Soft Substrate Materials Research Articles

A multiscale modeling to determine in vitro mechanical responses of different cells at the cell-substrate interface under fluid perfusion.

Investigating the influence of different cellular mechanical and physical properties on cells in vitro is important for assessing cellular activities like differentiation, proliferation, and migration. Evaluating the mechanical response of the cells lodged on a scaffold due to variations in substrate roughness, substrate elasticity, fluid flow, and the shapes of the cells is the main goal of the study. In this comprehensive analysis, a combination of the fluid structure interaction method and the submodeled finite element technique was employed to anticipate the mechanical responses across various cells at the interface between cells and the substrate. Fluid inlet velocity, substrate roughness, and substrate material were varied in this analysis. Different cell shapes were considered along with various components such as cell membrane, cytoplasm, nucleus, and cytoskeletons. This analysis shows the effect of these individual parameters on the elastic strain and strain energy density of cells at the cell-substrate interface. The results highlight that substrate roughness has a more significant impact on the mechanical response of cells at the interface than substrate elasticity. However, effect of the substrate elasticity becomes crucial for extremely soft substrate materials. The results of this research can be applied to identify the optimal parameters for fluid flow and create a suitable condition for cell culture.

Heating repairable superamphiphobic coatings for long-lasting antifouling application

Superamphiphobic materials exhibit broader applications and possess greater potential compared to their superhydrophobic counterparts. Therefore, it is crucial for superamphiphobic coatings to exhibit applications while maintaining a long service life. To address this challenge, the surface of natural clay kaolin particles was modified through the reaction of ethyl orthosilicate and 1 H, 1 H, 2 H, 2 H -perfluorodecyl triethoxysilane to form organic-inorganic cage fluorinated polyhedral oligomeric silsesquioxane (fluoroPOS) modifiers. Subsequently, antimicrobial ZnO nanoparticles were prepared in situ using hydrothermal methods. Finally, a durable superamphiphobic coating was achieved by physical blending of a polydimethylsiloxane (PDMS) solution with the superamphiphobic powder. Experimental results demonstrate that the as-prepared ZnO/kaolin@fluoroPOS/PDMS coatings are resistant to water, milk, coffee, soy sauce, tea, sunflower oil, lubricant base oils, and other everyday liquids at contact angles greater than 150 degrees, demonstrating superior superamphiphobic and self-cleaning properties. Moreover, the coatings can withstand harsh external environments such as strong acid and alkali chemical corrosion, high temperature heating, photo-radiation aging, mechanical friction and wear, and show good durability. More importantly, the low surface energy fluoroPOS can spontaneously migrate from the interior of the coating to the surface when exposed to heat, thus restoring their impaired superamphiphobic properties. The coatings also have good antimicrobial adhesion due to the incorporation of ZnO nanoparticles. In addition, coatings can be fabricated on a variety of soft and hard substrate materials, such as cotton fabrics, sponges, aluminum sheets, and wood. Therefore, the repairable and durable superamphiphobic antifouling coatings constructed in this study are expected to find applications in many areas, such as building coatings, oil and gas pipelines, fluid drag reduction, and biological anti-corrosion.

Relationship between flash temperature and wear characteristics in Ni-nano Al2O3 coating

Ni-nano Al2O3 composite coatings were deposited on soft Al6061 substrate material. The microstructures of the thin coatings, adhesive strength, hardness, and tribological behavior were studied. The increase in specific wear rate was observed with an increase in the load applied on the pin. This has also resulted in an increase in the flash temperature. This is attributed to the ploughing effect caused by the increase in the uneven surface contact. The study demonstrates that even under extreme loading conditions the Ni-nano Al2O3 composite coating exhibits higher wear resistance. This favors the application of the composite coatings at severe wear conditions.

