Measurement Of Wear Rate Research Articles

Tribological Performance of DLC/WC Coatings at Elevated Temperatures

Tribological properties of nanostructural DLC/WC coatings were measured with a high temperature pin-on-disc CSM Tribometer in the range from room temperature (RT) up to 500 °C. The tribological performance was evaluated with respect to the wear rates of balls and coatings, friction coefficient and wear debris analysis. The running-in phenomenon of steel ball sliding against DLC coating was studied by sequential in situ measurements of ball wear rate. The wear volume was almost constant from number of cycles of 1 500–5 000. This phenomenon was caused by lowering of contact pressure and could not be caused by changing of wear mode; the measured friction coefficient showed no fluctuation at 1 500 cycles. Friction and wear characteristics described in this study showed their limitations of DLC applicability.

Dry sliding of Cu–15 wt%Ni–8 wt%Sn bronze: Wear behaviour and microstructures

Dry sliding wear of Cu–15Ni–8Sn (in wt%) bronze against a stainless steel 440C counter surface is investigated using a pin-on-disc tester in air and flowing Ar gas. The microstructure of the debris, the worn surface and the subsurface of the pin have been characterized using X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy. The debris is found to comprise of particles of Fe 2O 3 and CuO phases, in addition to bronze particles. EDS analysis of the debris revealed that bronze picked up Fe and Cr elements from the stainless steel while the Fe 2O 3 particles picked up Cu, Ni and Sn elements from the pin, attesting the mechanical mixing of chemical species during the wear process. Cross-section SEM of the worn pin revealed a highly deformed subsurface layer, capped by a thin layer separating the outer surface and the deformed layer. Cross-sectional TEM investigations of the capped layer revealed it to be a set of mechanically mixed layers (MML) comprising nanograins with varying grain size and composition. SEM micrographs also revealed the formation of subsurface cracks in the vicinity of the interface between the deformed subsurface layer and the capping layer. Wear processes are discussed in the light of these microstructural observations, combined with wear rate and friction coefficient measurements.

Tribological behaviour and residual stress of electrodeposited Ni/Cu multilayer films on stainless steel substrate

In the present study, [Ni (4.5 nm)/Cu ( t Cu = 2, 4 and 8 nm)] multilayers were pulse electrodeposited on stainless steel (AISI SS 304) substrate from sulphate based single bath technique. X-ray diffraction (XRD) was used to investigate the structure and stress of the Ni/Cu multilayer. The results from XRD analysis indicated that the deposited multilayers had a preferred crystal orientation of [111] and presence of satellite reflection suggested the formation of superlattice. The stress level within the deposited multilayers was found to be sensitive to the sublayer thickness. Sliding wear behaviour of electrodeposited Ni/Cu multilayer films has been investigated against a tungsten carbide (WC) ball as the counter body and compared with that of the constituents, Cu and Ni coatings. The wear tests were carried out by using a reciprocating ball-on-flat geometry at translation frequencies of 5 and 10 Hz, slip amplitude of 1 mm and at five different loads of 3, 5, 7, 9 and 11 N. Friction force was recorded on-line during the tests. At the end of the tests, the wear scars were examined by laser surface profilometry and scanning electron microscopy (SEM). Friction coefficient was found to be dependent on load and Cu layer thickness ( t Cu) and the values for multilayers were border between Ni and Cu. Among multilayers, sample with minimum t Cu has shown the lowest friction coefficient and wear rate. With increasing t Cu, the wear mechanism changes from pure abrasive wear at t Cu = 2 nm, to particle entrapment at t Cu = 4 nm to particle embedding at t Cu = 8 nm. Detailed investigation of the wear scar morphology as well as wear rate measurement revealed that at low loads, ( H/ E) ratio and residual stress governed the wear rate and the principle wear mode was abrasive cutting. At intermediate loads, the role of residual stress became insignificant while wear was governed by ( H/ E) ratio and plastic deformation. However, at higher loads, plastic deformation played the major role.

