Smaller Wear Rate Research Articles

Friction and Wear Properties of Silicon Carbide in Water from Different Sources

Low friction and low wear of SiC sliding against itself in water at room temperature have been well reported in the past 20 years, and some practical applications have been developed. However, the properties of friction and wear in pure, deionized or distilled water have been mainly observed and not in water from sources in nature. In this article, the fundamental properties of friction and wear between SiC ball and disk are observed in water from ground, river, and sea, and the results are compared with those in deionized water in the viewpoints of modes of lubrication and wear and the resultant values of friction coefficient and wear rate. The smallest friction coefficient (μl = 0.005) in steady state is observed in deionized water and the largest (μl = 0.013) in sea water. The smallest wear rate (w s = 2.2 × 10−7 mm3/Nm) is observed in sea water and the largest (w s = 3.1 × 10−7 mm3/Nm) in deionized water. The intermediate values of μl and w s between the smallest and the largest ones are observed in ground and river water. The modes of lubrication and wear, which generated observed values of μl and w s, are considered as mixed lubrication and tribochemical wear. The chemical elements of Na, Cl, Mg, and K in sea water observed on wear particles and pits are thought effective to generate the largest value of μl and the smallest value of w s.

Lubricated Tribology of a Eutectic Aluminium-Silicon Alloy in the Ultra-Mild Wear and Mild Wear Regimes for Long Sliding Times

Aluminium-silicon alloy, an important material used for the construction of internal combustion engines, exhibit pressure induced distinct regimes of wear and friction; ultra-mild and mild. In this work the alloy is slid lubricated against a spherical steel pin at contact pressures characteristic of the two test regimes, at a very low sliding velocity. In both cases, the friction is controlled at the initial stages of sliding by the abrasion of the steel pin by the protruding silicon particles of the disc. The generation of nascent steel chips helps to breakdown the additive in the oil by a cationic exchange that yields chemical products of benefits to the tribology. The friction is initially controlled by abrasion, but the chemical products gain increasing importance in controlling friction with sliding time. After long times, depending on contact pressure, the chemical products determine sliding friction exclusively. In this paper, a host of mechanical and spectroscopic techniques are used to identify and characterize mechanical damage and chemical changes. Although the basic dissipation mechanisms are the same in the two regimes, the matrix remains practically unworn in the low-pressure ultra-mild wear regime. In the higher pressure regime at long sliding times a small but finite wear rate prevails. Incipient plasticity in the subsurface controls the mechanism of wear.

Wear properties and microstructures of alumina matrix composite ceramics used for drawing dies

The alumina matrix ceramics used for drawing dies were prepared by hot-press sintering method. The ceramics materials were made of Al 2O 3/TiC, Al 2O 3/(W,Ti)C and Al 2O 3/Ti(C,N). Mechanical and friction properties of these materials were tested and measured. The experiments for testing friction properties were carried on wear and tear machine. Mechanisms of frictions were analyzed with scanning electron microscope. Results showed that the alumina matrix composite ceramics have good physical and mechanical properties for used as drawing dies. Measured friction coefficients of alumina matrix composite ceramics showed a trend of decline and kept the value of 0.4–0.5 with the rotating speed of 550 rpm. Alumina matrix composite ceramics have smaller wear rate, while the wear rates of Al 2O 3/TiC and Al 2O 3/(W,Ti)C decrease gradually with a rising rotation speed. The wear of alumina matrix ceramics was severe at deformation zone. The primary wear behaviors of alumina matrix ceramics are scraping and furrowing. Even though the mechanisms for wear different, abrasive and adhesive wear were found to be the predominant wear mechanisms for the ceramic drawing die.

Electrodeposition and tribological properties of Ni–SrSO 4 composite coatings

Ni–SrSO 4 composite coatings were electrodeposited on superalloy Inconel 718 from a Watts electrolyte containing a SrSO 4 suspension. Ni–SrSO 4 coatings were investigated by scanning electron microscope, microhardness tester, and friction and wear tester in sliding against a bearing steel ball under unlubricated condition. The incorporation of SrSO 4 into Ni matrix increases the microhardness of electrodeposited coatings. Ni–SrSO 4 composite coating exhibits a distinctly low friction coefficient and a small wear rate as contrasted with pure Ni coating and the substrate. The effect of SrSO 4 particles on microstructure and tribological properties of Ni–SrSO 4 composite coatings is discussed.

