Interface Wear Research Articles

Challenges of the head-disk interface for near contact and contact recording

As the magnetic recording areal density approaches 10 Gb/in/sup 2/, the mechanical spacing between the head and the disk is expected to reduce rapidly below 20 nm. This lends to an increase of head-disk interaction which may induce an unacceptable level of interfacial wear. In this study experimental air bearing sliders were designed and fabricated to fly in close proximity or substantial contact with the disk. The durability of the interface decreased with decreasing mechanical clearance. The amount of head and disk wear was determined. The metrology and some of the challenges in maintaining a functional interface are presented.

Observation of fatigue damage process in SiC fiber-reinforced Ti-15-3 composite at high temperature

Unnotched SiC (SCS-6) fiber-reinforced Ti-15-3 alloy composite is subjected to a tension-tension fatigue test in a vacuum of 2×10−3 Pa at 293 and 823 K with a frequency of 2 Hz and R=0.1. Direct observation of the damage evolution process during the test is carried out by scanning electron microscopy (SEM). Test temperature dependent and independent fatigue damage behaviors are observed. The early stage fiber fractures observed at the polished surface are not influenced by the test temperature; however, matrix crack initiation and propagation behaviors differ greatly with temperature. The evolution of interface wear damage also differs with temperature, becoming more severe at 823 K, and the interface wear damage zone increases with the increase of the number of fatigue cycles. The macroscopic fatigue damage appears as a modulus reduction associated with interface sliding, matrix crack propagation, and plastic deformation of the matrix. The deformation zone of the composite tested at 823 K spreads more than that at 293 K. The fatigue life of the composite tested at 823 K is longer than that at 293 K. This behavior is related to the difference in spread of the damage zone in the matrix.

Fibrocartilage in tendons and ligaments — an adaptation to compressive load

Where tendons and ligaments are subject to compression, they are frequently fibrocartilaginous. This occurs at 2 principal sites: where tendons (and sometimes ligaments) wrap around bony or fibrous pulleys, and in the region where they attach to bone, i.e. at their entheses. Wrap-around tendons are most characteristic of the limbs and are commonly wider at their point of bony contact so that the pressure is reduced. The most fibrocartilaginous tendons are heavily loaded and permanently bent around their pulleys. There is often pronounced interweaving of collagen fibres that prevents the tendons from splaying apart under compression. The fibrocartilage can be located within fascicles, or in endo- or epitenon (where it may protect blood vessels from compression or allow fascicles to slide). Fibrocartilage cells are commonly packed with intermediate filaments which could be involved in transducing mechanical load. The ECM often contains aggrecan which allows the tendon to imbibe water and withstand compression. Type II collagen may also be present, particularly in tendons that are heavily loaded. Fibrocartilage is a dynamic tissue that disappears when the tendons are rerouted surgically and can be maintained in vitro when discs of tendon are compressed. Finite element analyses provide a good correlation between its distribution and levels of compressive stress, but at some locations fibrocartilage is a sign of pathology. Enthesis fibrocartilage is most typical of tendons or ligaments that attach to the epiphyses of long bones where it may also be accompanied by sesamoid and periosteal fibrocartilages. It is characteristic of sites where the angle of attachment changes throughout the range of joint movement and it reduces wear and tear by dissipating stress concentration at the bony interface. There is a good correlation between the distribution of fibrocartilage within an enthesis and the levels of compressive stress. The complex interlocking between calcified fibrocartilage and bone contributes to the mechanical strength of the enthesis and cartilage-like molecules (e.g. aggrecan and type II collagen) in the ECM contribute to its ability to withstand compression. Pathological changes are common and are known as enthesopathies.

