Robert Wood | University of Southampton (original) (raw)

Papers by Robert Wood

Repetitive nanoindentation tests offer a method to examine the time-dependent degradation mechani... more Repetitive nanoindentation tests offer a method to examine the time-dependent degradation mechanisms in coatings. In the case of coated systems for tribological and more specifically for erosion resistant applications, repeated indentation cycles can characterise their durability to repeated erodent impact. This paper reports preliminary observations on the response of 13-18 µm thick CVD boron carbide on tungsten carbide substrates to repetitive indentation cycles, at contact loads similar to those generated in previously reported solid-particle erosion tests on these coatings conducted by this laboratory [1].

Thermal Sprayed Coatings and their Tribological Performances

WC-based thermal-spray and High Velocity Oxy-Fuel (HVOF) coatings are extensively used in a wide ... more WC-based thermal-spray and High Velocity Oxy-Fuel (HVOF) coatings are extensively used in a wide range of applications ranging from downhole drilling tools to gas turbine engines. WC-based thermal spray coatings offer improved wear resistance as a result of hard phases dispersed in binder-rich regions. However, the presence of hard and soft phases within the coating can also lead to the formation of micro-galvanic couplings in aqueous environments leading to some reduction in combined wearcorrosion resistance. Furthermore, the coating also responds differently to change in mechanical loading conditions. This chapter examines the wear-corrosion performance of thermal spray coatings in a range of wear, electrochemical, and wear-corrosion tests under varying contact conditions to develop models and establish relationships between wear mechanisms, wear rates, and environmental factors such as pH and applied load.

Surface Topography: Metrology and Properties, 2021

In turbomachinery, their blade leading edges are critical to performance and therefore fuel effic... more In turbomachinery, their blade leading edges are critical to performance and therefore fuel efficiency, emission, noise, running and maintenance costs. Leading edge damage and therefore roughness is either caused by subtractive processes such as foreign object damage (bird strikes and debris ingestion) and erosion (hail, rain droplets, sand particles, dust, volcanic ash and cavitation) and additive processes such as filming (from dirt, icing, fouling, insect build-up). Therefore, this review focuses on the changes in topography induced by during service to blade leading edges and the effect of roughness and form on performance and efforts to predict and model these changes. The applications considered are focused on wind, gas and tidal turbines and turbofan engines. Repair and protection strategies for leading edges of blades are also reviewed. The review shows additive processes are typically worse than subtractive processes, as the roughness or even form change is significant with...

The aim of the present work is to analyze the evolution of microstructural and mechanical propert... more The aim of the present work is to analyze the evolution of microstructural and mechanical properties of Air Plasma Sprayed (APS) CoNiCrAlY coatings after early stage high-temperature oxidation. Phase analysis and oxide scale characterization were performed by using X-Ray Diffraction (XRD). The microstructural features of CoNiCrAlY coatings were analyzed by Scanning Electron Microscopy (SEM), while Nanoindentation (NI) technique was employed to study the evolution of the mechanical properties.

Wear, 2021

Wind turbine leading-edge erosion can degrade the aerodynamic properties of blades and reduce the... more Wind turbine leading-edge erosion can degrade the aerodynamic properties of blades and reduce their efficiency. Previous theoretical work has suggested that low temperatures might affect the erosion performance of leading-edges and protective leading-edge coatings. This study investigated solid particle erosion which is caused by dust, sand and hailstones impacting the leading edges. For polymer coatings, temperature is a particular concern; the low temperatures can cause a transition from ductile to brittle failures. Polyurethane (PU) coatings were eroded at two temperatures: ambient (25°C) and cold (-30°C). An adapted solid-air erosion facility was used to accelerate sub-angular sand particles of 96.2 µm mean size to a velocity of 68±8 m/s. Low volumetric sand concentrations of 1.3×10-4 % were studied at two impingement angles of 45 and 90 degrees. The results showed that cold temperatures influenced the erosion rate and erosion mechanism of the coatings, with the erosion rate at the cold temperature increasing significantly. The erosion classification values and the shape of the wear scar suggested plastic erosion behaviour of the PU at cold temperatures, as opposed to the more erosion-resistant elastic behaviour. A temperature-controlled nanoindentation study demonstrated that the ratio of hardness to modulus reduced and the plasticity index increased with a reduction in temperature, implying the PU coatings had an increased propensity to plastically deform during cold erosion. This supports the erosion performance seen in experiments; however, the cold erosion surfaces developed more pits than the ambient case. Cross-section analysis of the eroded coatings showed accumulation of damage subsurface with evidence of delamination at the weakest interfaces in the layered coating systems, across all temperatures.

