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.     

High-Temperature Friction and Wear Studies of Nimonic 80A and Nimonic 90 Against Nimonic 75 Under Dry Sliding Conditions

The present research focuses on dry sliding friction and wear behaviour of Nimonic 80A and Nimonic 90 against Nimonic 75 at high temperature up to 1023 K. The influence of temperature, sliding distance and normal load on friction and wear behaviour of Nimonic 80A and Nimonic 90 against Nimonic 75 was studied using pin (Nimonic 75)-on-disc (Nimonic 80A and Nimonic 90). Lower wear and lower friction of superalloys was observed at high temperatures, as compared to room temperature. Surface morphological and surface analytical studies of fresh and worn surfaces were carried out using optical microscopy, 3D profilometer, scanning electron microscope, energy-dispersive X-ray spectroscopy and Raman spectroscopy to understand the friction and wear behaviour. The mechanism of the formation of microscale glaze layer is also discussed.     

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.     

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.     

Interface wear reactions between nickel and a nickel-20 at. % molybdenum alloy in a simulated face seal

By suitable heat treatement, the properties of a nickel-20 at. % molybdenum alloy can be altered by controlling the disorder-order reaction. This alloy has been wear tested for hardnesses ranging from about 164 (disordered) to 413 (ordered) DPH against pure nickel (DPH 85), simulating commercial face seal conditions. The wear surface topology has been characterized in detail using scanning electron microscopy. In general, surface damage was severe and the features seen are similar to those found in more slow, controlled tests of relatively soft materials. Smearing, formations of layers and elongated dimples are seen. Complex wear particles were formed, and evidence of fatigue contributing to particle formation was noted. Considerable surface interaction occurred even with the harder (ordered) alloy mated against nickel, including damage to the alloy. Wear particles of the alloy were found on the nickel specimen.     

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.     

The nature and origin of wear particles from boundary lubrication with a zinc dialkyl dithiophosphate

It is well known that in many tribological situations antiwear additives act by reaction film formation on contacting surfaces. In the present paper we describe our observations on the reaction film formed with a zinc dialkyl dithiophosphate and the wear particles. Detailed structural and chemical information has been obtained by using optical microscopy, scanning electron microscopy, transmission electron microscopy and X-ray energy spectrometry. The results show a clear connection between the reaction film material and the nature of the wear particles present in the lubricant; both a highly dispersed phase system and a layered structure are present. The origin of the wear particles is discussed in terms of crack initiation mechanisms.     

Friction and wear performances of brake material dry sliding against a composite with a semi-interpenetrating network structure of ceramics and Al-alloy

The friction and wear performances of brake material dry sliding against semi-interpenetrating network ceramics/Al-alloy composites were determined using a SRV testing machine. For applied loads from 40-160 N, the friction decreased at 100 and 250 °C. The former friction was superior to the latter. Wear increased at 100 °C but decreased at 250 °C, and converged gradually in both cases. Friction fade took place at high temperatures, followed by overrecovery upon cooling. Higher temperatures increased wear. The proposed friction models incorporated with scanning electron microscopy and energy dispersive X-ray analysis explain the test results better.     

Formation of wear debris by the abrasion of ductile metals

Decohesion of wear debris by abrasive particles was studied using polycrystalline pure metals and alloys. Wear debris were formed by steel riders with attack angles of 30°, 60° and 90° and also in the pin-on-disk test on commercial abrasive paper. Microstructural changes due to abrasion were investigated by transmission electron microscopy and X-ray diffraction examination of wear debris and worn surfaces. Simple models for the interaction between abrasive particles and material surfaces used to estimate friction and wear provided a better quantitative understanding of the influence of microstructural factors such as hardness, work hardening, crystal structure, anisotropy and phase transformation.     

The corrosion wear behaviour of selected stainless steels in potash brine

Tests were conducted at 25 and 85 °C to evaluate the corrosion wear resistance of selected stainless steels in potash brine using a reciprocating motion wear apparatus. Four materials were tested: Ferralium 255 (UNS S32550), AL6XN (UNS N08367), 254SMO (UNS S31254) and AISI 1018 (UNS G10180) for comparative purposes. The evaluation methods employed included weight loss analysis, optical microscopy and scanning electron microscopy (SEM). The results show that Ferralium 255 has superior corrosion wear resistance in potash brine environment compared to AISI 1018 plain-carbon steel and the other stainless steels tested. Wear surface analysis using SEM shows evidence of brittle fracture damage, which is attributed to the presence of Cl⁻.     

