Nanoscratch Experiments Research Articles

Mechanical properties of electrochemically synthesised metal–organic framework thin films

We investigated the mechanical properties of metal–organic framework thin-film coatings grown by an electrochemical method, which allows fast deposition in environmentally friendly solvents. For the first time, Cu(CHDA) and Cu(INA)2 are electrochemically synthesised as dense coatings on Cu-electrodes, alongside the well-known Cu3(BTC)2 (CHDA = trans-cyclohexane-1,4-dicarboxylate; INA = isonicotinate; BTC = benzene-1,3,5-tricarboxylate). In order to probe the mechanical behaviour of the MOF coatings, both nanoindentation and nanoscratch experiments are performed. The indentation of a polycrystalline film allows the determination of average Young's moduli and hardness of the coatings. Cu(CHDA) exhibits the highest stiffness and hardness, with values of 10.9 GPa and 0.46 GPa, respectively. Intermediate values are obtained for the well-known Cu3(BTC)2 and the smallest values for Cu(INA)2. A close inspection of the crystal lattice of the MOF materials under investigation allows for correlating the mechanical properties and structural building units of these materials. Finally, the effect of the fundamental mechanical properties of MOF films on their scratch and wear resistance is illustrated.

Friction and wear performance of the 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 piezoelectric film

As a lead-free piezoelectric material with potential application, 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-0.5BCT) ceramics, which has a morphotropic phase boundary composition, deserves much attention due to its excellent ferroelectric and piezoelectric properties. BZT-0.5BCT lead-free piezoelectric film has been synthesized on a Si (100) substrate by Sol-Gel process. The topography of the film measured using an atomic force microscope and a scanning electron microscope shows that the surface of the prepared film is smooth, and the grain is in the shape of hemisphere with a diameter of 80-100 nm. The film is 1.7 μm in thickness, with pores inside. Friction experiments show that the friction between the tip and the piezoelectric film is much larger than that between the tip and the SiO2 substrate, because of the existence of electrostatic force between the film and the silicon tip. However, the friction coefficients obtained are approximately equal. Nano-scratch experiments show that the BZT-0.5BCT film has a high normal carrying capacity, but a poor tangential wear resistance. The average elastic modulus of the film is 23.64 GPa ± 5 GPa, and its hardness is 2.7-4 GPa, both being slightly lower than those of the bulk value in PZT ceramics.

Arsonic Acid Self‐Assembled Monolayers Protect Oxide Surfaces from Micronewton Nanomechanical Forces

AbstractThe development of new surface coatings is critical for combating wear and increasing the device lifetime in microelectromechanical systems (MEMS). Here, a class of arsonic acid self‐assembled monolayers (SAMs) is reported that form readily on oxide substrates including silicon oxide, borosilicate glass, and titanium oxide. Monolayers are easily prepared using a straightforward soaking technique, which is amenable to large‐scale commercial applications. Monolayer formation on borosilicate glass and titanium oxide is characterized using infrared spectroscopy. Monolayers on borosilicate glass, native silicon oxide and titanium oxide are evaluated with contact angle measurements, as well as wear measurements using nanoscratching experiments. On titanium oxide and borosilicate glass, monolayers prepared from hexadecylarsonic acid provide significantly greater surface protection than surfaces reacted under similar conditions with hexadecylphosphonic acid, a common modifying agent for oxide substrates.

Effects of probe tilt on nanoscratch results: An investigation by finite element analysis

The purpose of this paper is to investigate the effects of probe tilt on the results of nanoscratch by finite element analysis (FEA). In nanoscratch experiments, it is hard to assure absolute verticality between the scratch probe and the specimen. Simulation results show that different tilt cases of the probe have different extents of influences on the residual scratch profile, the projected contact area and the frictional coefficient of nanoscratch results. To get reliable results from the nanoscratch experiments, the verticality between the scratch probe and the specimen should be accurately guaranteed. On the other hand, the tilt phenomenon of the probe can also be used to obtain some wanted profiles.

