Polished Disks Research Articles

Effect of counterface surface roughness and its evolution on the wear and friction of PEEK and PEEK-bonded carbon fibre composites on stainless steel

The time-dependent variations in the dry sliding wear rate and friction of PEEK (450G and 100P) and carbon fibre-bonded PEEK (APC2) on stainless steel (316S16) have been investigated and the evolution of wear scratches measured with optical profilometry. A three-pin-on-disk tester was used, operating at 0.18 m s −1, with a pressure of 1.0 MPa on 5 mm diameter pin. Specific wear rates were calculated from mass lost by the pins at 15 km intervals and friction force was monitored by a strain-gauged torque beam. Two series of 90-km tests were performed for each pin/disk combination. The stainless steel disks had either a fine-ground or polished surface. The roughness of the ground stainless steel surface was chosen to coincide with the optimum value for low wear rate of the PEEK pins. To maximise pin/disk contact area, the PEEK and APC2 pin surfaces were run-in on 1000-grit silicon carbide paper and ultrasonically cleaned in acetone before the first wear test. There was no significant difference in steady-state wear between these pins and those tested with as-moulded surfaces. The disks were analysed at 15 km intervals with the UBM profilometer, providing 3D surface scans and 2D profiles for roughness parameters without damaging the wear track. All the surface roughness parameters reported in this work were produced from thhe UBM non-contacting optical profilometer. A marked difference in specific wear rate was observed between the two types of PEEK. The 450G had the lowest wear of 6 × 10 −6 mm 3 N −1 m −1 on both the polished and ground counterface, whereas the 100P had wear factors of 1 × 10 −4 mm 3 N −1 m −1 on ground and 2 × 10 −5 mm 3 N −1 m −1 on polished stainless steel. However, the friction forces measured between the 450G PEEK and the polished disk were up to three times higher than those against the ground disk, (0.35±0.01), decreasing to similar values as the polished surface became scratched. The APC2 pins showed very little difference in wear rate between the ground and polished disks. However, a steady decrease from 1 × 10 −6 to 1 × 10 −7 mm 3 N −1 m −1 over a distance of 90 km was measured as more fibres were ground into a graphite transfer film lubricant and the coefficient of friction dropped from 0.35 to 0.18. The specific wear rates and coefficients of friction of the APC2 samples were lower than those for PEEK, however, the APC2 caused more scratch deformation of the polished steel counterface.

The Effect of Intrinsic Fluoride in Cows’ Milk on in vitro Enamel Demineralization

The fluoride concentration in cows’ milk has been reported to vary with the fluoride levels in drinking water but it seldom exceeds 0.5 μg/ml. This raised a question as to whether any caries-protective effect could be attributed to the intrinsic fluoride of milk. Two samples of cows’ milk with intrinsic fluoride concentrations of 0.03 and 0.3 μg/ml, respectively, were assessed for their protective effect on enamel in an in vitro demineralization model at relatively severe and mild acidic challenges (pH 4.6 and 5.0, respectively). Polished enamel discs were incubated individually in 5.0 ml of demineralization solution for 20 h per day alternated with 1-hour incubations in 1.0 ml of milk or control buffers: group 1, demineralization solution only (negative control); group 2, milk with 0.03 μg/ml fluoride; group 3, milk with 0.03 μg/ml fluoride; supplemented with NaF to 0.3 μg/ml fluoride; group 4, milk with 0.3 μg/ml fluoride; group 5, 0.3 μg/ml fluoride in 20 mM HEPES, pH 6.7; group 6, milk with 0.03 μg/ml fluoride supplemented with NaF to 5.0 μg/ml fluoride (positive control). The solutions were renewed each day and the calcium concentration in the demineralization solutions was followed during 4 days. The results showed that the protective effect of intrinsic milk fluoride on enamel is limited by the severity of the acidic challenge: There was a significant inhibition of the demineralization in groups 3–6 compared to groups 1 and 2, but only at pH 5.0 (p < 0.0001) and not at pH 4.6 (p = 0.2). The organic components of milk had limited protection against demineralization because milk and HEPES with the same fluoride concentration gave similar results. The 36% reduction in calcium loss at pH 5.0 by treatment with milk with only 0.3 μg/ml fluoride is an indication that intrinsic milk fluoride has some caries-protective properties.

