Study of wear resistance of thermal-diffusion boron nitride coatings on titanium

The wear resistance of commercially pure titanium VT1-0 covered with boron nitride coatings in pair with steel U8 is studied. It is found that the boron nitride coatings deposited from amorphous boron by thermal-diffusion saturation in molecular nitrogen at temperatures of 800?C850°C using the noncontact method improve the wear resistance of titanium during boundary sliding friction. Their characteristics are compared with those of boride coatings on titanium deposited by the same method. It is shown that the high-gradient strengthened layers formed during contact thermal-diffusion boronitriding within the 900?C950°C temperature range affect adversely the tribological performance of the boron nitride coating-steel pair.     

Structural and tribological characterization of tungsten nitride coatings at elevated temperature

Transition metal nitrides exhibit excellent mechanical properties (hardness and Young's modulus), high melting point, good chemical stability and high electrical conductivity. However, tungsten nitrides still stand aside of the main attention. In our previous study, tungsten nitride coatings with different nitrogen content showed excellent wear resistance at room temperature. Nevertheless, many engineering applications require good tribological properties at elevated temperature. Thus, the present study is focused on the tribological behaviour (friction coefficient and wear rate) of tungsten nitride coatings at temperature up to 600 °C.

The structure, hardness, friction and wear of tungsten nitride coatings with nitrogen content in the range 30–58 at.% prepared by dc reactive magnetron sputtering were investigated. The tribological tests were performed on a pin-on-disc tribometer in terrestrial atmosphere with Al₂O₃ balls as sliding partner. The coating wear rate was negligible up to 200 °C exhibiting a decreasing tendency; however, the wear dramatically increased at higher temperatures. The coating peeled off after the test at 600 °C, which is connected with the oxidation of the coating.     

Friction and wear properties of Ni–Cr–W–Al–Ti–MoS2 at elevated temperatures and self-consumption phenomena

The composites of Ni–Cr–W–Al–Ti–MoS₂ with different adding amount of molybdenum disulfide (6–20 wt.%) were prepared by powder metallurgy (P/M) method. Their mechanical properties and tribological properties from room temperature to 600 °C were tested by a pin-on-disk tribometer. The effects of amounts of molybdenum disulfide, temperature, load, and speed on the friction and wear properties of composite were discussed. Besides, the tribological properties against different counterface materials, such as alumina, silicon nitride and nickel-iron-sulfide alloys were also investigated. Results indicated that the molybdenum disulfide was decomposed during the hot-press process and the eutectic sulfides of chromium were formed. The hardness and anti-bending strength can be improved by adding 6 wt.% molybdenum disulfide due to reinforcement of molybdenum. The friction coefficients and wear rates of composites decrease with the increase of adding amount of molybdenum disulfide until a critical value of 12 wt.%. The composite with 12% MoS₂ shows the optimum friction and wear properties over the temperature range of RT 600 °C. The friction coefficients of composite with 12% MoS₂ decrease with the increase of temperature, load, and sliding speed, while the wear rates increase with the increasing temperature and are insensitive to the sliding speed and load. The friction coefficients of less than 0.20 at 600 °C and mean wear rates of 10⁻⁵ mm³/N m are obtained when rubbing against alumina due to the lubrication of sulfide films and glaze layer formed on the friction surface at high temperature, while a relatively low wear rate of around 10⁻⁶ mm³/N m presents when rubbing against nickel-iron-sulfide alloys. At high temperature, wear rates of composite containing sulfide are inversely proportional to friction coefficients approximately.     

Influence of counterbody material on wear of ta-C coatings under fretting conditions at elevated temperatures

The high temperature tribological performance of tetrahedral amorphous carbon coatings has been analyzed at elevated temperatures up to 250 °C in air against three different counterbody materials—steel 100Cr6, α-alumina and silicon nitride. The results show that the counterbody material influences the friction and wear behavior and therefore coating life time strongly. This effect is well known for these coatings at room temperature under dry environmental conditions, equivalent to conditions above 100 °C when water molecules desorb from the surface. However, the sharp difference in tribological performance between silicon nitride on the one hand and alumina and steel on the other hand cannot be understood in this context. Analyzing the friction behavior during the running-in phase, it is evident that only alumina and steel form a stable interface with constant low friction and relatively low wear rates. Silicon nitride forms an unstable interface with fluctuating COF and relatively high wear rates due to its own inherent tendency to tribo-oxidation.     

