Sliding contacts for the pharmaceutical industry: failure analysis and dry sliding tests for the replacement of hard Cr on AISI 316L steel

Several alternatives were compared for the replacement of hard electroplated Cr coating to improve the tribological properties of the AISI 316L austenitic stainless steel for pharmaceutical packaging applications, including low temperature carburizing (LTC), thermal spray coatings (Al₂O₃-13TiO₂, WC-17Co), substitution of the AISI 301 reference counterface with polymeric materials (PTFE, UHMWPE, PEEK). In dry sliding block on ring tests, the LTC AISI 316L cylinders lead to the lowest wear rates of the AISI301 sliders under low loads (up to 10 N). When considering the polymer vs. uncoated AISI 316L couple, PEEK and UHMWPE lead to lower friction and comparable wear rates with respect to the reference couple (AISI 301 vs. Hard Cr coated-AISI 316L) in the whole range of tested loads.     

Influence of the countermaterial on the dry sliding friction and wear behaviour of low temperature carburized AISI316L steel

Low temperature carburising (LTC) allows a significant hardness increase, with a consequent increase in wear resistance, without deteriorating corrosion behaviour. However, wear resistance strongly depends on contact conditions, therefore this work focuses on the dry sliding behaviour of LTC-treated AISI316L austenitic stainless steel against several countermaterials (AISI316L, LTC-treated AISI316L, hard chromium or plasma-sprayed Al₂O₃–TiO₂). LTC produced a hardened surface layer (C-supersaturated expanded austenite), which improved corrosion resistance in NaCl 3.5% and increased wear resistance, to an extent which depends on both normal load and countermaterial. The best results were obtained when at least one of the contacting bodies was LTC-treated, because this condition led to mild tribo-oxidative wear. However, LTC did not improve the behaviour in terms of friction.     

On the influence of surface finish of SSiC on the results of tribological laboratory tests in the case of water lubricated oscillating sliding

The development of materials for tribological applications requires characterisation of their friction and wear behaviour. This characterisation is often based on tribological model testing, working with simple shaped specimens, running under well-defined conditions. Discrepancies in test results may arise from the fact that non-standard tests with different sets of operational parameters are used. An essential starting point for the development of tribological standards is knowledge of the main parameters that influence the tribological properties. One aspect that is not often adequately taken into account is the surface finish of the test specimens. Results are presented of friction and wear tests with self-mated SSiC couples (ball on disc), running in water in an oscillating sliding mode. The surfaces of the disc were ground, lapped, or polished, respectively, running against a polished ball. For certain test conditions, the influence of the surface finish on wear is found to be negligible, while for other conditions, the wear rate can differ by one order of magnitude or even more. The consequences for the standardisation of wear tests of ceramic materials are discussed.     

Comparative Study of Thermally Sprayed Coatings Under Different Types of Wear Conditions for Hard Chromium Replacement

The tribological properties of part surfaces, namely their wear resistance and friction properties, are decisive in many cases for their proper function. To improve surface properties, it is possible to create hard, wear-resistant coatings by thermal spray technologies. With these versatile coating preparation technologies, part lifetime, reliability, and safety can be improved. In this study, the tribological properties of the HVOF-sprayed coatings WC–17%Co, WC–10%Co4%Cr, WC–15% NiMoCrFeCo, Cr₃C₂–25%NiCr, (Ti,Mo)(C,N)–37%NiCo, NiCrSiB, and AISI 316L and the plasma-sprayed Cr₂O₃ coating were compared with the properties of electrolytic hard chrome and surface-hardened steel. Four different wear behavior tests were performed; the abrasive wear performance of the coatings was assessed using a dry sand/rubber wheel test according to ASTM G-65 and a wet slurry abrasion test according to ASTM G-75, the sliding wear behavior was evaluated by pin-on-disk testing according to ASTM G-99, and the erosion wear resistance was measured for three impact angles. In all tests, the HVOF-sprayed hardmetal coatings exhibited superior properties and can be recommended as a replacement for traditional surface treatments. Due to its tendency to exhibit brittle cracking, the plasma-sprayed ceramic coating Cr₂O₃ can only be recommended for purely abrasive wear conditions. The tested HVOF-sprayed metallic coatings, NiCrSiB and AISI 316L, did not have sufficient wear resistance compared with that of traditional surface treatment and should not be used under more demanding conditions. Based on the obtained data, the application possibilities and limitations of the reported coatings were determined.     

