Investigations of microstructures and defect structures in wear affected region created on Nimonic 80A during high temperature wear

The microstructures of a wear induced surface glazed layers formed during sliding wear of Nimonic 80A against Stellite 6 at 20–750 °C using a speed of 0.314 m s^-1 under a load of 7 N have been investigated using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) in combination with energy dispersive X-ray (EDX) analysis. The defects formed in the glazed layers were measured by positron lifetime spectroscopy. The results indicate the formation of a wear resistant nanostructured glazed layer. Positron lifetime and Doppler-broadening measurements demonstrated that the defects (mainly dislocations) existed in the glazed layers at low temperatures which increasing wear test temperature led to decrease in defects density. Positron measurements also suggested that, at the annealing temperature (1200 °C), the presence of dislocations might lead to the formation of ordered or partially ordered regions in Nimonic 80A.     

The friction and wear behaviour of nickel-base alloys in air at room temperature

Measurements are presented of the friction and wear during sliding of specimens of Nimonic 75, C263, Nimonic 108 and Incoloy 901 on like specimens in air nominally at room temperature. The worn specimens have been examined using microhardness measurements, optical and scanning electron microscopy, X-ray diffraction and electron diffraction. These techniques suggest mechanisms for the room-temperature wear of these alloys associated with their strength properties. In particular, changes in the coefficient of friction and the wear rate during sliding can be correlated with work hardening, and possibly some degree of age hardening, of the load-bearing areas, due to the severe mechanical and thermal stresses developed. There is no evidence that oxide films formed on the contact areas during sliding have a significant effect on the tribological behaviour of these alloys. Such films are merely removed from the surface as wear debris.     

The Effects of Elevated Ambient Temperatures on the Friction and Wear Behavior of Some Commercial Nickel Base Alloys

Measurements of friction and wear during sliding of specimens of Nimonic 75, C263, Nimonic 108 and Incoloy 901 on like specimens in air at temperatures from 20 to 800 C are presented. Under the sliding conditions used, all the alloys show a transition temperature, above which low wear and a low coefficient of friction during sliding are observed after a time and below which these parameters remain relatively high throughout. These temperatures are about 150 C for N75, about 200 C for C263 and N108 and between 200 and 300 for Incoloy 901. At given temperatures above the transition temperatures, the coefficient of friction-time loci show sharp, generally very reproducible, changes from relatively high to low coefficients of friction. The times at which these occur decrease with increasing temperature for a given alloy. Such changes can be closely correlated to the formation of a stable, adherent, thermally softened, oxide layer or glaze on the load-bearing areas during sliding. Once the glaze is established, very little further wear takes place. These tribological properties of the glaze are associated with its low shear strength and the high strength of the underlying alloy substrate. They depend more on its physical properties than on its precise chemical composition. It is concluded that high strength, relatively rapid transient oxidation rates, and appropriate physical properties of the resulting oxide films are important qualities in alloys employed under sliding conditions in air at elevated temperatures.     

Studies of high temperature sliding wear of metallic dissimilar interfaces

The evolution of microstructures in the glaze layer formed during limited debris retention sliding wear of Nimonic 80A against Stellite 6 at 750 °C and a sliding speed of 0.314 m s⁻¹ (7 N applied load, 4522 m sliding distance) was investigated using scanning electron microscopy (SEM), energy dispersive analysis by X-ray (EDX), X-ray diffraction (XRD), scanning tunnelling microscopy (STM) and transmission electron microscopy (TEM). The collected data indicate the development of a wear resistant nano-structured glaze layer. The process of ‘fragmentation’ involving deformation, generation of dislocations, formation of sub-grains and their increasing refinement causing increasing misorientation was responsible for the formation of nano-structured grains. The rapid formation of this glaze layer from primarily cobalt–chromium debris transferred from (and also back to) the surface of the Stellite 6, kept wear of both the Nimonic 80A and Stellite 6 to very low levels.However, increasing the sliding speed to 0.905 m s⁻¹ (750 °C) suppressed glaze formation with only a patchy, unstable glaze forming on the Stellite 6 counterface and an absence of glaze development on the Nimonic 80A sample (the Nimonic 80A surface was covered with at most, a very thinly smeared layer of oxide). The high levels of oxide debris generated at 0.905 m s⁻¹ instead acted as a loose abrasive assisting wear of especially the Nimonic 80A. This behaviour was attributed to a change in oxide chemistry (due to the dominance of nickel and chromium oxides generated from the Nimonic 80A) resulting in poor oxide sintering characteristics, in combination with increased mobility and reduced residency of the oxide debris at 0.905 m s⁻¹.     

