Papers by Keyword: DLC

Abstract: The trend in metal forming tribology is to develop new tribo-systems including new lubricants, tool materials and tool coatings in order to substitute environmentally hazardous lubricants by environmentally friendly tribo-systems. In preliminary testing the limits of lubrication of new tribo-systems for sheet forming production, it is advantageous to use dedicated simulative tribo-tests. This paper studies the influence of tool coatings on deep drawing operations using the Bending Under Tension (BUT) test and also under more severe tribological conditions by adopting the Strip Reduction Test (SRT) to replicate industrial ironing of deep drawn, stainless steel parts. Non-hazardous tribo-systems in form of a double layer Diamond-like coated tool applied under dry condition or with an environmentally friendly lubricant were investigated via emulating industrial process conditions in laboratory tests. Experiments revealed that the double layer coating worked successfully, i.e. with no sign of galling, when it was used with environmentally friendly lubricants, whereas the results were more prone to galling under dry condition.

Abstract: The study investigates the wear of microcrystalline diamond (MCD) and diamond-like carbon (DLC) coatings. The MCD and DLC coatings were grown by plasma enhanced chemical vapor deposition (PECVD) method on WC-Co substrates. The sliding wear tests were performed on the ball-on-plate type of tribometer in reciprocating mode. The ball-cratering wear tests were carried out using Calo tester. The mechanical profilometer, optical and scanning electron microscopes (SEM) were used for investigation of the surface morphology of the wear scars. The wear of DLC coating is more intense in comparison to the MCD coating. In contrast to the MCD coating, no evidence of the DLC coating deflection was found.

Abstract: Despite its high tensile strength and its brilliant fatigue behaviour, 7075-T6 aluminium alloy usage is dramatically reduced, due to its sensitivity to corrosion and its poor surface characteristics. In order to be adopted for advanced applications in the aeronautic, automotive and maritime fields, as well as in further innovative applications, 7075-T6 resistance must be improved. Controversial results are found in literature on coated 7075-T6 fatigue strength, due to the complex mechanical interaction between the substrate and the coating, and the high temperatures involved in the coating process. In the present work, testing on rotating bending fatigue (R = -1) 7075-T6 uncoated and PVD DLC coated specimens has been conducted. Different stress levels were considered, to assess the impact of the applied stress on the fatigue life of the substrate-coating system. SEM characterization of the fracture surfaces has been performed, to investigate the influence of the coating on the fracture mechanism

Abstract: This study investigates how to improve the anti-adhesion issues between Silicon mold and nanostructures of hard polydimethylsiloxane (H-PDMS). A Silicon mold with different depths and widths was made using a focused ion beam (FIB). During the soft-lithography molding process, anti-adhesion layers were needed between the Silicon mold and H-PDMS samples to prevent the de-molding failure caused by the adhesion issues between the interfaces. This study adopts three methods to deposit anti-adhesion layers, such as liquid immersion, vapor deposition, and fluorine-doped diamond-like carbon (F-DLC) film. Perfluorooctyl-trichlorosilane (PFOTCS) was used as a mold-releasing agent for the liquid immersion and vapor deposition methods. The contact angles between each film were measured to determine the effect of anti-adhesion on the molding process. In addition, atomic force microscopy (AFM) was used to measure the adhesion force between the H-PDMS and anti-adhesion layers. The results show that the coatings of anti-adhesion layers are an effective approach to improve the formability of molding.

Abstract: The Diamond like carbon (DLC) and diamond coatings were deposited on a steel substrate using plasma assisted chemical vapor deposition (PA CVD) method. The parameters of deposition were analyzed in relation to the effectiveness of the process and the quality of coatings. It was found that the DLC coatings formed only at specific conditions of temperature and pressure of precursor gases. The characterization of coatings were performed by Raman spectromicroscopy, X-ray diffraction and infrared spectromicroscopy which allowed us to recognize the dominant phases and the distribution of bonds inside the coatings. The chemical bonds such as sp² C-C, sp³ CH₃/CH₂ and sp³ CH were found in microstructure coatings. The maps of distribution of bonds in the coatings were also prepared. Additionally, their microstructure was investigated by scanning electron microscopes which have revealed a spherical grains morphology of the coatings.