Friction and rolling–sliding wear of DC-pulsed plasma nitrided AISI 410 martensitic stainless steel

In the present work, industrial-scale DC-pulsed plasma nitriding for 20 h at 673 K was used to improve the wear resistance of an AISI 410 martensitic stainless steel. The tribological behaviour was studied and compared to the behaviour of the same steel in as-received condition.Pin-on-disc dry tests, using an alumina ball as counter-body, were carried out to determine the evolution of the friction coefficient. The wear resistance was investigated using an Amsler-disc-machine, employing a dry combined contact of rolling–sliding with three different applied loads. The wear mechanisms involved during rolling–sliding of unnitrided and plasma nitrided steels were investigated by microscopic observation of the surfaces, the corresponding cross-sections and the produced wear debris.The combination of different wear mechanisms taking place in the wear process of unnitrided and nitrided materials were discussed and analyzed. In contrast to the unnitrided steel, DC-pulsed plasma nitrided samples presented an improvement in the friction coefficient and the wear rate.     

Tribological Behavior of New Martensitic Stainless Steels Using Scratch and Dry Wear Test

This paper focuses on the tribological characterization of new martensitic stainless steels by two different tribological methods (scratch and dry wear tests) and their comparison to the austenitic standard stainless steel AISI 316L. The scratch test allows obtaining critical loads, scratch friction coefficients, scratch hardness and specific scratch wear rate, and the dry wear test to quantify wear volumes. The damage has been studied by ex situ scanning electron microscopy. Wear resistance was related to the hardness and the microstructure of the studied materials, where martensitic stainless steels exhibit higher scratch wear resistance than the austenitic one, but higher hardness of the martensitic alloys did not give better scratch resistance when comparing with themselves. It has been proved it is possible to evaluate the scratch wear resistance of bulk stainless steels using scratch test. The austenitic material presented lower wear volume than the martensitic ones after the dry wear test due to phase transformation and the hardening during sliding.     

Tribological behaviour of stainless steel with respect to that of DLC in terms of energetic aspects

Abstract

The tribological behaviour of stainless steel (SUS 440C) relative to that of diamond-like carbon (DLC) was investigated in terms of tribometer input energy. The DLC was prepared on tungsten carbide (WC) substrates using radio frequency plasma chemical vapour deposition with benzene (C₆H₆) as a gas source. The stainless steel ball, as the counterpart, was tribotested. The input energy was calculated using the applied load, friction coefficient and sliding distance obtained from each tribotest. The wear loss of the ball increased as the sliding distance increased, whereas wear loss of the DLC was not directly observed. During evaluation of the input energy, the wear rate of the stainless steel ball decreased as the input energy increased. We propose a method for evaluating tribological properties using the input energy and discuss the wear behaviour of the stainless steel based on the input energy.     

The Sliding Friction of Hybrid Composite Journal Bearing Under Various Test Conditions

The friction and wear behaviour of SiC, Si₃N₄ and SiC/Si₃N₄ composite ceramics were investigated with oscillating sliding (gross slip fretting) at room temperature. The influence of counter body material and the humidity of the surrounding air was studied with a ball-on-disc configuration with different ball materials (1000Cr6, Al₂O₃ SiC and Si₃N₄). The effect of RH on friction is marginal with exception of SiC (low friction) as counter body material. The wear behaviour, however, is strongly affected by humidity, showing inverse trends for different counter body materials. Consequently, the wear behaviour of a tribo couple can be improved by selecting an adequate mating material. The results reveal the necessity to control RH in tribological tests. For estimation of the performance of tribo couples under varying environmental conditions, a variation of RH is required. In tribo couples with single phase SiC, either as ball or disc, the tribological behaviour of the system is dominated by SiC. The friction behaviour of the composite material is in between the behaviour of the two single phase materials, Si₃N₄ and SiC, whereas the wear behaviour is very similar to that of single phase Si₃N₄.     

