Single Scratch Tests Research Articles

Moisture Effects on Gold Nanowear

ABSTRACTThe addition of water results in the higher wear rate of gold compared to experiments performed in the ambient environment (approximately 60% humidity). This higher wear rate in water has been observed with the AFM, Hysitron Triboindenter, and additionally in single pass scratch tests performed with the Taber Shear/Scratch tester. These tests were preformed using silicon nitride cantilevers on the AFM and a conical diamond tip in the Taber instrument. Tests performed in the ambient atmosphere resulted in slightly reduced surface roughness, while much higher wear rate was observed in the wear tests performed in water. Ambient scratch tests produced slightly shallower scratch trenches than wet scratches consistently as a function of the varied normal load. Single scan lines provide valuable information about the mechanisms and progression of the nanoscale wear. The different components of scratch friction are investigated to explore the main contributors to the nanoscale scratching of gold.

Theoretical Analysis and Experimental Verification of Triangular Fracture Defects of MgO Single Crystal Substrate in Lapping or Polishing Process

MgO single crystal is mainly used as substrate for high temperature superconductor film. Surface quality of MgO substrate has significant effect on the function of high temperature superconductor film. MgO single crystal is a typical hard and brittle material, and is easily cleaved along the {100} face, so some defects are always generated on the substrate surface while lapping and polishing, which badly affects the surface quality of the substrate. In this paper, a kind of typical defect, the triangular fracture defect which is on the substrate surface after lapping and polishing, is analyzed in detail. According to the structure characteristics of the MgO single crystal, and based on the dislocation reaction theory, a formation mechanism of the triangular fracture defect in lapping and polishing processes is explored. Through the single grain scratch test in different directions on the polished surface of MgO{100} single crystal substrates, the formation mechanism of triangular fracture defect in lapping and polishing processes is verified. And during the scratch test, the plastic flow of the MgO single crystal material beside the scratch was observed.

Study on the local damage mechanisms in WC-Co hard metals during scratch testing

AbstractThe effect of the cobalt content and WC grain size on the deformation behaviour of WC-Co hard metals was investigated by studying materials with a varying WC grain size and cobalt content. The WC grain size ranged from 2.65 to 0.25 µm and the binder content ranged from 6 to 15 wt%. Single and multiple scratch tests were conducted using a Nano indenter with a Berkovich diamond tip and the load ranged from 5 to 500 mN with a tip sliding velocity of 10 µm/s. Several damage mechanisms were observed and these show a combination of ductile and brittle wear. The bulk properties i.e. composite properties of the hard metal determine the wear in the 6 wt% Co samples on the other hand the 15 wt% Co samples exhibited a localised response to the wear i.e. the wear is determined by the individual phases in the hard metal.

Correlation between adhesion and wear behaviour of commercial carbon based coating

Adhesion and wear behaviour of hard coatings are two important properties that concern researchers. We need to use different tests to obtain these two values and the correlation between adhesion and wear is not always obvious. The purpose of this paper is to find the relationship between the wear rate and the critical load for commercial hard coatings. Commercial carbon based coatings were deposited on M42 high speed steel by magnetron sputtering. Different lengths of pre-sputtering time were used to change the properties of the coatings. Single pass scratch tests and multi-pass bidirectional wear tests were used to obtain the critical load and wear rate values, respectively. Results showed that there was a correlation between wear and adhesion. It was found that adhesion increases, and wear rate decreases when the pre-sputtering time increases. It was also observed that adhesion strength varies with pre-sputtering time in a step function manner. To a large extent, the adhesion behaviour is related to the wear behaviour as far as the commercial carbon based coating is concerned. However, as different coatings have different microstructure and properties, further work should be done to decide whether a similar relationship can be applied in other cases.

Abrasion response and abrasion–corrosion interactions for a coated biomedical stainless steel

A simple screening test has been developed to assess the suitability of surface coatings to protect the femoral articular surfaces of Ortron 90 total hip replacement (THR) prostheses from abrasion damage. A detailed comparison was conducted of the dimensions of scratches on explanted Charnley (Ortron 90) femoral heads and those of scratches produced on polished Ortron 90 barstock (of similar hardness) in the laboratory using a Rockwell C indenter and a range of static loads. From this comparison a load of 0.5 kg was found to give similar scratch depths ( D) and lip heights ( H) to the upper limits of scratches on the explants. Additionally a “multi-scratch” grid of two sets of five intersecting scratches (giving 25 scratch intersections) was used to simulate the multi-directional nature of in vivo abrasion damage. Commercial titanium nitride (TiN) and diamond-like carbon (DLC) coated Ortron 90 samples were subjected to this multi-scratch test in addition to single scratch tests. Adhesive and cohesive coating failures were observed at some of the scratch intersections for all of the coatings except the magnetron sputter deposited DLC coating which showed only through-coating fracture. These adhesive and cohesive failures were also observed in single scratches but at higher loads. Corrosion testing of the coated samples showed that the multi-scratch grid introduced additional sites at which substrate corrosion could take place.