Influence of grain refinement on the high temperature fretting behaviour of IN 738 LC

The wear and friction behaviour of Inconel 738 LC in contact with SiSiC was studied for the case of oscillating sliding motion. The test temperature was varied in the range from room temperature up to 700 °C. A large-grain IN 738 LC and a grain-refined modification were compared. In both cases, the wear dropped drastically at temperatures above 400–500 °C and remained low for the grain-refined modification, but increased again for the large-grain modification at temperatures above 600 °C. The high wear/low wear transition was accompanied by a transfer of metal on the ceramic surface.     

Friction and wear of titanium alloys sliding against metal, polymer, and ceramic counterfaces

Recent advances in lower-cost processing of titanium, coupled with its potential use as a light weight material in engines and brakes has renewed interest in the tribological behavior of titanium alloys. To help establish a baseline for further studies on the tribology of titanium against various classes of counterface materials, pin-on-disk sliding friction and wear experiments were conducted on two different titanium alloys (Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo). Disks of these alloys were slid against fixed bearing balls composed of 440C stainless steel, silicon nitride, alumina, and polytetrafluoroethylene (PTFE) at two speeds: 0.3 and 1.0 m/s. The friction coefficient and wear rate were lower at the higher sliding speed. Ceramic sliders suffered unexpectedly higher wear than the steel slider. The wear rates, ranked from the highest to the lowest, were alumina, silicon nitride, and steel, respectively. This trend is inversely related to their hardness, but corresponds to their relative fracture toughness. Comparative tests on a Type 304 stainless steel disk supported the fracture toughness dependency. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses confirmed the tendency of Ti alloys to transfer material to their counterfaces and suggested possible tribochemical reactions between the ceramic sliders and Ti alloy disks. These reaction products, which adhere to the ceramic sliders, may degrade the mechanical properties of the contact areas and result in high wear. The tribochemical reactions along with the fracture toughness dependency helped explain the high wear on the ceramic sliders.     

Friction and wear properties of UHMWPE/Al2O3 ceramic under different lubricating conditions

Friction and wear behavior of ultra-high molecular weight polyethylene (UHMWPE) sliding against Al₂O₃ ceramic under dry sliding, and lubrication of fresh plasma, distilled water and physiological saline were investigated with a self-made pin-on-disk apparatus at 37±1°C. The worn surfaces were examined with a scanning electron microscope (SEM). The results show that the friction behavior of UHMWPE is very sensitive to its water absorption state. The wear rate of UHMWPE under dry sliding is the highest and under plasma lubrication is the lowest. The wear mechanisms are different under dry friction and various lubricating conditions.     

钢/玻璃的摩擦磨损性能动态观测研究

本实验在自行设计的摩擦磨损动态观测实验机进行,摩擦副之间的接触采用球一盘式接触。研究表明：当以较低速度滑动时,钢球表面的氧化物起到抗磨作用;滑动速度达到一定值时,氧化膜的生成速度小于氧化膜的磨损速度,摩擦表面为粘着磨损;当滑动速度继续升高时,摩擦表面的活化能增加,氧化加速．又出现氧化磨损;而滑动速度过高时,粘着磨损成为主要磨损形式,同时由于磨粒的作用,表面也发生疲劳磨损和磨料磨损．致使磨损急剧增加;表面层在摩擦热导致的高温条件下,氧化膜的生成速度又有所增加,氧化磨损为主要形式。     

Friction and Wear of Refractory Compounds

The sliding characteristics of the borides, carbides, nitrides, and silicides and oxides of several metals were investigated in air at temperatures up to 2000 F. Tests were of the crossed-cylinder type and friction and wear effects measured under repetitive sliding conditions.

Correlation of the friction and wear characteristics with known or predicted solid solubility was only fair. High hardness coupled with low fracture strength and excessive brittleness of these materials produced fracturing of asperities and abrasive wear before a true measure of the adhesion could be obtained. Oxidation products were found to provide some lubrication at elevated temperatures, particularly the formation of B₂O₃ on boron carbide. However, none was effective at room 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.     

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.     

