Scratch Properties Research Articles

Comparison between single and multilayered a-SiC:H coatings prepared by multi-frequency PACVD: Mechanical properties

Due to their low density and good mechanical properties, titanium alloys are commonly used to lighten structures in aeronautical applications. Unfortunately, their friction properties are poor due to titanium oxide layers which naturally occur. To confer to the surface both high mechanical resistance under load and low friction/low wear against other metals, amorphous silicon carbide (a-SiC:H) coatings are deposited on plasma treated substrates, using a multi-frequency plasma CVD device. The present study is devoted to compare scratch properties of single and multilayered a-SiC:H layers including up to 125 asymmetric periods of soft/hard coatings. Standard scratch-testing measurements reveals that the critical load corresponding to the formation of cohesive/adhesive cracks can be significantly increased (by a factor of 2.5) when using multilayered coatings. When optimized coatings are deposited, the substrate is not visible at the bottom of the flaked area until loads higher than 60 N are applied.

Alternative curing methods of UV curable automotive clearcoats

Alternative methods for curing UV curable clearcoats were characterized using confocal Raman microscopy, nano-scratch measurements, and dynamic mechanical thermal analysis (DMTA). Clearcoats were cured using a xenon flash lamp, fluorescent UV bulbs with various spectral power distributions, and a microwave powered lamp. Raman spectroscopy was used to track acrylate double bond conversion of the clearcoat after each method of curing. DMTA was used to correlate double bond conversion to crosslink density. Nano-scratch results showed scratch resistance to be sensitive to the surface cure state. A combination of the flash and fluorescent methods produced a degree of cure similar to that of the microwave powered lamp. Scratch tests showed that clearcoats with a similar surface cure state achieved using different curing methods effectively had equivalent scratch properties.

Viscoelastic effects on the scratch resistance of polymers: relationship between mechanical properties and scratch properties at various temperatures

Scratch durability of polymer surfaces and coatings is becoming critical for the increasing use of these materials in new applications, replacing other materials with harder surfaces. Scratch resistance of polymers has been the subject of numerous studies, which have led to specific definitions for plastic deformation characterization and fracture resistance during scratch testing. Viscoelastic and viscoplastic behavior during a scratch process have been related to dynamic mechanical properties that can be measured via dynamic nano-indentation testing. Yet, the understanding of the origin of the fracture process of a polymer during scratch remains approximate. Parameters like tip shape and size, scratch velocity and loading rate, applied strain and strain rates, have been considered critical parameters for the fracture process, but no correlation has been clearly established. The goal of this work is to define and analyze scratch parameters that relate to mechanical properties. The evolution of scratch resistance parameters as a function of temperature and strain rate, compared to the evolution of dynamic mechanical properties obtained from indentation and uniaxial tensile tests over a range of temperature for poly(methyl methacrylate) (PMMA) helped in identifying a correlation between the tensile stress–strain behavior and scratch fracture toughness. This correlation brings a new understanding of the origin of the fracture mechanisms during a scratch process. In particular, it is demonstrated that the characteristic strain applied by the indenter is a most relevant parameter to describe the fracture resistance during a scratch process, independently of the indenter geometry.

A new method for evaluating the scratch resistance of diamond-like carbon films by the nano-scratch technique

The nano-scratch technique was used as the method to evaluate the scratch resistance of diamond-like carbon films/Si composite systems. The nano-scratch behavior of DLC films on silicon substrates was analyzed to observe if this technique could be satisfactorily used for characterizing the scratch properties of DLC films. The experimental results showed that, during loading, the indent depth linearly increased with increasing normal load, up to the loading critical load (Lc L). After unloading, the films successively displayed fully elastic recovery, plastic deformation and delaminating processes with increasing load, and the unloading critical load (Lc U) was determined, which was less than Lc L in the present test. Therefore, the nano-scratch test not only obtained the cracking resistance (Lc L) characterizing the cohesion strength of films during loading, but also determined the Lc U related to the adhesion strength of the film and the substrate during unloading. As a result, the nano-scratch test was a suitable method to evaluate the scratch properties of DLC films/Si composite systems.