The tribological behaviour of nickel and nickel-chromium alloys at temperatures from 20° to 800 °C

Measurements are presented of friction and wear during sliding of specimens of Ni-Cr alloys containing 0% to 40% Cr on like specimens in air at 20°, 400° and 800 °C. The worn specimens have been examined by optical and scanning electron microscopy, electron probe microanalysis and electron diffraction and microhardness measurements have been made.Under the sliding conditions used, all the alloys show a transition temperature above which a low coefficient of friction and usually relatively low wear are observed after a time and below which these parameters remain relatively high throughout. Above the transition temperatures, the frictiontime loci show sharp reproducible changes from relatively high to low coefficients of friction. Such changes can be associated with the formation of a thermally softened oxide layer (termed a glaze) on the bearing areas during sliding. Once the glaze is formed, very little further wear occurs for the high chromium-content alloys, although further damage does take place with the weaker low chromium-content alloys, especially at temperatures just above the transition temperature. These tribological properties of the glaze are associated with its low shear strength and the strength of the underlying alloy substrate.During sliding at temperatures below the transition temperatures, metal-to-metal contact takes place, although oxide is formed on the bearing area of the low chromium-content alloys even at 20 °C. The friction and wear behaviour is largely determined by the strength and work-hardenability of the alloy.Correlations between the tribological behaviour of these binary Ni-Cr alloys and commercial Nimonic alloys indicate that the trace elements in the latter play only a relatively minor role in determining this behaviour. It is concluded that high strengths and relatively rapid transient oxidation rates of the alloys, and appropriate physical properties of the resulting oxide films, are important qualities of the alloys under the conditions used.     

Development of a simple ‘temperature versus sliding speed’ wear map for the sliding wear behaviour of dissimilar metallic interfaces

The variation in wear behaviour during limited debris retention sliding wear of Nimonic 80A versus Stellite 6 (counterface) between room temperature and 750 °C, at sliding speeds of 0.314, 0.654 and 0.905 m s⁻¹, was investigated. At 0.314 m s⁻¹, mild oxidational wear was observed at all temperatures, due to transfer and oxidation of Stellite 6-sourced debris to the Nimonic 80A and resultant separation of the Nimonic 80A and Stellite 6 wear surfaces. Between room temperature and 450 °C, this debris mostly remained in the form of loose particles (with only limited compaction), whilst between 510 and 750 °C, the particles were compacted and sintered together to form a wear protective ‘glaze’ layer.At 0.654 and 0.905 m s⁻¹, mild oxidational wear due to transfer and oxidation of Stellite 6-sourced debris was only observed at room temperature and 270 °C (also 390 °C at 0.654 m s⁻¹). At 390 °C (450 °C at 0.654 m s⁻¹) and above, this oxide was completely absent and ‘metal-to-metal’ contact resulted in an intermediate temperature severe wear regime—losses in the form of ejected metallic debris were sourced almost completely from the Nimonic 80A. Oxide debris, this time sourced from the Nimonic 80A sample, did not reappear until 570 °C (630 °C at 0.654 m s⁻¹), however, were insufficient to eliminate completely severe wear until 690 and 750 °C. At both 0.654 and 0.905 m s⁻¹, the oxide now preventing severe wear at 690 and 750 °C tended not to form ‘glaze’ layers on the surface of the Nimonic 80A and instead supported continued high wear by abrasion. This abrasive action was attributed to the poor sintering characteristics of the Nimonic 80A-sourced oxide, in combination with the oxides’ increased mobility and decreased residency.The collected data were used to compose a simple wear map detailing the effects of sliding speed and temperature on the wear of Nimonic 80A slid against Stellite 6, at these speeds and temperatures of between room temperature and 750 °C.     

