Experimental study of mechanical properties and scratch resistance of ultra-thin diamond-like-carbon (DLC) coatings deposited on glass

To improve the mechanical and tribological properties of glass, an ultra-thin diamond-like-carbon (DLC) coating of 2.2 nm thick was deposited on the surface of glass, using the linear ion beam deposition technique. The coated glass showed significant improvement in scratch resistance against severe damage, such as cracking, delamination, and chipping. To understand the mechanism, an experimental study was carried out. It was found that the major contribution to the significantly improved scratch resistance attributable to the compressive stress, which was yielded during the deposition process and resides in the coating, as well as the top layer of glass substrate.     

Tribology of Unfilled and Filled Polymeric Surfaces in Refrigerant Environment for Compressor Applications

The current study examines the tribological performance of polymer/metal contacts in the presence of refrigerant versus ambient air under conditions simulating refrigeration compressors. Ten different polymers were employed as potential compressor bearing materials; four unfilled polymers and six blended polymers. All polymers were tested against cast iron samples of RMS roughness 0.3--0.5 μm and representative testing was performed against aluminum alloy disks. Experiments conducted in R-134A refrigerant exhibited slightly favorable friction and wear characteristics compared to experiments conducted in ambient air. Moreover, all blended polymers have superior tribological characteristics to unfilled polymers and metals. PEEK and polyimide in both unfilled and blended forms exhibit minimal wear and do not adversely affect the metal disks. This study also shows that although coherent, uniform films were not produced under compressor-like conditions, as evidenced by scanning electron microscopy and energy dispersive X-ray spectroscopy, the tested polymers still have favorable tribological properties and are good candidates for tribological contacts in refrigeration compressors.     

Nanoindentation and nanowear study of Sn and Ni-Sn coatings

As potential high capacity anode materials for lithium ion batteries, the Sn and Ni-Sn alloy coatings have been investigated by many electrochemical researchers. However, their mechanical properties have not been extensively studied, despite the fact that such anode films may fail mechanically during service. Thus, in this study nanoindentation and nanowear tests have been performed. Nanoindentation tests reveal that the ability to carry the load dramatically reduces in the Sn coating after one charge-discharge cycle which makes the plastic strain accumulation in the copper substrate play a greater contribution to crack formation and propagation in repeated charge-discharge cycling. Upon the nanoindentation analysis, it also shows that the pores formed by lithiation/delithiation can easily collapse at low loads. Furthermore, nanowear tests explore that the damage resistance of the Sn-Ni alloy film significantly improves after one charge-discharge cycle but it decreases in the Sn film after the same charge-discharge cycle; this explains why the degradation rate of the Ni-Sn alloy is slow after the first charge-discharge cycle and why the high capacity is maintained in further cycling. The links between the mechanical characterization and the degradation in charge-discharge cycling are also discussed.     

Ability of quality controllers to detect standard scratches on polished surfaces

The production of polished metal surfaces addresses a large number of fields such as medical prostheses, jewellery or moulds. These surfaces are checked by people who rarely agree on the definition of the right geometry limit of scratches. The aim of this work is to study human vision of scratches. The first step was to produce calibrated scratches barely visible by the human eye on polished metal surfaces in order to define standard samples for polishing quality control. A nanoindenter with a Berkovich tip was used to produce these scratches. These standard samples were shown to polishing controllers. They were asked to perform a research task leading to the establishment of two thresholds that characterize the visualization of scratches: a visibility threshold as well as an acceptability threshold.     

In situ analysis of the fragmentation of polystyrene films within sliding contacts

Fracture processes of thin (10–100 μm) polystyrene films on PMMA substrates have been investigated within macroscopic single-asperity sliding contacts with rigid spheres. Using the resources of in situ contact visualization, the development of cracks has been analyzed under both elastic and plastic conditions for various values of the ratio of the contact radius to the film thickness. Under elastic contact conditions, damage mechanisms were dominated by the formation of a network of regularly spaced cracks at the leading edge of the contact. These processes were analyzed in the light of a fragmentation model based on contact mechanics simulations of the stress field induced within the cracked films. It emerged from this contact mechanics analysis that the mean spacing between adjacent cracks can be correlated to the strength of the polymer coating.     

Elasto-Plastic Contact of Rough Surfaces

An isothermal elasto-plastic asperity contact model is developed and presented in this paper, which deals with micro plastic flows of materials and the influence of the elasto-plastic deformation of materials on the behavior of contacting surfaces. The model is solved with the incremental form of a simplex-type algorithm. The von Mises yield criterion is used to determine the onset of the plastic deformation. The effectiveness and validity of the model are studied through analyzing a Hertzian contact problem. Substrate stresses are calculated and differences are observed. Furthermore, the contact pressure, real area of contact, and average gap of real rough surfaces under the elastic, elastic-perfectly-plastic, and the elasto-plastic contact conditions are numerically investigated and the results are compared.     

