Comparison of different abrasion mechanisms on aesthetic properties of organic coatings

Organic coatings are the most commonly used system for protection from corrosion. In many applications, the protective properties against corrosion are associated with several other properties, including resistance to abrasion and good aesthetic appearance. This is particularly important for the automotive and transport industry, building trade, domestic products and packaging.The aim of this work is to compare two different test methodologies to characterize mar performances of organic coatings. Taber test and Falling Abrasive test were chosen. In both tests sodium chloride and sucrose were used as abrasive agents in order to simulate a possible damage occurring in domestic environment. These abrasives produce a limited damage, due to the low hardness, that influences only the aesthetic aspect of the organic coating. The level of damage was evaluated through gloss measurements. The correlation between the changes of gloss and the damage was investigated using optical microscopy and environmental scanning electron microscopy.The two tests showed a different morphology of the damage of the organic coating due to the different mechanism of damage: abrasion in Taber test and erosion in the Falling Abrasive test.     

Mechanical and tribological investigations of sol–gel derived SiO2 optical coatings

Sol–gel silica coatings were deposited on soda lime glass substrates by dip-coating. The silica films were amorphous, crack free, and smooth with an average roughness of less than 3 nm and thickness of 0.8–1.2 μm. Mechanical and tribological properties were investigated using nanoindentation, Taber abrasion and a polishing wear test. The hardness increased with increased thermal exposure from 2200 MPa for samples fired at 480 °C for 2 min to 3800 MPa for those fired at 560 °C for 14 min. In Taber abrasion, failure was due to penetration of the coatings by the abrasive particles of the Taber grinders, which caused scratches and subsequent delamination. For polishing wear experiments, hardness was inversely proportional to polishing wear rate. This suggests that hardness is a good indicator for the resistance of sol–gel silica coatings to polishing.     

Possibility of the Abrasive Wear Resistance Determination with Scratch Tester

Abrasion wear resistance is very important in many applications and it is not a surprise that there are many laboratory test methods for its determination. In this article, a possibility of the abrasive wear resistance determination with scratch tester, as a relatively easy and quick test method, was analysed and compared with the standard test method for pin abrasion testing (ASTM G 132). Materials used in the tests were: two ferrous-based coatings (deposited on an Al–Si alloy substrate with atmospheric plasma spraying), two aluminium-based composite materials with 10 wt% of Al₂O₃ reinforcements (produced with compocasting technique) and grey cast iron, known as a material with good abrasive wear resistance. Coefficient of friction and wear of the samples were investigated with both abrasion wear test methods and analysed in correlation with their mechanical properties.     

Wear mechanisms in electroless nickel coatings

Electroless nickel coatings are susceptible to severe adhesive wear against plain carbon steel under dry sliding contact, because the low interfacial and high surface free energies of this material combination produce highly compatible surfaces. Controlled heat treatment eliminates severe wear by inducing crystallization of amorphous nickel to Ni₃P, which is incompatible with steel. Electroplating the counterface with chromium also eliminates severe adhesive wear owing to the efficient barrier properties of its surface oxide but a stainless steel counterface exacerbates the problem because of its single-phase microstructure and the low durability of its oxide film. The reciprocating diamond scratch test gives a different ranking order of wear rate from the Falex, pin-on-flat and Taber tests, because of its dependence on fracture toughness as the dominant material parameter rather than adhesive transfer. Wear mechanisms observed in the investigation include adhesive transfer, oxidation, three-body abrasion, micromachining, plastic deformation and delamination. In general, no correlation is found between wear rate and hardness; this is primarily because of changes in the mechanism of wear effected by processing, counterface materials or sliding conditions.     