Friction characterisation of polymers abrasion (UHWMPE) during scratch tests: single and multi-asperity contact

An understanding of abrasion resistance and the associated surfaces deformation mechanisms is of primary importance in materials engineering and design [Wear (1998)]. Instrumented scratch testing has proven to be a useful tool for the characterisation of the abrasion resistance of material. Although most studies on scratch resistance have been conducted for metals, assuming a purely plastic behaviour, recent studies focus on the effects of elastic and visco–elastic–plastic behaviour on the scratch mechanisms [Tribol. Int. (1998)]. In this study, normal and tangential scratch forces are measured during the scratch experiments using various indenter geometry and abrasive paper, under various temperature conditions (263–293 K). To complete the characterisation of the scratch process, three-dimensional topography of the scratched surface is measured. The comparison between single point scratch and multi-asperity abrasion testing is made possible thanks to morphological analysis of the abrasive paper topography. The single point scratch tests provide a good understanding of the effect of the contact geometry and temperature on the friction coefficient. These results are then used to explain the evolution of the friction coefficient obtained with two abrasive papers under various temperature and load conditions.

Evaluation of the scratch resistance with nano‐ and multiple scratching methods

The scratch resistance of automotive clear coats was investigated by a single and multi scratch test procedure. New data characteristic for the reflow capability, the scratch hardness and the lateral scratch resistance were generated and evaluated. A correlation between single and multi scratch data was established.

Abrasive wear properties of Cr–Cr 3Si composites

A series of composites based on the Cr–Cr 3Si system, and containing between 50 and 100%Cr 3Si, were fabricated by hot pressing. These composites have high stiffness, good thermal conductivity, excellent chemical resistance, and high temperature creep and oxidation resistance, making them potential candidates for hard-facing applications and cutting tools in harsh environments. In this study, the Cr–Cr 3Si composites were abrasion tested at ambient temperatures in order to evaluate their wear properties. Single scratch tests were performed to give insight into material removal mechanisms. Although like most metal silicides, these materials behave in a brittle manner, the results of this study indicate that the addition of a ductile second phase (Cr) can enhance both their fracture toughness and abrasive wear resistance. The addition of 10% of the rare earth oxide Er 2O 3 improves the density of the composite, but has no apparent influence on the wear resistance.

Influence of Tipradius and Substrate on the Nanotribological Characterization of Thin DLC Coatings

ABSTRACTIn this work diamond-like carbon films deposited via plasma enhanced chemical vapor deposition with a thickness of 250nm on different substrates are characterized by nanoindentation and microscratching in combination with scanning probe microscopy. The substrates (SU8 photoresist, quartz glass, Si(100) and AlTiC ceramic) provide a wide range of combinations between film and substrate properties. The experimental configuration allows the testing of samples with loads between 1μN and 10mN and a high local resolution. The tribological response of the various film/substrate systems is analysed in two different ways. A single scratch test with linear increasing load and an oscillating wear tests at constant loads is used. The tip radii of the conical diamond tips utilized vary between 0.6 and 6μm. Both, the substrates as well as the tip radii, show a significant influence on the tribological behavior of the systems.

A new electrochemical technique to study tribocorrosion at the micrometric scale

A new method to investigate the tribocorrosion properties of metals and alloys has been developed with which the current density of a metal probe in an electrolyte under rubbing conditions can be measured. The electrochemical microcell consists of a microcapillary (inner diameter 0.84 mm); the rubbing partner is an Al2O3 tube which rotates inside the microcapillary. Rotational speed, load and applied electrical potential can be varied, so that it is possible to analyse the corrosion rate during rubbing under various controlled conditions. With conventional tribocorrosion machines (e.g., pin-on-disc, ball-on-plate rig) and also with single-scratch test machines, the current measured also derives from surface areas which are not undergoing mechanical wear. In the present method, the activation of specific surface areas under rubbing conditions, and subsequent repassivation, can be studied separately.