Multi-walled Carbon Nanotube-Imidazolium Tosylate Ionic Liquid Lubricant

Multi-walled carbon nanotubes (MWCNTs) were added in a 0.5 wt% proportion to 1-alkyl-3-methylimidazolium room temperature ionic liquids (IL) The new IL + MWCNTs dispersions obtained by mechanical grinding were used as lubricants of the polycarbonate (PC) disc/AISI 316L stainless steel pin contact, and their tribological performance compared with that of the corresponding IL. The highest friction reduction at 0.98 N and 0.10 m s^?1, of a 54 %, was obtained when MWCNT were added to 1-ethyl-3-methylimidazolium tosylate ([EMIM]Ts). The [EMIM]Ts + MWCNT dispersion was further characterised by rheological measurements, contact angle, DSC, TGA, FTIR and Raman spectroscopies, TEM microscopy and XRD. The addition of MWCNTs increases the viscosity of the IL in a 50 % at room temperature and the wettability on the PC surface, while the IL increases the purity and alignment of the nanotubes. The variation of friction coefficient was determined under variable sliding velocity conditions. The higher friction reduction for [EMIM]Ts + MWCNT with respect to [EMIM]Ts is observed for sliding velocities higher than 0.075 m s^?1. Under the experimental conditions, the surface damage on the PC and AISI 316L surfaces was negligible.     

Tribological characterisation of hard coatings with and without DLC top layer in fretting tests

The potential of coatings to protect components against wear and to reduce friction has led to a large variety of protective coatings. In order to check the success of coating modifications and to find solutions for different purposes, initial tests with laboratory tribometers are usually done to give information about the performance of a coating. Different Ti‐based coatings (TiN, Ti(C,N), and TiAlN) and NiP were tested in comparison to coatings with an additional diamond‐like carbon (DLC) top coating. Tests were done in laboratory air at room temperature with oscillating sliding (gross slip fretting) with a ball‐on‐disc arrangement against a ceramic ball (Al₂O₃). Special attention was paid to possible effects of moisture (relative humidity). The coefficient of friction was measured on line, and the volumetric wear at the disc was determined after the test from microscopic measurements of the wear scar and additional profiles. The friction and wear behaviour is quite different for the different coatings and depends more or less on the relative humidity. The DLC coating on top of the other coatings reduces friction and wear considerably. In normal and in moist air the coefficient of wear of the DLC top‐layer coating is significantly less than 10⁻⁶ mm³/Nm and the coefficient of friction is below 0.1. In dry air, however, there is a certain tendency to high wear and high friction. Copyright © 2006 John Wiley & Sons, Ltd.     

The repeatability of friction and wear results obtained from unlubricated reciprocating sliding tests

Laboratory tests can help in the analysis of tribological failures of elements, and improve tribo‐systems by choosing appropriate materials. In order to characterise the friction and wear behaviour of candidate materials, various different test methods have been developed in the past and are still in use. One such method is the reciprocating sliding of a ball against a disc. In the work reported here, the repeatability of friction and wear results was evaluated with ten tests under identical conditions with a steel (100Cr6) or alumina (Al₂O₃) ball against a steel (100Cr6) disc under unlubricated conditions at room temperature. The influence of ambient humidity on friction and wear behaviour was determined in three additional tests in dry and in moist air, respectively. The repeatability of friction coefficient in normal air was better than 5% for alumina/100Cr6 and 12% for 100Cr6/100Cr6, while the repeatability of volumetric wear was slightly better than 10% for alumina/steel, and slightly worse than 10% for steel/steel. For both couples the coefficient of friction is lowest in moist air and about 50% higher in dry air. The coefficient of wear is also least in moist air and higher by a factor of 3(5) in dry air for tests with a 100Cr6 (alumina) ball.     

Tribological behaviour of duplex treated Ti–6Al–4V: combining nitrogen PSII with a DLC coating