Properties of Al 2O 3–40 wt.% ZrO 2 composite coatings from ultra-fine feedstocks by atmospheric plasma spraying

In the present study, both ultra-fine and coarse Al 2O 3–40 wt.% ZrO 2 grains were used as the starting materials to prepare ultra-fine structured and micro-structured Al 2O 3–40 wt.% ZrO 2 composite coatings (coded as NZTA coating and MZTA coating, respectively) by atmospheric plasma spraying. The ultra-fine Al 2O 3–40 wt.% ZrO 2 feedstocks for spraying were prepared by means of crushing sintered, starting from commercially availed powders of ultra-fine Al 2O 3 and ZrO 2. The microstructures and phase compositions of the crushing sintered powders and the corresponding composites coatings were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The friction and wear behaviors of the composites coatings sliding against stainless-steel under dry friction conditions and at room temperature were investigated using an optimol SRV oscillating friction and wear tester. The wear mechanisms of the coatings were discussed based on the SEM observation of the worn surface morphologies and wear debris, and the elemental composition analysis of the wear debris by energy dispersive X-ray analysis as well. Results showed that aside from the typical splat lamellae, equiaxle grains were also observed in the Al 2O 3–40 wt.% ZrO 2 composite coating made from the corresponding ultra-fine crushing sintered powders. The NZTA coatings had higher microhardness and better wear resistance than that of the MZTA coatings, which could be largely attributed to the better inter-splats bonding of the former. And the stainless-steel counterpart matched with the NZTA coatings had a smaller wear rate as well. Moreover, the two types of composites coatings were dominated by spalling and fracture as sliding against the stainless-steel counterpart, and the MZTA coatings experienced more severe worn surface damage at a larger load than the NZTA coatings tested under the same conditions, well corresponding to the difference in the wear resistance of the two types of composite coatings.

Friction and Wear Behavior of Plasma Sprayed Nanostructured and Conventional WC-Co Coatings under Water Environment

Nanostructured and conventional WC-Co coatings were deposited on 1Cr18Ni9Ti stainless steel substrate using an atmospheric plasma spraying facility. The friction and wear behavior of the resulting cermet composite coatings in water environment was comparatively investigated. It was found that the nanostructured and conventional WC-Co coatings had similar friction coefficients under the same testing conditions. However, the nanostructured WC-Co coating had better wear resistance than the conventional WC-Co coating as slid against both Si3N4 ball and stainless steel ball. At the same time, the stainless steel or Si3N4 counterpart matched with the nanostructured WC-Co coating had a much smaller wear rate as well, and as compared to rubbing against the ceramic ball counterpart, the two types of coatings rubbing against the stainless steel ball registered lower friction coefficients and wear rates.

A computerized analysis‐by‐synthesis algorithm improves precision of linear wear measurements in total hip replacements

Precision is important if small polyethylene wear rates are to be detected early and in small sample sizes. Using an automatic, computerized algorithm relying on a synthetic X-ray generated from a computer-assisted design (CAD) model of the implant may significantly improve precision of linear wear measurements. We compared this method to provide improved in vivo precision compared to the widely used Hip Analysis Suite software (version 8.0.1.7). Two anterior-posterior pelvic X-rays were taken on the same day of 18 total hip implants, and wear was measured by three observers using the two methods. Expected real wear was zero and defined as a reference value. Two sources of variability were estimated: one due to the instrument, and one due to different operators. A Wilcoxon Signed Rank Test was used for statistical comparisons. The overall precision (instrument variability and multioperator variability) given a 95% precision limit was significantly higher (p < 0.001) using the proposed method (+/-0.15 mm) when compared to the Hip Analysis Suite (+/-0.84 mm). Due to the availability of the full CAD data of the implant and to further automation of the measuring process, the newly proposed method provided improved precision in measuring polyethylene wear.

