Oxygen concentration dependence of microstructure formed on Ni by backward pulsed laser deposition

Abstract

In the automotive industry, direct joining between resin and metal without additional material is expected due to a growing need for hybrid structures composed of resin and metal. Roughening the metal surface before joining can improve the adhesion with the resin, and forming a microstructure on the metal surface by backward pulsed laser deposition could be a useful method. In the present study, we investigated the dependence of microstructure on the oxygen concentration in the ambient gas during surface processing for controlling the morphology of the microstructure. In the experiments, the oxygen concentration in the ambient gas composed of nitrogen and oxygen was controlled under atmospheric pressure, and microstructure characteristics, such as the shape and hardness, were analyzed. As a result, it was demonstrated that the formation range of the microstructure was constant regardless of the oxygen concentration, whereas a rougher microstructure was formed at higher oxygen concentrations, and a dense, flat microstructure was formed at lower oxygen concentrations. These results implied that the oxidation between the nanoparticles in the laser-induced plume and the ambient gas affects the mobility of the nanoparticles on the metal surface, leading to a transmutation in the morphology of the microstructure. Finally, it was shown that it is important to reduce the surface mobility of nanoparticles, such as processing under high oxygen concentration, to form a microstructure that improves adhesion.