Scratch properties of poly(methyl methacrylate) surfaces: The time‐temperature dependence of friction and hardness

AbstractViscoelastic‐viscoplastic behaviour is usually not taken into account in models describing the scratch properties of polymeric surfaces. In the case of a standard indentation test with stationary tip, the elastic‐plastic boundary and the boundary of the region being subjected to hydrostatic pressure beneath the tip are understood. Such well‐known models have been used in this study to understand the geometry of the groove left on the surface of a viscoelastic‐viscoplastic body by a moving diamond tip. A new apparatus was built that can control the velocity of the tip over the range 1 μm/s to 15 mm/s, at several different temperatures from −10 to +100°C. The material used was a commercial grade of cast poly(methyl methacrylate) (PMMA). The normal and tangential loads and groove size were used to evaluate the dynamic hardness, which behaved like a stress‐ and temperature‐activated process. The values for the activation energy and volumes of the dynamic hardness and of the interfacial shear stress were in good agreement with the mechanical properties usually attributed to PMMA.

金属添加ＤＬＣ膜のスクラッチ特性

The scratching properties of DLC films containing various metals such as titanium, molybdenum and iron were investigated. These films were deposited on Si substrate by using magnetron radio frequency sputtering. High pure metal/graphite combined plates having area ratios of 1/8, 1/16 and 1/32, were used as targets in order to change the metal content of the film. The properties of the film were examined by means of a nano-indentation hardness tester utilizing an atomic force microscope, and an oscillating type scratch tester with simultaneous AE detecting.The main results are summarized as follows: (1) DLC films containing titanium and molybdenum show larger nano-indentation hardness on the average than that of DLC film without metal. In particular, titanium is an effective element to get higher hardness. On the other hand, iron contained DLC film shows lower hardness. (2) The critical loads on the scratch test are affected by species and contents of metals. Especially, the load of titanium contained DLC film deposited by using a target of 1/16 is nearly two times larger than that of DLC film without metal. (3) Observation showed that many parts of the DLC film without metal wave damaged during scratching, however, there were no damaged parts for titanium contained film due to a higher adhesive strength. (4) Addition of titanium to a DLC film tends to increase the fracture size of the film in the scratching due to enhancement of the films rigidity, and increase the films hardness.

Viscoelastic Effects on the Scratch Resistance of Polymers: Relationship Between Mechanical Properties and Scratch Properties at Various Temperatures

ABSTRACTScratch resistance of polymers has been the subject of numerous studies, which have lead to specific definitions for plastic characteristic and fracture phenomena during scratch behavior. Viscoelastic and viscoplastic behavior during a scratch process has been related to dynamic mechanical properties that can be measured via dynamic nano-indentation testing. Yet, the understanding of the origin of the fracture process of a polymer during scratch remains approximate. Parameters like tip geometry and size, scratch velocity and loading rate, applied strain and strain rates, have been considered critical parameters for the fracture process, but no correlation has been clearly established.The goal of this work was to analyze the scratch resistance and indentation properties of PMMA as a function of temperature. Compression and tensile properties from literature have also been compared to the scratch results for more complete understanding of the material's behavior.The analysis of the evolution of the properties of PMMA at various temperatures, along with the evolution of the fracture toughness during scratch with temperature and scratch velocity has helped in identifying a correlation between the tensile stress-strain behavior and scratch fracture toughness for PMMA. This correlation brings a new understanding of the origin of the fracture mechanisms during a scratch process, and the strain effect on the fracture strength of PMMA.

Time and temperature dependence of the scratch properties of poly(methylmethacrylate) surfaces

Most existing models describing the scratch properties of materials take into account forces acting at the interface between the material and a grooving tip, but do not consider the stress and strain properties of the material far beneath or ahead of the tip. In the case of polymer scratches, there are no models at all which take into account the viscoelastic viscoplastic behaviour of the material. In standard indentation tests with a non moving tip, the elastic plastic boundary and the limits of the region subjected to hydrostatic pressure beneath the tip are known. These models were used to analyse the geometry of the grooves left on the surface of a viscoelastic viscoplastic body by a moving cone-shaped diamond tip having a radius of about 40 μm. A new apparatus was built to control the velocity of the tip over the range 1 to 104 μm/s, at several different temperatures from −10°C to 100°C. The material was a commercial grade of cast poly(methylmethacrylate) (PMMA). The normal and tangential loads and groove size were used to evaluate the dynamic hardness, which behaved like a stress and temperature activated process. Values of the activation energy and volume of the dynamic hardness and of the interfacial shear stress were in good agreement with those usually attributed to the mechanical properties of PMMA.