Apparent stiffening of ceramic-matrix composites induced by cyclic fatigue

This work carries on four different long-fibre-reinforced ceramic-matrix composites: a cross-weave SiC/SiC, a cross-ply SiC/MAS-L, a cross-weave C/SiC and a [0,+60,−60]n C/C laminate. Experimentally, cyclic fatigue effect has been observed at room temperature, at high temperature under inert atmosphere, and at room temperature after a previous ageing at high temperature under vacuum. For these four materials, the evolutions of the macroscopic mechanical behaviour with the number of cycles applied can be explained by an evolution of interfaces as well, fibre/matrix interfaces as neighbouring ply interfaces, according to the following mechanisms: (i) interfacial wear of interfaces due to to-and-fro sliding of fibres or of plies under cyclic loading, and (ii) dependence of the residual thermal stresses with the temperature of the test. Previous ageing at high temperature under vacuum can also enable in CMC some physical and chemical changes in the constituents leading for example to a slight removing of fibre/matrix interphases by oxidation. Usually, damage induced by cyclic fatigue in long-fibre-reinforced ceramic-matrix composites leads to a reduction of the tensile apparent elastic modulus as cycling proceeds. But an original macroscopic stiffening has been experimentally observed during cyclic fatigue. This phenomenon has been observed on C/C composite at room temperature, on C/SiC and on SiC/MAS-L at high temperature, and on SiC/SiC at room temperature after previous ageing under vacuum at high temperature. This apparent stiffening is not well understood at present time, but appeared in materials with low interfacial shear strength and is seemingly due to incomplete closure during unloading of the cracks present in transverse yarns.

Dry sliding wear of a Ti50Ni25Cu25 particulate-reinforced aluminum matrix composite

The objective of this article is to characterize the sliding wear behavior of a 30 vol pct Ti50Ni25Cu25 particulate-reinforced aluminum matrix composite under dry conditions. The transformation temperatures of Ti50Ni25Cu25 particles were measured before and after the compounding procedure by the differential scanning calorimeter (DSC) method. The wear tests were carried out on a pin-on-disc machine. A 10 vol pct SiC particulate-reinforced composite and pure aluminum were chosen as the comparison specimens. The results indicate that Al-30 vol pct Ti50Ni25Cu25 composites exhibit higher wear resistance than their unreinforced matrices and are comparable with Al-10 vol pct SiC composites in this experiment. A self-adaptive mechanism that contributes to the wear resistance of an Al-30 vol pct Ti50Ni25Cu25 composite is proposed. Scanning electron microscopy (SEM) and energy diffraction spectrum (EDS) examinations were carried out to investigate the wear mechanism and interface reactions. The results indicate that the interfacial reaction is a predominant factor in determining the wear behavior of the Ti50Ni25Cu25/Al composite.

Effects of temperature and of oxidation on the interfacial shear stress between fibres and matrix in ceramic-matrix composites

Under cyclic loading, the mechanical behavior of ceramic matrix composites (SiC/SiC, SiC/ MAS-L) changes with the number of applied cycles, as shown by life-time diagrams and shape evolutions of stress/strain loops. According to these observations, a shear-lag model has been developed where the cyclic fatigue effect is attributed to an interfacial wear between fibres and matrix. At high temperature under inert atmosphere, since physical and chemical changes are inhibited, the main effect of temperature on cyclic fatigue of ceramic matrix composites is the release of radial thermal residual stresses. But under vacuum when the temperature is high, fibre/matrix interfaces can be removed due to chemical instabilities. Hence, after ageing under vacuum at high temperature, cyclic fatigue at room temperature of SiC/SiC composites exhibits an increase followed by a decrease in mechanical hysteresis. This can be explained by a decrease in the interfacial shear stress due to the previous heating at high temperature under vacuum. For such treated composites, an original stiffening effect is also observed during cyclic fatigue. This original phenomenon is attributed to a contribution of cracks in transversal yarns.

Hot friction testing of ceramics

Reciprocating tests were carried out on a number of different ceramics at a range of temperatures up to 1450 °C in a high precision test system. The friction that was generated, and the damage to surfaces, were investigated. The aim of the experiments was to investigate the tribology of high-temperature ceramic contacts, and to provide data for high-temperature engineering applications of ceramics. In particular, information was needed on the friction and surface damage that occurs at the contacts between the test jig parts (made from ceramic) and ceramic test samples used for high-temperature mechanical testing. Significant errors in test results are likely to occur because of frictional effects, and it is important to measure and make allowance for this effect. The tests were carried out with both a sliding contact geometry, and also with a rolling contact. A range of ceramics were examined, including alumina, silicon nitride, silicon carbide, partially stabilised zirconia and soda-lime glass under a range of different loads and temperatures. The friction and surface damage generated in rolling contact were lower than those in sliding contact, with friction coefficients in the range 0.02–0.05 compared with sliding contact values rising from 0.2 in most cases at room temperature to 0.4–1 at higher temperatures. For the silicon-based non-oxide ceramics, oxidation of the test surfaces was found to occur, leading to the formation of glass at the wear interface at high temperature. In some tests where glass was formed, or was one of the bulk samples, pronounced stick-slip was observed above a critical temperature. The key recommendation for the study for high-temperature mechanical testing of ceramics is that rolling contact elements produce negligible errors in the results of strength tests, and so should be used wherever possible.