High-temperature friction and wear behaviour of different tool steels during sliding against Al–Si-coated high-strength steel

The recent years have witnessed an increasing usage of high-strength steels as structural reinforcements and in energy-absorbing systems in automobile applications due to their favourable high-strength-to-weight ratios. Owing to poor formability, complex-shaped high-strength steel components are invariably produced through hot-metal forming. The high-strength steel sheets are in some instances used with an Al–Si-coating with a view to prevent scaling of components during hot-metal forming. However, friction and wear characteristics of Al–Si-coated high-strength steel during interaction with different tool steels have not yet been investigated. With this in view, friction and wear behaviours of different tool steels sliding against Al–Si-coated high-strength steel at elevated temperatures have been investigated by using a high-temperature version of the Optimol SRV reciprocating friction and wear tester at temperatures of 40, 400 and 800 °C. In these studies both temperature ramp tests with continuously increasing temperature from 40 to 800 °C and constant temperature tests at 40, 400 and 800 °C, have been conducted. The results have shown that both the friction and wear of tool steel/Al–Si-coated high-strength steel pairs are temperature dependent. Friction decreased with increasing temperature whereas wear of the tool steel increased with temperature. On the other hand, the Al–Si-coated high-strength steel showed significantly lower wear rates at 800 °C as compared to those at 40 and 400 °C. The Al–Si-coated surface undergoes some interesting morphological changes when exposed to elevated temperatures and these changes may affect the friction and wear characteristics. The mechanisms of these changes and their influence on the tribological process are unclear and further studies are necessary to fully explain these mechanisms.     

Sliding speed-temperature wear transition maps for Si3N4/iron alloy couples

The superior high temperature resistance of silicon nitride (Si₃N₄) based ceramics makes them suitable for tribological applications above room temperature or in high speed unlubricated sliding. There are some published works on the wear behaviour of Si₃N₄/metal alloys. However, experimental data are shown in a form that is not of direct use for engineers involved in materials selection. In the present work, Si₃N₄ pins were tested against tool steel and grey cast iron on a pin-on-disc tribometer. Ceramics were produced by hot-pressing and tested without lubrication at variable temperature and sliding speed. SEM/EDS and XRD analysis were used for chemical and microstructural characterisation of worn surfaces and wear debris. At low speeds (0.05–0.5 m s⁻¹) and room temperature, Si₃N₄ surfaces are polished-like due to a combination of humidity-assisted tribo-oxidation and abrasive action of very fine wear debris. At high sliding speeds (2–3.5 m s⁻¹), as well as for temperatures in the range 400–600°C, an extensive coherent tribolayer mainly composed by iron oxides spreads over the ceramic surfaces. Polishing and protection by adherent tribolayers are the mechanisms responsible for observed severe and mild wear regimes, respectively. Wear maps are constructed showing the transition of wear regimes in Si₃N₄/iron alloys contacts determined by constant flash temperature curves. Equations for calculation of bulk and flash contact temperatures in tribocontacts between dissimilar materials are deduced.     

The Size Effect of Boron Nitride Particles on the Tribological Performance of Biolubricants for Energy Conservation and Sustainability

The size of particulate additives in a bio-based lubricant influences their friction and wear performance during sliding contact. The present investigation evaluates the effect of boron nitride particle size on the tribological performance of canola oil-based lubricant mixtures. During sliding experiments, micron-, submicron-, and nanometer-sized boron nitride particle additives were considered. Friction and wear measurements were carried out on the prepared lubricant mixtures using a pin-on-disk tribometer at ambient conditions. A scanning electron microscope and optical profilometer were used for topographical studies to evaluate the influence of particle size on wear damage and surface roughness. The results revealed that the nanometer-sized particulate mixture outperformed micron- and submicron-sized particulate combinations in terms of friction and wear performance and provided a 90 % smoother surface finish. Furthermore, the tribological response of canola oil containing micron- or submicron-sized particles was found to be significantly enhanced by the addition of nano-sized particles, where the friction and wear were reduced by 40 and 70 %, respectively. It was inferred that the nano-sized particles were able to better coalesce in the asperity valleys due to their small size and spherical shape, which provided them with enhanced tribological properties in comparison with the micron- and submicron-sized particles that were larger and exhibited a plate-shaped in geometry. Newly developed non-dimensional surface roughness parameters were introduced to quantify the influence of particle size and the mechanisms involved in the tribological phenomena. The state of lubricants derived from bio-based feedstock were subsequently explored for their influence on energy conservation and sustainability, as well as their potential impact on the lubricant market place.     

The lubricated wear of ceramics : Part II: The wear and friction of silicon nitride and steel in the presence of mineral oil or an ester based lubricant

The friction and wear characteristics of combinations of silicon nitride, alumina and AISI 52100 steel in the presence of mineral oil containing anti-wear, dispersant and detergent additives have been investigated in a tri-pin-on-disc machine. The tests were carried out at a nominal temperature of 100°C for a range of sliding speeds, loads and total sliding distances. In Part II of this two-part paper a comparison will be made between the tribological performance of these sliding pairs of materials in mineral oil and ester based lubricant environments. The results of the investigation showed that the alumina performed relatively poorly under these test conditions, whereas silicon nitride showed good potential as an improved wear resisting material compared with 52100 steel. Wear factors of the order of 10⁻¹⁰ mm³/Nm were deduced for the alumina, while values as low as 10⁻¹¹ mm³/Nm were typical of the silicon nitride sliding against 52100 steel discs. The alumina pins wore by a process of brittle fracture at the surface, whereas the silicon nitride pins wore primarily by a tribochemical polishing mechanism. The rate of tribo-chemical wear was found to be proportional to the nominal contact area.     

