characterized and compared with those of as-received (AR) specimen. According to the results, the corrosion resistance of LSM specimen was slightly increased compared with that of AR specimen, which might be due to elimination of inhomogeneities such as precipitates along grain boundary, inclusions and segregated interfaces by laser melting. LSA specimen showed much more improved resistance to corrosion compared with AR and LSM specimens. Intergranular corrosion resistance was also improved in both LSM and LSA specimens and there was no much difference between them. The improvement of corrosion resistance in the laser treated specimens was explained in terms of the observed microstructure and chemical composition.In order to increase corrosion resistance of Alloy 600 used as steam generator tubing of nuclear power plants, the surface of alloy 600 was modified by melting or alloying with a continuous CO2 laser beam. In case of laser-surface-melting (LSM), rapidly solidified surface layer of about 200μm in thickness was obtained. For laser-surface-alloying (LSA), before laser beam irradiation the specimen surface was coated with 50Cr+50Ni (in wt. %) mixed powder by plasma spray in order to add alloying elements. The corrosion properties of the laser-surface-melted and the laser-surface-alloyed specimens was characterized and compared with those of as-received (AR) specimen. According to the results, the corrosion resistance of LSM specimen was slightly increased compared with that of AR specimen, which might be due to elimination of inhomogeneities such as precipitates along grain boundary, inclusions and segregated interfaces by laser melting. LSA specimen showed much more improved resistance to corrosion compared ...