Organic ultrathin film adhesion on compliant substrate using scratch test technique

Many adhesion test techniques have been developed to measure the adhesion energy of thin films but they are hard to implement in the case of submicron organic thin films deposited on a flexible substrate. Recently the feasibility and repeatability of the scratch test technique as a tool for testing the adhesion and the damage behaviour of ultra-thin films on polymer substrates has been demonstrated. However, direct comparison of the critical load between samples was not straightforward since different failure mechanisms were induced. In the present work, we have performed nanoscratch experiments on submicron thin films deposited on a flexible substrate. The use of a tip radius of 5μm enabled a unique delamination mechanism to be induced by localizing and maximizing the stress closer to the interface. We have observed an increase of the critical load on samples processed with an adhesive plasma treatment prior to thin film deposition, confirming the effectiveness of this treatment. We have also performed mechanical ageing tests on specimens and proved that the scratch test technique is sensitive enough to monitor the degradation of the interface properties. Finally, we have discussed some existing energy models. Taking into account some limitations, Laugier's model gives an upper bound for the adhesion energy.

Effects of mechanical contact stress on magnetic properties of ferromagnetic film

Mechanical and magnetic degradation of ferromagnetic films under contact stress was systematically investigated through novel experiments and analytical simulations. Permalloy (Ni80Fe20) film was deposited onto silicon substrate, and two different thicknesses of permalloy film (50 nm for sample A and 300 nm for sample B) were examined in this study. Magnetic properties were obtained from B-H loop tracer hysteresis measurement, while the mechanical properties (i.e., hardness and elastic modulus) were measured using nanoindentation techniques. It was observed that the 50 nm thick permalloy film showed weaker magnetic strength (lower coercivity and saturation magnetic flux values) and lower hardness than the 300 nm thick permalloy film. To apply mechanical contact stress on the permalloy film samples, nanoscratch experiments were performed using ramp and constant loading scratch profiles. Then, the resulting mechanical degradation (surface physical damage) of the two samples was determined from atomic force microscope measurements, and the corresponding magnetic degradation was analyzed using magnetic force microscope measurements. It was found that the magnetic degradation was more sensitive to the applied contact stress than the mechanical degradation. Comparing the two permalloy film samples, it was observed that the 50 nm thick permalloy film showed more magnetic degradation under the same contact stress, which could be attributed to its lower material strength.

The influence of surface microstructure on the scratch characteristics of Kevlar fibers

In this work, nanoindentation and nanoscratching experiments are combined with atomic force microscopy to investigate the relationships between contact geometry, apparent friction, and deformation modes of two grades of Kevlar® (Dupont) fiber—Kevlar KM2 and Kevlar 49. Changes in the relative angle between the scratching probe and the fiber surface, often termed as the attack angle, result in changes in deformation mode, which correlate with the changes in the apparent friction. As attack angle increases, the observed deformation modes of the fiber surface change from a smoothing of the surface, often termed as ironing, to fibrillation, in which the fibrils break and coalesce in front of the progressing probe. A mixture of these two modes occurs at intermediate attack angles. When fibrillation occurs, material pile-up forms in front of the progressing probe. This pile-up introduces an additional component to the frictional response that is largely responsible for an increase in apparent friction with an increasing attack angle and/or scratch length. The level of friction associated with fibrillation is measured to be up to approximately three times higher than previously reported for Kevlar yarn–yarn friction. Fibrillation of Kevlar KM2 occurs at larger attack angles as compared to Kevlar 49, which is believed to be related to a near-surface region of reduced modulus and hardness previously observed in KM2 fibers. A detailed discussion of the measured response is given based on the interactions between the scratching probe and the fibrillar network and the resulting deformation mechanisms.

