Argon plasma treatment techniques on steel and effects on diamond-like carbon structure and delamination

Abstract

We demonstrate alteration in diamond-like carbon (DLC) film structure, chemistry and adhesion on steel, related to variation in the argon plasma pretreatment stage of plasma enhanced chemical vapour deposition. We relate these changes to the alteration in substrate structure, crystallinity and chemistry due to application of an argon plasma process with negative self bias up to 600 V.Adhesion of the DLC film to the substrate was assessed by examination of the spallated fraction of the film following controlled deformation. Films with no pretreatment step immediately delaminated. At 300 V pretreatment, the spallated fraction is 8.2%, reducing to 1.2% at 450 V and 0.02% at 600V. For bias voltages below 450V the adhesion enhancement is explained by a reduction in carbon contamination on the substrate surface, from 59at.% with no treatment to 26at.% at 450V, concurrently with a decrease in the surface roughness, R q , from 31.5nm to 18.9nm. With a pretreatment bias voltage of 600V a nanocrystalline, nanostructured surface is formed, related to removal of chromium and relaxation of stress; X-ray diffraction indicates this phase is incipient at 450V. In addition to improving film adhesion, the nanotexturing of the substrate prior to film deposition results in a DLC film that shows an increase in sp 3 /sp 2 ratio from 1.2 to 1.5, a reduction in surface roughness from 31nm to 21nm, and DLC nodular asperities with reduced diameter and increased uniformity of size and arrangement. These findings are consistent with the substrate alterations due to the plasma pretreatment resulting in limitation of surface diffusion in the growth process. This suggests that in addition to deposition phase processes, the parameters of the pretreatment process need to be considered when designing diamond-like carbon coatings.Prime Novelty: We elucidate the mechanisms behind the enhancement of diamond-like carbon film adhesion with increase in pretreatment bias voltage, and demonstrate the effect on the final film structure of alterations in the pretreatment process.

Substrate and material transfer effects on the surface chemistry and texture of diamond‐like carbon deposited by plasma‐enhanced chemical vapour deposition

“…The DLC coating, with thickness approximately three quarters of a micron, was deposited using parameters that have been shown to produce good substrate adhesion, wear resistance and low friction coatings for machine tools . An argon plasma pretreatment lower than 450 V was used to clean but not restructure the steel surface . After pretreatment, the bias voltage was adjusted to 450 V, and a silicate interface layer was formed by adjusting the argon flow rate to 10 sccm and by introducing tetramethylsilane with a flow rate of 25 sccm.…”

“…After pretreatment, the bias voltage was adjusted to 450 V, and a silicate interface layer was formed by adjusting the argon flow rate to 10 sccm and by introducing tetramethylsilane with a flow rate of 25 sccm. This layer has been previously shown to enhance the adhesion of the film to steel substrates . Once the interfacial layer was formed, acetylene gas at 60 sccm was introduced into the chamber.…”

“…However, high internal stresses within the applied film can limit useful DLC coating thickness to less than 10 µm, thus limiting practical application in some areas. To improve substrate‐film adherence, many groups have used thin interlayers, incorporating materials such as titanium, tungsten or silicon . An alternative strategy has been developed, which uses a thick epoxy layer with a DLC surface thin film, with applications for aircraft landing gear.…”

Surface characterisation of carbon films produced by plasma chemical vapour deposition method

“…An increase in surface diffusion can tend to promote the formation of surface nodules. 29 Increasing the argon flow, AFM ( Fig. 5b and c) shows nodule diameter decreases and demonstrates the formation of uniform and smoother film.…”

Low-friction and wear-resistant carbon nitride coatings for bearing components grown by magnetron sputtering

“…33 Several techniques have been used in the past for the improvement of adhesion of the C-based coatings on steel. [33][34][35][36] However, the conditions of the rolling operation in bearing applications are very demanding, including high contact pressures and lubrication, thus the coating-substrate adhesion is also a very essential research area. This issue is addressed herein by employing the treatment of the substrate surface prior to coating deposition.…”