The chemical structure and tribological behaviour of Ti–6Al–4V plasma source ion implanted with nitrogen then DLC-coated in an acetylene plus hydrogen-glow discharge (bias voltage −10 to −30 kV) were investigated. The as-modified samples have a TiN/H:DLC multilayer architecture (coating resistivity 1.6×10⁹ to 2.4×10¹¹ Ω/cm) and exhibit higher hardness, especially at low loads or plastic penetrations in the order of deposition bias voltage −10, −20 and −30 kV. At a lower contact load (1 N) and higher sliding speed (0.05 m/s), frictional properties in most cases improved, as did wear properties. At a higher contact load (5 N) and lower sliding speed (0.04 m/s), friction showed almost no improvement, and wear properties deteriorated. When the material of the counterbody was then changed from AISI 52100 to Ti–6Al–4V modified as the disc (contact load 5 N unchanged, sliding speed decreased), the friction coefficient decreased (but showed no improvement compared with the unmodified sample), while wear properties deteriorated further, and wear was changed from just the disc to both disc and ball, abrasive and adhesive dominated. Transfer films, mainly made up of wear debris transferred from the disc wear surfaces, were formed on the wear scars of the counterbodies. The deterioration of wear properties of the modified samples at the higher contact load is considered to be caused by the “thin ice” effect.     

Effect of sliding wear on tribocorrosion behaviour of stainless steels in a Ringer's solution

The dependence of the tribocorrosion of stainless steels AISI 304L and SS 3M^® orthodontic archwires sliding against corundum in a Ringer's solution on applied normal force, and sliding velocity, has been investigated using in situ electrochemical noise measurements. Applied normal force and sliding velocity were found to greatly affect current and potential during fretting-corrosion. An increase in normal force and sliding velocity induce an increase in current and a decrease in potential accelerating the depassivation rate of the tested stainless steels. The fluctuations in potential and current during fretting-corrosion are more pronounced at increasing sliding frequency than at increasing applied normal force. Sliding wear affects the repassivation behaviour of the tested materials by increasing the anodic current in the wear track area.     

Friction and wear properties of Fe7Mo6-based alloy in ethyl alcohol

In this study, the friction and wear properties of Fe₇Mo₆-based alloy, Fe and Mo disk specimens sliding against ASTM 52100 steel and Cu and SiC ball (or pin) specimens in ethyl alcohol were evaluated using an Optimol SRV oscillating friction and wear tester. The Fe₇Mo₆-based alloy disk specimens exhibited more stable friction coefficients than the Fe and Mo disk specimens when slid against the ASTM 52100 steel ball specimen. On the other hand, the Fe/SiC tribo-pairs exhibited the lowest average friction coefficients (0.14-0.17).     

Tribological behaviour and wear mechanism of MoS2–Cr coatings sliding against various counterbody

MoS₂–Cr coatings with different Cr contents have been deposited on high speed steel substrates by closed field unbalanced magnetron (CFUBM) sputtering. The tribological properties of the coatings have been tested against different counterbodies under dry conditions using an oscillating friction and wear tester. The coating microstructures, mechanical properties and wear resistance vary according to the Cr metal-content. MoS₂ tribological properties are improved with a Cr metal dopant in the MoS₂ matrix. The optimum Cr content varies with different counterbodies. Showing especially good tribological properties were MoS₂–Cr8% coating sliding against either AISI 1045 steel or AA 6061 aluminum alloy, and MoS₂–Cr5% coating sliding against bronze. Enhanced tribological behavior included low wear depth on coating, low wear width on counterbody, low friction coefficients and long durability.     

The wear characteristics of ultrahigh molecular weight polyethylene against a high density alumina ceramic under wet (distilled water) and dry conditions

In recent years there has been growing interest in the use of high density alumina ceramic material for the femoral ball in association with ultrahigh molecular weight polyethylene (UHMWPE) for the acetabular component in total replacement hip joints.The wear characteristics of UHMWPE pins sliding against a high density alumina ceramic disc in the presence of distilled water in a tri-pin-on-disc machine have been revealed in very long-term experiments reported in this paper. A total sliding distance in excess of 6000 km was achieved and very low mean wear coefficients of the order of 10^?8 mm³ N^?1 m^?1 were recorded.Experiments were also carried out over a shorter sliding distance under dry conditions and the average wear coefficient of 2 × 10^?7mm³N^?1m^?1 was consistent with earlier findings. In these dry tests, comet-like streaks of polyethylene were transferred to the ceramic counterface, but no such transfer was noted during the wet tests. When distilled water was added to the test chamber after a considerable period of dry sliding, the wear coefficient rapidly decreased to about 10^?8 mm³ N^?1 m^?1 and the streaky transfer film disappeared from the ceramic counterface.The possibility of hydrodynamic action between the wear face on the pins and the counterface was investigated by reversing the direction of sliding. Surface topography changes on both the pins and the discs and friction and bulk temperatures of the pins were recorded throughout the tests.It is concluded that the excellent dry wear coefficients of UHMWPE sliding on alumina ceramic counterfaces are about twenty times greater than those experienced by the same materials in the presence of distilled water. The tribological advantage of the ceramic with respect to stainless steel having a similar surface roughness has been confirmed in dry sliding involving UHMWPE, but further work is required to determine whether or not the same advantage can be achieved under wet conditions.     

