To increase the hydrophobicity, non-stickiness and wear resistance of DLC surface by surface texturing using a laser ablation process

Abstract

In this investigation, the hydrophobicity, non-stickiness and wear resistance of diamond-like carbon (DLC) coatings are systemically altered by introducing different surface textures. The surface textures existed in forms of regular dimples or pillars. Regular dimples or pillars perpendicular to substrate surface were introduced using a laser ablation method. DLC was subsequently deposited on the textured surface using the magnetron sputtering technique. The effect of the geometric parameters on the surface properties was studied by varying the dimple density from 0% to 30% for dimpled samples, and the distance a between two grooves from 25 to 250μm for the pillared samples. The hydrophobicity was measured by using a contact angle goniometer and the non-stickiness was evaluated by button shear tests. The wear performance of the textured DLC surfaces was studied by using a reciprocating ball on flat wear tester against UHMWPE balls in simulated body fluid environment. The results showed that DLC surface with pillared structure and small a values (≤40μm) could lead to high hydrophobicity (contact angle>130°). In addition, good non-sticking behavior was observed on this surface structure with significant reduction of residual material of egg yolk as evaluated by shear tests at either 100 or 300 °C. From the wear tests, the DLC coating with dimple density of 10% reduced the friction and the wear of the soft UHMWPE ball. The improved hydrophobicity and non-stickiness of the pillared DLC with small a value could be due to large cavity density (over 80%), thereby promoting the hydrophobicity of DLC coating. The improved wear performance of the dimpled DLC could be due to the action of reservoirs that enhanced lubricant retention during sliding motions.