Proposal of Ultrahigh Density Optical Disk System Using a Vertical Cavity Surface Emitting Laser Array

An ultrahigh density optical disk system of Tera bit/inch2 is described. This system utilizes a vertical cavity surface emitting laser (VCSEL) diode array as a parallel optical beam source which can make the disk system more useful at a high data transfer rate and bit density using evanescent waves from each laser cavity. In order to avoid the diffraction limited restriction to the optical beam the near-field optics is adopted to the parallel beam optical head. 1 bit size on the surface of the disk is 10–20 nm in diameter. A polished glass disk substrate is deposited by either phase change medium or photon mode optical medium. The medium thickness of the disk is approximately 10–20 nm. The optical gap size between the surface of the medium and laser output windows of a VCSEL array head is controlled within 20 nm using contact head technology.

Effects of microstructure on the corrosion behavior of CoCr porous coatings on orthopedic implants.

Cobalt-chromium alloy porous coatings have become increasingly popular as a means of achieving a stable, longer lasting fixation on orthopedic implants. However, sintering heat treatments cause changes in the microstructure that result in changes in the corrosion behavior of the porous coatings. Experiments were conducted to examine the effects of microstructure on the corrosion of CoCr porous coatings. Four distinct microstructures were characterized. Light microscopy revealed microstructures A and B had relatively fewer carbides and a large-grain structure, microstructures C and D displayed a finer grain size with significant carbide formation, predominantly within grains and fusion zones. Accelerated anodic corrosion experiments were conducted to study the localized attack of each microstructure. Experiments were conducted using metallographically polished porous-coated disks for durations of 1, 4, 16, 24, and 72 h. The disks were examined with SEM and EDS to observe preferential attack and element depletion. Results showed a progressive dissolution of the matrix, with preferential attack of the grain boundaries and regions adjacent to the carbides due to sensitization. A precipitation layer was found to be Cr-rich and possibly composed of chromium hydroxide or a chromium orthophosphate. In addition, the solution became yellow in color with longer exposure times, possibly due to the presence of chromate ions, as indicated by an increased chromium level detected by AAS.

Kinetic Meniscus Model for Prediction of Rest Stiction

The time dependence of static friction is an important aspect of tribological studies whereby the static friction increases with an increase in the time of stationary contact (rest static friction or rest stiction). This effect is commonly observed in computer disk drives especially at high humidities, in which the static friction increases rapidly with an increase in rest time between some head slider and the disk surfaces. For the first time, a comprehensive kinetic meniscus model is proposed to explain this phenomenon, both for a single asperity and multiple asperity contacts at a liquid mediated interface. It is found that the static friction increases up to a certain equilibrium time with a power law relationship after which it remains constant. The equilibrium time is dependent on the liquid film thickness, the liquid viscosity and the contact geometry. The model developed is applied to a rough textured disk, a polished disk and a super smooth disk. To study the effect of the scan size on the meniscus force, the static friction is calculated by using roughness parameters obtained from measurements at different scan sizes.

High-temperature oxidation of TiN/CrN multilayers reactively sputtered at low temperatures

The high-temperature (600–850°C) oxidation of multilayer hard TiN/CrN coatings was investigated. TiN/CrN multilayer coatings (2.6 μm thick) with modulation periods in the range 83–425 nm were deposited at low temperatures (150°C) onto polished tool steel discs and polished alumina ceramic substrates ( R a = 25 nm) using the plasma-beam sputtering technique. The oxidation rate was obtained from the weight gain as a function of the oxidation time. The activation energy for oxidation of TiN/CrN multilayers was determined and compared with that for CrN, TiN and CrTiN coatings. The depth profiles of samples oxidized at various temperatures were examined by Auger electron spectrometry (AES) and glow discharge optical spectrometry (GDOS) to determine the thickness and the composition of the oxide layer. The morphology of the oxidized coatings was investigated by scanning electron microscopy (SEM). Continuous in-situ electrical resistivity measurements were performed on the same coatings to detect grain-boundary oxidation. The adhesion and microhardness of the multilayers were also determined.