Wear of aluminium bronze in sliding contact with lubricated stainless steel sheet material

Aluminium bronze, well known for its good sliding properties, is frequently applied as tool material in sheet metal forming (SMF) of stainless steel, e.g. for the production of washing, refrigeration and cooking equipment. The limited hardness of the material makes it, however, sensitive to tool wear that is: volumetric wear of the tool due to sliding contact with the sheet material. Conventional wear tests like the rubber wheel abrasion test or the Taber abrader test cannot be used to simulate the interaction of the tooling with lubricated sheet material. Dedicated tribo tests are therefore conducted with the slider-on-sheet test. The aim of the research is to measure the specific wear rate of aluminium bronze at SMF-like conditions. Experimental results showed a pronounced influence of lubricant selection and sheet material selection. The measured specific wear rate varied from 10⁻⁸ mm³/N m for a smooth stainless steel sheet quality to 10⁻⁶ mm³/N m for a rough surface quality.     

Abrasive wear of steel against gravel with different rock–steel combinations

Wear testing equipment and tests used in research laboratories are often miniature or simplified versions of real applications. For example standardized ASTM dry sand rubber wheel abrasion test G 65 and pin abrasion test G 132 are widely used to study materials’ abrasion wear resistance. The test results, however, do not always correlate too well with the results obtained from real wear conditions. One reason for this is, for example, that in the crushing applications of mining industry the abrasive size is usually much larger than that used in the laboratory wear tests. To study the abrasive wear caused by larger size gravel, new three-body abrasion test equipment was therefore constructed. The equipment uses the pin-on-disk principle with free abrasive particles of sizes up to 10 mm. During the test the pin is repeatedly pressed against a fixed amount of abrasive that is rotating with the disk having confining walls. As the pin is prevented from touching the counterbody, only the abrasive acts as the wearing agent.Three steels of different hardnesses were cross-tested as pin–disk pairs and as pins against a rubber disk using three igneous rock gravels with different crushability properties as abrasives. The wear was measured as mass loss from both the pin and the disk, and the rock comminution was measured by sieving. The results indicate that the mechanism of wear is greatly affected by the hardness of the counterbody. When using large size abrasives, the rate of comminution is also a very important factor that can significantly affect the wear test results.     

Improved ball crater micro-abrasion test based on a ball on three disk configuration

An improved ball crater micro-abrasion test method has been developed that differs from the conventional ball crater method. A ball-on-three-disk (BOTD) configuration provides mechanical stability and three simultaneous measurements of abrasion. An inclined BOTD geometry allows the specimens to be totally immersed in abrasive, which allows the use of dry abrasives as well as slurries and pastes. Use of a rubber ball gives effective three-body abrasion and provides results that are highly correlated with the ASTM G65 method. Use of dry abrasive with a rubber surface, rather than use of slurries and a metal ball, provides cutting action that is closer to actual field conditions, and allows high temperature test. Flooding the substrate with abrasive also avoids the problems encountered in conventional ball crater tests in that it provides spherical scars even for large particle abrasives, and spherical geometry allows direct computation of the volume of wear. Modeling of the BOTD scar geometry indicates that the BOTD contact pressure is similar to the contact pressures used in the ASTM G65 test. The BOTD microabrasion method provided excellent ranking of the abrasion rates of bare steel and two thicknesses of a TiAlN coating.     

Abrasion resistance of high nodule count ductile iron with different matrix microstructures

Thin wall ductile iron is being used in the industry as a way to improve the strength to weight ratio. Nevertheless, thin walled sections promote microstructural changes such as an important increase in the nodule count. This paper examines the influence of the nodule count on the abrasion resistance of ductile iron castings, having different matrix microstructures, and analyzes the main nodule characteristic affecting abrasion. Different ductile cast iron test samples, from 1.5 to 25 mm in thickness, having nodule counts varying between 250 and 2000 nod/mm², were used. The samples for abrasion tests were heat treated in order to adjust the matrices to fully martensitic, ferritic, pearlitic and ausferritic microstructures. The abrasion resistance was evaluated according to the ASTM G 65 standard. The results showed that in all cases, when the nodule count increases the abrasion resistance decreases, as a consequence of the increase in total amount of nodules perimeter exposed to abrasion which increase the overall rate of wear.     

