Cutting precision is extremely affected by a phenomenon known as built up edge (BUE) that occurs on tungsten carbide tools during low cutting speed of aluminum alloy. BUE is responsible for early tool breakage due to excessive material build up from the machined part on the cutting face, leading to problems of shape irregularity and tool-tip breakage. Thus, diamond-like carbon (DLC) was deposited and tested to verify cutting precision in aluminum alloy by using tungsten carbide tools. The characterizations of the film were morphology analysis through scanning electron microscopy (SEM), structural atomic analyze of chemical bond from Raman backscatter spectroscopy, the distribution of carbon atoms on the film surface by X-ray photoelectron spectroscopy (XPS), and the evaluation of Young’s modulus and hardness using the Oliver–Pharr method. To analyze the cutting precision, drilling tests were performed on coated/uncoated drills at two cutting speeds (340 and 430 m/min). As an evaluation parameter in the aluminum alloy, the hole diameter deviation was measured after pre determined numbers of drilling operations. Statistical comparisons between the diameter deviation as a function of the number of drilling test indicated better cutting accuracy for the DLC-coated tool. The factors identified in this work, such as the reduction of the friction coefficient, and the hardness and Young’s modulus of the DLC helped in the performance of the tool, mainly in the lower cutting speed.

Polycrystalline diamond compacts (PDCs) are the main cutting unit of drill bits and are a major factor in determining the drilling efficiency and service life of drill bits. Drill bit failure is caused by the severe abrasive wear it undergoes during the drilling process. The drill bit failure can prolong the drilling period, which can result in borehole instability and cause collapse in the material. A solution that can address this issue is developing an appropriate drilling method that can expel the dust in a manner that will not increase the abrasive wear on the drill bit. Here, an Amsler friction and wear-testing machines was used to investigate the friction and wear characteristics of PDC and to study the effects of the dust expelled during drilling on the wear performance of drill bits under dry air and wetting conditions. The microstructures of the worn surfaces were examined by a scanning electron microscope (SEM) and metalloscope. In addition, the chemical compositions of the PDCs' surfaces were analyzed using X-ray diffraction (XRD) after the wear and friction tests. The results demonstrate that the friction coefficients and wear rate obtained in dry air were higher than those under wetting conditions. As expected, these values are mainly ascribed to the absence of the absorber layer and lubrication under dry air. Furthermore, under wetting conditions a number of cracks were observed on the PDC surface after testing at 700 °C, which was mainly caused by two factors: The different thermal expansion coefficients between the diamond and Cobalt phase; and the residual stress generated inside the PDC under wetting conditions.

This work focuses on the tribochemistry of molybdenum dithiocarbamate (MoDTC) oil additive to improve friction behavior of diamond-like-carbon (DLC) coated systems lubricated in boundary regime. Raman microscopy has been used to investigate surface tribolayers formed on coated (hydrogenated a-C:H and non-hydrogenated ta-C) and steel surfaces when lubricated with model lubricants and commercial engine oils. The effect of the additive package and the type of DLC played a crucial role in the development and composition of the tribolayer and the friction performance. The additive package contained in the fully formulated (FF) oils limited the friction reduction capabilities of MoDTC additive for every material pair. Accelerated a-C:H coating wear related to MoDTC tribochemistry was found. For the first time, it has been shown that a distinctive MoS 2 -containing tribolayer can be formed on the ta-C surface, leading to a coefficient of friction lower than 0.04. The underlying mechanisms of MoDTC/surface interactions and their effect on friction and wear are discussed.

