Effect of femtosecond laser power and overlap ratio on surface roughness parameters, contact angle, and tribological properties of the textured SKD 61 tool steel with oil lubrication

This study prepared samples with femtosecond(fs)-laser-induced periodic surface structures (LIPSSs) controlled by laser power (or peak fluence, F-0) and overlap ratio (OR) to improve the friction and wear behavior of the SKD 61 tool steel sliding against a hard Si(3)N(4)ceramic counterface in oil lubrications. Pin-on-plate (pin: Si3N4; plate: SKD 61 steel) tribological tests were conducted with the reciprocating motion perpendicular to the laser scanning direction and having an incline angle (40 degrees similar to 50 degrees) with respect to the LIPSSs. The contact angles () formed on the textured surfaces were measured for an oil lubricant. The ()(oil)results were found to have their correlation with the areal surface roughness (S-a), skewness (Sk), and kurtosis (Ku) of the textured surfaces produced at various F(0)and OR values. The mean friction coefficient (mu) and wear loss (W) of the steel specimens in oil lubrications are reduced by decreasing contact angle, ()(oil). The combined effect of F(0)and OR on the ()(oil)and the ()(oil)effect on mu and W are thus linked together, and the correlation provides an efficient and convenient way in the choices of laser operating conditions with the minimum mu and W. The minimum values of mu(=0.0089) and W (=2.124 x 10(4)mu m(3)) were obtained with OR = 50% and a laser power of 17 mW.