Tribology in the core of a sodium-cooled fast breeder reactor

The construction of safe and reliable Liquid Metal Cooled Fast Breeder Reactor plants involves knowledge of the friction and wear behavior of different materials in contact with or sliding against each other. Friction and wear problems have been investigated as part of a still continuing program to provide guidelines for reactor designers.Following initial experiments to select materials resistant to sodium corrosion and wear, wear rate as a function of the geometrical probe arrangements has been studied.The frictional characteristics of different probe arrangements at various sodium temperature under different movements with varied dwell times were investigated. The materials tested included Stellite 6, Hastelloy C, Inconel 718, Nimonic 90 and 10 CrMoNiNb 910.     

Studies of high temperature sliding wear of metallic dissimilar interfaces II: Incoloy MA956 versus Stellite 6

The development of wear surfaces formed during limited debris retention sliding wear of Incoloy MA956 against Stellite 6 between room temperature and 750 °C, and sliding speeds of 0.314 and 0.905 m s⁻¹ (7 N applied load, 4522 m sliding distance) were investigated. At 0.314 m s⁻¹, mild oxidational wear was observed at all temperatures, due to oxidation of Stellite 6-sourced debris and transfer to the Incoloy MA956; this debris separated the Incoloy MA956 and Stellite 6 wear surfaces. Between room temperature and 450 °C, the debris mainly took the form of loose particles with limited compaction, whilst between 510 °C and 750 °C the debris were compacted and sintered together to form a Co–Cr-based, wear protective ‘glaze’ layer. The behaviour was identical to that previously observed on sliding Nimonic 80A versus Stellite 6 at 0.314 m s⁻¹.At 0.905 m s⁻¹, mild oxidational wear was only observed at room temperature and 270 °C and dominated by Incoloy MA956-sourced debris. At 390 and 450 °C, the absence of oxide debris allowed ‘metal-to-metal’ contact and resulted in intermediate temperature severe wear; losses in the form of ejected metallic debris were almost entirely Incoloy MA956-sourced. This severe wear regime was also observed from 510 up to 630 °C, but increasingly restricted to the early stages of wear by development of a wear protective Incoloy MA956-sourced ‘glaze’ layer. This ‘glaze’ layer formed so rapidly at 690 °C and 750 °C, that severe wear was all but eliminated and wear levels were kept low.The behaviour observed for Incoloy MA956 versus Stellite 6 at 0.905 m s⁻¹ contrasts sharply with that previously observed for Nimonic 80A versus Stellite 6, in that the Incoloy MA956-sourced high Fe–Cr debris formed a protective oxide ‘glaze’, whilst the Nimonic 80A-sourced Ni and Cr oxides formed an abrasive oxide that at high sliding speeds assisted wear. The data indicates that the tendency of oxide to form a ‘glaze’ is readily influenced by the chemistry of the oxides generated.     

Friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon

A series of experimental tests were carried out using stainless steel rubbing against copper-impregnated metallized carbon under electrical current on a pin-on-disc test rig. The test parameters include the sliding speed of 60-100 km/h, normal force of 40-80 N and electrical current of 0-50 A. During testing, the friction coefficient and wear volume were recorded. The topography of worn surfaces was also observed with SEM. The cross sectional profiles of worn surfaces of stainless steel were measured with Ambios profiler. The result displays that electrical current, normal load and sliding speed have a distinct effect on the friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon. Without electric current, the friction coefficient is largest but the wear volume of copper-impregnated metallized carbon is lowest. With increasing electric current, the friction coefficient decreases while the wear volume of copper-impregnated metallized carbon increases. Through the whole test, it is found that the wear loss of stainless steel was light. The wear of copper-impregnated metallized carbon becomes severe when electrical current or sliding speed is high. When the electrical current or sliding speed is high, arc ablation is a dominant wear mechanism of copper-impregnated metallized carbon.     