Temperature dependence of the tribological mechanisms of amorphous PEEK (polyetheretherketone) under dry sliding conditions

In this work, the effect of temperature on the tribological behavior and mechanism of an amorphous polyetheretherketone (PEEK) coating was studied using a ball-on-disk tribometer. The temperature proved to play an important role on the tribological characteristics and the crystalline structure transition of the PEEK. Before crystallization of the PEEK, the friction coefficient and wear rate increase with increasing temperature. In this case, a stick–slip motion between the two counterparts, together with the strain-hardening effect of the PEEK surface layer, results in a periodic material stack on the worn track. The PEEK exhibits the biggest friction coefficient, but the smallest wear rate at a temperature slightly higher than the PEEK crystallization point. Under this condition, fatigue plays an important role on the wear mechanism.

High Temperature Tribology and Solid Lubrication of Advanced Ceramics

The high-temperature friction and wear characteristics of different ceramics and ceramic matrix composites (CMCs) incorporated with various solid lubricants have been investigated from room temper- ature to 1000oC. The solid lubricants considered in this paper include representative precious metals, hexagonal boron nitride, graphite, fluorides, soft oxides, chromates, sulfates, and combinations of various solid lubricants. General design considerations relevant to solid lubrication were proposed on the basis of friction and wear data of self-lubricating CMCs. The self-lubricating composites incorporated with SrSO4 or/and CaSiO3 exhibits low and stable friction coefficients of 0.2 to 0.3 and small wear rates in the order of 10-6 mm3/Nm from room temperature to 800oC. The optimized composites appear to be promising can- didates for long-duration, extreme environment applications with low friction and small wear rate.

Influence of the deposition techniques on the mechanical properties and microstructure of NiCrBSi coatings

The influence of processing conditions on microstructure and mechanical properties of NiCrBSi coatings deposited on a steel substrate has been studied. Three different techniques were used: laser cladding, flame sprayed combined with surface flame treatment and flame sprayed combined with laser treatment. The microstructure of the coatings was determined by scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX). Similar phases were observed in the three coatings, but their morphology and distribution were dependent on the deposition technique. Wear and indentation tests have also been carried out. Laser cladded coatings exhibit the higher hardness and the smaller wear rate.

Comportamiento a desgaste de recubrimientos de material compuesto de matriz de aluminio fabricados por proyección térmica

In this work, the wear behaviour of coatings made of aluminium matrix composites reinforced with 20% of SiC particles and manufactured by thermal spray method with oxyacetylene flame has been investigated. The wear behaviour between coatings with uncoated particles and sol-gel silica coated ones heat treated at 500 °C and 725 °C have been compared. The sprayed coatings with silica coated particles are more homogenous and less porous due to increase of wettability by molten aluminium that takes place on coated particles. The microstructure of the sprayed coatings, the wear surfaces and the wear debris have been anlysed using optical microscopy, scanning electron microscopy and microanalysis techniques (EDX). The results show a smaller wear rate, a lower friction coefficient and more reduced loss of mass for the coatings sprayed with particles with sol-gel silica coatings than those made with uncoated particles.

Self-lubricating mechanisms via the in situ formed tribofilm of sintered ceramics with CaF2 additions when sliding against hardened steel

Abstract Sliding wear tests against 45# hardened steel were performed on Al2O3/TiC ceramic composites with the additions of CaF2 solid lubricants. The friction coefficient and wear rates were measured. The wear surface features were examined by scanning electron microscopy. Results showed that the friction coefficient and the wear rate decreased with the increase of CaF2 content up to 10 vol%, with further increases in CaF2 content, the wear rate increased rapidly. The mechanisms responsible were determined to be an in-situ formed self tribofilm between the ring-block sliding couple. SEM observations showed that two types of tribofilms are formed on the wear surface depending on the CaF2 content. A dense self tribofilm with a smooth surface associated with small friction coefficient and low wear rate was formed by the releasing and smearing of CaF2 solid lubricants on the wear surface when with 10 vol% CaF2 content. This dense self tribofilm acted as solid lubricant film between the sliding couple, and thus significantly reduced the friction coefficient and the wear rate. Breakdown of the tribofilm on the surface associated with a large wear rate was observed on samples with 15 vol% CaF2 content. This is due to the large degradation of mechanical properties of the composite with higher CaF2 contents.