Fabrication of circuits by multi-nozzle electrohydrodynamic inkjet printing for soft wearable electronics

Wearable electronic devices are evolving from current rigid configurations to flexible and ultimately stretchable structures. These emerging systems require soft circuits for connecting the various working units of the overall system. This paper presents fabrication of soft circuits by electrohydrodynamic (EHD) inkjet-printing technique. Multi-nozzle EHD printing head is employed for rapid fabrication of electric circuits on a wide set of materials, including glass substrate (rigid), flexible polyethylene terephthalate (PET) films, and stretchable thermoplastic polyurethane (TPU) films. To avoid the effects of substrate materials on the jettability, the proposed multi-nozzle head is equipped with integrated individual counter electrodes (electrodes are placed above the printing substrate). High-resolution circuits (50 ± 5 µm) with high electrical conductivity (0.6 Ω □−1) on soft substrate materials validate our well-controlled multi-nozzle EHD printing approach. The produced circuits showed excellent flexibility (bending radius ≈ 5 mm radius), high stretchability (strain ≈ 100%), and long-term mechanical stability (500 cycles at 30% strain). The concept is further demonstrated with a soft strain sensor based on a multi-nozzle EHD-printed circuit, employed for monitoring the human motion (finger bending), indicating the potential applications of these circuits in soft wearable electronic devices.Graphic

Pre- and post-surface treatments using electron beam technology for load-related application of thermochemical and PVD hard coatings on soft substrate materials

With their specific layer features and properties, surface treatments such as thermochemical treatment (nitriding, boriding) and hard coating cover a broad field of application in the wear and corrosion protection of steels. Limitations exist, however, when applying these surface treatments to softer materials, such as cast irons and aluminum alloys in terms of both their treatability and load-bearing capacity.This contribution deals with investigations into duplex surface treatments, where a pre- and post-electron beam (EB) surface treatment (e.g., hardening, remelting, alloying etc.) was combined with one of the above-mentioned treatments. Among other characteristics, the thermal EB surface treatments were characterized by high heating and cooling rates that facilitated the generation of a variety of non-equilibrium microstructures, which exhibited increased hardness and had minimal thermal effects on the surrounding base material. Furthermore, the layer thicknesses were one or two orders of magnitude higher than those generated by thermochemical treatment or hard coating.Based on the comprehensive results and using cast irons and Al alloys as examples, the study demonstrates the extent to which duplex treatments can overcome the aforementioned limitations, and how the tribological and/or corrosive load behavior is affected. The property profiles achieved after duplex surface treatment were strongly dependent on the inherent microstructural and chemical processes. These complex processes were influenced by a range of factors, such as the thermal stability of the EB surface layer generated in the first process step, the respective temperature and time period of the secondary process, etc.Hardness measurements, scratch tests, unlubricated pin-on-disc wear tests using different normal loads and potentiodynamic corrosion tests were realized to facilitate characterization of the different load behaviors of the single- and duplex-treated layers.

Low-Temperature Variation of Acoustic Velocity in PDMS for High-Frequency Applications.

Polydimethylsiloxane (PDMS) and other related silicon-based polymers are among the most widely employed elastomeric materials in microsystems, owing to their physical and chemical properties. Meanwhile, surface acoustic wave (SAW) and bulk acoustic wave (BAW) sensors and filters have been vastly explored for sensing and wireless applications. Many fields could benefit from the combined use of acoustic wave devices, and polydimethylsiloxane-based soft-substrates, microsystems, or packaging elements. The mechanical constants of PDMS strongly depend on frequency, similar to rubber materials. This brings to the exploration of the specific mechanical properties of PDMS encountered at high frequency, required for its exploitation in SAW or BAW devices. First, low-frequency mechanical behavior is confirmed from stress strain measurements, remaining useful for the exploitation of PDMS as a soft substrate or packaging material. The study, then, proposes a temperature-dependent, high-frequency mechanical study of PDMS based on Brillouin spectroscopy to determine the evolution of the longitudinal acoustic velocity in this material, which constitutes the main mechanical parameter for the design of acoustic wave devices. The PDMS glass transition is then retrieved by differential scanning calorimetry in order to confirm the observations made by Brillouin spectroscopy. This paper validates Brillouin spectroscopy as a very suitable characterization technique for the retrieval of longitudinal mechanical properties at low temperature, as a preliminary investigation for the design of acoustic wave devices coupled with soft materials.