Effect of Temperature on the Dry Sliding Friction and Wear of Rice Bran Ceramics against Different Counterpart Materials

In this study, we investigated the effect of temperature on the friction and wear of rice bran (RB) ceramics, a hard porous carbon material made from rice bran, sliding against alumina, stainless steel, and bearing steel balls under dry conditions. Friction tests were performed using a ball-on-disk-type friction tester wherein a ceramic heater was installed in the rotational stage. The surface temperature of the RB ceramic disk specimens was controlled at 20, 100, 150, or 200°C. The normal load was 1.96 N, sliding velocity was 0.1 m/s, and number of cycles was 20,000. The effect of surface temperature on the friction and wear of RB ceramics substantially differed among the ball material types. The friction coefficient for the RB ceramics sliding against an alumina ball decreased with increasing temperature and exhibited an extremely low value (0.045) at 200°C. The friction coefficient in the case of the RB ceramics sliding against a stainless steel ball exhibited a stable value as the temperature was increased to 150°C and slightly decreased as the temperature was increased further, reaching a low value of 0.122 at 200°C. The friction coefficient for the RB ceramics sliding against bearing steel ball drastically increased with increasing temperature, reaching 0.381 at 200°C. The specific wear rate of the RB ceramics increased with increasing temperature; it was lowest when sliding against alumina and highest when sliding against bearing steel. The wear of the alumina ball was the lowest and that of the bearing steel ball was the highest under all investigated temperature conditions. On the basis of these results, we concluded that alumina is a promising counterpart material for RB ceramics sliding at high temperatures (≤200°C).     

High temperature friction and wear mechanism map for tool steel and boron steel tribopair

Abstract

Tribological systems working under severe conditions like high pressures, sliding velocities and temperatures are subjected to different phenomena such as wear, oxidation and changes in mechanical properties. In many cases, there are several mechanisms occurring simultaneously. The predominating type(s) of wear mechanism(s) presented will depend on the materials in contact, operating parameters and surrounding environment. In this work, high temperature tribological studies of boron steel sliding against tool steel were conducted using a pin-on-disc machine under unlubricated conditions at five different temperatures ranging from 25 to 400°C, three different loads: 25, 50 and 75 N (contact pressures of 2, 4 and 6 MPa respectively) and a sliding speed of 0·2 ms^?1. Scanning electron microscopy/energy dispersive spectroscopy and X-ray techniques were used for analysing the resulting damage and tribolayers of the worn surfaces. Additionally, hardness measurements were carried out in a special hot hardness rig in the same temperature range as that used in pin-on-disc tests. The results have shown that for a given load, the wear rate of boron steel decreased as the temperature increased, reaching its lowest value at 400°C at 50 N. In the case of the tool steel, it could be observed that at 200°C and above, the wear rate decreased as the load increased. This behaviour is consistent with the formation of a protective oxidised layer initiated at 100°C. At higher temperatures, such layers become more pronounced. The obtained data were finally used to construct a friction and wear mechanism map for this material pair that takes temperature and pressure into account.     

Tribological behaviour of plasma nitrided Ti-5Al-2Nb-1Ta alloy against UHMWPE

A detailed study has been made on the wear behaviour of untreated and plasma nitrided Ti-5Al-2Nb-1Ta orthopaedic alloy against ultra high molecular weight polyethylene (UHMWPE) using pin on disc tribometer under lubricated conditions. The effects of nitriding temperature and nitriding time on the basis of the evolution of the wear volume loss and friction coefficient were investigated. The wear resistance of the plasma nitrided alloys increased considerably when compared to the untreated alloy. The wear debris identified using X-ray diffraction measurements indicated the formation of titanium oxide and titanium oxynitride particles. The wear rate was found to increase with increase in load and sliding velocity.     

