Improvement of solar absorbing property of Ni-Mo based thermal spray coatings by laser surface treatment

Ni-Mo and Ni-Mo-Co high velocity oxy-fuel (HVOF) sprayed coatings were treated by Nd:YAG laser source, for the purpose of improving the solar absorbing effect. The coatings after laser treatment showed increment on solar absorptance (α) as the Ni-Mo sample increased from 0.84 to 0.88 and Ni-Mo-Co sample from 0.75 to 0.83. To elucidate the mechanisms for the improvement, microstructures of the coatings before and after laser treatment were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and laser scanning confocal microscope (LSCM). The results demonstrated that the enhanced α was attributed to multiple mechanisms including the decrease in nickel oxide content, the increase in metallic volume fraction, the reduction of micro-defects as well as the greater surface roughness.