Traffic Densification of Asphalt Concrete Pavements

A 5-year study of newly constructed pavements showed that a reduction in in situ air voids occurred both within and between wheelpaths for highways with an average daily traffic (ADT) load of less than 10,000 vehicles. Regardless of the level of voids immediately after construction, mixtures in the upper 65 mm (2.5 in.) within the wheelpath indicated a reduction in voids by 3 to 5 percent (e.g., from 10 to 6 percent voids), and by between 2 to 4 percent between the wheelpaths. Because only limited densification occurred below this depth for lower–traffic-volume facilities, reducing the mix design level of air voids from 4 percent to 2 percent for the lower lifts was suggested so that lower initial voids could be obtained during construction. An evaluation of older pavements indicated that moisture damage to the lower pavement layers was typical; thus, a change in mix design procedures might also help improve durability by increasing the film thickness. Pavements with high traffic volumes (>50,000 ADT) consistently indicated an increase in voids over time in the upper lift [40 mm (1.5 in.)], little change in the middle 65 mm (2.5 in.), and a decrease in the bottom 65 mm (2.5 in.). The hypothesis suggested to explain these findings was that a loss of material in the upper lifts was occurring, most probably due to moisture damage as the upper, more permeable wear course, commonly used in Minnesota, allowed water trapping at the wear and binder course (i.e., less permeable) interface. A further investigation of in situ void changes on an interstate indicated that for a pavement constructed with the same fine gradation in all lifts, traffic compacted the mixtures in a manner similar to that in low-volume roads. When the initial in situ voids increased from around 7 percent to nearly 10 percent, the influence of traffic on the densification was substantially increased.

A Model of Slider/Disk Interface Wear for Proximity Recording

Slider/disk interface wear is inevitable for ultra-low flying hard disk drives and is the central issue for proximity recording. While disk wear has been addressed in the literature, slider wear has been largely considered to be trivial and is ignored. However, with the improvement of disk overcoat and introduction of diamond-like-carbon overcoat on slider air bearing surface, the surface hardnesses of the slider and disk are approaching each other and, therefore, the slider surface wear becomes significant or, in some conditions, even dominant. In this study, a theoretical model is developed for semi-steady-state slider/disk interface evolution of proximity recording which takes account of both the disk and slider wear. It includes the effects of the air bearing characteristics, pitch stiffness, material properties, and surface topography of both the slider and disk. Numerical results are illustrated for typical proximity recording interface, where the evolutions of the slider, disk, contact force, and pitch angle are evaluated for various air bearing stiffnesses, material properties, and surface topographies. This model is intended to provide some fundamental understanding of the slider/disk interface evolution during proximity recording process.

Particle build-up on flying sliders and mechanism study of disk wear and head-disk interface failure in magnetic disk drives

A novel experiment was designed to promote the understanding of the mechanism of disk wear caused by particulate contamination. Obtained results suggest that the slider picks up particles and accumulates them on its surfaces as it flies above the disk. The instability of the flying slider, especially that induced by track seeking, leads to slider-disk impact which releases the accumulated particles. This results in abrasion amongst the slider, the contaminants, and the disk. The investigation also indicates that the outer two surfaces in a disk-stack and the corresponding sliders have higher likelihood of capturing flying particles. A model has been proposed to explain the observed phenomena.

