Tribology and superhydrophobicity of laser-controlled-melted alumina surfaces with hard particles

Laser-controlled melting of alumina surface with a carbon film of about 40-lm thickness formed prior to the laser treatment process is carried out to improve its hardness, durability, and superhydrophocity. The carbon film consisted of a uniformly distributed mixture of hard particles of WC, SiC, and B4C. The presence of carbon film improves the absorption of the laser beam during the treatment process. The morphology and hydrophobicity of the laser-treated surface were evaluated using optical microscopy, atomic force microscopy, and the contact angle measurement, respectively. The chemical changes of the treated layer were examined using scanning electron microscopy and energydispersive spectroscopy. The structure of the nitride compound formed at the surface was characterized using x-ray diffraction, which was also used to determine the residual stress at the surface. Both microhardness and fracture toughness of the laser-treated surface were determined using indentation tests. Scratch tests were conducted to measure the friction coefficient and scratch resistance of the laser-treated surface. Laser treatment produces micropoles, nanopoles, and small size cavities at the surface, which enhance hydrophobicity of the surface. The microhardness of the laser-treated surface increases almost 50% because of the dense layer formed at the surface and the residual stress is in the order of 2 GPa, which is compressive. The scratch resistance and friction coefficient of the laser-treated surface is superior.