Laser surface processing of Cr coated 9Cr-1Mo ferritic steel for improved corrosion/oxidation resistance

The high temperature oxidation and aqueous corrosion behaviour of 9Cr-1Mo steel, coated with Cr, followed by laser irradiation have been investigated. Chromium powder was deposited by two different techniques, i.e., plasma spraying and direct powder feeding method. For the laser treatment, a 3 kW Continuous Wave (CW) CO2 laser with line focus mode was used. Detailed characterisation of the coated and laser alloyed samples was carried out using optical microscope, XRD and SEM/EDAX. The oxidation tests were carried out at 800 degrees C in air and anodic polarisation tests in 1N H2SO4 solution. Laser alloyed specimens showed improved oxidation resistance compared to as-coated and un-coated specimens. The critical current density, the passive current density and the range of passivity were determined for the laser alloyed specimens and compared with that of the bare specimen and plasma coated specimens