Lapping is still an efficient and economical way in diamond shaping process, which is important in both industrial and scientific applications. It has been known that the material removal originates from the phase change or amorphization of diamond crystal carbon atoms that are chemically activated by stress, forming a top layer of amorphous carbon atoms. In this paper, the phase change of amorphous carbon atoms undergoing the nanocutting of amorphous layer during diamond lapping process is studied by molecular dynamics (MD) simulation. Two regions, the debris layer and cutting surface underneath, are studied. In the debris layer, the change of sp 2 carbon atoms is directly affected by impact, while underneath the cutting surface the changes of carbon atoms are almost not affected; the change speed of amorphous carbon atoms is higher than that of pristine crystal ones; the main phase change is transformation of sp 3 into sp 2 ; cutting depth to different extent affects the phase changes of sp 3 and sp 2 carbon atoms. Our study expands the understanding of diamond lapping process.

An effort was made to study and characterize the tribological characteristics of diamond nanoparticles as compared to neat mineral oil in the presence of sliding contact typically observed in the standard ASTM D4172 four-ball test. Four-ball tests were conducted with a solution of diamond nanoparticles and mineral oil, both at varying run times and bulk oil temperatures, and a consistent reduction in wear rates was observed. Numerical simulations were performed; it was observed that by enhancing the thermal conductivity of the lubricant, the wear reduction rate was observed to match the diamond nanoparticles solution results remarkably. This effort provides evidence that this additive wear reduction is in part caused by reduced lubricant temperatures due to the enhanced conductivity of the diamond.

Even when the charging of lapping plates can extensively influence their subsequent finishing performance, the subject has been scarcely treated in specialized literature. The present paper aims to help fill such a gap and gain a better insight of the charging process. A semiquantification of the diamond particles integrated into the lapping plate surface as a function of charging time was performed by Raman spectroscopy and scanning electron microscopy, together with a simple image-analysis procedure. The corresponding evolution of surface rough features was followed from atomic force micrographs with the aid of fractal-analysis tools. It was observed that charging proceeds in two stages, both with different rates of diamond particle integration. This leads to a significant waste of diamond slurry. During the first stage, the charging ring seems to preferentially promote a further flattening of the lapping-plate surface. Diamond particles are apparently more readily incorporated into such “flattened” regions during the second stage. The results suggest a specific topographic condition must be attained before the diamond can be efficiently integrated into the lapping plate surface. A lapping-plate preconditioning step could help improve this situation and reduce the amount of abrasive waste during charging.

Spring constants and damping coefficients of a thin lubricant bridge of a perfluoropolyether (PFPE) lubricant intervening between a diamond probe tip and a diamond-like carbon (DLC) surface of a magnetic disk are identified through regression analysis of tip damping vibration. PFPE lubricants with functional end groups were used to form a lubricant bridge between the DLC surface and a probe tip with a notably small curvature radius of 0.1 μ m . The tip was both retracted from and extended toward the disk surface at four different progressive distances to attain varied elongation of the bridge. It was also vibrated at each step to provide damping waveforms. By applying regression analysis to the observed waveforms, the spring constant and the damping coefficient of the lubricant bridge were identified within an elongation range from 50 nm to 800 nm . Spring constant of the lubricant bridge k b had a negative value varying from − 0.15 N ∕ m to − 0.1 N ∕ m . The damping value expressed in the form of frequency-multiplied damping c b × ω ranged from 0.02 N ∕ m to 0.06 N ∕ m . Note that both the absolute value of spring constant ∣ k b ∣ and frequency-multiplied damping c b × ω exhibited U-shaped variation with lubricant bridge elongation; that is, those values decrease with bridge elongation and they begin to increase after reaching the minimum. The variation in the spring constant was found to be in good accordance with the quasi-static stiffness of the lubricant bridge, and variation in the damping coefficient was explained by energy loss arising in the vibrating lubricant bridge.