Plasma Surface Modification of Medical-Grade Ultra-High Molecular Weight Polyethylene for Improved Tribological Properties

AbstractUltra-high molecular weight polyethylene (UHMWPE) is the principal material used to replace damaged cartilage in total joint replacement surgeries. This publication presents preliminary results from a new class of surface treatments to modify the surface chemistry and microstructure of UHMWPE under controlled processing conditions. Radio frequency plasmas were used to lightly crosslink the subsurface of UHMWPE and to modify the surface chemical state through the attachment of low-surface-energy fluorocarbon groups. A pin-on-disk apparatus was used to slide CoCrWNi pins with spherical tips on polished disks of plasma- treated and untreated UHMWPE immersed in a bath of preserved bovine serum. The wear resistance and surface chemical composition of tested specimens were characterized by surface profilometry and X-ray photoelectron spectroscopy (XPS), respectively. Changes in the surface hydrophobicity due to plasma treatment were evaluated using contact angle measurements. The prospect of surface plasma treatment in orthopedic applications is elucidated in the context of the obtained friction, wear, distilled water contact angle, and XPS results.

Characterization of alpha sources prepared by direct evaporation using Rutherford backscattering spectrometry

Standardization of solutions containing alpha emitting nuclides by direct evaporation onto metal supports is a widely used technique due to its simplicity in providing good quantitative results. In order to avoid inhomogeneity in the deposition surface, polished stainless steel disks and a spreading agent are generally used. These sources are usually measured by alpha spectrometry using passivated implanted silicon detectors. The resolution of the source is a measure of the thickness and homogeneity of the evaporated layer. Rutherford backscattering of He + and H + was here used to measure directly this thickness and homogeneity. The results were in agreement with semiconductor detector alpha spectrometry.

Mechanical and morphologic investigation of the tensile strength of a bone-hydroxyapatite interface.

For load-bearing calcium-phosphate biomaterials, it is important to understand the relative contributions of direct physical-chemical bonding vs. mechanical interlocking to interfacial strength. In the limit of a perfectly smooth hydroxyapatite (HA) surface, a tensile test of the bone-HA interface affords an opportunity to isolate the bonding contribution related to HA surface chemistry alone. This study measured the bone-HA interfacial tensile strength for highly polished (approximately 0.05 micron alumina) dense HA disks (5.25 mm in diameter, 1.3 in mm thickness) in rabbit tibiae. Each of five rabbits received four HA disks, two per proximal tibia. Pull-off loads ranged from 3.14 +/- 2.38N at 55 days after implantation to 18.35 +/- 11.9N at 88 days; nominal interfacial tensile strengths were 0.15 +/- 0.11 MPa and 0.85 +/- 0.55 MPa, respectively. SEM of failed interfaces revealed failures between HA and bone, within the HA itself and within adjacent bone. Tissue remnants on HA were identified as mineralized bone with either a lamellar or trabecular structure. Oriented collagen fibers in the bone intricately interdigitated with the HA surface, which frequently showed breakdown at material grain boundaries and a rougher surface than originally implanted. Mechanical interlocking could not be eliminated as a mode of tissue attachment and contribution to bone-HA bonding, even after implanting an extremely smooth HA surface.

Mechanical and morphologic investigation of the tensile strength of a bone‐hydroxyapatite interface

For load-bearing calcium-phosphate biomaterials, it is important to understand the relative contributions of direct physical-chemical bonding vs. mechanical interlocking to interfacial strength. In the limit of a perfectly smooth hydroxyapatite (HA) surface, a tensile test of the bone-HA interface affords an opportunity to isolate the bonding contribution related to HA surface chemistry alone. This study measured the bone-HA interfacial tensile strength for highly polished (−0.05 μm alumina) dense HA disks (5.25 mm in diameter, 1.3 in mm thickness) in rabbit tibiae. Each of five rabbits received four HA disks, two per proximal tibia. Pull-off loads ranged from 3.14 ± 2.38N at 55 days after implantation to 18.35 ± 11.9N at 88 days; nominal interfacial tensile strengths were 0.15 ± 0.11 MPa and 0.85 ± 0.55 MPa, respectively. SEM of failed interfaces revealed failures between HA and bone, within the HA itself and within adjacent bone. Tissue remnants on HA were identified as mineralized bone with either a lamellar or trabecular structure. Oriented collagen fibers in the bone intricately interdigitated with the HA surface, which frequently showed breakdown at material grain boundaries and a rougher surface than originally implanted. Mechanical interlocking could not be eliminated as a mode of tissue attachment and contribution to bone-HA bonding, even after implanting an extremely smooth HA surface. © 1997 John Wiley & Sons, Inc.

