Laser decoating of DLC films for tribological applications

Abstract

Damaged DLC coatings usually require remanufacturing of the entire coated components starting from an industrial chemical de-coating step. Alternatively, a complete or local coating repair can be considered. To pursue this approach, however, a local coating removal is needed as first operation. In this context, controlled decoating based on laser sources can be a suitable and clean alternative to achieve a prefixed decoating depth with high accuracy. In the present study, we investigated a laser-based decoating process executed on multilayered DLC films for advanced tribological applications (deposited via a hybrid PVD/PE-CVD technique). The results were acquired via multifocal optical digital microscopy (MF-ODM), which allowed high-resolution 3D surface reconstruction as well as digital profilometry of the lasered and unlasered surface. The study identifies the most critical process parameters which influence the effective decoating depth and the postdecoating surface roughness. In particular, the role of pulse overlap (decomposed along orthogonal directions), laser fluence, number of lasing passes and assist gas is discussed in text. A first experimental campaign was designed to identify the best conditions to obtain full decoating of the DLC + DLC:Cr layers. It was observed that decreasing the marking speed to 200 mm/s was necessary to obtain a sufficient pulse overlap and a nearly planar ablation profile. By operating with microsecond pulses and 1 J/cm 2 (fairly above the ablation threshold), less than 10 passes were needed to obtain full decoating of the lasered area with an etching rate of 1.1 μm/loop. Further experiments were then executed in order to minimise the roughness of the rest surface with the best value found at around 0.2 μm. Limited oxidation but higher R a values were observed in Ar atmosphere.

Investigation of Multiparameter Laser Stripping of AlTiN and DLC C Coatings

“…al. [ 22 ] used 10 laser beam passes to strip a DLC coating with a scanning speed of 200 mm·s −1 . In another study, Marimuthu.…”

“…They compared the use of an excimer laser and a solid state Ti:sapphire laser for removal of TiAlN coatings. Zivelonghi et al [ 22 ] presented successful removal of a DLC coating by laser stripping; several low-power passes were used to gradually remove a CrC/Cr–Cr:DLC–DLC coating with a thickness of 6 µm. Additionally, Assurin et al [ 23 ] presented KrF excimer laser removal of a multilayer coating consisting of 4 μm TiCN + Al 2 O 3 and 3.2 μm CrN + DLC layers.…”

Experimental Investigation of a Method for Selective and Precise Laser De-Coating

“…The values of the incubation coefficient are dependent on the specific laser-matter interaction. In the references [1,10,12] the S values ranges from 0.7 to 0.9 for similar materials.…”

“…Coating removal was futher analysed by elemental energy dispersive spectroscopy (EDX). Research focused on the laser de-coating of a DLC/CrC interface coating was presented by Zivelonghi et al [12]. In their paper, a parameter called the 'average etching rate' (with a value of 1.1 μm/loop) was presented, which represents the average removal thickness for one pass of the laser beam.…”

Nd:YOV4 laser surface texturing on DLC coating: Effect on morphology, adhesion, and dry wear behavior

“…As reported in the literature, performances of textured surfaces change as a function of texture geometry [3]. Therefore, texture parameters can be selected in order to fulfil specific applications such as improve surface roughness [4,5], realize full decoating [6], obtain specific design [7] or evaluate the effect in changing parameters in tribological properties [8].Textured surfaces find location in a huge field of applications like automotive [9,10], biomedical [11,12], electronics, packaging, etc.…”