Tribology Letters, 2018

An experimental study is presented to evaluate the influence of anisotropically shaped textures o... more An experimental study is presented to evaluate the influence of anisotropically shaped textures on the behaviour of sliding friction and sensitivity to sliding direction. The plate samples were textured with triangular sloped dimples using an ultrafast laser surface texturing technique. Reciprocating cylinder-on-plate tests were conducted with steel sliding pairs using mineral base oil as a lubricant to compare the tribological performance of reference non-textured specimen and dimpled samples. The dimples were designed with varying converging angles in the transverse y-z plane and top-view x-y plane. In this study, no dimple was fully covered in the contact area since the dimples size is much larger than the Hertzian line contact width. Stribeck style dynamic friction curves across boundary, mixed and hydrodynamic lubrication regimes were used to determine the benefit or antagonism of texturing. Observation of the directional friction effect of the anisotropic textures indicated that the converging shapes are beneficial for friction reduction, and the dimpled specimens have a lower friction coefficient particular under prevailing boundary lubrication conditions. It was also found that the real contact length variation rate is a major factor controlling the local friction response. The sloped bottoms of the textures produce effective converging wedge action to generate hydrodynamic pressure and contribute to the overall directional friction effects.

Wear, 2009

The abrasion seen on some of the retrieved CoCrMo hip joints has been reported to be caused by en... more The abrasion seen on some of the retrieved CoCrMo hip joints has been reported to be caused by entrained hard particles in vivo. However, little work has been reported on the abrasion mechanisms of CoCrMo alloy in simulated body environments. Therefore, this study covers the mapping of micro-abrasion wear mechanisms of cast CoCrMo induced by third body hard particles under a wide range of abrasive test conditions. This study has a specific focus on covering the possible in vivo wear modes seen on metal-onmetal (MoM) surfaces. Nano-indentation and nano-scratch tests were also employed to further investigate the secondary wear mechanisms-nano-scale material deformation that involved in micro-abrasion processes. This work addresses the potential detrimental effects of third body hard particles in vivo such as increased wear rates (debris generation) and corrosion (metal-ion release). The abrasive wear mechanisms of cast CoCrMo have been investigated under various wear-corrosion conditions employing two abrasives, SiC (∼4 m) and Al 2 O 3 (∼1 m), in two test solutions, 0.9% NaCl and 25% bovine serum. The specific wear rates, wear mechanisms and transitions between mechanisms are discussed in terms of the abrasive size, volume fraction and the test solutions deployed. The work shows that at high abrasive volume fractions, the presence of protein enhanced the wear loss due to the enhanced particle entrainment, whereas at much lower abrasive volume fractions, protein reduced the wear loss by acting as a boundary lubricant or rolling elements which reduced the abrasivity (load per particle) of the abrasive particles. The abrasive wear rate and wear mechanisms of the CoCrMo are dependent on the nature of the third body abrasives, their entrainment into the contact and the presence of the proteins.

Tribology - Materials, Surfaces & Interfaces, 2008

Cast CoCrMo (F-75) based metal-on-metal (MOM) hip resurfacing implants are an increasing option f... more Cast CoCrMo (F-75) based metal-on-metal (MOM) hip resurfacing implants are an increasing option for younger and more active patients as they are less invasive to the human body. However, symptoms such as inflammation, tissue necrosis and metal sensitivity have been reported for some patients with MOM joints, which may be associated with the liberated metal debris and the elevated metal ion levels from such joints. Therefore, there is a requirement to assess the tribocorrosion performance of the CoCrMo alloy in physiological environments. In this study, the wear corrosion of cast CoCrMo, more specifically, sliding wear corrosion and abrasive wear corrosion (using y4 mm SiC abrasive particles) have been investigated using a modified ball cratering rig with a three-electrode electrochemical cell. The concentration effects of proteinaceous material (25 and 50% bovine serum) and pH levels, i.e. pH 4?0 (the pH for an infected joint area) and pH 7?4 (the normal pH for a healthy joint) on the tribo-corrosion performance of the alloy are explored. Electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy have been deployed to study the protein adsorption/corrosion of the alloy under static, non-abrasive conditions, whereas in situ electrochemical current noise measurements were employed to quantify the mechanoelectrochemical mechanisms present in the tribocorrosion of the alloy under dynamic conditions. In general, protein adsorption was found to be dependent on pH and protein concentration. Protein adsorption in turn influenced the overall tribocorrosion performance of the CoCrMo alloy, including the in situ electrochemical current noise, the specific wear rates, as well as the wear scar morphologies. The presence of bovine serum enhanced the separation of the bearing surfaces and for the sliding wear corrosion the wear rate was markedly reduced. However, the bovine serum appeared to increase the abrasive particle entrainment and lead to accelerated wear in the presence of abrasive particles (abrasive wear). For the more acidic physiological environment, in comparison to pH 7?4, higher corrosion rates occurred under wear corrosion conditions leading to increased metal ion release. Consequently, the proteins and the pH level of hip joint environments play a significant role in the tribocorrosion performance of the cast CoCrMo and a discussion of the combined wear and corrosion mechanisms will be presented.

