Picosecond Laser Fabrication of the Riblet-Array Surface Texture on Ti64 Alloy Substrate

In the paper, laser surface texturing process was studied systematically to fabricate riblet array surface structure on Ti64 substrate with 1.06um 10W ps laser which has a pulse duration of 10.3 ps. The optimum laser surface texturing process parameters were identified, under which the desired riblet-array textures were produced on Ti64 substrate with the required specifications in terms of dimension and quality. The fabricated riblets have a trapezoidal shape with a period of 60 urn and riblet height of 30 [micro]m and a bottom surface roughness (Ra) of 2.115 [micro]m. Compared with non-textured sample, the laser-fabricated riblets induced around a 10% reduction in the drag force. Also, it was found that laser surface treatment did not induce any change on the microstructure of Ti64 during ps laser riblet surface texturing of Ti64 substrate. With XRD measurements, the laser riblettextured Ti64 surface was found to exhibit tensile stress of 87.5 MPa, which may be due to the heat shock from laser treatment resulting in larger d-spacing between lattice planes. Keywords: picosecond laser, riblet array texture, Ti64, metallurgical microstructure, residual stress