Modelling of keyhole dynamics and melt pool flow in laser powder bed fusion process

Thermal Stability and Weather Resistance of a Bionic Lotus Multiscale Micro-Nanostructure TiC/TiN-Ni/Mo Spectral Selective Absorber Based on Laser Cladding-Induced Melt Foaming

As the core of a solar collector, a solar selective absorbing coating has become the key material for efficient utilization and development of solar energy. In order to overcome the core scientific problem of poor high-temperature stability of optical properties caused by atomic diffusion between layers in the high-temperature environment of traditional multilayer solar absorption coatings, the multiscale lotus bionic porous structure was constructed by using a TiC/TiN-Ni/Mo material system with excellent intrinsic absorption performance. The melt foam method and laser cladding technology were combined to deposit the multiscale bionic porous structure solar selective absorption coating in situ by a laser-induced melt foaming strategy. It was found that the bubbles in the molten pool were affected by Marangoni force, gravity, buoyancy, and surface tension. The unescaped bubbles formed pores near the surface of the coating and showed a bimodal distribution. For the multiscale addition of 1.8 and 0.4 μm pore-forming agents with a mass fraction of 15 wt %, the multiscale pores enhance the scattering and secondary absorption of light and reduce the amplitude of electromagnetic wave to electron vibration; at the same time, the small-size conductor effect formed by the hole increases the surface electron concentration, strengthens the absorption of light, and enhances the magnetic field strength at the hole, and the structural absorbing effect is significant. The coating absorptivity α reaches 85%, and the temperature stability is excellent. Compared with the substrate, the coating has a smaller corrosion current density, larger polarization resistance, and strong corrosion resistance. The research shows that the laser-induced multiscale bionic porous structure coating obtains the intrinsic absorption-structural absorption composite absorption mechanism and realizes the integration of flexible design and efficient manufacturing of high-temperature solar absorption coatings.