Femtosecond laser texturing of DLC-based coatings by DLW method with sub-micrometer precision

Abstract

The enhancement of functional surfaces by laser texturing has been investigated in many studies; however, it has been often applied to the substrate. New laser technologies, such as the direct laser writing (DLW) method using a femtosecond laser, allow the production of extremely precise textures into both substrates and thin lms. This paper investigates two distinct methods producing various textures:(i) the substrate is textured before the deposition of the diamond-like carbon coating (DLC), and (ii) the texture is produced into DLC coating deposited on a polished substrate. Our goal was to achieve identical topography in both cases; the textured area was as large as 170 mm 2 . The textured topography was assessed by 3D laser scanning microscope, which con rmed the repeatability of fs laser processing. Raman spectroscopy mapping, SEM, and XPS were combined to investigate the effect of laser processing on DLC coating in terms of oxidation or structural changes. 1. Introduction Many industrial areas face various pressure such as cost-effectiveness, environmental aspects, substitutability of different technologies and its consequent exibility of change. Surface treatments, namely surface texturing by ultra-short pulsed (USP) lasers has been already used in many industrial elds: in the cutting tool industry [1] to improve the cutting process, in piston rings [2], dies preparations for metal forming [3], in bearings [4] for friction reduction; and in other elds such as biomedical equipment [5] or storage devices [6]. Many scienti c papers [7]-[13] dealt with laser surface texturing of DLC coatings, which consisted of dimple shapes limited by applied laser spots from d = 10µm [12] up to 30µm [8] in rectangular/square patterns. The performed experiments showed the coe cient of friction (CoF) reduction when using ultrashort pulsed laser processing [8], [11],[13], instead of short-pulsed laser processing [14], where the heataffected zone (HAZ) seems to be limiting improvement in tribological properties. Other studies [15]-[17] aimed to fabricate different textures, e.g., squares, lines, or circles in many possible patterns.These studies were mainly focused on the impact of various densities of geometrical entities, but not on the achieved depth of textures, which did not allow a proper insertion of laser texturing into various places of the technological production chain. In the study of Dumitru et al. [10], laser texturing was performed in two variants: into the substrate before deposition of DLC coating and after the deposition.However, the depths of the texture were not provided.This study focuses on the fabrication of textures with de ned geometrical entities and conditions by ultra-short pulsed (USP) laser system tuned to a pulsed length of 240fs. Our main goal is to compare the feasibility of two texturing processes. In the rst case, designed textures were micromachined directly into the substrate (tool steel 1.2379) and then the samples were deposited by DLC coating (hereinafter textured-coated). In the second...

Enhancing Surface Temperature Uniformity in a Liquid Silicone Rubber Injection Mold with Conformal Heating Channels

“…Thus, improving the mechanical properties of the fabricated LSR injection mold [32][33][34] by adding stainless steel or iron powder [35] is an interesting research topic. In addition, it was interesting to observe the surface roughness [36] of the 3D print mold on the surface of the lens using a scanning electron microscope [37] or a 3D optical profilometer [38]. Also, it was interesting to analyze the chemical composition and changes that produced variation in fabrication temperature using Raman spectroscopy [39] or at- This paper presented a conformal heating channel to enhance the temperature uniformity of the mold surface in the LSR injection molding of an optical convex lens.…”

“…In addition, it was interesting to observe the surface roughness [35] of the 3D print mold on the surface of the lens using a scanning electron microscope [36] or a 3D optical profilometer [37]. Also, it was interesting to analyze the chemical composition and changes that produced variation in fabrication temperature using Raman spectroscopy [38] or attenuated total reflectance using Fourier-transform infrared spectroscopy [39]. This research is ongoing and the results will be presented in a later work.…”