Use of nanoindentation and nanoscratch experiments to reveal the mechanical behavior of sol–gel prepared nanocomposite films on polycarbonate

Sol–gel based UV cured hybrid coatings were prepared by combining different silanes with various urethane acrylate monomers. Effects of precursor concentration and inorganic to organic weight ratio were investigated. Nano indentation, nanoscratch and Taber tests were utilized to assess the behavior of the coatings. It was revealed that lower acrylic silane content and higher inorganic to organic weight ratios improved hardness, elastic modulus and scratch resistance. Increasing inorganic phase increased elastic modulus and hardness. Higher elastic modulus enhanced elastic recovery and scratch resistance of the films. Moderate level of hardness was found to perform better in abrasion resistance.

Investigation of mechanical and tribological properties of bone cement by nano-indentation and nano-scratch experiments

The mechanical and tribological properties of PMMA-based bone cement (CEMEX RX, TECRES Company, Italy) were measured using nano-indentation and nano-scratch tests. The polymer samples were prepared using two different mixing methods i.e., hand mixing and vacuum mixing. Cubic CEMEX RX specimens were produced and the nano-indentation and nano-scratch tests were performed on both the hand-mixed and the vacuum-mixed specimens by a nano-indenter setup and atomic force microscopy (AFM) observation.The values of Young's modulus, hardness and wear resistance obtained on the hand-mixed and the vacuum-mixed cements were compared. The results indicate that the vacuum-mixed cement has better mechanical and tribological properties compared with the hand-mixed one. Since the nano-indentation and the nano-scratch test methods need less sample material, decrease costs and obtain reliable results, they can be considered as suitable techniques for determination of the mechanical and tribological properties of bone cements.

The study of nanoscratch and nanomachining on hard multilayer thin films using atomic force microscope

In this study, nanoscratching and nanomachining were conducted using an atomic force microscope (AFM) equipped with a doped diamond-coated probe (DDESP-10; VEECO) to evaluate the fabrication of nanopatterns on hard, Cr₂N/Cu multilayer thin films. The influence of normal force, scratch speed, and repeated scratches on the properties of hard multilayer thin films was also investigated. The nanoscratch experiments led researchers to establish a probe preparation and selection criteria (PPS criteria) to enhance the stability and accuracy of machining hard materials. Experimental results indicate that the depth of grooves produced by nanoscratching increased with an increase in normal force, while an increase in the number of scratches in a single location increased the groove depth but decreased friction. Therelationships among normal force and groove depth more closely resembled a logarithmic form than other mathematical models, as did the relationship between repeated scratching and its effect on groove depth and friction. The influence of scratch speed on friction was divided into two ranges. Between 0.1 and 2 µm/s, friction decreased logarithmically with an increase in scratch speed; however, when the speed exceeded 2 µm/s, the friction appeared stable. In this study, multilayered coatings were successfully machined, demonstrating considerable promise for the fabrication of nanopatterns in multilayered coatings at the nanoscale.

Nano-scratching and nano-machining in different environments on Cr 2N/Cu multilayer thin films

Five nanostructured Cr 2N/Cu multilayer coatings were deposited by a bipolar asymmetric reactive pulsed DC magnetron sputtering system, and various bilayer periods (Λ) were achieved by controlling the holding time of Si substrates in the plasma of Cr or Cu. The hardness and elastic modulus of multilayer coatings were investigated by means of a nanoindenter. Nano-scratch and nano machining experiments on multilayered coatings were conducted using atomic force microscopy (AFM) in air and DI-water, respectively. According to the groove depth, width , and coefficient of friction (COF) obtained from nano-scratch tests, influences of scratch cycle numbers and bilayer periods on the scratchability of Cr 2N/Cu multilayered thin films were examined. It was observed that after nano-scratch experiments in air and water, the COF values and the amount of removed material increased with increasing bilayer period. After nano-machining tests in air and water, different types of the cutting chip pile-ups were observed. In this work, the surface tribological properties and machinability of Cr 2N/Cu multilayered thin films when using an AFM are discussed.