Ceramic seals are widely used in many severe applications such as in corrosive, high temperature and highly loaded situations especially in hot chemical water-based extreme environments for automobile water pumps. Presently, polymeric materials are used as the counter part for alumina ceramic seals to reduce the ceramic-to-ceramic wear. As a result, leaks are very commonly observed from water pump during services. Consequently, it is needed to improve the surface properties of the ceramic seals using a surface modification technique such as a thin film coating process to meet the increasing demand of more stability, more durability, and lower friction of coefficient in those extreme environments. To meet these challenges, we have applied DLC (diamond-like carbon) coatings on alumina using a PIID (plasma immersion ion deposition) technique intended for seal applications. The DLC-coated specimens were tested under a wide range of temperature conditions, from room temperature up to 400 ° C , using a high temperature pin-on-disk tribo-tester. After that, the wear-tested specimens were analyzed using SEM with EDS to characterize the worn surfaces. Morphological changes of the DLC coated surfaces before and after the wear tests were studied. Under certain deposition conditions DLC performed very well up to 400 ° C . However, under other conditions, DLC failed catastrophically. In this paper we will present the friction and wear characteristics of the DLC-coated alumina. Finally, we will discuss the failure mode of DLC coatings.

Molecular dynamics simulations of a rigid diamond tip sliding on a face-centered-cubic copperlike substrate were performed in order to examine the dependence of the friction coefficient on the tip–substrate interference and the shape and size of the tip. For a square-base prismatic tip, the friction force is mainly due to interactions of atoms at the front face of the tip and substrate atoms ahead of the tip, while the normal force is due to interactions of atoms at the tip base and substrate atoms under the tip. However, for a pyramidal tip, both normal and friction forces are mainly due to interactions between atoms at the front face of the tip and substrate atoms in the vicinity of the sliding tip. Consequently, the friction coefficient is either sensitive (square-base prismatic tip) or insensitive (pyramidal tip) to the tip–substrate interference distance. In addition, tip size and orientation effects on the friction coefficient were observed with square- and triangle-base prismatic tips, respectively. Lower friction coefficients were obtained with a larger base area and edge-front sliding with a triangle-base prismatic tip. The results provide insight into atomic-scale friction anisotropies due to the effects of the tip size and shape and the tip–substrate interference.

The frictional behavior of diamond-like carbon (DLC) films varies with environmental condition. One theory asserts that the cause of variations in the frictional performance is environmental contaminants adsorbing onto the DLC film surface. Testing of the frictional performance of DLC films in a pin-on-disk contact has mapped the transient behavior of the friction coefficient. A model for fractional coverage, based on the adsorption of environmental contaminants and their removal through the pin contact, is developed. The rate of adsorption is taken from Langmuir’s model [17], which is combined with the removal ratio from Blanchet and Sawyer [18]. The coefficient of friction is based on the average fractional coverage under the pin contact. The model also gives a closed-form expression for the steady-state fractional coverage. Model calculations compared favorably to the time progression of the friction coefficient for a series of earlier experiments on a superlow friction DLC coating [7], when the fractional removal term was allowed to increase with increasing sliding speed.

This paper presents a numerical study of the effects of different shapes of deterministic microasperities in sliding surface lubrication when hydrodynamic films are found. Positive (protruding) and negative (recessed) asperities of constant height (depth) are considered with circular, square, diamond, hexagonal and triangular cross-sections. Of particular interest is the impact of asperity/cavity cross-sectional geometry on friction and leakage, which has importance in sealing applications. The results indicate that the friction coefficient is insensitive to asperity/cavity shape, but quite sensitive to the size of the cross-section. By contrast, leakage rates are found to be quite sensitive to both cross-sectional shape and size, with triangular asperities giving the smallest leakage rate and square asperities giving a largest leakage rate. The minimum coefficient of friction for all shapes is found to occur at an asperity area fraction of 0.2 for positive asperities and 0.7 for negative asperities. Finally, the results indicate the existence of a critical asperity area fraction where the performance curves for positive and negative asperities cross over. These cross-over points are identified for friction coefficient and leakage rate.

