Showing papers on "Tribometer published in 2010"

Tribological properties of Cr- and Ti-doped MoS2 composite coatings under different humidity atmosphere

Abstract: Solid-lubricant MoS 2 coatings have been successfully applied in high vacuum and aerospace environments. However, these coatings are very sensitive to water vapor and not suitable for applications in moist environments. In this work, Cr- and T-doped MoS 2 composite coatings were developed. The results demonstrated that these composite coatings are promising for applications in high humidity environments. MoS 2 –Cr and MoS 2 –Ti composite coatings with different Cr or Ti content were deposited on high speed steel substrate by unbalanced magnetron sputtering. The composition, microstructure, and mechanical properties of the as-deposited MoS 2 -metal composite coatings were analyzed by energy dispersive analysis of X-ray (EDX), X-ray diffraction (XRD), and nanoindentation experiments. The tribological properties of the coatings were evaluated against an alumina ball under different relative humidity atmosphere using a ball-on-disc tribometer. The MoS 2 –Cr and MoS 2 –Ti coatings showed a maximum hardness of 7.5 GPa and 8.4 GPa at a dopant content of 16.6 at.% Cr or 20.2 at.% Ti, respectively. The tribological test results showed that, with a small amount of Cr and/or Ti doping, the tribological properties of MoS 2 coatings under humid atmosphere could be significantly improved. The optimum doping level was found to be around 10 at.% for both MoS 2 –Cr coatings and MoS 2 –Ti coatings to show the best tribological properties, with both the lowest friction coefficient and wear rate. The excellent tribological properties of the MoS 2 –Cr and MoS 2 –Ti coatings with an appropriate metal doping level in moist atmosphere are found due to their ability to form stable transfer layer on the surface of the counterbody, which supplies lubrication for the contact surface.

The Effect of Morphology on the Tribological Properties of MoS2 in Liquid Paraffin

Abstract: The tribological properties of liquid paraffin (LP) containing molybdenum disulfide (MoS2) additives, including nano-balls, nano-slices, and bulk 2H-MoS2, are evaluated using a four-ball tribometer. Results show that all MoS2 additives used can improve the tribological properties of LP, and that nanosized MoS2 particles function as lubrication additives in LP better than micro-MoS2 particles do. The LP with nano-balls presents the best antifriction and antiwear properties at the MoS2 content of 1.5 wt%. This is ascribed to the chemical stability of the layer-closed spherical structure of nano-balls. The Stribeck curves confirm that the rotation speed of 1,450 rpm used is located at the mixed lubrication region under 300 N. MoS2 nano-slices have small sizes and easily enter into the interface of the friction pair with a roughness of 0.032 μm, functioning as a lubricant in LP better than nano-balls do at the MoS2 content of 1.0 wt%. The Stribeck curves also show that the differences between the two nano samples were magnified at high rotation speeds in hydrodynamic lubrication region. The application of nano-slices in high sliding speeds will be more advantageous. This work furthers the understanding of the relationship between the tribological properties and morphology of MoS2.

Mechanical and tribological properties of nanocomposite TiSiN coatings

Abstract: TiSiN coatings with a thickness of 2.5 μm were deposited using a Large Area Filtered Arc Deposition (LAFAD) technique with TiSi targets having different Si content. The influence of the Si content in the coatings on the mechanical properties and tribological behaviors of the TiSiN coatings were systematically studied using nanoindentation and a pin-on-disk tribometer. Nanoindentation results show that the hardness and Young's modulus of the TiSiN coatings increase with increasing Si content in the coatings. Wear test results indicate that the wear rate and friction coefficient of the 440a stainless steel coupons were significantly reduced by deposition of the TiSiN coatings, and the tribological behaviors of the TiSiN coatings are strongly dependent on the Si content in the coatings and the testing ball material. TiSiN coatings exhibit similar friction coefficient when tested against Al 2 O 3 and 302 stainless steel balls, but increasing Si content in the coatings causes an increase in the friction coefficient of the TiSiN coatings. With the increase in the Si content in the coatings, the wear rate of the TiSiN coatings decreases when tested against Al 2 O 3 balls, but increases significantly when tested against 302 stainless steel balls. The capability of forming a transfer layer on the ball surface contributes to the change in the friction coefficient and wear rate with Si content in the coating and ball materials.

Mechanical and tribological properties of TiN/Ti multilayer coating

Abstract: A large area filtered arc deposition (LAFAD) technique was used to deposit TiN/Ti multilayer coatings with fixed TiN layer thickness and different Ti layer thickness. Nanoindention and pin-on-disk tribometer were used to characterize the hardness, elastic modulus, plasticity, friction coefficient, and wear rate of the multilayer coatings. The dependence of the mechanical and tribological properties of the coating on the Ti interlayer thickness was systematically studied. It was found that the increase in the Ti layer thickness resulted in a decrease in the effective hardness and elastic modulus, and an increase in the wear rate, plasticity, and toughness. The coatings with a Ti layer thicknesses of 0, 25 nm and 50 nm possess an excellent combination of high effective hardness (> 20 GPa), high plasticity (> 69%), low friction coefficient, and high wear resistance.

