The effect of laser surface melting on tin-modified Cu-Ni

Laser surface melting (LSM) was utilized to quench rapidly (10 6 K s -1) the uppermost 20 μm of tin-modified Cu-Ni (UNS designation C72500) surfaces. The surface topography and melt region cross sections were characterized with optical and scanning electron micrography. Auger electron spectroscopy in combination with ion sputtering was used to quantify improvements in the corrosion resistance of LSM relative to non-LSM surfaces exposed to gaseous H 2S and Cl 2 test environments. Specifically, coupons exposed to 5 ppm H 2S at a relative humidity of 80% developed a corrosion film on both LSM and non-LSM surfaces. There was a 20% reduction in film thickness on the LSM surface. In the case of 1.8 ppm Cl 2 at a relative humidity of 80% the corrosion film was reduced in thickness from 36 000 to 9000 Å during an exposure of 4 days. The improvements are attributed to the homogenization of the quenched layer.