Dentin demineralization: Effects of dentin depth, pH and different acids

Objectives This investigation sought to determine: 1) if dentin demineralization rates are proportional to acid concentration for demineralization in phosphoric acid (10% or 1.76M, 0.025M, 0.0001 M, with pH=0.95, 2.0, 4.0 respectively); 2) if the etching characteristics are independent of dentin depth; and 3) if the etching characteristics for phosphoric acid were comparable to those for citric acid over a similar pH range. Methods Highly polished dentin disks from freshly extracted, non-carious, third molars were prepared with a reference layer. Samples were prepared from either superficial or deep coronal dentin. The samples were etched for periods of up to 30 min using phosphoric acid solutions (pH = 0.95, 2.0, 4.0) in a wet cell of an atomic force microscope (AFM). Depth changes with respect to the reference layer were determined for the intertubular and peritubular dentin to quantify structural changes. The results were compared with similar studies using citric acid (pH = 1.0, 2.15 or 3.4). Etching characteristics were statistically compared using 2-way repeated measures ANOVA at p < 0.05 and the Tukey's multiple comparison test. Results The relation between time and recession for peritubular dentin was initially linear. The intertubular dentin recession started rapidly but then reached a plateau within a very short interval for etching solutions at pH = 2.0 and 4.0. At the highest concentration, the recession decreased with time, but a clear plateau was not established. There was no statistical difference between peritubular etching rates of superficial and deep dentin surfaces with phosphoric acid at any concentration. There was also no difference in the intertubular dentin recession at the location of the plateau that depended on dentin depth. Etching rates increased dramatically with decreased pH for both phosphoric and citric acids, but were higher for citric acid than for phosphoric acid. Significance The AFM allowed quantification of changes during etching of wet dentin. Peritubular dentin etching rates increased with decreasing pH, as expected, but changes were not linear and were different for the two acids studied over a similar pH range. Intertubular dentin surface recession was small and plateaued for low concentrations. The peritubular etching rate and intertubular dentin recession did not depend on dentin depth.

Mixed transport/reaction control of gypsum dissolution kinetics in aqueous solutions and initiation of gypsum karst

Experiments with gypsum in aqueous solutions at 25°C, low ionic strengths, and a range of saturation states indicate a mixed surface reaction and diffusional transport control of gypsum dissolution kinetics. Dissolution rates were determined in a mixed flow/rotating disc reactor operating under steady-state conditions, in which polished gypsum discs were rotated at constant speed and reactant solutions were continuously fed into the reactor. Rates increase with velocity of spin under laminar conditions (low rates of spin), but increase asymptotically to a constant rate as turbulent conditions develop with increasing spin velocity, experiencing a small jump in magnitude across the laminar–turbulent transition. A linear dependence of rates on the square root of spin velocity in the laminar regime is consistent with rates being limited by transport through a hydrodynamic boundary layer. The increase in rate with onset of turbulence accompanies a near discontinuous drop in hydrodynamic boundary layer thickness across the transition. A relative independence of rates on spinning velocity in the turbulent regime plus a nonlinear dependence of rates on saturation state are factors consistent with surface reaction control. Together these behaviors implicate a `mixed' transport and reaction control of gypsum dissolution kinetics. A rate law which combines both kinetic mechanisms and can reproduce experimental results under laminar flow conditions is proposed as follows: R=k t 1−Ω ± b +ζ 1− 1+ 2(1−Ω ± b ζ 1/2 where k t is the rate coefficient for transport control, and Ω ± b is the mean ionic saturation state of the bulk fluid. The dimensionless parameter ζ(=D m ± eq /2δk + where m ± eq=mean ionic molal equilibrium concentration, D is the diffusion coefficient through the hydrodynamic boundary layer, δ equals the boundary layer thickness and k + is the rate constant for surface reaction control) indicates which process, transport or surface reaction, dominates, and is sensitive to the hydrodynamic conditions in the reactor. For the range of conditions used in our experiments, ζ varies from about 1.4 to 4.5. Rates of gypsum dissolution were also determined in situ in a cavern system in the Permian Blaine Formation, southwestern Oklahoma. Although the flow conditions in the caverns were not determinable, there is good agreement between lab- and field-determined rates in that field rate magnitudes lie within a range of rates determined experimentally under zero to low spin velocities A numerical model coupling fluid flow and gypsum reaction in an idealized circular conduit is used to estimate the distance which undersaturated solutions will travel into small incipient conduits before saturation is achieved. Simulations of conduit wall dissolution show end-member behaviors of conduit formation and surface denudation that depend on flow boundary conditions (constant discharge or constant hydraulic gradient) and initial conduit radius. Surface-control of dissolution rates, which becomes more influential with higher fluid flow velocity, has the effect that rates decrease more slowly as saturation is approached than otherwise would occur if rates were controlled by transport alone. This has the effect that reactive solutions can penetrate much farther into gypsum-bearing karst conduits than heretofore thought possible, influencing timing and mechanism of karst development as well as stability of engineered structures above karst terrain.