Influence of friction modifier and antiwear additives on the tribological performance of a non-hydrogenated DLC coating

Abstract: The use of diamond-like carbon (DLC) coatings in engine tribocomponents is increasingly a strategy to improve fuel economy and component durability to simultaneously provide low friction and excellent wear protection. The influence of conventional additives on the tribological performance of various types of DLC coatings is still poorly understood. This paper addresses the friction and wear performance of a non-hydrogenated DLC (a-C) coating as a function of additive chemistry. Tests were performed in a pin-on-plate tribometer under boundary lubrication conditions. Surface analyses were carried out using Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). Results showed that the antiwear additive zinc dialkyldithiophosphate (ZDDP) provided excellent wear protection to a-C coating by forming zinc phosphate in the tribofilm. However, when friction modifier Moly Dimer (MD) or Moly Trimer (MT) was added with ZDDP, zinc phosphate was found to be absent, resulting in higher wear than ZDDP alone. Both friction modifiers decomposed and supplied MoS 2 to the tribological interfaces. The transfer of the worn coating material, which was a function of the antiwear performance of additives, was shown to have an influence on friction performance.

Tribological Behavior of Composites Based on ZA-27 Alloy Reinforced with Graphite Particles

Abstract: The objective of this investigation is to assess the influence of graphite reinforcement on tribological behavior of ZA-27 alloy. The composite with 2 wt% of graphite particles was produced by the compocasting procedure. Tribological properties of unreinforced alloy and composite were studied, using block-on-disk tribometer, under dry and lubricated sliding conditions at different specific loads and sliding speeds. The worn surfaces of the samples were examined by the scanning electron microscopy (SEM). The obtained results revealed that ZA-27/graphite composite specimens exhibited significantly lower wear rate and coefficient of friction than the matrix alloy specimens in all the combinations of applied loads (F n ) and sliding speeds (v) in dry and lubricated tests. The positive tribological effects of graphite reinforcement of ZA-27 in dry sliding tests were provided by the tribo-induced graphite film on the contact surface of composite. In test conditions, characterized by the small graphite content and modest sliding speeds and applied loads, nonuniform tribo-induced graphite films were formed leading to the increase of the friction coefficient and wear rate, with increase of the sliding speed and applied load. In conditions of lubricated sliding, the very fine graphite particles formed in the contact interface mix with the lubricating oil forming the emulsion with improved tribological characteristics. Smeared graphite decreased the negative influence of F n on tribological response of composites, what is manifested by the mild regime of the boundary lubrication, as well as by realization of the mixed lubrication at lower values of the v/F n ratio, with respect to the matrix alloy.

Synthesis and Tribological Performance of Novel MoxW1−xS2 (0 ≤ x ≤ 1) Inorganic Fullerenes

Abstract: Inorganic fullerene-like (IF) MoS2 and WS2 nanoparticles were found to be good friction modifiers and anti-wear additives when dispersed in a lubricant. Their tribological performance seems to be related to the structure, size, and shape of these nanomaterials. The present study describes the tribological properties of a new inorganic fullerene IF-Mo x W1−x S2 containing both molybdenum and tungsten disulfide under boundary lubrication. Mo x W1−x S2 amorphous inorganic fullerene nanostructures were synthesized by means of MOCVD using an induction furnace setup. The average diameters range from 25 to 45 nm. Upon variation of the amounts of precursors and S, various solid solutions of IF-Mo x W1−x S2 were obtained. In addition, a morphological, chemical, and structural analysis of the samples was performed using high resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD). Friction experiments were carried out with a ball-on-flat contact using an environmental tribometer. The results show interesting friction reducing and wear properties of these nanomaterials. The change in the molecule stoichiometry, which led to a variation of particles size but also to a variation of the crystallinity of the particles, affects the tribological performance.

Tribocorrosion behaviour of nanostructured titanium substrates processed by high-pressure torsion

Abstract: Aseptic loosening induced by wear particles from artificial bearing materials is one of the main causes of malfunctioning in total hip replacements. With the increase in young and active patients, complications in revision surgeries and immense health care costs, there is considerable interest in wear-resistant materials that can endure longer in the harsh and corrosive body environment. Here, the tribological behaviour of nanostructured titanium substrates processed by high-pressure torsion (HPT) is investigated and compared with the coarse-grained samples. The high resolution transmission electron microscopy reveals that a nanostructured sample has a grain size of 5–10 nm compared to that of ~ 10 µm and ~ 50 µm for untreated and annealed substrates, respectively. Dry and wet wear tests were performed using a linear reciprocating ball-on-flat tribometer. Nanostructured samples show the best dry wear resistance and the lowest wear rate in the electrolyte. There was significantly lower plastic deformation and no change in preferred orientation of nanostructured samples attributable to the wear process. Electrochemical impedance spectroscopy (EIS) shows lower corrosion resistance for nanostructured samples. However, under the action of both wear and corrosion the nanostructured samples show superior performance and that makes them an attractive candidate for applications in which wear and corrosion act simultaneously.

