Pitting corrosion of the laser surface melted Alloy 600

The effect of laser surface melting (LSM) on the resistance to pitting corrosion of Ni-base Alloy 600 was investigated by a potentiodynamic polarization test in 1 M NaCl solutions at pH values of 4 and 10 at temperatures of 30, 60 and 90degreesC. The pitting potentials of Alloy 600 were markedly increased by the LSM process, when compared with those of the non-laser treated Alloy 600. From the microscopic examination after the corrosion test, it was found that the pitting was initiated at the junction between a TiN inclusion and the matrix, possibly at the site of a sulfide physically associated with the TiN inclusion. The homogeneous micro-structure associated with the reduction of the inclusion size during the LSM process could be attributed to the improvement of the pitting corrosion properties in the LSM alloy 600. (C) 2004 Elsevier B.V. All rights reserved.