Influence of Sliding Speed on the Tribological Characteristics of Si3N4-hBN Ceramic Materials

The influence of sliding speed on the unlubricated tribological behaviors of silicon nitride–boron nitride (Si₃N₄-hBN) composites was investigated with two modes in air by a pin-on-disc tribometer. Using the upper disc–on–bottom pin test mode, as the sliding speed increased, the friction coefficient of the sliding pairs showed an upward trend; for example, from 0.18 at the sliding speed of 0.40 m/s to 0.54 at the sliding speed of 1.31 m/s for the Si₃N₄/Si₃N₄–20% hBN pair. The surface analysis indicated that a tribochemical film consisting of SiO₂ and H₃BO₃ formed on the wear surfaces of the Si3N4/Si3N4–20% hBN sliding pair at sliding speeds of 0.40 and 0.66 m/s. Moreover, the formation of this film lubricated the wear surfaces. At the sliding speed of 1.31 m/s, no tribochemical film formed on the wear surfaces, most likely due to the increase in surface temperature. In the upper pin–on–bottom disc test mode, the wear mechanism was dominated by abrasive wear, and no tribochemical products could be detected on the wear surfaces. The increase in sliding speed weakened the degree of abrasive wear, leading to a decrease in the friction coefficients.     

Adhesion and friction of transition metals in contact with non-metallic hard materials

An investigation was conducted to examine the adhesion and friction behavior of transition metals in contact with various non-metallic hard materials and the nature of the metal transfer to the hard materials. Sliding friction experiments were conducted with the metals yttrium, titanium, tantalum, zirconium, vanadium, neodymium, iron, cobalt, nickel, tungsten, platinum, rhenium, ruthenium and rhodium in sliding contact with singlecrystal diamond, silicon carbide, pyrolytic boron nitride and ferrite. All experiments were conducted under the following conditions: loads, 0.05 –0.3 N; sliding velocities, 3 × 10^?3 and 0.7 × 10^?3 m min^?1; in a vacuum of 10^?8 Pa; at room temperature. Auger electron spectroscopy analysis was conducted with the metals and non-metals to determine the surface chemistry and the degree of surface cleanness. The results of the investigation indicate the adhesion and friction of the transition metals in contact with diamond, silicon carbide, boron nitride and ferrite are related to the relative chemical activity of the metals. The more chemically active the metal, the higher the coefficient of friction and the greater the amount of transfer to the non-metals.     

The use of nickel graphite composite coatings for the mitigation of gross slip fretting wear on Ti6Al4V interfaces

In metallic contacts, surface oxides, adhesion, and material transfer play a primary role in the initial stages of fretting wear degradation. Given this behavior, the focus of this study was to mitigate fretting wear within Ti6Al4V contacts at room temperature and 450 °C with the use of thermally sprayed nickel graphite composite coatings with 5–20% graphite. The results show that the embedded graphite particles reduced the friction of the nickel thermal sprayed coatings during both low and high temperature fretting wear experiments. Friction and wear mechanisms are discussed with correlations of contact chemistry, morphology, and mechanical performance. Wear on the mated Ti6Al4V surfaces was reduced by the formation of uniform transfer films that were identified as graphitic based at room temperature and NiO based at 450 °C.     

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.     

Tribological behavior of polyetheretherketone, a thermotropic liquid crystalline polymer and in situ composites based on their blends under dry sliding conditions at elevated temperatures

The elevated temperature dry sliding friction and wear behavior of injection molded polyetheretherketone (PEEK), a thermotropic liquid crystalline polymer (TLCP), and in situ composites based on PEEK-TLCP blends were investigated. Results from sliding tests conducted on a pin-on-disk tribometer at selected temperatures within the range from 20 to 250°C are reported. Friction and wear mechanisms are related to the microstructure and phase behavior of the material systems investigated. TLCP concentration and thermally activated molecular relaxation processes are related to the mechanical properties and tribological performance of the PEEK-HX1000 blends. The potential of TLCP in situ reinforcement as a route towards the development of performance thermoplastic-based tribomaterials for high temperature use is discussed.