PEEK不同表面粗糙度与分形维数关系研究

为探究PEEK不同表面粗糙度与分形维数之间的关系,在触针式表面轮廓仪上测量PEEK不同表面的粗糙度并采集了其轮廓曲线和数据。运用分形理论随机过程的结构函数方法,分析轮廓曲线的分形特征,并计算出不同表面粗糙度的分形维数。利用SPSS统计软件对粗糙度和分形维数关系进行拟合并得到最佳的拟合模型。结果表明:分维可以作为一个独立的表征参量来表征粗糙表面的复杂程度和粗糙度水平;PEEK的分形维数与粗糙度存在单调递减的关系,粗糙度数值越大,分形维数值越小;通过分形维数值与粗糙度之间的关系式,在一定范围内,可以通过粗糙度值计算得出分形维数值。     

Tribological Behaviour of Polymeric Coatings: II. SCF‐Reinforced PEEK Nanocomposite Systems

This paper focuses on coatings based on poly(ether ether ketone) (PEEK) applied to metal substrates and their tribological investigation. Short carbon fibres (SCF), graphite, and 300 nm titanium dioxide (TiO₂) and zinc sulphide (ZnS) particles were used as filler materials for the PEEK. These filler materials and their combinations were found to have a significant influence on the tribological behaviour of the corresponding PEEK compounds. One of the compounds (PEEK6) was found, especially at higher temperatures and under higher normal loads, to be a good coating material showing superior tribological behaviour. For PEEK6, a specific wear rate and a coefficient of friction (COF) lower than those for the best commercially available PEEK compound (PEEK4) were measured. For specific test parameters, PEEK6 showed a COF of less than 0.1. The tribological results were also compared with those of a conventional sliding bearing material based on poly(vinylidene fluoride) (PVDF).     

Contact analysis of three-dimensional rough surfaces under frictionless and frictional contact

A methodology for surface and sub-surface stress calculation of nominally flat on flat rough surface contact has been developed. This methodology is applicable for both large area contact (Hertzian contact) and small area of asperity contact (point load contact) with and without surface friction. A total of nine rough surfaces are generated by the computer with specified standard deviation of surface heights, σ, of 0.3, 1.0 and 3.0 nm, and correlation length, β^*, of 0.1, 0.5 and 0.9 μm. Under the typical applied load at the magnetic head slider-disk interface, small numbers of contact points are obtained and the deformation is purely elastic. Since these contact points are scattered and isolated, asperity contact behaves like point load contact. As β^* becomes larger, more adjacent points will be in contact at a certain contact spot and this is especially true at small σ. All the cases of flat on flat rough surface contact yield maximum von Mises stress on and near the surface at both frictionless and frictional contacts; no local maximum occurs in the sub-surface. In general, the friction effect in the vicinity of contact point is to increase the stress magnitude, while outside this region it also alters the stress distribution. For a surface of small β^* and large σ at high load of 1000 times of the nominal pressure at the head-disk interface, the contact pressure reaches the hardness at a few contact points and plastic deformation takes place in the near surface.     

The Effect of Topography on Water Wetting and Micro/Nano Tribological Characteristics of Polymeric Surfaces

The effect of surface topography on the water-wetting nature and micro/nano tribological characteristics of polymer surfaces was experimentally studied. A plasma-treated thin polymer film and ion-beam-treated PTFE (polytetrafluoroethylene) were used as flat specimens. Thin polymer films were deposited on Si-wafer (100) by the parallel-plate plasma technique. The ion-beam-roughening treatment was performed to change the PTFE surface topography using a hollow cathode ion gun under different argon-ion dose conditions in a vacuum chamber. Micro and nano tribological characteristics, water-wetting angles and roughness were measured with a micro-tribotester, SPM (scanning probe microscope), contact anglemeter and profilometer, respectively. The plasma-treated thin polymer film and ion-beam-treated PTFE surfaces were rendered increasingly hydrophobic as a function of the treatment time. The wetting characteristics were strongly dependent on the micro-roughness and the sharpness of the asperities. The tribological characteristics on the nano-scale showed different results from those on the micro-scale. It was noted that the contact-size ratio, especially the ratio of the tip or ball to the average surface roughness at a standard cut-off length, should be considered for evaluating the micro- and nano-scale tribological test results.     

