Effect of Laser Irradiation on Micro Structure of Carbide Coatings

In the thermal spraying technique, the process includes some problems such as insufficient cohesive strength between particles in the coating. It is considered that the laser treatment of thermal spray coating will be effective method to improve the coating properties. In this study, an yttrium aluminum garnet (YAG) laser treatment was carried out on the sprayed coating in order to examine the effect of laser beam on the coating properties and post laser treatment method and hybrid spraying method were carried out. Irradiation laser power conditions were 1.5kW, 2.0kW and 2.5kW, and defocus distance conditions were ±0mm, +30mm, +60mm, +90mm, changing the energy density and the traverse speed conditions were 100mm/s, 200mm/s, 300mm/s. In post treatment method the affected region in the Cr₃C₂-Ni-Cr coating is smaller with increasing traverse speed. Laser energy density affected the microstructure. In the case of defocus distance ±0mm and traverse speed is 100mmm/s there are three different regions, melted region, heat affected region and no affected region in the coating. The micro Vickers hardness of melted region of coatings was lower and heat affected region of coatings was higher than no laser treatment coating. It was considered that with post laser treatment method it was very difficult to treat the coating uniformly. In the blast erosion test, the wear-out rate of hybrid spray coating was lower than that of the HVOF spray coating. It is considered that the improvement of micro Vickers hardness of Cr₃C₂-Ni-Cr hybrid sprayed coating resulted from the precipitation of fine chrome carbide in the matrix and their strengthening affect cohesive strength between lamella in the coating. In WC-Co hybrid sprayed coating, the improvement of micro Vickers hardness resulted from the porosity decrease. The coating structure was different even in the identical processing condition by the place. The micro Vickers hardness of melted area of coatings was lower and heat affected area of coatings was higher than no laser treatment coating.