Laser texturing for high friction applications

A nanosecond pulsed Nd:YAG fibre laser with wavelength of 1064nm was used to texture several different steels, including grade 316 stainless steel, Cr-Mo-Al ‘nitriding’ steel and low alloy carbon steel, in order to generate surfaces with a high static friction coefficient. Such surfaces have applications, for example, in large engines to reduce the tightening forces required for a joint or to secure precision fittings easily. For the generation of high friction textures, a hexagonal arrangement of laser pulses was used with various pulse overlaps and pulse energies. Initial friction testing of the samples suggests that the pulse energy should be around 0.8mJ and the laser pulse overlap should be higher than 50% in order to achieve a static friction coefficient of more than 0.5 (compared to a value of µ_s∼0.22 for the untextured samples). It was also noted that the laser processing increases the surface hardness of samples, which appears to correlate with the increase in friction. Use of an external hardening process, either before or after laser texturing was found to increase the static friction coefficient even further. By using a plasma nitriding process with the laser texturing, friction coefficients consistently greater than 0.8 have been observed, with some textures achieving a friction coefficient of 1.