Performance profiling of minimum quantity lubrication in machining

This study develops the analytical understanding of mechanical and environmental effects of minimum quantity lubrication (MQL) in machining and profiles the MQL performance as functions of machining and fluid application parameters. Physics-based predictive models are formulated to quantitatively describe the resulting contact stress and temperature distributions under completely dry, MQL (under boundary lubrication), and flood cooling conditions in cylindrical turning. On that basis, the air quality effects in terms of cutting fluid aerosol emission rate and droplet size distribution have been derived through the modeling of evaporation, runaway aerosol atomization, and dissipation processes. Additionally, the abrasion, adhesion, and diffusion wear mechanisms under time-evolving cutter geometry have been quantitatively evaluated for the development of a tool wear and tool life relationship with the fluid application condition. Experimental measurements of force, temperature, aerosol concentration, and tool flank wear rate in dry, MQL, and fluid cooling cases has also been pursued to calibrate and validate the predictive models. The MQL performance profile is assessed through the sensitive analysis of tool utilization, power consumption, and air quality with respect to MQL application parameters; and it serves as a basis to support the overall optimization of machining process by incorporating both mechanical and environmental considerations.

Nanometer scale measurement of wear rate and vibrations by fiber-optic white light interferometry

A white light interferometric method for nanometer scale measurement of wear events by fiber-optic sensing configuration is presented. The proposed contactless technique is capable of measuring the wear rate and vibrations of the pin in a standard pin-on-disc tribometer remotely and simultaneously. All data are obtained by an interferometric reading of the sensing fibers displacement using a passive demodulation technique employing a 3 × 3 fiber-optic coupler and mechanical scanner. We obtained a pin position resolution better than 100 nm in the range of 400 μm as well as minimal detectable amplitude of the pin vibration of about 50 pm / Hz .

Cobalt based alloy PTA hardfacing on different substrate steels

Components from equipment for different processing industries are exposed to severe service conditions. Parts are therefore manufactured so that specific demands can be met through adequate selection of surface processing techniques and hardfacing alloys. Whenever surface welding techniques are used to improve a component's performance, quality requirements such as controlled dilution of the deposited alloy by the substrate are a priority. This work has evaluated this interaction between a hardfacing Co based alloy and the substrate steel. A high carbon cobalt based alloy was 'plasma transferred arc' (PTA) deposited on three different substrate steels. The role of the chemical composition of the substrate on the characteristics of the coatings was evaluated for two sets of processing parameters, targeting two extreme dilution levels. Coatings characterisation was assessed through microstructure analysis, microhardness measurements, dilution levels, and wear rate measurements. Results showed that the influence of the substrate chemical composition was more significant for coatings of controlled low dilution deposits. The selection of the substrate steel affected dilution levels, microstructure, hardness values, and sliding wear rates exhibited by the coatings. On both sets of coatings deposits made on carbon steel gave better wear performance than those deposited on the stainless steels tested.

Tribological Investigations of Parts Sintered and Coated by Laser Beam

In this work we intend to investigate the surface properties of laser sintered and coated parts, by measurement of friction coefficient and wear rate. The main aim of this research is to justify laser sintered prototype tools for injection molding of fibre-reinforced polymers. For increase of wear resistance we used hard Co-based and Fe-based coatings on laser-sintered phosphorous bronze and unalloyed steel substrate. Short carbon- and glass-fibre-reinforced polymers were used as counter bodies. For the tribological laboratory model tests a pin-on-disk test rig was used. In case of coated parts – with higher wear resistance – we used a cylinder-on-cylinder tribometer. The tribological properties were determined at different load conditions. Our results show that the friction coefficient and wear resistance of laser treated surfaces are good. The coefficient of friction of coated specimens is slightly less, but the wear rate is significantly less.