Room and high temperature wear behaviors of nickel and cobalt base weld overlay coatings on hot forging dies

The lifetime of dies used for production of forged parts is variable and determined by wear rate, plastic deformation, thermal and mechanical fatigue. These tools are subjected to extreme temperature at high unit pressures for short durations and must withstand multiple cycles while maintaining dimensional stability. This paper is an investigation into the use of nickel and cobalt base superalloys as wear resistant hardfacing materials on H11 tool steel. Three weld overlay alloys including Inconel 625, Stellite 6 and Stellite 21 were deposited on H11 steel substrates using tungsten inert gas welding (TIG) process. Wear tests were carried out using a pin-on-disk wear tester at room temperature and 550 °C. Microhardness of the weld overlays was obtained and the worn surfaces were examined by scanning electron microscopy (SEM). The results of the laboratory tests were then compared with the results obtained from field studies. The results showed a much lower wear at high temperature with the weld overlays due to formation of smooth compacted oxide layers on the wear surfaces. Inconel 625 showed the best wear behavior among the weld overlays at high temperature.     

Friction and wear behavior of Ni-P coated Si3N4 reinforced Al6061 composites

Al6061 matrix composite reinforced with nickel coated silicon nitride particles were manufactured by liquid metallurgy route. Microstructure and tribological properties of both matrix alloy and developed composites have been evaluated. Dry sliding friction and wear tests were carried out using pin on disk type machine over a load range of 20-100 N and sliding velocities of range 0.31-1.57 m/s. Results revealed that, nickel coated silicon nitride particles are uniformly distributed through out the matrix alloy. Al6061-Ni-P-Si₃N₄ composite exhibited lower coefficient of friction and wear rate compared to matrix alloy. The coefficient of friction of both matrix alloy and developed composite decreased with increase in load up to 80 N. Beyond this, with further increase in the load, the coefficient of friction increased slightly. However, with increase in sliding velocity coefficient of friction of both matrix alloy and developed composite increases continuously. Wear rates of both matrix alloy and developed composites increased with increase in both load and sliding velocity. Worn surfaces and wear debris was examined using scanning electron microscopy (SEM) for possible wear mechanisms. Energy dispersive spectroscope (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) techniques were used to identify the oxides formed on the worn surfaces and wear debris.     

Some microscopical investigations of grinding and abrasive wear*

This work forms part of a broader investigation which explores the relationship between grinding and abrasive wear. Wear experiments were performed over a wide range of loads and speeds in which solid abrasives (typical of those in grinding wheels) were rubbed against metals (usually steels). Under certain conditions the rate of wear decreased with time; at the same time the worn debris changed from metallic particles to finely divided oxides and the surface of the abrasive became glazed. Optical and scanning electron microscopy have been used to study this transition in the wear mechanism and its relationship to the structure of abrasives and the nature of abraded surfaces. The investigation illustrates the role of microscopy in the examination of a complex engineering process.     

The effect of oxide-forming alloying elements on the high temperature wear of a hot work steel

A great deal of research has been conducted to clarify the role of oxide films in the wear of metals. Oxides formed during dry sliding of steels at high temperatures determine their tribological behavior. The present work deals with the influence of the oxide-forming alloying elements aluminum and silicon on the oxidation and wear of three selected hot work steels. For this investigation, ball-on-disc experiments were carried out in ambient air and 500 °C. Wear tracks on the disks and balls were characterized using both a scanning electron microscope and an optical profiler. The oxidation products were characterized using X-ray photoelectron spectroscopy and energy-dispersive electron probe microanalysis. The results show that the alloying elements aluminum and silicon yield a reduction of the oxide film thickness and thus lead to an increase in mechanical wear as temperature rises.     

Studies of high temperature sliding wear of metallic dissimilar interfaces IV: Nimonic 80A versus Incoloy 800HT

Wear variations of Nimonic 80A slid against Incoloy 800HT between room temperature (RT) and 750 °C, and sliding speeds of 0.314 and 0.905 m s⁻¹ were investigated using a ‘reciprocating-block-on-cylinder’, low debris retention configuration. These were considered alongside previous observations at 0.654 m s⁻¹.Different wear types occurring were mapped, including high transfer ‘severe wear’ (RT and 270 °C, also 0.905 m s⁻¹ at ≤570°C), low transfer ‘severe wear’ (0.314 m s⁻¹ at 390 °C to 510 °C oxide abrasion assisted at 510 °C), and ‘mild wear’ (0.314 m s⁻¹ at ≥570 °C; 0.905 m s⁻¹ at ≥630 °C). Wear surfaces at 750 °C were cross-sectioned and profiled.     