Solid particle erosion behaviour of hardfacing deposits on cast iron—Influence of deposit microstructure and erodent particles

Solid particle erosion (SPE) behaviour of different hardfacing electrodes deposited on gray cast iron (ASTM 2500) was studied using quartz sand and iron ore as erodent particles. Erosion test was carried out as per ASTM G76 test method. Considerable differences in erosion rates were found among different hardfacing electrodes at normal impact. Both volume fraction of carbides and type of carbides played an important role in the erosion behaviour of the deposits when quartz sand was used as erodent particles. On the other hand, only volume fraction of carbides irrespective of carbide type mainly controlled the erosion rate of the same deposits when iron ore was used as erodent particles. Such difference is attributed due to difference in metal removal mechanisms by the two erodent particles used. Hard quartz sand particles were capable of causing damage to most of the carbides while relatively softer iron ore particles were unable to fracture any carbides present in the microstructures. Furthermore, relatively brittle matrix led to high erosion rate which is significant in case of quartz sand as erodent, but not in case of iron ore particles. Like abrasion resistance, hardness is not a true index of erosion resistance of hardfacing deposits.     

Mechanism of material removal during three-body abrasion of FRP composite

The low-stress abrasive wear behaviour of chopped-glass-fibre-reinforced polyester composites has been studied by using a rubber wheel abrasion test (RWAT) apparatus. Silica sand particles of two different size ranges were used in the current study as dry and loose abrasives. Weight loss of the composites during three-body abrasion has been examined as a function of the sliding distance. Abrasive wear of the composites shows dependence both on abrasive particle sizes and applied load, as well as the weight fraction of glass fibre reinforcement. It has also been observed that the wear rate becomes constant with the increasing sliding distance. Scanning electron microscopy was used to observe the worn surfaces and to understand the mechanism involved in material removal. This revised version was published online in June 2006 with corrections to the Cover Date.     

The evaluation of tribo-corrosion synergy for WC-Co hardmetals in low stress abrasion

WC-based hardmetals are materials that are widely used in applications where abrasion resistance is required. This paper describes the results of tests that were performed using a modified ASTM G65 rubber wheel test system incorporating an abrasive (silica sand) and media (sulphuric acid, deionised water, and calcium hydroxide solution). The first of these media was used in order to simulate conditions found in ash disposal equipment found in coal-fired power stations. The calcium hydroxide solution was intended to simulate conditions found in forming tools used in the manufacture of ceramic roofing tiles.Under very acidic conditions (pH 1.1), undermining of WC grains by binder dissolution appeared to be the rate-governing step in determining volume loss. Under mildly acidic conditions (pH 2.6 and 6.3) there was more evidence of WC grain fracture and correspondingly less of binder dissolution. Exposure to the alkali (pH 13 Ca(OH)₂ solution) caused the least wear.Results were correlated with physical and microstructural and parameters commonly used for quality assurance in the hardmetal industry. Corrosion-abrasion synergies were also evaluated using the same test rig in conjunction with the respective acidic solutions, but omitting the silica sand.These results are complemented by SEM examination of wear surfaces and of metallographically polished cross-sections of wear surfaces, and by bend strength evaluation of samples after simultaneous exposure to the various media and silica sand and the media in isolation.     

A statistical model describing wear traces in three-body abrasion

Cutting wear is a mechanism by which material is removed through three-body abrasion. In the present paper, a statistical model describing the wear traces on a worn surface is proposed for three-body abrasion, to estimate cutting wear as a proportion of the total wear of the test materials. Using this model, a statistical analysis of the traces on the worn surface was made after short-travel, three-body abrasion tests. The results showed that cutting was not a great proportion of the total wear of the test materials under the conditions of three-body abrasion.     