Nonlinear magnetoelectric effect in PZT/Terfenol-D nanobilayer on a substrate with surface stress

Based on a linear piezoelectric constitutive relation and a nonlinear magnetostrictive constitutive relation, a nonlinear magnetoelectric (ME) effect model for lead zirconate titanate (PZT)/Terfenol-D nanobilayer on a substrate has been developed. In this study, the nonlinear ME coefficients at bending mode for two cases (without surface stress and with surface stress) are calculated by using Gurtin-Murdoch theory. The difference between two cases and the influence of residual surface tension are discussed. At the same time, the clamping effect of the substrate on ME effect is studied by altering the thickness ratio of the substrate and selecting different substrate materials. The influences of frequency of the magnetic field, PZT volume fraction on the ME effect are investigated, respectively. Finally, the dependence of ME effect on pre-stress is presented. The results show that for the nanobilayer, both the residual surface tension and surface stress have non-ignored effects on the ME effect. Besides, the resonant frequency of the nanobilayer is very low at the bending mode, which can be enhanced by increasing the thickness ratio of the substrate. Also, the substrate can weaken the ME effect due to the clamping effect, and a more soft substrate material should be selected for large ME effect. In addition, pre-stress plays an important role in the nonlinear ME coupling effect of the model developed.

Control of the Morphology of Lipid Layers by Substrate Surface Chemistry

In this study, surface coatings were used to control the morphology of the deposited lipid layers during vesicle spreading, i.e., to control if liposomes self-assemble on a surface into a supported lipid bilayer or a supported vesicular layer. The influence of the properties of the surface coating on formation of the deposited lipid layer was studied with quartz crystal microbalance and two-wavelength multiparametric surface plasmon resonance techniques. Control of lipid self-assembly on the surface was achieved by two different types of soft substrate materials, i.e., dextran and thiolated polyethylene glycol, functionalized with hydrophobic linkers for capturing the lipid layer. The low-molecular-weight dextran-based surface promoted formation of supported lipid bilayers, while the thiolated polyethylene glycol-based surface promoted supported vesicular layer formation. A silicon dioxide surface was used as a reference surface in both measurement techniques. In addition to promoting supported lipid bilayer formation of known lipid mixtures, the dextran surface also promoted supported lipid bilayer formation of vesicles containing the cell membrane extract of human hepatoblastoma cells. The new dextran-based surface was also capable of protecting the supported lipid bilayer against dehydration when exposed to a constant flow of air. The well-established quartz crystal microbalance technique was effective in determining the morphology of the formed lipid layer, while the two-wavelength surface plasmon resonance analysis enabled further complementary characterization of the adsorbed supported lipid bilayers and supported vesicular layers.

Effects of Substrate Hardness and Spray Angle on the Deposition Behavior of Cold-Sprayed Ti Particles

In this study, finite element analysis combined with experimental observation was conducted to clarify the effects of substrate hardness and spray angle on the deposition behavior of cold-sprayed Ti particles. It is found that metallurgical bonding is highly possible to occur between the Ti particle and Cu substrate due to the intensive metal jet at the rim of the interface which helps to remove the cracked oxides. Because metallurgical bonding and large interfacial contact area can guarantee high adhesion strength, the thick Ti coating is achieved after deposition on the Cu substrate. As for the soft Al substrate, the first layer Ti particles are embedded in and then trapped by the soft substrate material, which results in the occurrence of mechanical interlock at the interface. As a consequence, the final coating thickness is also relatively large. When using hard stainless steel as the substrate, the essential conditions for forming the mechanical interlock are lacked due to the high hardness of the substrate material. In addition, the metal jet at rim of the interface is less prominent and also the interfacial contact area is smaller in comparison with the Ti-Cu case. Therefore, the particle-substrate bonding strength and the consequent coating thickness are relatively low. Besides, it is also found that the particle deformation and coating quality are significantly affected by the spray angle. The deformation of the particle localizes at only one side due to the additional tangential momentum. Also, such localized deformation becomes increasingly intensive with decreasing the spray angle. Moreover, the coating thickness is found to reduce with the decrease in spay angle, but the coating porosity shows a reverse trend.