Cyclic fatigue of ceramic-matrix composites at ambient and elevated temperatures

Under cyclic loading, the mechanical behaviour of ceramic-matrix composites changes with the number of cycles applied even at room temperature. In order to identify the microstructural mechanisms of damage due to cyclic fatigue, the macroscopic behaviour is experimentally observed from the lifetime diagram and the evolution of the stress/strain loops with the number of cycles applied. From this approach a micromechanical model has been developed where the cyclic fatigue effect is ascribed to interfacial wear between fibres and matrix. At high temperature, since the testing temperature is low enough to inhibit any physical and chemical change in the materials, the main effect of temperature is due to the release of residual thermal stresses. This phenomenon has been experimentally observed on two ceramic-matrix composites: SiC SiC 2D and SiC MAS L [0,90], where the signs of the residual thermal stresses are different.

Improvement in the fatigue life of fiber-reinforced ceramics by use of interfacial lubrication

Continuous-fiber reinforced ceramics are potential materials for high temperature load carrying structures. Most applications involve cyclic loading. Recent work has shown that the interfacial shear stress in ceramic matrix composites decreases rapidly in the initial stages of cyclic loading. This brings up a key question. Namely can fatigue life be improved by altering the initial wear rate of the fiber/matrix interface. This letter reports such an attempt, where micro-cracked specimens were immersed in oil prior to cyclic loads, in an attempt to change the interface wear rate. A Nicalon SiC-fiber/calcium aluminosilicate matrix (SiC{sub t}/CAS-II, Corning Glass Works, Corning, NY) composite was used in the study. The composite was processed with 16 plies and had a nominal fiber content of 40 vol.%. Edge loaded specimens, similar to those used in earlier studies were machined from 6 in. x 6 in. panels with fibers parallel to the tensile loading direction. To facilitate the observation of matrix cracking, the specimens were polished along an edge (minor face) with diamond paste to a final finish of 1 {mu}m.

Dry sliding wear of particulate-reinforced aluminium alloys against automobile friction materials

Two magnesium/silicon aluminium alloys each reinforced with 20 vol.% SiC particulates have been worn against three makes of automobile friction linings (brake pads). Two of the friction linings are commonly used against cast iron rotors in automobile braking systems while the third has been specifically formulated for use against aluminium metal matrix composite (MMC) brake rotors. Wear processes at the interfaces of the specific rotor-pad combinations have been characterised through the analysis of friction traces and the use of electron microscopy. For aluminium MMCs sliding against organic pads formulated for use against cast iron, wear rates are low and friction traces constant due to the formation of a solid lubricant graphitic layer at the wear interface. When these MMCs are worn against semi-metallic pads formulated for use against cast iron, wear rates are extremely high due to three body abrasion which leads to subsurface delamination and early melt wear in the MMC. For an aluminium MMC developed for its use in automobile brake rotors sliding against a semi-metallic pad specifically formulated for its use against MMC brake rotors, wear rates at low loads are low although friction traces are highly irregular and fracture of the SiC particulates occurs at the lowest load and sliding velocity. This fracture of SiC is induced by the abrasive action of hard alumina particles within the pad. At high loads and sliding velocities cohesiveness of materials within the pad is poor and the wear rate of the MMC is extremely high. If the structure and composition of friction linings are arranged correctly, the wear resistance and frictional properties of aluminium MMC brake rotors are superior to those of cast iron brake rotors.

Dry sliding wear of particulate-reinforced aluminium alloys against automobile friction materials

Two magnesium/silicon aluminium alloys each reinforced with 20 vol.% SiC particulates have been worn against three makes of automobile friction linings (brake pads). Two of the friction linings are commonly used against cast iron rotors in automobile braking systems while the third has been specifically formulated for use against aluminium metal matrix composite (MMC) brake rotors. Wear processes at the interfaces of the specific rotor-pad combinations have been characterised through the analysis of friction traces and the use of electron microscopy. For aluminium MMCs sliding against organic pads formulated for use against cast iron, wear rates are low and friction traces constant due to the formation of a solid lubricant graphitic layer at the wear interface. When these MMCs are worn against semi-metallic pads formulated for use against cast iron, wear rates are extremely high due to three body abrasion which leads to subsurface delamination and early melt wear in the MMC. For an aluminium MMC developed for its use in automobile brake rotors sliding against a semi-metallic pad specifically formulated for its use against MMC brake rotors, wear rates at low loads are low although friction traces are highly irregular and fracture of the SiC particulates occurs at the lowest load and sliding velocity. This fracture of SiC is induced by the abrasive action of hard alumina particles within the pad. At high loads and sliding velocities cohesiveness of materials within the pad is poor and the wear rate of the MMC is extremely high. If the structure and composition of friction linings are arranged correctly, the wear resistance and frictional properties of aluminium MMC brake rotors are superior to those of cast iron brake rotors.

