Multilayer Diamond-like Carbon Research Articles

Multilayer Diamond‐Like Carbon Films on Monocrystalline Diamond

Multilayer films of diamond‐like carbon (DLC) on monocrystalline diamond substrates have been for the first time obtained by plasma‐chemical deposition. Their chemical composition and structural and morphological properties are studied. The DLC individual layers differ in their sp3 carbon content. The multilayer nature of the resulting coatings is confirmed by periodic density modulation on the small‐angle X‐ray reflectometry curve and modulations in the CsC8, CsC6, CsC4 lines on the crater depth profile of secondary ions of elements (secondary ion mass spectrometry). The dependence of the deposition rate of multilayer DLC films on diamond, their composition and properties on the argon additive to the reaction gas mixture, as well as on methane flow, pressure and growth time, are studied.

Enhanced Long-Term Corrosion Resistance of 316L Stainless Steel by Multilayer Amorphous Carbon Coatings.

Diamond-like carbon (DLC) coatings are effective in protecting the key components of marine equipment and can greatly improve their short-term performance (1.5~4.5 h). However, the lack of investigation into their long-term (more than 200 h) performance cannot meet the service life requirements of marine equipment. Here, three multilayered DLC coatings, namely Ti/DLC, TiCx/DLC, and Ti-TiCx/DLC, were prepared, and their long-term corrosion resistance was investigated. Results showed that the corrosion current density of all DLC coatings was reduced by 1-2 orders of magnitude compared with bare 316L stainless steel (316Lss). Moreover, under long-term (63 days) immersion in a 3.5 wt.% NaCl solution, all DLC coatings could provide excellent long-term corrosion protection for 316Lss, and Ti-TiCx/DLC depicted the best corrosion resistance; the polarization resistances remained at ~3.0 × 107 Ω·cm2 after immersion for 63 days, with more interfaces to hinder the penetration of the corrosive media. Meanwhile, during neutral salt spray (3000 h), the corrosion resistance of Ti/DLC and TiCx/DLC coatings showed a certain degree of improvement because the insoluble corrosion products at the defects blocked the subsequent corrosion. This study can provide a route to designing amorphous carbon protective coatings for long-term marine applications in different environments.

Designing hydrogen-free diamond like multilayer carbon coatings for superior mechanical and tribological performance

Diamond like carbon (DLC) coatings are extensively employed for their outstanding mechanical and tribological properties. To overcome the inherent high residual stress, therefore brittleness, DLC coatings with multilayer architecture were developed in the form of stacking alternate hard and soft layers to avoid premature failure under severe loading conditions. The current study was designed to investigate the impact of bilayer thickness (hard & soft) on wear of multilayer DLC particularly at high contact stress (2.0 GPa, 2.7 GPa, 3.0 GPa, 3.4 GPa). Seven DLC multilayer (1:1 bilayer ratio) samples with 1, 2, 5, 10, 20, 40, 80 bilayers were deposited on 440C steel and the overall coating thickness was mainatined at ∼1 µm. Moreover, the bilayer thickness effect was determined on mechanical, scratch adhesion and structural properties. Transmission electron microscope (TEM) was used to visualize discrete hard and soft layers in 80 bilayers (∼6 nm thin layer). G peak suppression and ID/IG increment were observed with reduction in bilayer thickness. Hardness, modulus, elastic strain to failure (H/E), plastic deformation resistance (H3/E2) and residual stresses showed an inverse relation with bilayer thickness. Furthermore, micro scratch adhesion decreases with layer thickness reduction. Only 100 nm and above bilayer thickness samples (1, 2, 5, 10 bilayers) could survive under high contact stress while the other three (20, 40, 80 bilayers) showed brittle failure using pin-on-disc tribometer. Additionally, 10 bilayers (100 nm thickness) produced the minimum wear (∼7.9 ×10−8 mm3/Nm) at 80 N.