Effect of environmental embrittlement on wear resistance of alloys in corrosive wear

The wear resistance of alloys in corrosive medium always becomes worse, when the environmental variables, such as evolution of hydrogen from acidic media, certain content of chloride in acid solution and polluted sea water, etc., are sensitive to rupture of alloys. An unusual high removal rate of alloys could not be explained only in terms of chemical aggression. An energy criterion of surface embrittlement of alloys has been investigated by means of single pendulum scratch test. Specific consumed energy (SCE) (energy loss per groove volume during an impact scratching) is suggested for evaluating environmental embrittlement. Hydrogen-induced embrittlement wear of HSLA steel and Ti alloy, Cl − impelling embrittlement tear of stainless steel, surface embrittlemental wear of copper alloys in sea water polluted by S 2− and NH 3 and Ni–P electroless coating in alkaline solution have been described.

Determination of dynamic mechanical properties of metals from single pendulum scratch tests

This paper describes evaluations of dynamic mechanical properties of typical metals (Al, Cu, Ti, Ni, Co, and Mo) with single pendulum scratch tests. The curve fitting method with a polynomial has been used to calculate the geometrical parameters of the scratch track during the scratching process. The methodology and analytical modeling are developed for determining a series of mechanical properties, such as elastic modulus, shear modulus and cohesive strength of materials, with the help of calibrations to those of these metals. These parameters are effective to describe the dynamic mechanical properties of massive materials and modified surfaces of materials. Using these methods, the mechanical properties of plasma sprayed Ni–ZrO 2 coatings are determined.

Fractional design of experiments applied to a wear simulation

A multidisciplinary approach to wear simulation to investigate rolling-sliding abrasion is described. Wear is a stochastic process where fatigue combines with abrasion, adhesion and corrosion. Statistical methods were found to be highly suitable for conceiving and analysing laboratory simulation of the wear process. A special procedure of so-called two-level complex design of experiments is described. By the way of an example, a fractional experimental design is presented showing a procedure for simulataneous evaluation of the influence of force, temperature, material and sliding on abrasion of rolling mill tool materials. A set of laboratory treatments was conducted via two-disc testing and single-scratch testing. The results, including analyses of the wear track via profilometry and metallography are described. Wear phenomena are discussed from statistical, mechanistic and microstructural viewpoints. The heterogeneous polycrystalline materials exhibit inherently stochastic attributes. The additional factors causing the dispersion in the measured wear rate were the technical characteristics of the laboratory devices. However, by virtue of the statistical design of the experiments and subsequent analyses, these variations were monitored, and the main effects and interactions, characterising the abrasive wear, were satisfactorily diagnosed.

Scratch testing of advanced composite surfaces

The friction and wear characteristics for AS4/3501-6 composites were tested via single scratch tests by a Vickers diamond indenter. Variables for the tests were the orientation of the surface ply fibers with respect to the scratch direction and the normal load applied to the indenter. The scratch velocity was held constant at 0.89 mm/s. The orientation of the fibers in the surface ply had little effect on the coefficient of friction. The normal load also had little effect on the value of the friction coefficient, but at higher loads, the data showed less scatter than at lower loads. The wear profiles for the scratches were shown to be very random, both from scratch to scratch, and within each furrow.

Effect of carbide orientation on abrasion of high Cr white cast iron

Wear resistant, high chromium white cast irons contain high volume fractions of M 7C 3 type carbides, which grow as rods and blades during solidification to produce a highly anisotropic microstructure. In this study, the effect of carbide orientation on the wear properties of these alloys is examined using both a high-stress pin-on-drum abrasion test and a single scratch test. It is found that when the carbides are oriented with their long axes perpendicular to the wear surface, abrasion resistance is considerably reduced. When the long axes of the carbides are parallel to the wear surface, the cast irons are more wear resistant, and the alloys show the least wear when the long axes of the carbides are parallel to the wear surface and oriented perpendicular to the wear direction. Scanning electron microscopy reveals that fracture of the carbides depends upon the orientation of the carbides with respect to the wear surface and the wear direction.

Impact abrasive behavior of SiCp/2024Al composites in single pendulum scratch testing

Impact abrasive behavior of SiCp/2024Al composites has been investigated using a single pendulum scratch device. The results show that most of the composites exhibit better abrasive resistance than the unreinforced matrix alloy except the one containing 15 vol.% particles of 20 μm in size. The impact abrasive resistance of the composites increases with decreasing particle size and increasing volume fraction. The matrix alloy presents a thin softened layer immediately under the scratch bottom, succeeded by a hardened one for greater depth. The scratching process of the composites containing large particles was that the surface particles were compressed into a surface layer, shocked fragmentally or debonded from the matrix at interfaces, and finally pulled out. For composites containing small particles, the particles could coordinate with the matrix in deformation and were subjected together with the matrix to being ploughed, cut and finally removed.