Slider/Disk Interaction During the Landing Process

In rigid disk drives, slider/disk interface (SDI) wear should ideally occur only during the start/stop (S/S) process. Good S/S wear performance is crucial, but often difficult to achieve. This is due in part to a lack of understanding of slider/disk interaction during the S/S process. The intent of this study is to provide a thorough theoretical model to aid in our understanding of the slider/disk interaction during the landing process. In contrast to assessments in the literature, this model includes more rigorous surface characterization, the statistical nature of summit interaction, and the nonlinear rarefaction effects in the modified Reynolds equation. In this paper, we present results of a baseline slider/disk configuration, together with a crown sensitivity study.

Wear resistant coatings for contact recording applications

To achieve low stiction and low interface wear in contact recording, a hard coating having a high hardness, elastic modulus, and scratch resistance is required. In this study, mechanical and tribological characterization of carbon coatings deposited by various deposition techniques and SiC has been carried out. Based on nanoindentation and microscratch studies, it is concluded that cathodic arc carbon coatings exhibit the highest hardness, elastic modulus, scratch resistance, and wear resistance.

An oscillating tester for head/disk interface durability study

An oscillating tester is built for the head/disk interface durability study. This tester uses an in-production head and disk, records friction build-up, and allows easy observation of interface wear. It can be used to quickly evaluate the tribological performance of a head/disk interface. Tests carried out on this tester showed qualitative agreement with CSS test results.

Fiber push-out testing apparatus for elevated temperatures

A newly developed apparatus has been designed for performing fiber push-out testing on continuous fiber-reinforced composites at elevated temperatures. This test measures the force at which a fiber resists being pushed by a flat-bottomed indenter moving at a constant speed. The applied load versus time curve characterizes the fiber debonding and sliding behavior. Extending measurements to elevated temperatures required incorporating sample/indenter heating in a nonoxidizing environment. With this new apparatus, fiber push-out tests have been performed up to 1100 δC in a vacuum of 10-6 Torr. A line-of-sight to the sample is maintained during the test which allows video monitoring of the push-out process. Results are shown for SCS-6 SiC fiber-reinforced Ti-24Al-llNb (at. %) and Ti-15V-3Cr-3Sn-3Al (at. %) matrix composites. The results are discussed in terms of residual stresses, interfacial wear, matrix ductility, and changing modes of interfacial failure. The effect of temperature-dependent interfacial wear on the interfacial roughness contribution to frictional shear stresses during fiber sliding is examined.

Elevated Temperature Fiber Push-Out Testing

ABSTRACTThe potential use of fiber-reinforced composite materials for high temperature applications makes the development of interface test methodology at those high temperatures very desirable. A facility for performing high temperature fiber push-out tests will be described with emphasis on critical issues in experimental procedure. Examples from several composite systems illustrate the temperature dependence and environmental sensitivity of fiber debonding and sliding. Interpretation of the temperature dependence will be made primarily in terms of changes in residual stresses along with additional effects due to changes in matrix ductility and interfacial wear. Examples will show that high temperature fiber push-out testing can often distinguish between chemical and frictional fiber/matrix bonding in cases where room temperature only testing cannot.

Examination of alumina ceramic components from total hip arthroplasties.

Materials analysis has been conducted on retrieved Mittelmeier-Autophor ceramic components from total hip arthroplasties, correlating articulating surface wear morphology with clinical reasons for failure. Plastically deformed, agglomerated wear debris (30-60 microns) has been identified on femoral head articulation wear surfaces, displaying exaggerated wear, especially during the initiation stage. Such surfaces were associated with clinical failures involving displacement of the acetabular cup and perforation of the cortex by the femoral stem. It is thought that this wear debris may play an important role in the promotion of the 'avalanche' wear mechanism, as it is adherent and thus difficult to remove from the wear interface.