A study of abrasive wear mechanisms in cobalt-base alloys

Single-point scratch tests were used to investigate material removal mechanisms in two cobalt-base powder metallurgy alloys 6 and 19. Each alloy was produced with fine, medium and coarse chromium-rich M₇C₃ carbides in a cobalt-rich f.c.c. matrix phase. In a separate study, the low stress abrasion resistance was found to increase with carbide size. The present scratch test study was designed to simulate low stress abrasion conditions by using single quartz abrasive particles as scratch tools, and the results are compared with those from scratches made using regularly shaped diamond tools.Single- and multiple-pass scratches were made with several different loads using Vickers diamond pyramids and single quartz abrasive particles on metallographically prepared surfaces. Single-pass scratches were also made on preworn surfaces by using a Vickers diamond.Single-pass diamond scratches exhibited ploughing and extensive coarse slip bands in the matrix phase of metallographic specimens. Evidence of carbide deformation and of slip band cracking of the matrix material was observed also. Coarse slip bands were not observed on preworn surfaces. On both polished and preworn surfaces, thin layers of the matrix phase were often smeared over the carbides, and coarse carbides were extensively cracked. Multiple-pass diamond scratches on metallographic specimens exhibited thin detached layers of matrix material in the scratch groove and tongue-like extruded lips of material stretching away from the ridge. Particles of similar size and shape were found on the diamond pyramid.Scratch tests with quartz particles exhibited slip band cracking, smeared matrix material over the carbides and cracking and pulling out of carbides similar to observations with diamond tools. However, extensive ploughing and shear lip formation were not observed in quartz scratches, and wear debris particles in the scratch and on the tool were rounded and very much smaller than those produced by multiple-pass diamond scratches. Wear debris in multiple-pass quartz scratches were observed to pile up at the leading edges of the carbides, which protruded from the surface because of preferential wear of the matrix phase, as observed in low stress quartz abrasion.With both quartz and diamond tools, the material with the finest carbides (alloy 19A) exhibited large pits where cracks had traveled along the carbide-matrix interface and between carbides. Very little evidence of pulling out of carbides in the fine carbide materials was found.     

Comparative Study of Thermally Sprayed Coatings Under Different Types of Wear Conditions for Hard Chromium Replacement

The tribological properties of part surfaces, namely their wear resistance and friction properties, are decisive in many cases for their proper function. To improve surface properties, it is possible to create hard, wear-resistant coatings by thermal spray technologies. With these versatile coating preparation technologies, part lifetime, reliability, and safety can be improved. In this study, the tribological properties of the HVOF-sprayed coatings WC–17%Co, WC–10%Co4%Cr, WC–15% NiMoCrFeCo, Cr₃C₂–25%NiCr, (Ti,Mo)(C,N)–37%NiCo, NiCrSiB, and AISI 316L and the plasma-sprayed Cr₂O₃ coating were compared with the properties of electrolytic hard chrome and surface-hardened steel. Four different wear behavior tests were performed; the abrasive wear performance of the coatings was assessed using a dry sand/rubber wheel test according to ASTM G-65 and a wet slurry abrasion test according to ASTM G-75, the sliding wear behavior was evaluated by pin-on-disk testing according to ASTM G-99, and the erosion wear resistance was measured for three impact angles. In all tests, the HVOF-sprayed hardmetal coatings exhibited superior properties and can be recommended as a replacement for traditional surface treatments. Due to its tendency to exhibit brittle cracking, the plasma-sprayed ceramic coating Cr₂O₃ can only be recommended for purely abrasive wear conditions. The tested HVOF-sprayed metallic coatings, NiCrSiB and AISI 316L, did not have sufficient wear resistance compared with that of traditional surface treatment and should not be used under more demanding conditions. Based on the obtained data, the application possibilities and limitations of the reported coatings were determined.     

An improved method for determining the wear of polymeric coatings

A modification on the Taber Abrader is described in which a $\text{1}\text{4}$ in steel ball is substituted for the conventional sandpaper wheel. As a result, the endpoint of the test becomes much clearer and the test data are suitable for quantitative interpretation. The modified test is applicable not only to high pressure laminates but also to a wide variety of plastics and coatings. Further modifications are proposed to convert the wear path to a straight line instead of the circle found on the Taber Abrader and to increase the load on the ball. These changes are expected to make the testing time comparable to the present sandpaper wheel method.     