The effect of an alumina counterface on friction reduction of CuO/3Y-TZP composite at room temperature

The friction behavior of CuO/yttria-stabilized tetragonal zirconia (3Y-TZP) composite in dry sliding against alumina at room temperature has been investigated. The results show that an alumina counterface has a crucial role on the frictional behavior when sliding against CuO/3Y-TZP composite in comparison with other counter materials. Pure 3Y-TZP shows high friction and wear under the same conditions. It is found that the friction reduction behavior is dependent on the sliding test conditions such as load and humidity. A thin aluminum-rich layer less than 200 nm thick on the contact surface during the low friction situation has been found by various analyzing techniques including interference microscopy, micro-Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microcopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The induced change of contact conditions and interfacial chemical reaction between CuO and alumina to form the phase CuAlO₂ increase the wear of alumina and accelerates the formation of an aluminum-rich surface layer. The presence of such a layer in the contact is beneficial for reducing friction. After a certain sliding distance, the coefficient of friction shifts from a low value to a high value due to a change in the dominating wear mechanism. This transition is shown to be caused by a different composition and thickness of the interfacial layer.     

Tribological characterization of thin hard coatings by reciprocating sliding tests

Thin hard coatings on metal or ceramic surfaces offer a large spectrum of improvements of the friction and/or wear behaviour of tribosystems. The development of coatings and the tailoring of their properties require test methods providing information about their friction and wear behaviour. A new wear test standard (ASTM) is under development for the evaluation of friction and wear quantities for sliding motions using the reciprocating sliding mode. The applicability of this test method to coated specimens was checked by testing uncoated and coated steel specimens in contact with alumina balls, whereby lower loads were used than in the ASTM proposal for bulk materials. Additionally, the influence of the relative humidity of the surrounding air at room temperature on friction and wear results was examined.     

Tribological Behavior of Ti3Al2.5V Alloy Sliding against EN-31 Steel under Dry Condition

This article aims to study the friction and wear behavior of Ti3Al2.5V alloy sliding against EN-31 steel under dry condition using a multi-tribotester. The effect of variation in load and sliding velocity on wear rate, average coefficient of friction, and contact temperature has been studied and analysis of wear debris has been carried out. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were employed to study the morphology of the wear tracks and deduce microchemical information at the elemental level of worn samples, respectively. Results reveal that the wear rate of Ti-3Al-2.5V increases with increasing sliding velocity and increasing normal load with few exceptions. The average coefficient of friction decreases as the normal load increases with exceptions at some loads. SEM micrographs of worn samples obtained at different loads and sliding velocities show the formation of wear tracks on the surface due to ploughing and flaking of the matrix. The main mechanism responsible for wear of Ti3Al2.5V alloy sample is rupture of the matrix and abrasion. Wear debris analysis shows irregular-shaped wear particles with very sharp edges that appeared to be plastically deformed at high sliding velocity, whereas the wear debris is very loose and fine at lowest sliding velocity.     

Sliding wear behavior of Fe-based bulk metallic glass at high temperature

In the past decade Fe-based bulk metallic glasses (BMGs) have attracted increasing attention due to their beneficial properties, including high glass forming ability (GFA), high strength and hardness and high fracture toughness in both fundamental science and engineering application. Most research using these materials has been conducted at room temperature environment, and research that assesses their behavior especially at high temperature has been scarce. We present the results of high temperature effect on the friction and wear behavior of Fe-based bulk metallic glass (BMG), and we tested that this material may satisfy wear and oxidation resistance at high temperature as well as to explore the high temperature wear mechanism of the Fe-based BMG. The dry sliding tribological behaviors of Febased BMG against Si₃N₄ ceramic were conducted with a pin-on-disc friction and wear tribometer. The morphology of the worn surfaces of Fe-based BMG was examined by scanning electron microscopy (SEM) and the chemical composition characterized with energy dispersive spectroscopy (EDS) to observe the wear characteristics and investigate the wear mechanisms. The overall average friction coefficient value generally decreased with increasing temperature, and the glass transition and the formation of protective oxide film played an important role in the tribological behavior of BMG. The wear resistance of Fe-based BMG was not only from their hardness but also from the formation protective oxide layer. Analysis of the worn surface revealed abrasion, plastic deformation and oxidation during sliding test.     