Temperature dependence of tribological properties of MoS 2 and MoSe 2 coatings

Transition metal dichalcogenides are well known for their lubricating properties. MoS 2 is the most popular member of this family and it is widely used as a solid lubricant in vacuum and inert gases. However, the lubricating properties of MoS 2 are deteriorated in humid air. It is known that molybdenum diselenide (MoSe 2) has the same crystal structure and also exhibits suitable lubricating properties, but their dependence on air humidity has not been studied yet in details. This paper is aimed to the comparison of tribological properties of MoS 2 and MoSe 2 coatings measured in air of different humidity and at elevated temperatures. Both coatings were prepared by non-reactive DC magnetron sputtering and tested with ball-on-disc high temperature tribometer. The results of measurements of friction coefficient and wear rate vs. tribometer revolutions and the resulting dependencies of friction coefficient and wear rate on ambient air relative humidity are presented. These results show that the friction coefficient of MoSe 2 was not influenced by air humidity. Wear rate of MoSe 2 in dry air was substantially higher than that of MoS 2; in humid air, the MoS 2 wear rate increased rapidly while wear rate of MoSe 2 remained unchanged. The operating temperature of both coatings was limited to 350 °C.

Friction and wear measurements of laser-sintered and coated parts

The aim of this research is the investigation of surface properties, the measurements of friction coefficient and wear rate of laser-sintered and coated parts. The industrial background of this research is to prove applicability of laser-sintered prototype tools for injection moulding of fibre-reinforced polymers, furthermore to increase the wear resistance of unalloyed steel tools by laser coatings. The materials of the test specimens were laser-sintered phosphorous bronze and unalloyed steel. For increase of wear resistance we used hard Co-based and glassy-like Fe-based (FeB) coatings. As counter bodies we used polymers reinforced with short carbon and glass fibres. The laboratory model tests of selective laser-sintered parts were carried out on a pin-on-disk machine. In case of coated parts—with higher wear resistance—we used a cylinder-on-cylinder tribometer. The tribological properties were determined at different load and temperature conditions. The results of the investigation show that the friction coefficient and wear resistance of laser treated surfaces are good. The coefficient of friction of coated specimens is slightly less, but the wear rate is significantly less.

ピンオンディクス試験機の試作と摩耗速度評価法の検討(OS.18 機械要素のトライボロジー)

A pin-on-disk tribometer was constructed as a trial machine, with which an endeavor was made to obtain the wear rate in step load method throughout the run. Experiments were conducted for aluminum alloy and cast iron using some lubricants, in which the friction coefficient, the contact potential and the wear length were determined. By making the correction of the wear length based on thermal expansion and elastic deformation of test specimen, it was found that the measurements of wear rate on the tribometer had a sufficiently accurate data.

Ultra thin layer activation by implantation of recoil radioactive nuclei: Experiments and simulations

The ultra thin layer activation (UTLA) by recoil implantation of heavy radioactive nuclei has a great potential in wear or corrosion rate measurements, because of its nanometric sensibility. In regard of the complexity of its calibration, a Monte Carlo simulation program (Implantation of Recoil Ions Simulation) was developed to calculate the depth profile of implanted nuclei. It is associated to SRIM software for the transport of particles in matter. In this paper, the different simulation parameters and the potentiality of IRIS program are described. Implantation experiments with the 56Fe(p,n) 56Co nuclear reaction have been performed at 22.8 MeV protons to measure the angular and depth distributions of 56Co nuclei emerging from the iron target. In comparison with experiments, the simulated angular distribution has a good magnitude of implanted activity, but presents an excess of nuclei in high angles of implantation. This excess comes from too great emission probability around the critical angle. For depth profile, the simulated spectrum of transmitted particles is too energetic.