Abstract: Excellent tribological properties of hard materials surface are desirable in several sectors of industry. Diamond-like carbon (DLC) coatings are well known for their low friction, excellent wear resistance, and high hardness. In this work, DLC films were deposited on AISI M2 steel using a modified PECVD pulsed-DC discharge. Multilayer of carbon and silicon were grown, alternately. Samples were produced with different layer thickness for carbon and silicon, and the same parameters for each material layer, in order to investigate friction coefficient in each layer, evaluate rate deposition variation and the gradient behavior of different layers. Raman spectroscopy was used to verify the structural arrangement of carbon atoms. The films were also characterized by scanning electron microscopy and EDX. Tribological tests were performed to observe adhesion between layers and substrate, friction, and wear. The results showed the variation of friction coefficient and that deposition rate declines when increasing number of layers.

Abstract: Diamond-like carbon (DLC) films are widely known for their attractive properties. High adhesion between coating and substrate is necessary to ensure these properties. The bombardment by energetic species during growth tends to generate high intrinsic compressive stresses levels, which have several consequences in coating performance. However, this problem can be solved with the deposition of a thin interlayer with intermediary properties. In this work, films were grown on M2 steel using a modified plasma enhanced chemical vapor deposition PECVD pulsed-DC discharge. In order to improve the coating adherence on the substrate, a silicon interlayer was deposited varying the growth time, which generated different interlayer thickness. Tribological tests were performed to study adhesion and friction gradient. Raman spectroscopy was used to verify the structural arrangement of carbon atoms. The results showed that thickness variation in silicon interlayer leads to significative changes in adhesion between coating and substrate.

Abstract: The implement of direct load control can reduce power system load at peak times by restricting the given load at the required time straightforwardly. These actions also have a positive influence on the distribution system reliability along with the increase of load rate. Thus, in order to make further research on the impact of DLC on distribution system reliability, a mathematical model of DLC on the basis of linear programming method should be set up firstly. Then, according to the change of load rate, establishing a cubic spline interpolation function represents the reliability index changing with load rate. Finally, the validity of above model and the method are studied through numerical tests on modified RBTS BUS 6 test system. As the result shows, the effectively direct load control can improve the distribution system reliability.

Abstract: Household refrigeration represents 17.3% of home energy consumption in the USA and 47% in Brazil. This article overviews a multidisciplinary approach to develop a traditional hermetic compressor (oil lubricated, with several rotating parts), into an oil-less, linear motion, innovative compressor, with improved efficiency, versatility and sustainability. This involves the development of surface engineering processes combining purpose-oriented phases applied to soft substrates to achieve high wear resistance and load support and low friction coefficient. Initially, the role of the environment (air, CO₂ and R600a) on the tribological behaviour of a commercially available Si-rich multifunctional DLC coating deposited on AISI 1020 steel is illustrated. In sequence, the influence of the thickness of different layers (DLC and CrN) on sliding wear is analysed. Results are presented using an original approach (3D triboscopic maps) for two distinct configurations (increasing load and constant load) and findings are confronted with numerical simulations using Film Doctor^®. Finally, a low cost process to obtain a multifunctional coating (different nitrided layers + DLC) is described, which uses a unique thermal cycle reactor capable of coating parts in industrial scale with reduced cost.

Abstract: 7075-T6 aluminium alloy is commonly adopted in high performance structures and components. Its fatigue behaviour is however dramatically worsened by exposure to aggressive environments. The deposition of PVD coatings, which are commonly adopted to increase the surface properties of structural elements in terms of hardness, contact fatigue and wear resistance, could be beneficial also for the fatigue behaviour of a 7075-T6 substrate in an aggressive environment. In the present work, Diamond Like Carbon (DLC) PVD coated 7075-T6 specimens immersed in methanol have been analysed, by means of step-loading rotating bending fatigue tests (R = -1) at 2·10⁵ cycles. Coated specimens were tested in laboratory air for comparison, and uncoated polished samples were studied in both the environments to obtain reference values. SEM micrographs of the fracture surfaces were taken to investigate the effects of the corrosive environment on the failure mechanism.