Microscale interpretation of tribological phenomena in Ti/TiN soft-hard multilayer coatings on soft austenite steel substrates

Microscale interpretation of tribological phenomena in Ti/TiN soft-hard multilayer coatings on soft austenite steel substratesThe mechanical and tribological behavior of physical vapor deposited coatings on soft substrate materials gains increasing interest due to economical and environmental aspects - e.g. substitution of steels by light-weight metals or polymers in transport vehicles. Nevertheless, such soft materials require surface protection against wear in tribological contacts. Single layer hard coatings deposited at room temperature are brittle with a relatively poor adhesion. Therefore, they should be better substituted by tough multilayer coatings of soft-hard material combinations. However, the mechanics of such multilayer coatings with several 10 nm thick bilayer periods is difficult and yet not well described. The presented work tries to fill the gap of knowledge by focusing both on mechanical investigations of hardness, adhesion, and wear and on microscopic elucidation of deformation mechanisms. In the paper 1 μm thick Ti/TiN multilayer stacks were deposited by magnetron sputtering on soft austenitic steel substrates at room temperature to prevent distortion of functional components in future applications. High hardness was found for 8 and 16 bilayer films with modulation ratio Ti: TiN = 1:2 and 1:4. This was attributed (with use of transmission electron microscopy) to stopping the crack propagation in thin Ti layers of the multilayer systems by shear deformation combined with different fracture mechanisms in comparison with that for the TiN single layers (edge cracks at the border of the contact area and ring cracks outside, respectively).

A modified scratch test for the mechanical characterization of scratch resistance and adhesion of thin hard coatings on soft substrates

The scratch resistance of coatings and the adhesion between coating and substrate are usually determined in model experiments performed with sharp diamond indenters. These common methods as described for example in EN 1071-3 often fail for the combination of hard coatings on soft substrates due to very small critical loads or no detectable failure modes at all. Hence in the industry a lot of highly subjective and provisional test methods are used. On the one hand, quantitative comparability is difficult with common methods since defects already occur at very small loads for ductile and relative soft substrate materials like plastics. On the other hand, wear of the indenter in contact with hard coatings like pure diamond coatings requires its cost-intensive replacement.In this article a macroscopic tribological–mechanical test method is suggested which uses balls of hardened steel as indenters. A wide scope can be applied for both soft and hard coatings and different substrate materials. By variation of the ball-diameter, the normal contact force and the sliding speed different levels of stress and wear can be induced to analyze the tribological and mechanical behavior between body and counterpart as well as the interface of coating and substrate. To determine scratch resistance close to reality as usual scratch conditions on consumer products are better represented by a small ball than a sharp diamond indenter. Another benefit of the presented test method is the cost saving acquisition of the balls for indentation in very high quality as they are standard parts in the ball bearing industry. For every test on very hard coatings a new ball can be used with the possibility to detect the wear both on the base object and the counterpart. The occurring failure modes of coating and substrate also can be compared with comparatively easy numerical models to verify the results. Additionally to the test concept, first results of different coatings will be presented in this paper and compared with the results of common scratch tests.

Cavitation Erosion of 6061 Aluminum Alloy Coated with TiAlN Thin Film

Cavitation erosion is one of the major problems to be solved in hydraulic machinery. Propellers of high speed boats require a light weight metallic material for their improved high performance. This example tells us that solutions are the developments of way for the improvement of cavitation erosion resistance of light weight metallic material. Coatings on aluminum alloy can enhance the cavitation erosion resistance. This study discussed the cavitation erosion behavior of 6061 aluminum alloy coated with TiAlN thin film. TiAlN coatings were deposited by DC magnetron sputtering method at various nitrogen partial pressures of the coating process using Ti based alloy cathode. The composition of target material was 90wt%Ti, 6wt%Al and 4wt%V. Using the TiAlN coated 6061 aluminum alloy specimen, cavitation erosion tests were carried out to investigate its resistance to the ultrasonic cavitation erosion. Prior to and after the tests, the specimen surfaces were analyzed by using the surface analysis techniques such as micro-hardness test, AFM, SEM, GXRD and scratch test to measure the microstructure of thin film and bonding properties of the applied TiAlN coatings to the substrate material. An improvement in cavitation erosion resistance could be seen with TiAlN coating on 6061 aluminum alloy. Especially, the coating at a nitrogen flow rate of 0.85 sccm or more were very effective in reducing the surface cavitation erosion from the ultrasonic cavitation. In the observation of surface damages during the cavitation erosion tests, the surface cracks in TiAlN were created by the bending of TiAlN coating which were resulted from the plastic deformation of the soft substrate material of aluminum alloy. Once the cracks initiate, drastic delaminations of TiAlN from the substrate material occured. The mean depth erosion rate (MDER) could be evaluated by critical and delamination loads measured by scratch test.