Reduction in the initial wear of ultrahigh molecular weight polyethylene after compressive creep deformation

Although the wear of ultrahigh molecular weight polyethylene (UHMWPE) total joint implant components has received much attention, the creep of this polymer has been inadequately studied. The objectives of this study were to determine whether creep affects the wear of UHMWPE and, if so, to measure the magnitude of this effect. Cylindrical specimens were machined from GUR 4150HP extruded unirradiated UHMWPE rod stock, compressed at three different pressures (0, 4 and 8 MPa) for 10 000 min to simulate creep, and then unloaded for 10 000 min. Wear tests were conducted by unidirectionally sliding the ends of these UHMWPE cylinders at a speed of 125 mm s −1 on a highly polished stainless steel disc with a contact pressure of 4 MPa in bovine serum. Wear of the compressed specimens was only 38% as great as that of the noncompressed specimens ( p < 0.01). There was no significant difference in the amount of wear of specimens compressed at pressures of 4 MPa vs. 8 MPa. It is presently unclear whether this reduction in wear is due to a creep-induced reduction in asperity height, or to a creep-induced increase in UHMWPE's wear resistance.

Annealing Effects on Breakdown Threshold of Radio-frequency Windows.

The breakdown threshold of alumina rf windows depends not only on the bulk characteristics, but also on surface treatments such as polishing and annealing. Sapphire and alumina-ceramic disks, polished and annealed, were examined by high-power tests. The polished disk exhibited a lower threshold value than the annealed one, probably due to its surface charging at defects mechanically introduced by polishing. The elimination of the charged sites present on the surface is considered to be important.

Mold manufacture with plasma spraying

A process has been developed to produce molds or tooling using a steel or chrome- plated steel model. The investigation examined the effect of coating and model materials, model temperature and spray angle on the coating separation from the model surface, coating delamination, and surface quality. A polished model disk was heated and then plasma sprayed with iron, nickel, Ni- Al, or Ni- Cr- B- Si. It was found that the minimum temperature to facilitate entire coating removal was lower for steel models and varied be tween 200 and 450 °C depending on the material. However, at higher temperatures the higher bond strength produced by oxidation on the steel resulted in significant coating pullout. A chrome- plated model, heated to 600 to 700 °C, is required to produce a defect- free coating. The effect of substrate angle on open porosity is most critical for the Ni- Cr- B- Si alloy and least important for Ni- Al coatings. The sur face roughness of the plasma- sprayed molds is comparable to the corresponding models, permitting good surface detail reproducibility. Several molds and tools were produced for use in the glass, rubber, and plastics industries.

Inelastic effects in a thermoplastic adhesive used for bonding a diamond disk

A 1-in.-diam polished diamond disk was bonded to a disk of zinc sulfide (ZnS) using a high-temperature thermoplastic adhesive to form an optical structure that may be used for infrared applications. A postbonding thermal-stress-induced deformation in the structure at room temperature was observed to decrease exponentially over time. This curvature decrease may be attributed to viscoelastic stress relaxation within the adhesive layer. The relaxation behavior of the adhesive layer was characterized over a range of temperatures above room temperature by observing curvature changes in the structure heated to these temperatures. This characterization has led to knowledge of the deformational behavior of this structure during manufacturing and service conditions. In addition, relaxation and approximate physical properties of the adhesive were extracted from the observed behavior.