Electrochimica Acta, 2016

Corrosion induced structural failures continue to be a costly problem in many industrial situatio... more Corrosion induced structural failures continue to be a costly problem in many industrial situations, and the development of robust corrosion sensing systems for structural health integrity monitoring is still a demanding challenge. The applicability of corrosion monitoring of copper alloys using a boron-doped diamond electrode (BDD) has been performed based on determination of copper ions within localised corrosion microenvironments. The electrochemical behaviour of copper ions on the BDD electrode surface were first reported in details in 0.60 M NaCl aqueous solution, and the results revealed that the electrochemical processes of copper ions on the BDD electrode proceed as two successive single electron transfer steps producing two well-separated pairs of peaks in cyclic voltammograms in the chloride ion containing electrolyte solutions. Compared with perchlorate and sulphate ions, chloride ions were observed with a significant stabilization effect on copper ions via the formation of CuCl 2 À complex, thus having two well-separated pairs of peaks in the obtained cyclic voltammograms on the BDD electrode in the chloride ion electrolyte solution. The apparent rate constant for the redox couple of Cu 2+ /Cu + in chloride ion electrolyte was determined as 0.94 Â 10 À6 cm s À1 by using quasi-steady polarisation technique, thus indicating a quasi-reversible electron transfer process of Cu 2+ /Cu + redox couple. Moreover, differential pulse voltammetric results exhibited the BDD electrode is promising for corrosion monitoring of copper alloys with an excellent relationship between peak current and concentration of copper ions without significant interference from the commonly presented metal ions within the simulated marine corrosion environments.

Tribology International, 2017

This paper presents a study on the influence of anisotropically shaped texture arrays on friction... more This paper presents a study on the influence of anisotropically shaped texture arrays on friction behaviour of an oil lubricated sliding contact, especially on directional friction control based on the diverging and converging characteristics of the textures. Experiments have been conducted on a TE77 reciprocating cylinder-on-plate test rig, where steel rollers were used to slide against steel plate samples with or without textures. A mineral base oil was used to lubricate the contacts. Three geometries of dimples were designed and laser textured on the steel plate samples with varied 3-dimensional features, including Square Flat (SF), Square slope (SS) and Triangular Flat (TF) shapes representing the shape in x-y (top view) and x-z (side view) planes respectively. These shapes were chosen to vary the converging and diverging properties of the lubricated contacts depending on the sliding direction. Relatively large dimple sizes (side length ~ and depth ~) have been used in this study to enable observation of the effect and easy control of the texturing process. The texture density has been kept at as most literature suggested. The large dimple sizes resulted that the dimples were not be fully covered by the contact area, i.e. the dimple sides were bigger than the Hertzian contact width of the roller-flat contacts. This has eliminated the 'lift' or 'load bearing' effect discussed in most papers thus focuses on other effects investigated in this study. The results show that beneficial effects of the anisotropic textures present in all lubrication regimes including the boundary, mixed and hydrodynamic lubrications, especially under prevailing boundary lubrication conditions. Using high sampling rate for the friction data during the tests, it was able to study local friction effect due to individual dimple array especially at their leading and trailing edges. The results show that a local friction reduction is observed at the leading while an increase at the trailing edge. Overall directional friction effect of the anisotropic textures has been observed that the converging shape in both y-z plane and the x-y plane reduces friction. Furthermore, it was found that the triangular shape dimples have a greater local frictional response at each dimple array, while the sloped bottom square dimples have a more significant overall directional fricition effect.