Automotive tribology overview of current advances and challenges for the future

This keynote address will provide a comprehensive overview of various lubrication aspects of a typical powertrain system including the engine, transmission, driveline, and other components, as well as the integration of these lubrication and surface engineering concepts into a unified automotive powertrain system. In addition, this presentation will focus on the current status and future trends in automotive lubricants including discussion of current and anticipated future requirements of automotive engine oils. This presentation will also review the current standard ASTM (American Society for Testing and Materials) test methods for engine lubricants and other compilations of automotive standards. In addition to engine oil test development, industrial researchers are developing light-weight materials such as non-ferrous materials (Al, Mg) for engine and drivetrain materials to replace the current heavy-weight cast iron blocks. Recent industrial developments include high strength and high density of composite materials, high volume liquid molding and hydroforming technology, structural adhesive boding, and the ability to mold large structural components. Industrial researchers have also developed processing improvements for forming more complex stamped aluminum parts or panels, more robust stamping, and improved casting techniques. In this paper, our insights and perspectives on future trends in light-weight tribological material and nonotribology will also be reviewed.     

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.     

Boundary Lubrication of Steel Surfaces with Borate,Phosphorus, and Sulfur Containing Lubricants at Relatively Low and Elevated Temperatures

Prolonging the life of engineering components through lubricant formulation to achieve better wear resistance and higher oxidation stability is of paramount importance to many mechanical systems, such as automotive gears and bearings. This can be accomplished with formulated lubricants that limit the generation of wear debris causing severe abrasion and protect the contacting surfaces through the formation of wear-resistant tribofilms. In this study, a ball-on-disk tribometer was used to characterize the friction and wear properties of steel surfaces slid in the boundary lubrication regime. An experimental scheme was developed to allow the statistical screening of various lubricant formulations. Sliding experiments were performed in baths of different lubricants at relatively low and elevated temperatures, approximately 32 and 100°C, respectively, under conditions of constant load and sliding speed. Surface profilometry, optical microscopy, and scanning electron microscopy were used to characterize the dominant friction and wear mechanisms. The tribological properties were found to strongly depend on the temperature and the additives (e.g., borate, phosphorus, and sulfur) present in the blended lubricants. The superior high-temperature wear performance of the lubricant with the higher borate content is indicative of the formation of a durable tribofilm that reduces metal-to-metal adhesion, material transfer, and surface plowing by wear debris.     

Wear performance and wear debris of semimetallic automotive brake materials

Wear performance of automotive brake material is addressed and debris collected after brake dynamometer test and after ball-milling of identical semimetallic friction lining is characterized using a combination of analytical techniques. The differences between dynamometer wear debris and ball-milled samples are demonstrated. Wear debris is typified by the presence of numerous nanoparticles formed during wear process. Their chemistry resembles the chemistry of friction layer described previously. Contradicting findings by different research groups addressing automotive wear particulates are discussed and further refinement of analytical and testing techniques as well as their combination is suggested.     

Cemented carbide and cermet tooling for film-perforating

The tools used to perforate a particular photographic film started to wear at an unacceptable rate when the film base was changed from cellulose triacetate to polyester (PET). A laboratory investigation was initiated to screen candidate tool materials and identify ones with potential for 10 times life improvement over cemented carbide (WC/10% Co).

The screening tests started with abrasion and corrosion tests on various grades of cemented carbide, cermets and selected ceramics. Concurrent production trials indicated that the laboratory corrosion tests were not correlating with production results. To address this problem, a “nibbler” test was developed which simulates perforating and material removal on a punch after 10⁶ perforations (nibbles) became the screening test metric.

It was determined that abrasion tests do not accurately predict tool material behavior when chemicals are present on or in the materials being perforated. Static corrosion tests do not predict tool response under production conditions. The rubbing of the film on the tool surfaces removes protective films and there can be a significant corrosion component in tool erosion. The nibbler simulates real tool conditions because erosion is produced by actual cutting of coated webs. Nibbler tests in this study indicated that alumina/zirconia resisted film erosion better than cemented carbide, even cemented carbide with PVD coatings. The nibbler tests also indicated that leaving recast layers from electrical discharge machining on cemented carbide greatly increases erosion rates. It should be removed.

Production tests conducted since completion of these laboratory studies suggests that nibbler results correlate with production results. Coated cemented carbides are providing 3 times the service life of uncoated cemented carbides as predicted by the nibbler test.