Melting behavior of in-flight particles in ultra-high speed laser cladding

The melting of particles is a unique characteristic that differentiates ultra-high speed laser cladding (UHSLC) from conventional laser cladding (LC). However, the investigation on the melting behavior of in-flight particles in UHSLC is inadequate and difficult due to the mutual impacts of laser, particles and substrates. Therefore, a smart experiment was designed to explore the melting behavior of in-flight particles, in which the impact of substrates was eliminated. The surface morphology and the cross-sectional views of the molten 316L and Ti6Al4V particles were characterized using a scanning electron microscope (SEM). The interfaces between the particles and substrates were analyzed using a transmission electron microscopy (TEM). The melting model was built using ray tracing method (RTM) and finite element method (FEM). The results show that the in-flight particles presented semi-molten morphology with the laser power of 1800 W. Meanwhile some full-molten particles were observed with the laser power of 3000 W. The simulation results show that the particle temperature was regulated by the particle sizes and velocities instead of the feeding rates. The temperature of the 316L particles with a size of 30 μm decreased from 2718 K to 725 K as the particle velocity increased from 3 m/s to 20 m/s. The temperature of the Ti6Al4V particles with a velocity of 10 m/s decreased from 3859 K to 867 K as the particle size increased from 5 μm to 60 μm. The incident laser is dominant in temperature rising. The sheltering effect cannot be neglected. The temperature of 316L, Ag, Al6061, Cu, Inconel 718 and Ti6Al4V particles in UHSLC was predicted. The results offer a new perspective to understand the melting behavior of in-flight particles in UHSLC.