Dry sliding wear behaviour of in-situ fabricated TiC particulate reinforced AA6061 aluminium alloy

Aluminium alloy AA6061 reinforced with different mass fractions of (0, 2.5, 5, 7.5 & 10 weight percentage) TiC particles was fabricated by the in-situ reaction process. The in-situ synthesized aluminium matrix composite (AMCs) were examined using X-ray diffraction, field emission scanning electron microscope and electron backscatter diffraction. The results from the aforesaid tests revealed the formation of TiC particles. The in-situ formed particles were found to have a homogenous distribution, clear bonding and good interface with the aluminium alloy AA6061. The dry sliding wear test results revealed an improvement in wear performance of aluminium alloy AA6061 due to the presence of TiC particulate. Furthermore, the in-situ formed TiC particulates refined the grain structure. The in-situ formed TiC particles improved the load bearing ability of the AMCs. The wear mechanisms recorded during the wear test were ploughing and adhesion at lower load and delamination at higher load.     

Some microscopic aspects of the mild wear of steel*

The paper reviews the experimental classifications of the unlubricated sliding wear of metals, together with some of the suggested relationships between the wear rates, the real area of contact, the load, the hardnesses of the metals and the probability of producing wear particles at the real areas of contact. The microscopic nature of the interactions between sliding surfaces is discussed, with special emphasis on the advantages (and limitations) of using electron microscopy for studying these interactions, and the importance of using X-ray diffraction techniques to complementthe electron microscopy. Examples are then given of how the use of electron microscopy has revealed many facets of the mild wear of steel which would not otherwise have been suspected. For instance, the areas of contact between sliding steel surfaces are comparatively large and few in number, in contradistinction to the situation occurring in stationary contact. These large contact areas crack in a characteristic fashion reminiscent of fatigue failure or brittle fracture. They then flake off at a critical thickness (～ 10^?4cm) to provide the source for the wear debris. The wear debris collects initially in the rough regions which are left behind when the flakes become detached. In this position, the wear debris probably acts in an abrasive fashion. Eventually, the wear debris is thrown clear of the contact area. Analysis of this debris using X-ray diffraction techniques has shown that there is a strong correlation between the presence of certain oxides in the wear debris and the severity or mildness of the wear. It has also been used to estimate the temperatures occurring between the areas in sliding contact. This estimate is consistent with previously published dynamic thermocouple measurements. It also gives rise to consistent values of the activation energy required for oxidation during wear.     

Friction and wear properties of rice husk ceramics under dry condition

The friction and wear behaviors of rice husk (RH) ceramics, prepared by carbonizing the mixture of rice husk and phenol resin at 900 °C in N₂ gas environment, sliding against high carbon chromium steel (JIS SUJ2), austenitic stainless steel (JIS SUS304), and Al₂O₃ under dry condition were investigated using a ball-on-disk tribometer. The test results show that the friction coefficient of RH ceramics takes very low values 0.05–0.08 and 0.06–0.11 sliding against SUJ2 and SUS304, respectively, and much higher values around 0.14–0.23 against Al₂O₃. It was also shown that SUJ2 provides the lowest specific wear rate values below 10⁻⁹ mm²/N, while, those of SUS304 and Al₂O₃ mostly stayed between 10⁻⁹ to 10⁻⁸ mm²/N range. The worn surfaces of counterparts were observed with optical microscopy and analyzed using cross-sectional transmission electron microscopy with energy dispersive X-ray spectroscopy and electron diffraction. It was suggested that the tribological behaviors of RH ceramics are closely related with the formation of a transferred film, consisted of amorphous silica and carbon particles, on a counterpart surface. The transferred film was formed readily on SUJ2 balls, whereas for SUS304 the presence of the film was subject of the sliding conditions. Moreover, formation of the transferred film could not be detected on Al₂O₃ counterparts.     

Sliding wear transition for the CW614 brass alloy

Dry sliding wear tests were performed on a CW614 brass alloy using a pin-on-ring configuration. Wear kinetics were measured within a load range of 20–80 N and sliding velocity ranging from 1 to 7 m/s. Chemical compositions, morphologies and microstructures of worn surfaces and wear debris were characterised by scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS). Two main wear regimes have been observed: severe wear and mild wear. The results of wear tests and metallographic investigations on worn surfaces have been summarised in a wear mechanism map. It was found that the wear transition is controlled by a critical temperature at the contact surface.     

A reciprocating wear test for evaluating boundary lubrication

A reciprocating wear tester was used to investigated the nature of antiwear boundary lubrication films formed by several ZDDP additives in mineral oil. Under the test conditions examined in this work, antiwear films are relatively thick (approximately 0.1 μm), and so can be readily detected by optical microscopy. Film formation occurs after only a few centimetres of sliding on smooth hard surfaces, whereupon wear essentialy ceases. On rough surfaces, film formation does not take place until the surfaces have run-in, whereupon wear again ceases. Antiwear films did not form on steel pins softer than Rc 25, which wore by an oxidative mechanism. The extent of run-in or rough surfaces before film formation can be used as a measure of the effectiveness of an antiwear additive. Antiwear films are resistant to wear, so once formed they can provide sustained wear protection in base oil. However, antiwear films can be removed by wear in the presence of hydroperoxides, or by running against a new rough countersurface.