The synergistic mechanism of transition layer and transfer layer on dry sliding wear of multi-layered diamond-like carbon (DLC) coating at wide temperature

The wear resistance of 17-4PH stainless steel was improved at wide temperature (25–200 °C) by depositing multi-layered Cr/CrC/DLC coating. The results showed that the lubricating effect of the transfer layer led to a reduction of the friction coefficient to 0.03. DLC coating had a protective effect on the 17-4PH substrate, and the surface of the coating was basically not worn at 25–100 °C. This study focused on the wear mechanism and frictional chemical reaction mechanism of multi-layered coatings at wide temperatures. With the increase of temperature, the wear mechanism of DLC coating changed from abrasive wear to adhesive wear, and finally delamination. The complex tribochemical reaction in the wear process led to the dynamic change of its graphitization transformation, which affected the formation of the transition layer and the change in surface mechanical properties of the coating. This was mainly because the transition layer Cr/CrC and Si3N4 played a role in inhibiting the graphitization transformation of DLC layer during the wear process, thus affecting the friction properties of DLC.

Comparative study on infrared properties of PLD-grown DLC film and SiC film

Diamond-like carbon and silicon carbide coatings were grown by pulsed laser deposition under different laser fluences, and their infrared transmission spectra were compared with each other. Raman spectroscopies and their deconvolutions for the silicon carbide films prepared by different laser fluences exhibited no changes nearly in micro-structure, and the infrared spectra showed these layers had high infrared transmission. On the other hand, the obvious changes in micro-structure of the diamond-like carbon films grown by the different laser fluences, which indicated laser fluence played an important role in the growth process of the diamond-like carbon films. A relatively higher laser fluence could grow the diamond-like carbon film with higher sp3 bond content, increasing the infrared property, while a lower one increased the absorption of the layer, reducing its infrared transmission seriously. Nano-scratch test showed that silicon carbide layer can be used as the buffer layer for the multilayer diamond-like carbon film enhancing the adhesive performance of the whole coating on the substrate with the protective and anti-reflective properties.

OPTIMIZATION OF DIAMOND-LIKE CARBON COATINGS FOR MECHANICAL AND TRIBOLOGICAL APPLICATIONS. REVIEW

Diamond-like carbon (DLC) coatings are used to improve the quality of industrial products due to a wide range of exceptional physical, mechanical and tribological properties. Problems that limit the scope of application of hard non-hydrogenated DLC coatings with properties closest to those of diamond are considered. The scientific literature is reviewed devoted to improving the characteristics of DLC-based wear-resistant coatings. The approaches currently used to reduce internal compressive stresses, improve adhesion to the substrate, and increase the strength of coatings are analyzed. Aspects of optimization of deposition parameters, doping, constructing the gradient and multilayer structure are considered. Based on the generalization of the results of the reviewed publications, a conclusion is made about the advantages of using coatings with a multilayer structure. A promising design undoped multilayer DLC coatings with high protective properties is discussed.

Comparative Study on the Scratch and Wear Resistance of Diamond-like Carbon (DLC) Coatings Deposited on X42Cr13 Steel of Different Surface Conditions

Tribological investigations are of great importance, especially in the case of novel combinations of materials used for the tribosystem. In the current research, multilayer diamond-like carbon coating deposited by plasma enhanced chemical vapour deposition on an X42Cr13 plastic mould tool steel is studied with two different surface conditions of the substrate. On the one hand, it is secondary hardened; on the other hand, it is additively plasma nitrided preceding the diamond-like carbon coating. This latter combined treatment, called duplex treatment, has an increasingly wide range of applications today. However, its effectiveness largely depends on applying the appropriate nitriding technology. The tribological behaviour was characterised by an instrumented scratch test and a reciprocating ball-on-plate wear test. The results demonstrate better scratch resistance for the duplex-treated samples, while they show weaker performance in the applied wear type of loading. The current comparative study reveals the reason for the unexpected behaviour and highlights some critical aspects of the heat treatment procedure. The architecture of the tested multilayer DLC coating is unique, and no tribological results have yet been published on tribosystems combined with an X42Cr13 steel substrate. The presented results may particularly interest tribologists and the materials research community.