Numerical Simulation of Fracture in Coated Brittle Materials Subjected to Tribo-Contact

Manufacturing processes used to deposit hard coatings often produce cracks which reside within the coating, at the interface, or in the substrate. These cracks originate from material defects and thermal expansion mismatch. When subjected to stress (from solid body contact) the cracks can act as flaws which initiate and/or propagate subsequent fracture contained entirely in the coating, substrate, interface, or combinations thereof. The finite element method has been used in conjunction with a numerical interface fracture mechanics model to investigate the structural response of coated brittle materials subjected to normal and shear loads (tribo-contact). Residual stresses from depositing TiC onto a WC-TiC-TaC-Co substrate were superimposed with loads that simulate a single point scratch test. Experimental observations of metallographic cross sections, taken through scratched TiC films, were used for verification and guidance in modeling. This study has examined how flaw orientation affects crack propagation through the coating, interface, and substrate. The importance of interface fracture toughness and anisotropy in coating mechanical properties are discussed in light of wear particle formation.

Repassivation of 304 Stainless Steel Investigated with a Single Scratch Test

Abstract Reformation of the passive film on 304 stainless steel (UNS S 30400) was investigated with a scratch test. Regrowth of the passive film was measured by recording the current that resulted from forming the scratch. Charge consumed during the reformation of the film was compared to wear produced by the scratch. The current density from an incremental area of the scratch was extracted from the measured current transients using the width of the scratch as a function of time. The maximum current density and the charge density were dependent linearly on the area fraction of bare surface. Other parameters used in the model of current transients did not change as the area fraction of bare surface changed. Results showed the passive film remained adherent to the surface of the stainless steel during the rubbing mode of wear.

Wear and scratch hardness of 304 stainless steel investigated with a single scratch test

The wear and scratch hardness of 304 stainless steel was investigated with a scratch test developed by the US Bureau of Mines. The scratch was produced by a diamond indenter with a 0.2-mm spherical tip in air and in a corrosive environment. Scratch hardness was calculated from the width of the scratch and was correlated with Vickers hardness. Wear was measured by integrating the area between the profile of the scratch and the original surface. At low loads wear occurs in a rubbing mode. At higher loads wear debris was formed. The transition from rubbing wear to wear with a continuous formation of debris occurred at a critical value of the attack angle. A relationship between the attack angle, the radius of the tip of the scratcher, the load on the scratcher, and the hardness of the material is presented. Stainless steel was scratched at an anodic potential (with a passive film on the surface) and at a cathodic potential (with no passive film on the surface). The presence or absence of the passive film had no effect on the scratch hardness or wear for either the rubbing mode or the mode of wear with debris. The interface shear strength was not affected by the change in potential.

Tribological studies of various magnetic heads and thin-film rigid disks

Tribological characterization of three different magnetic heads (Mn-Zn ferrite, CaTiO 3 and Al 2O 3-TiC) and two different magnetic storage thin-film rigid disks have been made. The abrasive wear characteristics of the two disks (only differing in protective overcoat; diamond-like carbon and yttria-stabilized zirconia, respectively) have been investigated using a precision dimple grinder in order to grind small and well defined wear scars on the disks. The scratch response of the magnetic heads and the rigid disks have been studied using a single tip scratch test equipment in situ in the scanning electron microscope. Finally, the friction characteristics of the six possible magnetic head/rigid storage disk couples have been tested using in situ sliding tests in a scanning electron microscope. The results from the abrasive test show that one of the disks (with a diamond-like carbon overcoat) only displays abrasive wear, while the other disk (with a zirconia overcoat) besides abrasive wear also displays extensive spalling of the magnetic coating. The scratch tests show that for all three magnetic heads the friction coefficient increases rapidly with increasing normal force until a constant value, independent of the normal force applied, is reached. For the two disks, the friction coefficient increases with increasing normal force within the entire normal force interval investigated (0–0.5 N). The in situ friction tests show that, for a given head material, sliding against the disk with the zirconia overcoat yields lower friction than sliding against the disk with the diamond-like carbon overcoat. It was also found that, for a given disk material, the Al 2O 3-TiC head yields the highest friction. All heads, with the possible exception of the Al 2O 3-TiC head, were found to be virtually unaffected by sliding against the disks. Further, it was found that scratching of the disks occasionally occurs for the following head/disk combinations: CaTiO 3/diamond-like carbon overcoat, Al 2O 3-TiC/diamond-like carbon overcoat and Al 2O 3-TiC/zirconia overcoat.