Lubricants, 2016

Surface texturing has been shown to be an effective modification approach for improving tribologi... more Surface texturing has been shown to be an effective modification approach for improving tribological performance. This study examined the friction reduction effect generated by square dimples of different sizes and geometries. Dimples were fabricated on the surface of ASP2023 steel plates using femtosecond laser-assisted surface texturing techniques, and reciprocating sliding line contact tests were carried out on a Plint TE77 tribometer using a smooth 52100 bearing steel roller and textured ASP2023 steel plates. The tribological characterization of the friction properties indicated that the textured samples had significantly lowered the friction coefficient in both boundary (15% improvement) and mixed lubrication regimes (13% improvement). Moreover, the high data sampling rate results indicated that the dimples work as lubricant reservoirs in the boundary lubrication regime.

Tribology Lubrication Technology, 2014

Soft Nanoscience Letters, 2011

When referring to this work, full bibliographic details including the author, title, awarding ins... more When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g.

Wear, 1999

This document constitutes the PhD thesis of the author's project Solid Particle Erosion of CVD Di... more This document constitutes the PhD thesis of the author's project Solid Particle Erosion of CVD Diamond Coatings. It details the experimental work carried out over the period October 1997 to September 2000. The project was undertaken at the University of Southampton under the auspices of an Engineering and Physical Sciences Research Council CASE award, in collaboration with De Beers Industrial Diamonds (UK) Ltd. The objective of this project was to investigate the behaviour of CVD diamond coatings when subject to high velocity impact from sand particles as well as relating damage mechanisms to microstructure. In the experimental work, diamond coatings deposited on both tungsten and tungsten carbide-cobalt substrates were investigated. The thickness of the coatings ranged from 10 to 200}im and the samples were supplied in both as-grown and lapped forms. The coatings were characterised using a number of techniques including X-ray diffraction, Raman spectroscopy, indentation, surface profilometry as well as optical and electron microscopy. The grain size and surface roughness were also measured for comparison with the size of damage features generated in the erosion studies. The results revealed that the coatings were close to natural diamond in both chemical (i.e. negligible graphite content) and mechanical (i.e. hardness and elastic modulus) characteristics. In the erosion studies, two test facilities were used: a water-sand slurry rig and a high velocity air-sand rig. The erodent used was silica sand with average diameters 135pm, 194pm and 235pm with the velocities in the range 16 to 268 m s"' and 90° nominal impact angle. The erosion rates were plotted against particle kinetic energy and compared with those for cemented tungsten carbide and stainless steel. At 268 m s'\ the most erosion-resistant coating was a 120pm lapped sample, which had an erosion resistance more than 10 times that of cemented WC-7Ni. The coatings were examined both pre-and post-test by scanning electron microscopy in order to determine the degradation mechanisms. Ultrasonic imaging and taper polishing of eroded samples were also performed to reveal sub-surface damage and to elucidate its contribution to coating degradation. The results suggest that the erosion mechanism consists of a three-stage process consisting of micro-chipping, development of pin-holes and interfacial debonding, followed by catastrophic failure. The principal damage features, the circumferential cracks and pin-holes, were examined in detail in an attempt to identify the mechanism responsible for their formation. When compared with Hertzian impact theory the measured circumferential crack diameters were found to be at least double the diameter predicted by Hertz. Moreover, a trend of increasing circumferential crack diameter with coating thickness, which is not predicted by Hertzian impact theory, was fovmd. The diameters of the circumferential cracks were closer to that predicted by the theory of stress wave reinforcement, which is more commonly associated with damage in brittle materials subjected to liquid impact. This suggested that stress wave reinforcement was responsible for the formation of the pin-holes. This hypothesis was supported by work using scanning acoustic microscopy, which found that circumferential cracks and pinholes were only found on areas of the coating that had become delaminated during the erosion tests. The experiments also indicated that the coatings became delaminated under the action of sub-surface shear stresses that are generated by the particle impacts. When the maximum shear stress was located at the coating-substrate interface (i.e. z/Ct = 1) the coating failed rapidly. This work indicates that for optimum coating performance z/Cr < 0.3 and the stress field contained within the coating. 