Wear behavior and self tribofilm formation of hot-pressed Al 2O 3/TiC/CaF 2 ceramic composites sliding against cemented carbide

Al 2O 3/TiC ceramic composites with the additions of CaF 2 solid lubricants were produced by hot pressing. Sliding wear tests against cemented carbide were performed on these ceramic composites using the ring-block method. The friction coefficient and wear rates were measured. Results showed that the friction coefficient and the specific wear rate decreased with the increase of CaF 2 content up to 10 vol.%, with further increases in CaF 2 content, both the friction coefficient and the wear rate increased rapidly. SEM observations showed that self tribofilms were consistently formed on the wear surfaces. Two types of tribofilms are present on the worn surface depending on the CaF 2 content. A dense self tribofilm with a smooth surface associated with small friction coefficient and low wear rate was formed by the releasing and smearing of CaF 2 solid lubricants on the wear surface when with low CaF 2 content (less than 10 vol.%). This dense self tribofilm acted as solid lubricant film between the sliding couple, protected the ceramics from severe wear by brittle microfracture, and thus significantly reduced the friction coefficient and the wear rate. A broken tribofilm associated with high friction coefficient and large wear rate was formed when with high CaF 2 content (more than 10 vol.%). The reason is that large degradation of mechanical properties occurred in samples with high CaF 2 contents.

Rare Earth Containing SiAlONS: Microstructure, Mechanical and Tribological Properties

Silicon nitride based ceramics have been investigated since more than forty years. Nevertheless, a good understanding of the microstructure-properties relationships on the level of small samples is not enough to bring ceramic parts into the industrial market. More convincing is a demonstration of the excellent potential in specific applications where the requirements of a more complex system are considered. In this work, sialons are investigated for a use in lubricated wear applications. The target system is a fuel injection pump for pressures up to 30 MPa. It requires very small friction coefficients and wear rates. Isooctane was used as lubricating liquid. A friction coefficient of 0.3 has been achieved with a piston-on-plate configuration for two sialon ceramics with different a/b-ratios. The sample surfaces were in a ground condition. For comparison, tribological testing was also performed with commercial alumina and silicon nitride materials which exhibited higher friction coefficients. In order to be closer to the real conditions a test rig has been designed and constructed with a piston running in a cylinder that actually pumps isooctane at the desired pressures of up to 30 MPa. With it, the high potential of sialon ceramics for lubricated sliding applications was proven. In the fields of microstructural design neodymia and ytterbia containing sialons with varying a/b-sialon ratios and different amounts of additives have been investigated. These parameters have a strong effect on the achieved aspect ratios of the sialon grains which can be correlated to the amount of liquid phase during sintering, kinetic considerations and the additives' cationic radii. Finally, the effect of these varying grain shapes on the mechanical properties hardness and fracture toughness has been determined.

Frictional behavior of DLC films in a water environment

Three types of Ar incorporated DLC films were deposited using a thermal electron excited plasma CVD apparatus at bias voltages of −0.5 to −3 kV. Their friction and wear properties were evaluated under water and air environments using a ball-on-plate type reciprocating friction tester. The anti-wear properties of Ar-DLC films in water were superior to that in air; the smallest wear rate in water was approximately 8×10 −9 mm 3/Nm. The reduction in the friction coefficient in water was not clear, compared to that in air. The lowest friction coefficient in water was approximately 0.1. The transferred materials were observed on the wear scar of the mating ball in every experiment, but the transferred materials in water were greater in quantity than those in air. Furthermore, there seemed to be a qualitative difference in transferred materials between water and air environments, based on micro-Raman analysis. The difference in such transfer phenomena seemed to affect both the friction coefficient and wear rates. These friction and wear behaviors suggest that our Ar-DLC films are good candidates for use in rubbing machine parts when in use with water hydraulic systems.