Zinc oxide nanorod-based heterostructures on solid and soft substrates for white-light-emitting diode applications

ZnO nanorods with excellent optical and electro-optical emission characteristics were grown using high- and low-temperature techniques on solid and soft substrate materials. The solid crystalline substrates included p-4H-SiC and p-GaN, while the soft amorphous substrates included p-type polymers deposited on glass and flexible plastic. Two different growth approaches were used to produce these samples. We used the vapor–liquid–solid (VLS) technique (high temperature) and aqueous chemical growth (ACG), which is a low-temperature technique. These ZnO nanorod samples were characterized by room temperature photoluminescence (PL) and processed to fabricate light-emitting diodes (LEDs). The LED characteristics were further investigated by I–V and electroluminescence (EL). As observed by PL measurements, all samples revealed a sharp narrow ultraviolet (UV) peak due to band-edge emission, indicating the good crystalline quality of the grown ZnO nanorods. The origin of the different peaks within the visible region was correlated to different deep level defects reported earlier for ZnO. All fabricated LEDs showed EL providing a wide band extended through the whole visible spectrum and hence produced clear white light observable to the naked eye. The emitted color quality investigation showed that superior color quality was manifested in a high color rendering index and stable color under current variation, indicating that these heterojunction and hybrid LEDs have potential for the development of future light sources. The ZnO nanorod-based LEDs grown by low-temperature ACG on glass and flexible plastic can, after further development, be candidates for future large-area white-light sources.

Structural and mechanical evaluation of the effect of oxygen boost diffusion on a gamma based titanium aluminide of Ti–45Al–2Nb–2Mn–1B

Air oxidation, vacuum heating and a subsequent oxidation (DT treatment) of Ti–45Al–2Nb–2Mn–1B (at.%) titanium aluminide resulted in several oxide layers and a hard Ti 3Al as an interlayer between the substrate and the oxide layers. Surface characterization was carried out using X-Ray Diffraction (XRD), Glow Discharge Spectroscopy (GDS), electron microscopy, microhardness tests, ball-on-disk tests and profilometry. The compositions of oxides were TiO 2 and Al 2O 3 at the surface layers after final air oxidation and Ti 3Al interlayer was enriched with oxygen. Multi step treatment improved the hardness of treated surfaces significantly in comparison with that of the sample thermally oxidized only at 800 °C (TO treatment). The hard Ti 3Al interlayer containing soluble oxygen supported the top oxide layers of the DT treated sample against indentation. Such supporting layer did not form between the soft substrate materials and the oxide layers of TO treated materials. The mean value and variation of friction coefficient on multi step treated surfaces were less than that of the untreated material. The friction behavior of worn surfaces on the multi step treated material against steel and WC-Co ball sliders was rather smoother than that of TO treated samples. Top surface layers of TO treated material were removed at very shorter sliding distances and lower loads than those of DT treated surfaces against both steel and tungsten carbide sliders.

Size Distribution Measurement of Carbonaceous Particulate Matter Using a Low Pressure Impactor with Quartz Fiber Substrates

The collection characteristics of a small deposit area low pressure impactor (SDI) were studied in order to employ the impactor for size distribution measurements of carbonaceous matter. In this work, the SDI was calibrated for soft and porous quartz substrate material in a series of laboratory experiments. The collection efficiency curves were measured by using monodisperse dioctyl sebacate particles and by applying two different detection methods. One method was based on the detection of current carried by charged test particles, and the other measured number concentrations of particles in bipolar charge equilibrium by two condensation particle counters. Concerning the particle size corresponding to a 50% collection efficiency (D 50 ), significant shifts toward smaller particle sizes were found for the quartz fiber substrates compared with the flat plates. Also the shapes of the collection efficiency curves differed considerably: quartz substrate gave less steep curves than plain impaction plates. The new calibration was applied to field data from urban and rural sites. Compared with the original calibration of the SDI, the new calibration changed the measured size distributions of organic and elemental carbon. In addition, a reasonable size-segregated mass closure was achieved by combining data from thermal-optical analysis and ion-chromatography.