Improvement of Surface Properties of Aluminum Alloy-Based Composites by Multi-Layer DLC Coating

In recent years, it has been a challenge for the transportation sector to reduce the weight of vehicles for higher fuel efficiency. This expands the use of light metals such as Al alloys. However, these materials have low hardness and surface strength. In this study, Al-alloy (AC8A; Al–Si–Cu–Ni–Mg) composites reinforced with Al2O3 fibers were used as base materials and were coated with multilayer diamond-like carbon (DLC) films to improve their properties. The multilayer DLC films were deposited on the Al alloy composites by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) using methane and acetylene gases as the raw materials. As the number of DLC film layers increased, the Young’s modulus of the samples decreased and the following ratios of hardness (H) to elastic modulus (E) also increased: H/E, H3/E2, H2/E. In addition, the critical number of peeling slides increased as the composite volume fraction and the number of layers increased.

Enhanced tribological and corrosion properties of DLC/CrN multilayer films deposited by HPPMS

Diamond-like carbon (DLC)/CrN multilayer composite films with different modulation ratios were prepared by high power pulsed magnetron sputtering (HPPMS). The strengthening mechanism of tribological properties and corrosion resistance of multilayer DLC films were detailedly discussed. The results showed that the single layer DLC film peeled off after 25 min of friction, while the DLC/CrN multilayer films exhibited good wear resistance. The furrow phenomenon of wear track weaken, the depth of wear track decreased, and the wear resistance of the film enhanced with the increase of modulation ratio. The wear resistance of DLC film is directly related to its hardness, plastic deformation resistance and residual internal stress, and the DLC/CrN multilayer film with modulation ratio of 2:1 had the best wear resistance. Electrochemical experiments show that improving the density of the film, inhibiting the formation of corrosion ion diffusion channel and forming passive film at the interface are important factors to enhance the corrosion performance, and the DLC/CrN multilayer film with modulation ratio of 1:1 film had the best corrosion properties.

Exploration of a micron and mesoscale steps/slots composite manufacturing technology based on thin-film compensation

The geometrical characteristic of micron and mesoscale parts/structures is within 0.01–10 mm. However, it is challenging to ensure machining accuracy by using traditional methods. This paper proposed a new composite manufacturing technology of combining precision cutting with film compensation, i.e., a method of subtractive manufacturing followed by additive manufacturing, which can not only achieve high machining quality of micron and mesoscale parts/structures, but also endow the surface with excellent wear resistance and high hardness given by the film. In this work, a multilayer diamond-like carbon (Ti-DLC/α-C:H)n was selected as the compensation film, while the steps and slots with design dimensions of 400 μm and 700 μm were set as the final processing objectives. The tolerance theory of the composite manufacturing technology, including dimensional tolerance of micron and mesoscale, process tolerances of precision machining and measuring, and film thickness tolerance, was investigated. The results showed that after precision cutting and (Ti-DLC/α-C:H)n compensation, the surface hardness of the steps/slots increased from HV775.96 to HV1016.34, while the wear resistance was significantly improved with the friction coefficient reducing from 0.75 to 0.08. Additionally, the steps and slots were processed successfully with a primary size of 400 μm and 700 μm, achieving IT5 machining accuracy.

Pulsed laser deposition of multilayer diamond-like carbon film grown on stainless steel

The amorphous SiC layers played an essential role of improving adhesive property in the pulsed laser deposition-grown multilayer DLC coating. Comparison of several experiments exhibited that the adhesive SiC layer enhanced the adhesive strength of the DLC layer on the transitional Ti layer. Meanwhile, the ‘inserted’ buffer thin SiC layers, which had strong binding force with the DLC layers, divided the thick DLC layer (about 1.2 μm) into several relatively thin layers. It's thought that the buffer SiC layers reduced accumulation of internal stress in each finite thickness and then prevented the cracking of the DLC layer. And the total thickness of optimized multilayer DLC coating reached to 2 μm. The multilayer DLC coating with the adhesive SiC layer and buffer SiC layers showed an excellent adhesive performance on the stainless steel. The similar tribological property of SiC layer to the DLC layer conferred this multilayer DLC coating a low friction coefficient and a low wear rate.