5.4 X-Ray Diffraction 87 5.5 Indentation studies 87 5.6 Microscopy 88 5.7 Air-sand erosion tests 88 5.8 Water-sand slurry erosion tests 91 6. MLALlTEINVULS 97 6.1 Coating micro structure 97 6.2 Raman spectroscopy 97 6.3 X-ray diffraction 99 6.4 Hardness and elastic modulus 99 6.5 Fracture toughness 6.6 Conclusions 7. RESIDUAL STRESS 7.1 Introduction 7.2 Experimental 7.3 Results and Discussion 7.4 Conclusions 8. EROSION PERFORMANCE OF CVD DIAMOND 8.1 Erosion rates 8.2 Effect of coating thickness on erosion performance 8.3 Effect of substrate material on erosion rate 8.4 Coating behaviour during the test 129 8.5 Effect of thickness on coating life 131 8.6 Comparison of different types of CVD diamond 133 8.7 Conclusions 134 9. SURFACE EROSION DAMAGE 148 9.1 Introduction 148 9.2 Surface micro chipping 148 9.3 Erodent behaviour during impact 150 9.4 Circumferential crack and pin-hole formation 154 9.5 Comparison of crack diameters with Hertz theory 156 9.6 Use of stress wave theory to explain circumferential cracks 164 9.7 Appearance of circumferential cracks 171 9.8 The nature of the erodent-target combination Pages 136 to 147 8.1 Graph of Erosion Rate (Vu) vs Kinetic Energy (Ek)-8.2 Graph of Erosion Rate (Vu) vs Coating Thickness (Cr) for lapped and as-grown coatings. 8.3 Graph of Cumulative Mass Loss (CML) vs Time for two lapped 120pm diamond coatings. 8.4 Bar chart showing the comparative values for diamond and other materials. 8.5 Schematic diagram showing the diiference in impact conditions between asgrown and lapped coatings. 8.6 Graph showing cumulative mass loss against time for the erosion of 46pm coating at 268 m s'\ 8.7 Schematic diagram showing the three stages in erosion of the coatings. 8.8 Micrographs of a lapped 120nm coating in (a) the untested condition; and (b) after erosion at 268 m s"' for 4 hours. 8.9 Micrographs of an as-grown 90(im coating in (a) the untested condition; and (b) after erosion at 268 m s"' for 1 hour. 8.10 Micrograph of a circumferential crack in a lapped 46coating tested at 268m s"'. 8.11 Micrograph of a pin-hole in a lapped 33p,m coating tested at 268m s'\ 8.12 Micrograph of a pin-hole in a lapped 46pm coating tested at 268m s"'. 8.13 Micrograph of a pin-hole in a lapped 43 pm coating tested at 268m s"^ 8.14 Micrograph of a pin-hole in an as-grown 30pm coating tested at 268m s'\ 8.15 Micrograph of a pin-hole in an as-grown 60pm coating tested at 268m s"'. 8.16 Micrograph of a pin-hole in an as-grown 60pm coating tested at 268m s"'. 8.17 Graph showing cumulative mass loss and number of pin-holes against time for a lapped 60pm coating. 8.18 Micrograph of a pin-hole in a lapped 60pm coating tested at 268m s"'. 8.19 Graph of Time to Failure (//) against Coating Thickness (Cr) for lapped diamond coatings. 8.20 Micrographs of a lapped 600pm free-standing diamond in (a) the untested condition; and (b) erosion at 268 m s'' for 5 hours. Pages 181 to 207 9.1 Micrographs of Redhill Mix sand in (a) the unused condition and (b) following impact with diamond at 268 m s"'. 9.2 Sand size distribution of unused Redhill Mix sand. 9.3 Sand size distribution of Redhill Mix sand following impact with diamond at 268 m s"'. 9.4 Micrographs of sand smearing on the surface of diamond following impact at 268 ms\ 9.5 High-speed photographic sequence showing the fragmentation of a sand particle on diamond. 9.6 Graph of Particle Rebound Angle vs Air Flow Rate for the air-sand erosion rig. 9.7 Schematic diagram of the terms used in calculating the coefBcient of restitution. 9.8 Graph of CoefBcient of Restitution vs Impact Velocity. 9.9 Micrograph of a pin-hole in a lapped 46pm coating tested at 268m s"'. 9.10 Schematic diagram of the pin-hole shown in Figure 9.9. 9.11 Micrograph of a columnar grain in a 60|im coating on WC-6C0. 9.12 Micrograph from the 46(im lapped coating showing two views of a pin-hole showing the side in detail. 9.13 Micrograph from the 46p.m lapped coating taken from the edge of the spalled region. 9.14 Micrograph showing a circumferential crack on the surface of a 60|J,m lapped coating erosion tested at 268 m s'' for 4 hours. 9.15 Micrograph showing a circumferential crack on the surface of a 60]um lapped coating erosion tested at 268 m s"' for 6 hours. 9.16 Micrograph showing a circumferential crack on the surface of a 60p,m lapped coating erosion tested at 268 m s'' for 9 hours. 9.17 Micrograph showing a circumferential crack on the surface of a 60jiim lapped coating erosion tested at 268 m s'* for 11 hours. 9.18 Micrograph showing a pin-hole on the surface of a 60}am lapped coating erosion tested at 268 m s"' for 6 hours. 9.19 Micrograph showing a pin-hole on the surface of a 60 pm lapped coating erosion tested at 268 m s"' for 9 hours. 9.20 Micrograph showing a pin-hole on the surface of a 60pm lapped coating erosion tested at 268 m s"' for 11 hours. 9.21 Micrograph of a 60pm lapped coating showing two circumferential cracks and a pin-hole taken after 4 hours at 268 m s'\ 9.22 Detail from Figure 9.21 showing the pin-hole. 9.23 Micrograph of a 60pm lapped coating showing a pin-hole taken after 6 hours at 268 m s"'. 9.24 Micrograph of a 60jim lapped coating showing a pin-hole taken after 11 hours at 268 m s'\ 9.25 Schematic diagram of Hertzian contact showing the parameters. 9.26 Schematic diagram showing the two possible stress wave reinforcement processes. 9.27 Graph of Measured Circumferential Crack Diameter vs Coating Thickness for lapped diamond coatings tested at 268 m 9.28 Graph of Measured Circumferential Crack Diameter vs Impact Velocity for lapped diamond coatings. 9.29 Micrograph of a circumferential crack and pin-hole taken from a 60pm diamond coating tested at 268 m s"' (30° impact). 9.30 Micrograph of a circumferential crack and pin-hole taken from a 60|am diamond coating tested at 268 m s"' (60° impact). 9.31 Graph showing the relationship between Impact Angle and the Time at which the first pin-hole was observed for 60p.m diamond coatings on tungsten at 268 m s'\ 9.32 Graph of Mean Circumferential Crack Diameter vs Impact angle for 37-43p,m and 60|-im lapped diamond coatings tested at 268 m s'\ 9.33...

