Microstructure And Properties Of Metallic Coatings With Low Dilution Ratio By High Speed Laser Cladding

By specially designing the cladding head, the optimal coupling of laser beam and powder flow could be achieved in the newly developed high speed laser cladding (HSLC) process. Using such head, the particles melt in flight while the surface of substrate forms a micro-melt pool, so that a coating with metallurgical bonding can be obtained due to the high deposition speeds and powder utilization rate. As a result, producing high quality coatings with thickness < 100 mu m and dilution < 5% is possible by using HSLC. In order to characterize the microstructure of the HSLC coatings and expand its applications, four different coatings with low dilution ratio are fabricated and the microstructure and properties of the coatings were studied under a relatively low laser power. Results show that high-quality pore-and crack-free coatings with thickness of 120 similar to 500 mu m are produced by HSLC. All coatings have compact structure with coarse columnar crystals around the interface and fine grains near the coating surface. The melt area of the substrate reaches a micrometer range, and the dilution rate is less than 1%. For the nickel-based WC coating and the wear resistance coating on aluminum alloys, the hardness of the coatings is much bigger than the that of substrate. For the burn resistant coating on titanium, the depth of the laser-melt hole and range of HAZ is significantly reduced. For the diffusion resistant coating on high entropy alloy, the oxide film (Al2O3) forms by pre-oxidation. Overall, the coatings with low dilution ratio prepared by HSLC exhibit good protection for the substates studied.