Friction induced mechanochemical and mechanophysical changes in high performance semicrystalline polymer

By using X-ray photoelectron spectroscopy (XPS) and Fourier transform Raman (FT-Raman) spectroscopy, the worn specimens of polyetheretherketone (PEEK) tested under unlubricated sliding friction and wear conditions at a constant sliding speed were investigated in order to reveal mechanochemically and mechanophysically induced structural changes of polymer as well as wear mechanisms on a molecular scale. Chain scission was found on the worn surface layer. The results suggest that oxidation was the major mechanochemical reaction that followed the chain scission on the top surface. Evidence for chain branching or even crosslinking in bulk materials was also presented. Moreover, two-stage loading dependencies were found for both surface and subsurface in the bulk as revealed through wear rate measurement and wear debris analysis. It was proved that a thermo-activation of polymer segments may be responsible for the transition in the dependence of structure on load. The results of the present work also provide a method (based on spectral analyses) that can be used for studying micromechanisms accounting for shear deformation and failure.

Tribological behaviour of plasma-sprayed zirconia coatings

Various layers of zirconia, coated on cast iron plates and steel discs by plasma spraying, were studied to gain a better understanding of their tribological behaviour. Coatings selected for this investigation were zirconia-5% CaO, zirconia-8% yttria, zirconia-20% yttria and alumina-zirconia coatings. Wear tests were conducted under conditions of dry contact with reciprocating motion at a temperature of 200 °C. Measurements of friction and wear rate were made in association with sliding distance for various friction pairs: self-mated contact between zirconia-sprayed specimens, sprayed plate against chromium-plated disc, and uncoated cast iron plate against chromium-plated disc which represents the contact between cylinder liner and piston ring in diesel engines. To identify the wear mechanism, an X-ray diffractometer, scanning electron microscope, transmission electron microscope, surface roughness tester and micro-hardness tester were used. 92%-8% zirconia-yttria, 80%-20% zirconia-yttria and alumina-zirconia composite coatings exhibited excellent wear resistance. Wear debris were considerably involved in the wear process in the steady state. It is shown that the plastic deformation and forming of a smooth film by material transfer on the sliding surface strongly influenced the wear rate and friction coefficient. Phase transformation in the contact region was discussed. Phase transformation from the tetragonal to monoclinic phase was not noticeable but the transformation of the tetragonal phase to the t' tetragonal phase was observed to influence the tribological behaviour of the coatings.

On the wear debris of polyetheretherketone: fractal dimensions in relation to wear mechanisms

It has been recognized that wear debris contains extensive information about wear and friction of materials. Investigation of wear debris is important for tribological research. In order to find out an effective way that is able to diagnose and predict the wear state of polymers, the authors investigated the relationship between the wear debris morphology and the wear behaviour of the bulk material. Polyetheretherketone (PEEK) was employed as the model material. Its sliding wear and friction properties were measured by means of a pin-on-disc apparatus. At a constant sliding velocity of 1 m s −1, the specific wear rate was independent of load under lower loading conditions (1–4 MPa) but increased with a rise in load under higher loading conditions (4–8 MPa). The coefficient of friction was insensitive to the variation of contact pressure. The possible mechanisms involved were analysed on the basis of the wear debris morphology as well as the wear performance. Fractal geometry, which describes non-Euclidean objects, was applied to the quantitative analysis of the boundary texture of the wear debris due to the fact that the qualitative assessment of the wear debris morphology was not effective enough to reflect the geometrical variation of the fragmental shapes. The experimental results demonstrated that the wear debris were fractals, and could be characterized with the fractal dimensions which were determined by the slit island method. In addition, it was found that the fractal dimension of the wear debris was closely related to the wear behaviour of PEEK, and can be regarded as a measure of wear rate.