The dependence of the nanotribological properties of ultrathin amorphous carbon (a-C) films, deposited on Si(100) substrates by radio frequency sputtering, on their nanomechanical properties was investigated using surface force microscopy. The thickness and nanohardness of the a-C films were found to be in the range of 7–95 nm and 9–44 GPa, respectively. Sharp conical diamond tips with a 90 deg included angle and radius of curvature of about 20 μm and 100 nm were used to perform friction and wear experiments, respectively. The effect of the substrate compliance on the nanomechanical and nanotribological properties of the a-C films is interpreted in terms of the indentation depth and the film thickness. The coefficient of friction and wear rate of the a-C films are related to their nanomechanical properties, thickness, and surface roughness. The dependence of the coefficient of friction on contact load and the dominant friction mechanisms of elastically and plastically deformed films are discussed in light of friction force and surface imaging results. High effective hardness-to-elastic modulus ratio and low surface roughness characterize high wear resistance a-C films. Below a critical load, the steady-state removal rate of the film material is insignificantly small, revealing a predominantly elastic behavior.

The nanomechanical and nanotribological properties of 10-nm-thick amorphous carbon ( a -C) films and 100-nm-thick polycrystalline chromium (Cr) and titanium carbide (TiC) films were investigated using a surface force microscope (SFM). The films were deposited on Si(100) substrates by radio frequency (RF) sputtering and pulsed laser deposition (PLD) techniques. The experiments were performed with diamond tips of nominal radius of curvature equal to 20 nm, 100 nm, and 20 μm, and contact forces in the range of 3–400 μN. Nanoindentation experiments performed with the 20-nm-radius pyramidal diamond tip revealed that, for a 20 μN maximum contact force, the deformation of the a -C films was purely elastic, whereas that of the Cr film and Si(100) substrate was predominantly plastic. Although the RF sputtered a -C films and the PLD films of TiC exhibited similar nanohardness (∼40 GPa), the a -C films showed a superior nanowear resistance. Despite the identical hardness-to-elastic modulus ratio values of the RF sputtered polycrystalline Cr films and the single-crystal Si(100) substrate, the Cr films demonstrated a greater nanowear resistance. The wear behavior of the films is interpreted in terms of the relative specific energy dissipated during the nanowear process. Results from nanowear tests show that, in addition to the nanohardness and hardness-to-elastic modulus ratio, the microstructure, type of atomic bonding, and deposition process affecting the composition and residual stress in the films influence the nanowear resistance of the films.

Experimental and theoretical studies on hydrodynamic fluid pressure were conducted for the cases of plane grinding with nonporous metal bonded diamond wheels of SD140 and SD4000. Hydrodynamic force was successfully separated from the actual grinding force using the device developed in this study. Both experimental results and theoretical analysis showed that the effect of side leakage of grinding fluid on hydrodynamic pressure is negligible under grinding condition and therefore the infinite width cylindrical bearing theory is applicable. The effective clearance includes the effects of both the protrusion of cutting points and the waviness of the wheel surface for SD140. However, for a fine wheel such as SD4000, the waviness is predominant. Hydrodynamic force predominates normal grinding force even for a coarse wheel as SD140. [S0742-4787(00)01302-3]

The wear behavior of diamond-like carbon (DLC) coated sliders for proximity recording is investigated as a function of sliding distance, spindle speed and slider “interference height” using Raman spectroscopy. Both constant speed drag tests simulating track following and “slew” tests simulating track seeking were performed. The results indicate that track seeking increases the wear rate of DLC coated sliders dramatically during the first stages of a seek test. The results also show that wear of the DLC layer depends strongly on sliding distance and interference height of the slider. [S0742-4787(00)03801-7]

The physical damage at the Head-Disk Interface (HDI), caused by common ceramic particles found in the manufacturing environments of the heads and disks in hard magnetic disk drives, is reported. The need for this study arises from industry wide reliability problems due to particulate induced damage at the HDL The intent of this study is to characterize the head/disk damage caused by 1 μm diamond, 1–2 pm Tie particles, 0.2–1 μm alumina particles, the alumina and TiC grains sintered to make Al-TiC (the slider body), and sputtered alumina. These particles were introduced to the HDI in over thirty disk drives. The drives were then made to perform magnetic recording and retrieval operations for known data sequences, with the resultant reading errors tabulated. After the functional testing, the drives were opened and resulting damage was examined with a number of surface characterization tools. This study confirms that the severity of problems with the read-back signal, caused by particle damage, has an inverse relationship with the magnetic track width. In addition, the harshness of physical damage to the HDI has a positive relationship with particle hardness. Finally, particle shape and size can be contributing factors in damaging the HDL.