Analysis of the HASI accelerometers data measured during the impact phase of the Huygens probe on the surface of Titan by means of a simulation with a finite-element model

The Huygens Atmospheric Structure Instrument (HASI) [Fulchignoni, M., Ferri, F., Angrilli, F., Bar-Nun, A., Barucci, M.A., Bianchini, G., Borucki, W., Coradini, M., Coustenis, A., Falkner, P., Flamini, E., Grard, R., Hamelin, M., Harri, A.M., Leppelmaier, G.W., Lopez-Moreno, J.J., McDonnell, J.A.M., McKay, C.P., Neubauer, F.M., Pedersen, A., Piacardi, G., Pirronello, V., Schwingenschuh, K., Seiff, A., Svedhem, H., Vanzani, V., Zarnecki, J.C., 2002. The characterisation of Titan atmosphere physical properties. Space Sci. Rev. 104, 395–431] was a very complete instrument suite installed on board the Huygens probe, the planetary lander of the Cassini Huygens Mission to Saturn system, which successfully completed its mission in January 2005. HASI comprised a set of accelerometers, temperature sensors, pressure transducers and permittivity analysers aimed at the investigation of Titan atmosphere, which were fully operative during a several hour-long parachuted descent from an altitude of 157 km to planetary surface. Accelerometers were the only instruments activated earlier, just after Cassini separation, and recorded data during all the mission phases from atmospheric entry to landing, providing essential information for elaborating probe trajectory as well as Titan atmospheric profiles [G. Colombatti, et al. Reconstruction of the trajectory of the Huygens probe using the Huygens Atmospheric Structure Instrument, this same PSS issue]. Although not specifically designed for monitoring very fast dynamic events, HASI accelerometers have also recorded the trace of probe impact with the planetary surface, building up along with the data from Huygens Surface Science Package (SSP) instrument [ Zarnecki, J.C., Leese, M.R., Garry, J.R.C., Ghafoor, N.A.L., Hathi, B., 2002. Huygens Surface Science Package. Space Sci. Rev. 104, 593–611] the only set of direct measurements of the mechanical properties of the Titan soil. Though not considered secondary with respect to SSP data, HASI data provide peculiar information related to the dynamic response of the whole Huygens probe when impacting the surface, whereas the SSP data were collected mainly by sensors located on a small penetrometer below the main probe dome. Therefore, although having a sensibly lower sampling frequency, HASI Accelerometer Subsystem (ACC) data complete the information of SSP data in the study of impact deceleration profiles, which can provide key information for the estimation of the mechanical parameters of the soil and get an insight of its consistency and composition. In the analysis of Huygens mission data some unexpected features were present in the ACC data sets, so a dedicated study was needed to investigate the presence of dynamic interferences during an acquisition and correct the impact signature. The developed method is based on dynamic analysis of the impact through a three-dimensional finite-element dynamic model of the Huygens probe and the results lead to a corrected interpretation of accelerometer readings and provided an improved description of key aspects of the planetary landing. Although some aspects of probe's state after impact need some further analysis, as for final resting attitude which is to date not completely agreed on, this study disclosed that the probe experienced a vertical decelerating action which is compatible with two possible scenarios: the first one implies the penetration in a soft substrate material followed by a lateral bounce out of the generated hole and the second one suggests the displacement of pebbles from the surface into the soil. Numerical elaboration of impact data calculated a 12 cm penetration into the surface, which may have been experienced either by the lower dome of the probe or from pebbles that were situated under the dome when contacting the planet. In either case after a few seconds of motion the Huygens probe finally rested above Titan's surface with a negligible penetration. Since HASI piezo-accelerometer design was driven by the need of high full-scale values to monitor critical events during entry and descent phase, it was not possible to reconstruct horizontal motion after main deceleration phase without consistent uncertainties due to the poor overall accuracy in a low-acceleration range.