Predictability of wear status provided by fractal dimensions of wear particles

Wear particles are produced when materials rub against each other. It has been identified that wear particles carry substantial information about the wear processes experienced by a material working in a tribological environment. Through careful examination of the wear particles, the wear mechanisms and the cause of wear can be successfully deduced [I]. In addition to the scientific significance, investigation of wear particles is also important in the industrial field, for example, a ferrography technique is now being used for on-line inspection of metallic frictional couples. However, such an analysis and interpretation depending on unreliable visual assessment cammt always guarantee the necessary objectivity and accuracy. Evidently, a numerical method that is independent of subjectivity is needed. A recent development in this direction is the application of fractals to the quantitative characterization of wear particles [2, 3]. Fractal geometry describing non-Euclidean objects [4] has proved to be effective for analysing the chaotic morphology of wear particles. It was further found that the fractal dimensions of wear particles were closely related to the wear behaviour of the bulk material, and can serve as a measure of wear rate [5]. The present letter is a continuation of previous work [5] in which the fractal dimensions of wear particles generated at different loadings were measured by the "slit island method" following sliding wear of polyetheretherketone (PEEK) under unlubricated conditions against steel. The main objective here was to examine the sensitivity of a different fractal characterization technique, i.e. the Richardson method [6]. The materials employed in this investigation were PEEK plates with a reduced viscosity of 0.62 ml gl , kindly supplied by Jilin University, China. The specimens for wear tests were machined from these plates with a geometry of 5 x 10 x 15 mm, resulting in an apparent contact area of about 5 x 10 man 2. Room temperature sliding wear tests were carried out on a pin-on-ring apparatus [7] under different loadings at a constant velocity (v = 0.4 msi ) . The carbon steel rings (0.42-0.45 wt% C, 0.170 .37wt% Si and 0 .50-0.80wt% Mn, HRC 50) had a diameter of 40 mm and an initial surface roughness Ra of 0.1 Nm. When the apparatus had operated for 2 h in steady state, the wear test was

IS POLYETHYLENE STILL THE BEST PROSTHETIC BEARING SURFACE?

The increased number of joint prostheses now being implanted into younger and more active patients has made wear and tear on polyethylene bearing surfaces more apparent and more important. Many papers have described the measurement of wear rate, mainly in the hip, and also the biological consequences of the tissue response to polyethylene particles liberated by wear. There is now good evidence that these particles accumulate in periprosthetic tissues, cause an inflammatory reaction, and lead to bone lysis. Implant loosening made worse by severe bone loss presents the surgeon with a difficult task of revision, and this is becoming a major problem in limiting the life of joint replacements. The level of interest in this ‘UHMWPE disease’ (Sedel 1992) can be gauged from the presentation of more than 50 polyethylene-related papers at the 1996 Orthopaedic Research Society meeting in Atlanta. Research into the problem of wear is complex, since ultra-high-molecular-weight polyethylene (UHMWPE) is variable in its manufactured state. This material was chosen because polyethylene has little biological and chemical reactivity and its high molecular weight imparts resistance to wear. The manufacture of implants of this polymer is difficult. Many of the normal processes, such as injection moulding, break down the long-chain molecules of UHMWPE and make it more liable to wear. The polymer is available as a base powder, which could be used to mould implants, but the cost and difficulties of this process mean that most of the manufacturers of implants obtain their stock as sheets or bars from specialist companies such as Hoechst. The prosthetic components are then machined from this solid stock. It is possible for manufacturers to modify UHMWPE by subjecting it to elevated pressures and temperatures, but as yet there is no evidence that this leads to reduced wear in clinical use. Orthopaedic implants use much less than 1% of the world production of UHMWPE, with the result that there is little implant-related commercial pressure on the polymer producers. Indeed, concern about litigation is causing polymer manufacturers to consider withdrawal from the field. Thus, changes may be made in a polymer without the knowledge of the end user or the manufacturer of the prosthesis. The material is still UHMWPE, but minor changes in the catalyst or the fusion process at fabrication can lead to changes in the final product. These may alter the wear or degradation resistance of prostheses, and make it almost impossible to perform valid comparative tests between implants, and very difficult to verify claimed advances in polymer quality. Li and Wright (1995) have recently offered

Dry sliding wear of NiAl

The dry sliding wear behavior of the B2-structured (ordered body-centered cubic) compound NiAl has been studied. Pin-on-disk experiments were conducted at room temperature in air using pins made from extruded NiAl with compositions of 50, 48, and 45 at.% aluminum. Partially stabilized zirconia was the disk material. Wear rate measurements showed an inverse relation between wear and hardness. Hardness increased with increasing nickel content as the composition moved away from stoichiometric composition. Friction results indicate higher friction coefficients for Ni-50Al than for either Ni-48Al or Ni-45Al. Surface examinations of the pin wear scars, by both optical microscopy and scanning electron microscopy, show the wear process of NiAl is dominated by plastic deformation in all compositions, with little evidence of material loss by brittle fracture.