Comparative Investigation of the Mechanical and Wear Properties of Multilayer Si-DLC/DLC Films

In this study, multilayer diamond-like carbon films 1 µm thick with different numbers of multilayer repetitions were deposited onto austenitic stainless steel SUS304 substrates using different source gases. The influence of the gas and the difference in the number of multilayer repetitions on the adhesion strength and wear resistance of the films was subsequently investigated. The samples were subjected to cross-sectional microstructure observations, elemental analysis by glow-discharge optical emission spectroscopy, nano-indentation tests, Rockwell indentation tests, friction and wear tests, and delamination tests. The nano-indentation tests showed that the films prepared using C2H2 gas were harder than those prepared using CH4 gas. In addition, irrespective of the gas used, the film hardness was improved when four layers rather than two layers were deposited. However, the hardness of the eight layers film decreased. The Rockwell indentation tests showed no improvement in adhesiveness when the gas or the number of multilayer repetitions was varied. The wear tests revealed that the friction coefficient of the films prepared using C2H2 gas was smaller than that of films prepared using CH4 gas. No difference was observed with increasing number of multilayer repetitions. The delamination tests showed that the distance until delamination of the films prepared using C2H2 gas was longer than that of the films prepared using CH4 gas. In addition, the distance until delamination was improved by changing the number of multilayer repetitions from two layers to four layers for both gases but decreased when the number of repetitions was extended to eight layers. In this study, the value of H/E (hardness/Young’s modulus) increased and various characteristics improved with increasing number of multilayer repetitions.

Synthesis of Multilayered DLC Films with Wear Resistance and Antiseizure Properties.

Diamond-like carbon (DLC) films have attracted considerable interest for application as protective films in diverse industrial parts. This is attributed to their desirable characteristics, such as high hardness, low coefficient of friction, gas-barrier properties, and corrosion resistance. Antiseizure properties, in addition to wear resistance, are required during the die molding of polymer and polymer-matrix composite parts. Graphite films can be easily peeled because the vertically stacked graphene sheets are bonded via weak van der Waals forces. The present study demonstrates the fabrication of multilayered DLC/Cu films, where the Cu film functions as a catalyst for the formation of a graphite-like layer between the DLC and Cu films. The DLC/Cu film was synthesized on a Si (100) substrate via plasma-enhanced chemical vapor deposition and magnetron sputtering. The peelability, wear resistance, microstructure, texture, and cross-section of the film were experimentally analyzed. The results indicated a variation in the peelability with the deposition conditions of the Cu film that comprised particles with diameters of several nanometers. The DLC film at the interface in contact with the Cu film was transformed into a graphite-like state i.e., graphitized. The surface of the multilayered film exhibited antiseizure properties with the peeling of the upper DLC film. The multilayered film also exhibited wear resistance owing to the repeated appearances of a new DLC film. It is expected that the wear-resistant films with antiseizure properties demonstrated in the present study will be utilized in various industrial sectors.

Temperature measurement with thin film sensors during warm forging of steel

Warm forged components have better surface properties and higher dimensional accuracy than hot forged components. Diamond-like-carbon (DLC) coatings can be used as wear protection coatings, which are anti-adhesive and extremely hard (up to 3500 HV), to increase tool service life. In the first funding period of the research project at the IPH – Institut für Integrierte Produktion Hannover gGmbH and the Institute for Surface Technology (IOT) of the Technical University of Braunschweig in cooperation with the Fraunhofer Institute for Surface Engineering and Thin Films (IST), the influence of different coating types and process temperatures on tool wear was investigated. The result is, that DLC coatings can reduce tool wear in some cases significantly, but that their service life is strongly dependent on the temperature. Coating-integrated temperature measurement could not be realised at that point, due to adhesion challenges. During the second funding period, the effect of multilayer DLC coatings on tool wear was investigated. Also, an additional method of the temperature measurement on the engraving surface using thin film sensors was developed in order to correlate the local process temperature and local layer wear. In this work, the development of and the results gathered by the thin film temperature sensors are presented, which enable for more accurate temperature measurements than commonly used thermocouples. Their functionality and durability under high loads were investigated and showed to be promising.