Studies on friction and wear characteristics of cam and follower: influences of soot contamination in engine oil

In order to clarify the friction and wear mechanism of the contact between cam and follower in the valve train incorporated in an EGR system, an experimental investigation was performed with a cam-follower test rig. A fresh CD-class SAE10W-30 multigrade oil and its deteriorated versions with different contaminants were tested. Changes in friction force and amount of wear were measured during the course of the tests. The influence of the soot in the deteriorated oil was examined by mixing the exhaust gas soot blended with the dispersant, ZnDTP and MoDTC additives. Results are summarized as follows. (1) The friction fluctuated and gradually increased with the lapse of time in case of contaminated oils with the soot. (2) Under the coexistence of ZnDTP and MoDTC, however, the friction gradually decreased in spite of existence of soot. (3) The soot dispersed in the oil increased wear rate and reduced the anti-wear effect of the ZnDTP. (4) The smallest wear rate was observed because the anti-wear effect was maintained owing to the MoDTC.

1531 炭素鋼のシビヤーマイルド摩耗間の遷移に及ぼす荷重変動の効果

Pin-on-disk friction and wear experiments of a mild steel in contact itself were carried out under unlubricated conditions in wet air, to investigate the effects of varying load on the transition behavior between severe and mild wear. The endurance of mild wear surface depends on load and sliding distance under mild wear conditions before a change to increased load. The severely work-hardened wear surface under severe wear promotes the transition to mild wear on decreasing the load, resulting in a very small wear rate.

Tribofilm formation on boron carbide in sliding wear

A hot isostatically pressed boron carbide (B 4C) containing some free carbon was evaluated in self-mated sliding tests. Special attention was paid to the formation of tribofilms and their effect on the friction and wear properties. Sliding tests were performed in a pin-on-disc configuration pressing pins with rounded ends towards a rotating disc. The effects of load, sliding speed and relative humidity (RH) of the surrounding air were particularly investigated. The friction was continuously measured and the wear volumes of the pins were estimated after different sliding distances. The worn surfaces were characterised utilising scanning electron microscopy and X-ray diffraction. It was confirmed that B 4C forms tribofilms of oxides that have pronounced effects on the wear and friction properties. Depending on the load conditions and the surrounding humidity, transitions to low friction levels occur. At suitable conditions of high RH and unexcessive loads, the material shows friction coefficient values around 0.1, small wear rates and smooth tribosurfaces. The conditions for these transitions are described and discussed.

含繊維粉体混合物の造粒

Granulation of powder compounds containing fibrous materials was studied by using basic materials that form brake pads. Because the mixture is easy to segregate during granulation process, stabilization process is necessary. In this study, two different granulation processes were employed and was compared with a dry mixing process. The strengths of test pieces made by these processes were compared by applying the three points bending strength tests and the friction characteristic test. As a result, we found that the granules with napped surface and a lower bulk density have a smaller wear rate and a higher bending strength.

Characterization of the Resistance of Pyrolytic Carbon to Abrasive Wear

Si-alloyed pyrolitic carbon (PyC) is currently employed in many biomedical devices, due to its fairly good biological compatibility and non biodegradeability. For prosthetic heart valve applications, required to operate safely for many years, the resistance to abrasive wear is one of the limiting factors which must be accurately evaluated. The present study reports on abrasive wear testing of Ti/PyC and PyC/PyC sliding couples. For both couples it was found that the wear behaviour can be shifted from a low wear regime, characterised by very small wear rates and reduced scatter, to a high wear regime, characterised by high wear rates and high scatter, due to the presence of particle contamination coming from the environment and/or from the specimen polishing process. Actual biomedical devices, particularly heart valves, should not experience the high wear regime, due to the absence of any hard particle contamination source. The wear observed in these items is in fact minimal and may depend on mechanisms other than abrasive wear. In these conditions the experimental evaluation of the wear behaviour should definetely be performed by tests on actual devices.