A model for the erosive wear of rubber at oblique impact angles

A model has been developed to predict the erosive wear behaviour of elastomers under conditions of glancing impact by small hard particles. Previous work has shown the erosive wear mechanism of elastomers under these conditions to be similar in nature to that of abrasive wear by a sharp blade. The model presented here was developed from the model of Southern and Thomas for sliding abrasion, by combining their treatment of the growth of surface cracks with a model for particle impact in which the force - displacement relationship for an idealized flat-ended punch on a semi-infinite elastic solid was assumed. In this way an expression for the erosive wear rate was developed, and compared with experimental measurements of wear rate for natural rubber, styrene - butadiene rubber and a highly crosslinked polybutadiene rubber. Good qualitative agreement was found between the predictions of the model and the experimental measurements. The variation of erosion rate with impact velocity, impact angle, particle size, elastic modulus of the material, coefficient of friction and fatigue properties were all well accounted for. Quantitative agreement was less good, and the effects of erosive particle shape could not be accounted for. The reasons for these discrepancies are discussed.

Nanoindentation Hardness of 17–4PH Stainless Steel Irradiated With 2.5 MEV PER Nucleon 20NE2+ Ions

ABSTRACTDirect ion implantation of radioactive isotopes, such as 7Be or 22Na, has recently been of interest as a means of surface layer activation for purposes of wear-rate measurement in material systems for which activation by conventional proton irradiation is ineffective. Though direct implantation doses anticipated for adequate wear measurement sensitivity are expected to be quite low (∼1012 cm−2), the potential for alteration of wear properties by ion damage cannot be ignored. The present work was designed to simulate 22Na implantation with non-radioactive 20Ne irradiations into specimens of 17–4PH stainless steel which had been deliberately heat treated to contain 98 vol% metastable martensite. Specimens were subjected to doses of 2×1012, 2×1013 and 2×1014 cm−2 of 20Ne2+, applied at a total energy of 50 MeV, giving a projected ion range (determined by TRIM-91 computations) of approximately 10 μm. Nanoindentation surface hardness traverses were conducted to detect any material softening which may have resulted from ion-solid interactions within the projected range. Though doses of > 1014 cm−2 produced a detectable softening (apparent as a dip in the hardness level corresponding to locations near the end of the ion range) the maximum dose for a negligible effect on nanoindentation hardness was found to be approximately 1013 cm−2, well above the doses anticipated for use in wear studies employing direct ion implantation of radioisotopes.

Wear and friction of thin film high temperature oxide superconductors

We have examined the sliding properties of a NdFeB magnet against a thin film YBa 2Cu 3O 7 superconductor. Pin-on-disk experiments were performed at room temperature and in normal air using a 10 mm magnetic NdFeB ball loaded to 31.2g and a sliding speed of approximately 0.57 cm s −1. Such conditions produced a steady-state friction coefficient of 1.1±0.3. Wear rate measurements indicated that NdFeB will wear YBa 2Cu 3O 7 at a rate of 1.3 × 10 −14 m 3 m −1 and that the NdFeB/YBa 2Cu 3O 7 sliding system possess a wear coefficient of 4.2 × 10 −14 m 3 Nm −1. These high values appear to be the result of both abrasive and adhesive wear. Adhesion between the sliding surfaces is most probably enhanced by the oxygen reactivity of the pin material and the high oxygen content in the superconductor.