Tribological Behaviour of Orthopaedic Ti-13Nb-13Zr and Ti-6Al-4V Alloys

Abstract: The aim of this study is to compare the tribological behaviour of novel orthopaedic implant alloy Ti-13Nb-13Zr with that of the standard Ti-6Al-4V ELI alloy, available in four different microstructural conditions produced by variations in the heat treatments. The friction and wear tests were performed by using a block-on-disc tribometer in Ringer’s solution at ambient temperature with a normal load of 20–60 N and sliding speed of 0.26–1.0 m/s. It was found that variations in microstructures produced significant variations in the wear resistance of Ti-6Al-4V ELI alloy. The wear losses of materials solution treated (ST) above the β transus temperature are significantly lower compared with those of materials ST in the (α + β) phase field and are almost insensitive to applied load and sliding speed. Wear loss of the (α + β) ST Ti-6Al-4V ELI alloy continuously increased as applied load was increased and was highest at the highest sliding speed. The Ti-6Al-4V ELI alloy in all microstructural conditions possesses a much better wear resistance than cold-rolled Ti-13Nb-13Zr alloy. Friction results and morphology of worn surfaces showed that the observed behaviour is attributed to the predominant wear damage mechanism.

Origin of friction in running-in sliding wear of nitride coatings

Abstract: To investigate the origin of running-in friction in unlubricated sliding wear, a magnetron sputtered multilayer coating TiAlN/VN was tested on a ball-on-disc tribometer for a series of sliding durations from 10 to 1000 cycles, followed by careful observation of the obtained worn surfaces using an field-emission gun scanning electron microscope. Three steps of friction variation were found: (1) prior to wear particle generation, low initial friction coefficient was around 0.2–0.25 purely attributed to the asperity contact; (2) then it increased steeply to a range of 0.4–0.5 in the first 100 cycles following the generation, breaking and agglomeration of wear particles, and in particular the scaling-up of fish-scale-like tribofilm; (3) eventually it approached to a steady-state value around 0.5 when the friction was governed by the viscous shearing of the tribofilm. It is concluded that, under unlubricated sliding wear, the friction behaviour of transition metal nitride hard coating is dominated by the viscous shearing of tribofilm adhesively bonding to the parent nitride coating.

The effect of Mo content in plasma-sprayed Mo-NiCrBSi coating on the tribological behavior

Abstract: NiCrBSi is a material popularly used as a hard thermal sprayed coating. The coating performs well as a wear resistant coating under low stress. At higher stress in metal-to-metal sliding wear condition, however, the NiCrBSi starts to experience surface deformation, which will inevitably lead to seizure as the stress increases. In order to improve the tribological properties of the NiCrBSi plasma-sprayed coating, Mo is added to the coating to reduce the friction between the coating and other metal contacting surface, thus, improving its dry sliding wear resistance. In this study, various amounts of Mo were mixed with NiCrBSi at 0, 25, 50, 75 and 100 wt.%. The powders were sprayed using an air plasma spraying technique onto stainless steel samples to form coatings, which were ground to achieve flat surfaces and a thickness of 350–400 μm. The mechanical properties of the coatings were determined. The coating samples were then tested using a reciprocation ball-on-flat tribometer. It was found that as the Mo/NiCrBSi ratio increases, the wear mechanism changes. Coatings containing 75%Mo and 25%NiCrBSi exhibit the highest wear depths corresponding to the cracking of the thin NiCrBSi splats. On the other hand, coatings containing 25%Mo and 75%NiCrBSi possess the lowest wear depths with no surface cracks. The presence of Mo covering the coating surface hinders the metal seizure between NiCrBSi and steel counter surface.

Tribology of UHMWPE film on air-plasma treated tool steel and the effect of PFPE overcoat

Abstract: The effects of air-plasma treatment, film thickness, normal load and sliding speeds on the tribological properties of a thin film of Ultra-High Molecular Weight Polyethylene (UHMWPE) coated onto a tool steel substrate sliding against a Φ 4 mm silicon nitride ball was investigated Wear tests are carried out on a ball-on-disk tribometer Air-plasma treatment has enhanced the adhesion of the polymer film to the steel substrate which led to an increased wear life (> 100,000 cycles) and low coefficient of friction (~ 014) of the thin film A film of optimum thickness of 163 ± 2 μm shows the maximum wear resistance The effect of varying loads (03, 1, 2 and 4 N) and speeds (200, 400, 600, 1000 and 2000 rpm) on wear life and coefficient of friction were also studied The dual-film (UHMWPE/PFPE) on the air-plasma pre-treated tool steel surface further increased the wear life (> 200,000 cycles) at a load of 4 N and a rotational speed of 1000 rpm