Laser consolidation of arc-sprayed coatings

An investigation into the laser consolidation of arc-sprayed coatings of 13% Cr steel deposited on a medium carbon steel is reported. The 600 W CW CO₂ laser beam was used to irradiate arc-sprayed coatings to remove the pores in the coated layer and to produce a strong metallurgical bond between the coated layer and base metal. The heat flow in this process was analyzed using a finite-difference method to predict the hardened zone in the workpiece surface. Arc-sprayed coatings showed a substantial increase in laser absorptivity when compared to ground or sand-blasted surfaces, which could improve the effectiveness of materials processing using lasers. As a result of laser treatment pores in arc-sprayed coatings were fully excluded, and a metallurgical bond could be formed in the thin surface layer of the workpiece by applying appropriate process parameters. The width and depth of the hardened zone in the workpiece surface could be correctly predicted using the finite-difference model. Separation of the untreated layer from the workpiece and the spheroidizing tendency of the molten part were the primary obstacles in single-scan processes. These problems can be overcome using the multi-scan process, but in this case some softening was observed in pretreated parts of the melted metal coating and the hardened base metal.