Microtribology: new tools to fill measurement gap

Microtribological experiments are currently becoming an important tool in the tribological practice by offering maximum experimental benefits with minimum technical complexity. In this perspective paper several microtribological case studies are presented to illustrate potential methodologies. Results are presented and discussed in relation to: nanoscratch and nanowear experiments, accelerated nanowear technique, nano-impact test and method of capturing topography and material phase features. Two commercially available systems are used in this study, namely, NanoTest Platform and MUST tester. A general classification of tribological techniques has been proposed distinguishing between classical tribometers, atomic force microscopy based techniques and microtribometers.

Experimental and FEA Scratch of Magnetic Storage Thin-Film Disks to Correlate Magnetic Signal Degradation With Permanent Deformation

Scratch-related magnetic signal degradation can occur during magnetic storage hard disk drive operations when the read-write heads contact the spinning multilayer disks. To investigate this phenomenon, controlled nanoscratch experiments were performed on perpendicular magnetic recording media using various indenters of different radii of curvature. Various loading conditions were used to cause permanent scratches that were measured using atomic force microscopy. The nanoscratch experiments were simulated using finite element analysis (FEA) that included the detailed nanometer scale thin-film multilayer mechanical properties. The permanently deformed field in the subsurface magnetic recording layer was extracted from the FEA results. The residual scratch widths measured on the surface of the magnetic storage disk were directly compared with the residual subsurface widths of the region on the magnetic recording layer, where extensive permanent lateral deformation was present. It was found that the subsurface widths of the deformed regions were significantly larger than the surface scratch widths. Thus, subsurface thin-film layers, such as the magnetic recording layer, could be damaged without observable damage to the protective top surface carbon overcoat. The exact location and extent of damage to the magnetic recording layer depends on the scratch load, size of scratch tip, and the friction at the interface. Such permanent deformation in magnetic recording layer could lead to demagnetization, which has been reported in the literature.

Tribomechanisms of pure electrodeposited Ni at ultra-fine and nanoscale level

Atomic force microscopy (AFM) and scanning probe microscopy (SPM) were used to study the surface topography of electrodeposited pure nickel with different grain sizes from ultra-fine to nanoscale level. Such technique, coupled with nanoindentation and nanoscratch experiments allowed to map the nano-tribomechanism acting on the same pure metal with different mechanical and topographical properties.

Mechanical performance of metallic glasses during nanoscratch tests

Nanoscratch experiments on four bulk metallic glasses using a pyramidal diamond tip (Berkovich) indenter have been carried out under different loads and scratching velocities. There exists a general correlation between the hardness and wear resistance, i.e., a lower hardness produces a lower wear resistance. Scratch velocity appears to have little effect on the scratch depths of the four alloys studied. However, faster scratch velocity leads to finer shear bands. Compared with ribbon sample with the same chemical composition, Ti-based bulk glassy sample that experienced slower cooling rate during solidification, and thus contained less free volume, exhibits better wear resistance.

Correlation between nanoindentation and nanoscratch properties of carbon nanotube reinforced aluminum composite coatings

Abstract Nanoindentation and nanoscratch experiments are conducted on cold-sprayed aluminum composite coatings reinforced with and without carbon nanotubes (CNTs). Analytical model is developed to correlate nanoscale mechanical and tribological properties of the solid material. The geometry factor of Berkovich tip and its orientation during nanoscratch is taken into account to describe the deformation behavior of the solid material underneath indenter. Nanoindentation and nanoscratch experiments in conjunction with the computed results illustrate that the addition of carbon nanotubes into aluminum matrix contributes to increase in elastic modulus, hardness, yield strength, shear strength and nanoscale wear resistance. The coefficient of friction is unaffected by the addition of CNTs up to 1 wt.%.

