Microstructure and hardness analysis of carbon nanotube cladding layers treated by laser beam

Medium carbon steel coated with carbon nanotubes was surface treated by a continuous wave CO2 laser beam. The surface remelting layer formed a gradually distributed microstructure of hypoeutectic, eutectic and hypereutectic from the interface of the heat-affected zone (HAZ) and the cladding layer to the top surface of the cladding layer. The microstructure and hardness of the laser-affected zones were studied as a function of the laser beam parameters. The results show that the carbon nanotubes considerably decomposed and dissolved in the molten surface and strongly carburized the cladding layer. The microhardness of the cladding layer and the HAZ decreased with increasing the laser energy of per unit area. Compared with that of the substrate, the microhardness of the cladding layer was considerably increased, reaching 900–1000 HV200, the HAZ was also significantly hardened. The wear resistance of the cladding layer was greatly increased compared with the substrate, the medium carbon steel.