Investigation on cavitation erosion of diamond-like carbon films with heterogeneous multilayer structure

Cavitation tests of three heterogeneous multilayer diamond-like carbon (DLC) films (Ti/DLC, TiCx/DLC and Ti-TiCx/DLC) were performed using a vibratory test rig to evaluate their cavitation erosion resistance. Results indicated that the cavitation erosion of multilayer DLC films resulted from flexural cracks in the bending regions, then fatigue failures were developed along the uplifted regions of the films. Comparing to TiCx/DLC film and Ti-TiCx/DLC film, Ti/DLC film had the lowest average erosion area. It was concluded that multilayer structure with titanium as adhesion layer improved the adhesion strength and reduced the plastic deformations of the DLC films in the incubation phase; these Ti layers also decreased the residual stress of the DLC films and reduced the cracks within the films in the attenuation phase; lower ID/IG ratio could improve the fatigue resistance of the multilayer films in the steady phase.

Different Cr Contents on the Microstructure and Tribomechanical Properties of Multi-Layered Diamond-Like Carbon Films Prepared by Unbalanced Magnetron Sputtering

To investigate the effects of Cr doping on the microstructure and tribological properties of multi-layered diamond-like carbon (DLC) films, Cr-DLC films with Cr contents ranging from 0 to 22 at.% were deposited on 0Cr19Ni10 stainless steel and Si wafer surfaces by unbalanced magnetron sputtering. The thickness of the transition layer is 180 nm and the Cr-DLC film ranging from 1.3 to 1.5 µm. The microstructure, mechanical and tribological properties of the films were systematically investigated at room temperature in atmospheric environment. Results show that increasing the Cr target current can effectively improve the incident particle density and reduce surface roughness. As a strong carbon metal, Cr has significant influence on the structure and properties of the film for bonding with carbon atoms during deposition. High-energy Cr particles are favorable for films to increase the sp3 hybrid bond ratio and reduce internal stress. The high-hardness sp3 hybrid phase, Cr carbide, oxide dispersion can effectively improve the mechanical properties of the film, but overdoping is detrimental for mechanical properties of the film. The internal stress shows a continuous trend of decreasing with the increasing Cr content and it reduced up to 80% compared with pure DLC films. The films prepared with Cr sputtering current of 0.4 A demonstrate the best tribological properties, and the friction coefficient and wear rate are 0.15 and 2.9 × 10−7 mm3/Nm, respectively.

Improvement on uniformity of diamond-like carbon coatings inside metal tubes using high power pulse supply

Hollow cathode plasma-enhanced chemical vapor deposition (HC-PECVD) technique with high power pulse supply was employed to deposit multi-layer diamond-like carbon (DLC) coatings on the inner surface of 304 stainless steel (SS304) tubes. Pulse width of high power pulse supply was varied from 2 to 20 μs with constant frequency, negative bias voltage, and power to investigate the effects on the uniformity, microstructure, mechanical properties, and tribological performance of the deposited coatings. The results implying the uniformity of DLC coatings inside SS304 tubes can be improved significantly using the high power pulse supply. At the low pulse width, the uniformity of DLC coatings is outstanding along the axis direction of tube. At the high pulse width, the uniformity of DLC coatings became poor along the axis direction of tube as the plasma density and deposition rate are high; however, the mechanical properties and tribological performance are superior. Besides, the ion bombardment effect and the heating effect appear the competition relationship inside SS304 tubes with the increase of pulse width.

