Enhancement of corrosion resistance of nickel based superalloys by laser surface melting

Laser surface melting of Ni based superalloys (alloys 600, 690 and 693) was carried out to study the effect of surface modification on the corrosion behaviour in simulated nuclear high level waste (HLW) and chloride medium. Surface characterisation was performed by optical microscopy, scanning electron microscopy and X-ray diffraction. The alloys exhibited cubic crystal system and cellular microstructure. Double loop electrochemical potentiokinetic reactivation test in 0·5M H₂SO₄ containing 0·0001M KSCN showed a low degree of sensitisation compared to the solution annealed specimens. Laser surface melting resulted in enhancement of corrosion resistance of the alloys in simulated HLW and chloride medium when compared to as received and solution annealed specimens; nevertheless, no discernable difference was found between the laser surface melted alloys 600, 690 and 693 in simulated HLW. However, the laser surface melted alloy 690 showed superior pitting corrosion resistance. The results of the present investigation are discussed in this paper.