Nanoindentation and nanowear of extremely thin protective layers of C–N and B–C–N

Carbon nitride (C–N) and boron and carbon nitride (B–C–N) films, 1 and 3 nm thick, were deposited on magnetic disks by means of a complex treatment method involving plasma irradiation and CN or BCN reactive sputtering in nitrogen and helium mixed gas using two targets of h-BN and graphite. The properties of these extremely thin coatings were evaluated by indentation using an atomic force microscope and nanowear tests using a lateral modulation friction force microscope. The extremely thin B–C–N coatings show highest indentation hardness and good wear resistance properties. It is proposed that this is due to their graduated composition and interfacial properties.     

On the Relation of Load to Average Gap in the Contact Between Surfaces with Longitudinal Roughness

A computer simulation model for the contact between longitudinally-oriented rough surfaces has been formulated. This model closely duplicates the actual surf ace contact deformation behavior by taking into account the elastic interactions between the asperities. There were no assumptions made about the shapes, or any deformation behavior of the asperities, except for their obeying the laws of elasticity. The plastic deformations on the high asperity peaks were taken into account by setting a ceiling on their contact pressures at the material hardness value. The simulations used real surface profiles which were digitized from unworn circumferentially ground steel surfaces. Each pair of these profiles was mathematically combined to form an equivalent rough profile pressing against an infinitely rigid flat and having the appropriately adjusted elastic modulus. A total of 28 different pairs of profiles were used in the simulations. Each contacting pair was subjected to 30 different load levels and the local contact pressures and deformations were calculated. The contact simulations yielded some important mathematical relationships between parameters, such as the real area of contact, average gap, and average asperity load through statistical curve fitting. Two analytical functions were generated to relate the average load to average gap and the real area of contact to load.     

The Frictional Response of VC(100) Surfaces: Influence of 1-Octanol and 2,2,2-Trifluoroethanol Adsorption

In this report, we present ultrahigh vacuum (UHV) atomic-scale measurements of the frictional response of the VC(100) surface and the influence on friction through the adsorption of 1-octanol (CH₃(CH₂)₇OH) and 2,2,2-trifluoroethanol (CF₃CH₂OH). Atomic force microscopy (AFM) has been used to determine the changes in interfacial friction and adhesion, while scanning tunneling microscopy (STM) has revealed changes in surface morphology upon adsorption. X-ray photoelectron spectroscopy (XPS) has been utilized to determine the composition of the surface formed through the reaction of these adsorbates with VC. Adsorption of 1-octanol on the VC(100) surface at room temperature causes a 15% reduction in the friction measured between a clean VC surface and a silicon nitride AFM tip. STM images, combined with XPS results, reveal that 1-octanol does not completely cover the surface and that saturation occurs approximately at a 500L exposure. Adsorption of 2,2,2-trifluoroethanol on the VC(100) surface at room temperature produces a significant increase in friction while at the same time producing a decrease in adhesion. These contrasting results are interpreted in terms of differences in interfacial shear strength, chemical composition, and the molecular details of the adsorbed layer.     

Short‐Term Response of Human Osteoblast‐Like Cells on Titanium Surfaces With Micro‐ and Nano‐Sized Features

Since the way that human bone cells behave on contact with different surfaces topographies seems to be crucial to osseointegration, the aim of the present study is to evaluate the participation of some micro‐ and nanosized features of Ti surfaces in the short‐term response of primary human osteoblast‐like cells (HOC). Surfaces were prepared as ground (G‐Ti), hydrofluoric acid etched (HF‐Ti), and sandblasted/HF‐etched (SLA‐Ti), and analyzed using both three‐dimensional (3D) profilometer and atomic force microscope (AFM). Cell morphology was assessed using scanning electron microscopy (SEM) after 4 and 24 h in culture. Cell viability, adhesion, and spreading were also evaluated 4 and 24 h after seeding over each surface. Data were compared by analysis of variance (ANOVA) complemented by Duncan test. Cell morphology, cell counting, and membrane integrity (Neutral Red, NR) were not affected by surface treatment at any time. However, HF‐Ti presented the smallest surface area and did not increase tetrazolium hydroxide (XTT) reduction from 4 to 24 h. On the other hand, a higher level of spreading was only found on the rougher and isotropic SLA‐Ti at 4 h. In conclusion, although all evaluated Ti surfaces allowed HOC short‐term adhesion, the finer topography introduced by HF as single treatment did not favor HOC mitochondrial activity and spreading. The rougher and more complex SLA surface seems to provide a better substrate for HOC short‐term response. SCANNING 34: 378‐386, 2012. © 2012 Wiley Periodicals, Inc.