Tribology International, 2009

Some retrieved CoCrMo hip implants have shown that abrasive wear is one of the possible wear mech... more Some retrieved CoCrMo hip implants have shown that abrasive wear is one of the possible wear mechanisms invoked within such joints. To date, little work has focused on the third body abrasion of CoCrMo and therefore there is a general lack of understanding of the effect of abrasive size and volume concentration on the tribo-corrosion performance of the CoCrMo alloys. The present work assessed the tribo-corrosion behaviour of cast CoCrMo (F-75) under various abrasion-corrosion conditions by using a modified microabrasion tester incorporating a three-electrode electrochemical cell. The effects of reduced abrasive size/hardness and volume concentration, as well as the role of proteins on the tribocorrosion performance of the cast CoCrMo alloy were addressed. The correlation between electrochemical and mechanical processes for different abrasion-corrosion test conditions has been discussed in detail. Results show that the reduction in abrasive size and volume concentration can significantly affect the abrasion-corrosion wear mechanisms and the wear-induced corrosion response of the material. The finding of this study implies that the smaller/softer third body particles generated in vivo could also result in significant wear-induced corrosion and therefore potential metal ion release, which could be potentially detrimental to both the patient health and the life span of the implants.

Tribology International, 2007

This study focuses on the influence of load and temperature on the formation and stability of tri... more This study focuses on the influence of load and temperature on the formation and stability of tribo-films for bearing steel on bearing steel contacts lubricated with an aviation oil, EXXON Turbo 2380 (TCP based-tricresyl phosphate) at ambient temperatures. Experiments were carried out on a pin-on-disc (POD) tribometer (with a ball-on-flat geometry) under an average loading rate of 0.17 N s À1 and sliding speed of 3 m s À1. The X-ray photoelectron spectroscopy (XPS) analysis on the worn surfaces of ball and disc shows that a tribo-film forms on both surfaces at room temperature. The formation and removal of the tribo-film are faster on the ball due to the nature of contact between the ball and disc. It was found that the tribo-films formed at room temperature are vulnerable to initial disc temperature. The higher the initial temperature the higher the load carrying capacity. The tribo-film growth and contact deterioration have been monitored by acoustic emission (AE) and electrostatic charge (ESP) sensing systems in real time. The results show that both AE and ESP can detect the tribo-film and contact breakdown and have great potential for on-line condition monitoring of lubricated tribo-contacts.