Wear and mechanical characterisation on micro- to picoscales using AFM

Atomic force/friction force microscopy (AFM/FFM) techniques are increasingly used for tribological studies of engineering surfaces at scales ranging from atomic and molecular to microscales. An AFM with a suitable diamond tip can be used to measure microscratching/microwear and nano-/picoindentation behaviour of solid surfaces and thin films. AFM has also been used for nanofabrication/nanomachining purposes. Scratch and wear properties of a variety of materials have been measured. Mechanisms of material removal on microscales are studied. Wear precursors can be detected at early stages of wear using localised surface potential measurements. Localised surface elasticity maps of composite materials with penetration depths of less than 100 nm can be obtained. Nanoindentation hardness and Young's modulus of elasticity can be measured with a depth of indentation as low as 1 nm. Scratching and indentation on nanoscales are the powerful ways to screen for adhesion and resistance to deformation of ultrathin films. These studies provide insight into failure mechanisms of materials and thin films. Furthermore, in situ surface characterisation of local deformation of materials helps to develop better understanding of fracture mechanisms and the brittle to ductile transition in materials. These studies are directly applicable to interfacial phenomena of microdevices and magnetic storage devices.

Preparation of Hard Coatings on Polycarbonate Substrate by High Frequency Ion Beam, Deposition using CH4/H2 Gases

ABSTRACTPolycarbonate is one of the most widely used engineering plastics because of its transparency and high impact strength. The poor wear and scratch properties of polycarbonate have limited its application in many fields. In order to improve the wear and scratch properties of polycarbonate we have deposited diamond like carbon (DLC) coatings. The diamond like carbon coatings were made using a high frequency ion beam gun by introducing H2 and CH4 gases. The coatings were characterized with scanning electron microscope, Raman spectroscopy, ellipsometer, and microscratch tester. Polymer hard coating was applied onto the polycarbonate substrate before depositing a diamond like carbon coating to see the effect of interlayer on the system's failure mechanism.

Mechanical characterization of Ormosil films on plastics: Young's modulus determination by three points bending

A protective layer has been deposited to improve the scratching properties of polycarbonate organic glasses. The starting solution consists of a mixture of organosilicon compounds, silicon alkoxides or silica colloidal solutions. The deposition is carried out using the dip coating technique. The thickness is about 2–5 µm for the film and 1 mm for the substrate.

On the chemical and mechanical properties of sputtered silicon nitride films

Selected chemical and mechanical properties of sputtered silicon nitride films have been studied as a function of deposition conditions. The presence of water vapor in the deposition chamber affects the properties of silicon nitride. This dependence on the chamber conditions can be significantly reduced by ion bombardment of the film during growth. Ion bombardment is thought to preferentially remove residual hydrogen, thus densifying the material. The extreme sensitivity of the etch rate of silicon nitride to relatively small amounts of oxygen present during deposition is demonstrated. When the network connectivity is systematically changed, by the controlled incorporation of hydrogen into the material, the etch rate of the silicon nitride films is shown to correlate with its mechanical wear and scratch properties.

High-rate sputter deposition of SiO2 and TiO2 films for optical applications

This paper describes a process to produce SiO2 and TiO2 films at high rates of deposition by using chemically reactive gases (etch gases). Experiments were conducted using Cl2, CCl4, CCl3F, CClF3, and H2 mixed individually in Ar and O2 plasma in a magnetron sputtering process. Oxide films were deposited on glass and Si substrates from sputter-etching of Si, SiO2, Ti, and TiO2 targets. An attempt was made to understand the mechanism involved in the increased rate of deposition. The results showed that considerable enhancement of the rate of deposition was obtained for SiO2 and TiO2 films when sputtered from their pure elemental targets. The enhancement in the rate of deposition ranged between 5 and 30 times over that obtained in a conventional reactive sputtering process. The analysis of the process during sputtering indicated that deposition was accompanied by the formation of volatile chlorides resulting from the chemical etching of the targets. In most cases the coatings had refractive indices close to those of the bulk SiO2 and TiO2, the films were clear and had good resistance to scratching. However, at high concentrations of the etch gases, the optical and scratch properties of the films deteriorated.