Aluminum forming processes such as rolling, extrusion, and ironing involve the transfer of large loads through a tooling/workpiece interface to plastically deform the workpiece to a desired shape. Sharp tool surface asperities can plow the workpiece and lead to elevated friction and temperatures in the interface with a subsequent increase in abrasive wear debris which in turn degrades the surface aesthetics of the final product. To minimize associated friction and wear levels in aluminum forming processes, a base oil with one or more boundary additives is used as a lubricant. At the present time, however, little is known about the mechanisms by which a given additive influences abrasive wear in an aluminum metal forming interface. In the present work, a series of single asperity plowing experiments on a 3004-O aluminum alloy with selected lubricant components was conducted. Three additives were separately investigated, viz., stearic acid, butyl stearate, and lauryl alcohol. The plowing motion of a pyramidal diamond indentor with a cutting edge oriented in the plowing direction (i.e., a sharp indentor) was controlled with the piezo-electric transducers of an atomic force microscope. The experiments help to provide insight about the interplay between additive reaction with the surface and plowing mechanics. Further insight into this interplay and abrasive wear debris generation was sought, albeit qualitatively, through additional experiments involving a diamond indentor for which no one cutting edge was oriented in the plowing direction (i.e., a blunt indentor). The tests allowed evaluation of the boundary lubricant mechanism and propensity for generating wear debris.

The load-dependency of the friction coefficient under a contact load in the order of sub-micronewtons was revealed. The frictional force was measured experimentally with a diamond tip of 0.1 μm radius on silicon-oxide surfaces in a laboratory atmosphere. The frictional force was obtained even under a certain amount of negative external force. The contact load was regarded as the sum of the external force and the attractive force between two surfaces, the latter being estimated from an elastic contact theory which took into account the van-der-Waals force. The friction coefficient, as the ratio of the frictional force to the contact load (not to the external force), was plotted against the contact load. Below 0.4 μN in the contact load, the friction coefficient increased in inverse proportion to the decrease in contact load. Above 0.4 μN in the contact load, the friction coefficient was stable at about 0.1. We discussed this load-dependency, and derived a hypothesis that the real area of contact should include some part of the attractive region around the repulsive region at the contact point when the contribution of the attractive force is not negligible to the contact load.

Single- and dual-cathode DC magnetron sputtering was used to produce TiB 2 coatings and CN x /ZrN multilayers, respectively, with hardness exceeding 40 GPa. The composition, structure, topography, and mechanical properties were determined by various techniques, including Auger electron spectroscopy, X-ray diffraction, high-resolution electron microscopy, atomic force microscopy, and nanoindentation. An optimum combination of the sputtering pressure and substrate bias results in the production of ultrasmooth TiB 2 coatings with hardness up to 50 GPa and excellent wetting properties. The rationale for studying the CN x /ZrN system is that ZrN(111) provides excellent lattice match to the hypothetical β-C 3 N 4 (0001) face (β-C 3 N 4 was predicted to have mechanical properties comparable to diamond). Using a dual-cathode sputtering system, we produced crystalline multilayers of CN x /ZrN with bilayer thickness of 1–2 nm. Using various combinations of nitrogen partial pressure, target powers, and substrate bias, we found that the hardness of these coatings correlates very strongly with the occurrence of (111) texture of ZrN, consistent with the lattice-match strategy. Even with a ZrN volume fraction of 70 percent, such multilayer coatings have been synthesized with hardness in the 50 GPa regime.