Effect of the chemical structure of fluorinated esters on the tribological properties of a steel‐on‐steel system

The effect of the chemical structure of fluorinated esters on the friction and wear behaviour of a steel‐on‐steel system was investigated. The friction and wear testing of a steel disc sliding against a counterpart ball of the same steel was carried out using an Optimal SRV oscillating friction and wear tester. The chemical features of the worn steel surfaces were analysed by means of X‐ray photoelectron spectroscopy, and the morphologies and elemental compositions of the worn steel surfaces observed and determined using scanning electron microscopy. The results indicate that a fluorinated ester with methylene groups that are not substituted by fluorine in the acid structure gives the best friction‐reducing behaviour and a keto‐ester shows the best antiwear properties.     

Author index

The friction and wear properties of a cured epoxy resin pin sliding against a steel disc were examined. It was found that the initial (single traversal) coefficient of friction is relatively low (about 0.25) and temperature dependent, while the steady state friction coefficient is relatively high (about 0.8) and temperature independent. It has been determined that the steady state value reflects the friction of iron oxide sliding on itself rather than the epoxy-steel friction. Optical microscopy observations and preliminary electron spectroscopy for chemical analysis experiments suggest that, as in the case of metallic friction, the wear particles form by oxidation of the steel fragments transferred by adhesion to the epoxy surface rather than by direct oxidation of the steel counterpart.     

On sliding friction and wear of polyetheretherketone (PEEK) composites at elevated temperatures

The friction and wear behaviour of polyetheretherketone (PEEK) composites, incorporating different amounts of short carbon fibres with different surface treatments, was studied under dry sliding conditions against smooth steel on a pin-on-disc apparatus at different temperatures. Wear of the composites was reduced considerably in all cases, but, whatever the surface treatment, wear increased with increasing temperature for all proportions off fibres. For minimum friction coefficient there was an optimum proportion of fibre volume fraction of about 10 vol.%. The effect of the fibre surface treatment was not significant for the tribological behaviour of the PEEK composites. To predict wear performance, a wear model proposed by Friedrich and Voss seemed to work properly, and, furthermore, a friction model was developed to predict the friction behaviour of PEEK composites with short carbon fibres.     

Mild Sliding Wear of Fe–0.2%C,Ti–6%Al–4%V and Al-7072: A Comparative Study

The mild sliding wear of Fe–0.2%C, Ti–6%Al–4%V and Al-7072 was investigated by means of pin-on-disc sliding tests. The applied pressure was 1 MPa and the sliding velocity was varied between 0.2 and 1 m/s. The sliding behaviour was followed by continuous measurements of the friction coefficient, pin wear and pin temperature. For the Fe alloy, wear was mixed (delamination and oxidation), and friction and wear coefficients were found to decrease with sliding velocity. The Al and Ti alloys displayed a different behaviour, characterised by the occurrence of sliding distance transitions at 0.8 and 1 m/s for the Al alloy, and at 0.4 up to 1 m/s for the Ti alloy. Before the transition, the wear coefficient of the Al alloy was very low, because of the presence of a compacted tribolayer on the sliding surface. After the transition wear was by delamination: the wear rate increased but the friction coefficient decreased. For the Ti alloy, wear occurred by oxidation and was quite high before the transition. After the transition, both the wear rate and the friction coefficient decreased, although the wear process became unstable with repeated oscillations in the friction coefficient. The results allowed us to highlight the role of flash temperature in determining the wear mechanisms of the alloys under study and the necessity of properly considering the sliding distance transitions to make reliable comparisons and obtain guidelines for safe operations.