Microtribological behaviour of thin DLC films using different testing methods

AbstractTo enhance the lifetime and reliability of microcomponents, thin microtribological films are applied to microparts. With reduction of the component size, investigation methods for tribological testing must be adapted. This paper studies the microtribological behaviour of thin diamond‐like carbon (DLC) films using different testing methods. To tie in with macroscopic results, to determine friction we used the well‐known pin‐on‐disc test with spherical surfaces of 10 mm diameter under a typical load of 3 N. For investigations of the behaviour under single asperity contact, Atomic Force Microscope (AFM) methods with applied loads of a few hundred micronewtons were used. Investigations on thin DLC films showed that the friction coefficient under single asperity contact is strongly dependent on the applied load and the resulting contact area. Especially for thin films (up to a few hundred nanometres) the friction coefficient is influenced by the substrate material. With decreasing substrate Young's modulus the friction coefficient also decreases. On the other hand, an increase in the abrasive wear resistance was observed using soft substrate materials. In this paper we show that the friction coefficient was also reduced by a simple surface structure. For investigations we used photolithography to create concentric circles in different substrates. This resulted in a behaviour like riding on rails for the pin‐on‐disc test. Depending on the tribological pairing the friction coefficient was reduced to more than 50% of the original value. Copyright © 2006 John Wiley & Sons, Ltd.

2911 セグメント構造DLC膜の形状設計とトライボロジー特性評価(J21 表面改質とトライボロジー,2005年度年次大会)

Diamond-Like Carbon films (DLC films) show the excellent tribological properties. Therefore, many industrial applications are going on in variety of products. In these applications, DLC coatings on soft substrate materials are one of the problems. It is a fatal problem that deformation of substrate causes cracks and delaminations of DLC films from substrate. In this study, "segment-structured DLC coating" has proposed to solve this issue. Deformation behavior and tribological properties of segment structured DLC films are discussed from the results of 4-point bending test and ball-on-disk test, respectively. Finite element analyses of substrate deformation are also evaluated as compared with experimental results.

インデンテーション法におけるセラミックＴｉＮ薄膜の破壊機構解明とその強度評価

Micro-Vickers indentation tests in conjunction with acoustic emission (AE) monitoring were performed for TiN films deposited on three kinds of substrates, soft and hard steel by physical vapor deposition (PVD) method. We aimed to evaluate the intrinsic strength of thin films. In this study, three types of substrate with different hardness were employed. One was a WC-Co cermet, denoted as hard substrate, while the others were mild steel (SS400) and metastable austenitic stainless steel (SUS304), denoted as soft substrate. Equidistance step-wise terrace, or rippled cracks were observed and detected AEs only for soft substrates materials. Detected AE waveforms were analyzed using the polarity pattern in order to classify the cracking behavior. Most AEs detected were produced by Mode-I cracking with opening vector in the direction parallel to the film surface. Internal stress in the films was analyzed by the finite element method (FEM) to study the influence of substrates on the fracture mechanism. It was revealed that bending stress was developed by indenter penetration and it induced rippled crack initiation for the soft substrate materials. It was also found that the rippled cracks initiated at a certain distance of spacing. Using the FEM and the value of cracking space (Lc), we proposed the method to determine the bending strength of the thin films.

Tribological behavior of DLC coatings with functionally gradient interfaces

Initial evidence showed that soft substrate materials (such as Ti–6Al–4V alloy) might not be able to provide adequate support for hard DLC films, adversely affecting their tribological performance and durability. An innovative concept in the development of advanced tribological systems involves coatings with a functionally-graded interface (FGI). This concept was experimentally studied in the present work by developing a model system involving DLC coatings with FGI based on theoretical finite element analysis (FEA) predictions. It was found that the durability of the DLC film is affected by the presence of the FGI and the loading level. Under low loading, FGI has a small effect due to the limited yielding occurring in the substrate. Under high loading conditions, the presence of FGI produced significant improvements (∼80% increase in coating lifetime). In view of the FEA predictions, these effects can be attributed to reduction of the plastic zone size and prevention of yielding at the coating/substrate interface.