Nanoscratch behavior of carbon nanotube reinforced aluminum coatings

Nanoscratch experiments have been carried out on plasma sprayed aluminum alloy coatings reinforced with 0, 5 and 10 wt.% carbon nanotubes (CNTs). Scratches have been performed at loads of 1000, 2000 and 3000 μN load using Berkovich indenter. The contact and true wear volumes of the scratches have been calculated. The nano-scale wear resistance is shown to increase by 4 times by addition of 10 wt.% CNTs. Improvement in the wear resistance is discussed with respect to strengthening effect and increased elastic recovery by addition of CNTs. Direct evidence of increased recovery and small decrease in the coefficient of friction with CNT content is provided using the true and instantaneous depth plots and the corresponding scanning probe microscope and scanning electron microscope images of the scratches. Friction coefficient was found to be load independent and was found to vary slightly with the CNT content.

Characterization of Microplasma Sprayed Hydroxyapatite Coating

Microplasma sprayed (MIPS) HAP coatings on SS316L substrates were characterized by x-ray diffraction, Fourier transformed infrared spectroscopy, optical microscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), atomic force microscopy and image analysis. The coating showed a high degree of crystallinity ~92%, a high porosity level of 20 vol.% and a moderate bonding strength of about 13 MPa. The displacement controlled three-point bend tests and associated results of optical microscopy indicated that crack deflection, crack branching, and also local crack bridging occurred during crack propagation in the coating. The nano-hardness (H) and Young’s modulus (E) of the MIPS-HAP coatings as measured by nanoindentation technique were about 6 and 92 GPa, respectively. The fracture toughness (K ic) of the coating was ~0.6 MPa·m0.5. From the nano-scratch experiments, the critical normal load at which localized microcracking led to delamination was measured to be ~400 mN.

Analysis of nanoindentation and nanoscratch experiments of thin amorphous carbon coatings and multilayers: friction, wear and elastic – plastic deformation

Abstract The determination of mechanical properties of thin films is of crucial interest for applications of protective layers. Nanoindentation and nanoscratch experiments of diamond-like carbon coated (100) silicon surfaces under ambient conditions have been performed with a conical indenter on a Hysitron system, mounted on an atomic force microscope system. Single layers and multilayers with hard soft stacking were tested as well. Microhardness, friction and wear behaviour were determined with multi-indentations, single scratches and oscillating multicycles scratch. The indentation experiments revealed that critical force plastic deformation takes place. The oscillating multicycles scratch experiments determined the high wear resistance of the diamond-like carbon coatings. Multilayer systems were compared with single layer coatings.

Characterization and tribology of PEG‐like coatings on UHMWPE for total hip replacements

A crosslinked hydrogel coating similar to poly(ethylene glycol) (PEG) was covalently bonded to the surface of ultrahigh molecular weight polyethylene (UHMWPE) to improve the lubricity and wear resistance of the UHWMPE for use in total joint replacements. The chemistry, hydrophilicity, and protein adsorption resistance of the coatings were determined, and the wear behavior of the PEG-like coating was examined by two methods: pin-on-disk tribometry to evaluate macroscale behavior, and atomic force microscopy (AFM) to simulate asperity wear. As expected, the coating was found to be highly PEG-like, with approximately 83% ether content by x-ray photoelectron spectroscopy and more hydrophilic and resistant to protein adsorption than uncoated UHMWPE. Pin-on-disk testing showed that the PEG-like coating could survive 3 MPa of contact pressure, comparable to that experienced by total hip replacements. AFM nanoscratching experiments uncovered three damage mechanisms for the coatings: adhesion/microfracture, pure adhesion, and delamination. The latter two mechanisms appear to correlate well with wear patterns induced by pin-on-disk testing and evaluated by attenuated total reflection Fourier transform infrared spectroscopy mapping. Understanding the mechanisms by which the PEG-like coatings wear is critical for improving the behavior of subsequent generations of wear-resistant hydrogel coatings.