On the influence of some test parameters on the results of oscillating sliding tests

The friction and wear behaviour of materials is often characterised in laboratory tests using a simple ball-on-flat configuration. From this type of test can be derived information useful in guiding the development of tribomaterials and in helping select candidate materials for specific applications. A large variety of tribotesting methods exists, and indeed several are not yet standardised. One of these methods is the oscillating sliding test, where a ball moves in relation to a disc, usually with small strokes. This method is almost non-destructive and can be applied to very small specimens. One of the most important parameters in laboratory tests is the humidity of the surrounding air. Experimental results on the friction and wear characteristics of different ceramics tested against different ball materials at room temperature in oscillating sliding contact are presented here and discussed, taking into account the effects of the test duration, relative humidity, and counterbody material.     

Tribological Properties of Borided AISI 4140 Steel with the Powder Pack-Boriding Method

The present study evaluates the tribological properties of boride layers on the surface of AISI 4140 steel, formed using the pack-boriding method. Commercial EKabor^®2 was used as the boronizing agent and the treatment was carried out at 900, 950, 1000, and 1050 °C for 2, 4, and 6 h, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM), and microhardness tests were used to characterize the phase composition, microstructure, and local hardness, respectively, of the borided steel samples. Block-on-disc tests were used to investigate tribological properties. Abrasive wear tests were carried out using emery paper at a fixed sliding speed and three different loads. Adhesive wear tests were executed against AISI 52100 steel at a fixed load and distance. The coefficient of friction values (COF) of the samples were determined simultaneously during the tests. The weight loss and COF of the borided samples were compared with untreated samples and the results suggest that both wear resistance and friction properties of the AISI 4140 steel improve with boriding.     

Wear of metals at high sliding speeds

High speed sliding wear of AISI 1020 steel, AISI 304 stainless steel and commercially pure titanium (75A) was studied using a pin-on-ring geometry. All the tests were carried out in air without any lubricant. The sliding speed was 0.5–10.0 m s^?1 and the normal force was 49.0 N (5 kgf).The friction coefficient of all the materials tested decreased with the sliding speed; this appears to be a consequence of oxide formation. The wear rate of 304 stainless steel increased monotonically with speed, whereas the wear rate of 1020 steel and titanium first decreased and then increased and again decreased, with a maximum occurring at about 5 m s^?1. The complex variation of the wear rate as a function of speed is explained in terms of the dependence of the friction coefficient, hardness and toughness of the materials on temperature. Microscope examinations of the wear track, the sub-surface of worn specimens and the wear particles indicate that the wear mode was predominantly by subsurface deformation, crack nucleation and growth processes, i.e. the delamination process, similar to the low speed sliding wear of metals. Oxidative and adhesion theories proposed in the past to explain the high speed sliding wear of metals are found to be incompatible with the experimental observations.     

Oscillating sliding wear behaviour of SiC,TiC, TiB2, 59SiC–41TiB2 and 52SiC–24TiC–24TiB2 materials up to 750°C in air

The tribological behaviour of different monolithic and composite ceramics was evaluated in the temperature range between room temperature and 750°C. The test method was oscillating sliding with a ball‐on‐disk arrangement in an SRV machine. Alumina balls were used as counter body. The friction behaviour was determined on‐line, and the wear behaviour was determined from calculations on the basis of wear scar dimensions and profilometric measurements. The friction depends on temperature and shows an increase for most materials for increasing temperature; the smallest friction at all temperatures is found for monolithic TiC. The wear behaviour shows different trends for the different materials. In tests against SiC a maximum of wear is found at 500°C, for TiC at 200°C and for TiB₂ at 750°C. The composite ceramics suffer the smallest wear of all materials in the range from 200°C to 500°C. Copyright © 2006 John Wiley & Sons, Ltd.