Oxidation of TiN, ZrN, TiZrN, CrN, TiCrN and TiN/CrN multilayer hard coatings reactively sputtered at low temperature

All the coatings and multilayer structures were deposited in a Sputron plasma-beam-sputtering apparatus at a temperature below 150 °C on polished alumina substrates ( R a= 25 nm) and polished tool steel discs. The coatings were annealed in an oxygen flow at temperatures in the range 500–850 °C. The oxidation kinetics of these coatings were studied by means of the weight gain as a function of the oxidation time at each temperature. On the same coatings, continuous in situ electrical resistivity measurements were taken and these indicate grain boundary oxidation. The composition and the depth profiles of the oxidation products formed were investigated using AES and XPS combined with sputter profiling. The oxide layers were found to grow according to a parabolic diffusion law with activation energies of 1.04, 1.89, 1.92, 2.37,2.91 and 3.98 eV for Ti 0.63Zr 0.37N, TiN, CrN, ZrN, TiN/CrN and Cr 0.72Ti 0.28N, respectively.

Regulation of human osteoblast integrin expression by orthopedic implant materials

Integrins are transmembrane proteins that mediate attachment to extracellular matrix (ECM) proteins. Integrins act as ECM receptors and are believed to play a role in signal transduction and gene regulation, potentially influencing several cellular functions, including differentiation, growth, and migration. Several integrins have previously been found in bone cells in vivo and in vitro. Because the biologic fixation of orthopedic implants depends on optimal cell interactions at the interface, we examined whether integrins are involved in the attachment of osteoblasts to implant materials. In this study, we have used immunohistochemistry to examine the expression of integrins in primary human osteoblasts cultured on tissue culture polystyrene (PS), and rough and polished disks of the orthopedic alloys titanium-aluminum-vanadium (Ti) and cobalt-chrome-molybdenum (CC). The integrin subunits, alpha 2, alpha 3, alpha 4, alpha 5, alpha v, alpha 6, beta 1 and beta 3, were expressed by primary human osteoblasts cultured on PS coated with various ECM molecules. However, alpha 5 and alpha 6 were notably absent in cells attached to the alloys. Also, alpha 3 was not present on rough Ti, polished CC, or rough CC, and beta 3 was not expressed by cells on rough CC. Thus, the nature of the metal alloy appeared to influence the expression of particular integrins. As a result, the ability of cells to adhere to and receive messages from the extracellular matrix may also be influenced by the substratum. These differences may explain previously observed differences in degree of cell attachment to these metals.

Experimental Study of Long-Term Static Friction and Magnetic Slider/Disk Interplanar Separation

Abstract Capacitance between a slider and disk was measured to relate slider/disk interplanar separation to static friction. The parallel plate capacitance formula was used to convert the capacitance into separation with a resolution of less than 1 nm. Separation and coefficient of static friction (stiction) were measured using assorted lubricant thicknesses with and without bonding on polished and textured disks. Separation was measured during contact start/stop (CSS) and long term slider dwell times, after which static friction was measured. Polished disks had high stiction events with smaller separations during and after the stiction event, unlike textured disks. Long-term dwell studies showed the coefficient of static friction and slider micro descent (decrease in interplanar separation) to be greatest with greater lubricant thickness and polished disks. Static friction and separation with bonded and unlubricated disks were time independent.

Dynamic load head-disk interface durability of 50 percent sliders and polished disks

The dynamic load head-disk interface durability is experimentally investigated using 50 percent TPC sliders and super-smooth disks. Severe head-disk contact conditions are applied and disk-synchronized head loading motions are performed in order to see the effect of repeated dynamic load head-disk contacts. Readback signals are recorded and analyzed, and the disk surfaces of the head-disk contact area are examined after 100,000 repeated contacts. The results are compared with those of our previous study. We find that the dynamic load head-disk interface durability of 50 percent TPC sliders and polished disks is superior to that of 70 percent taper-flat sliders and textured disks, and the experimental results suggest that better dynamic load head-disk interface reliability can be achieved with good head-loading velocity control, even though head-disk contact may occur during loading.