Enhancement in the corrosive and tribological properties of the inner wall of 6063Al and CI pipes by thick multilayer Si-DLC coatings

Corrosion and wear on the inner wall of metal pipes is considered as a challenging issue for their service lifetime in application of delivery systems. Diamond-like Carbon (DLC) coating is a widely investigated material and one of the best choices to be used as protective coating. In this report, Thick multilayer Si-doped DLC (Si-DLC) coatings with high quality was deposited on the inner wall of 6063 aluminum alloy (6063Al/Si-DLC) and cast iron (CI/Si-DLC) pipes by hollow cathode plasma enhanced chemical vapor deposition (HC-PECVD). The structure of the as-deposited coatings on 6063Al and CI pipe are similar, which consists of 10 deposition periods. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests were employed to assess the corrosive resistance of 6063Al/Si-DLC and CI/Si-DLC in 3.5 wt% NaCl solution. The long-term corrosive resistance of the coatings system was measured by neutral salt spray test. Compared with bare 6063Al and CI pipes, 6063Al/Si-DLC and CI/Si-DLC possess excellent corrosion resistance and long-term stability when exposed to corrosive medium, which attributes to the deposition of the coatings on bare substrates. In addition, 6063Al/Si-DLC and CI/Si-DLC show lower and stable friction coefficients and lower wear rate. Consequently, the coatings system what afforded in this study is an extremely potential design to enhance the service life of 6063Al and CI pipes for industrial delivery.

Molecular descriptions of functionalised multi layered diamond like/ amorphous carbon coatings

Diamond-like carbon (DLC) coatings are increasingly used in multiple applications due to excellent biocompatibility and outstanding mechanical, optical, and electrical properties. However, many aspects of the synthesise and functionality of these films, especially at the surface, are still uncertain. Here, we were successful in synthesising a multi functionality multi-layer DLC and amorphous carbon(a-C:H) coatings, deposited on Si wafers, to create different materials attributes. Time-of-Flight Secondary Ions Mass Spectroscopy (ToF-SIMS), combined with Principal component analysis (PCA) analysis, was used to provide molecular characterisation of the coatings that were synthesized using plasma immersion ions implantation and deposition (PIII&D) technique. We used acetylene (C2H2), methane (CH4) and oxygen (O2) and their mixtures as precursor in the plasma treatment process. The organic layer (s) deposition’s uniformity, thickness, chemical composition, molecular structure, organics and inorganics contaminants in the film were revealed and linked to the plasma deposition conditions. The thickness of the deposited films can be determined according to their Si and O2 content. Samples with higher O content also have higher SiO and NOx contents. ToF-SIMS is successful as a stand-alone technique to provide information and knowledge regarding the surface compositions and the depth interface profile of plasma deposited DLC and a-C:H coatings.

Corrosion and wear resistance properties of multilayered diamond‐like carbon nanocomposite coating

Multilayered diamond‐like carbon (DLC) nanocomposite coating has been deposited on silicon and stainless steel substrates by combination of cathodic arc evaporation and magnetron sputtering. In order to make DLC coating adhered to metal substrate, a chromium interlayer has been deposited with constant bias voltage of −150 V applied to the substrate. Dense multilayered coating consists of metallic or nonmetallic and tetrahedral carbon (ta‐C) layers with total thickness of 1.44 μm. The coating has been studied for composition, morphology, surface nature, nanohardness, corrosion resistance, and tribological properties. The composition of the coating has been estimated by energy‐dispersive spectroscopy. Field‐emission scanning electron microscopy and atomic force microscopy have been used to study the surface morphology and topography. ID/IG ratio of ta‐C:N layer obtained from Raman spectroscopy is 1.2, indicating the disorder in the layer. X‐ray photoelectron spectroscopy studies of individual ta‐C:N, CrN, and Cr‐doped DLC layers confirm the presence of sp2C, sp3C, CrN, Cr2N, and carbidic carbon, and sp2C, sp3C, and Cr carbide. Nanohardness studies show the maximum penetration depth of 70 to 85 nm. Average nanohardness of the multilayered DLC coating is found to be 35 ± 2.8 GPa, and Young's modulus is 270 GPa. The coating demonstrates superior corrosion resistance with better passivation behavior in 3.5% NaCl solution, and corrosion potential is observed to move towards nobler (more positive) values. A low coefficient of friction (0.11) at different loads is observed from reciprocating wear studies. Wear volume is lower at all loads on the multilayered DLC nanocomposite coating compared to the substrate.