Sliding metallic wear test with in-process wear measurement: A new approach to collecting and applying wear data

A wear test is described in which the edge of a hard wedge is loaded against the periphery of a rotating disc of softer specimen material. The applied normal load is kept approximately constant during a test. As the test progresses and the disc diameter is reduced by the wear taking place the wedge moves radially inward. By measuring this inward movement during a test it is shown how the wear can be continually monitored. Results are given and it is shown how these might be applied in practice, taking into account the influence of both surface roughness and lubrication.     

Dry reciprocating wear of Al-Si-SiCp composites: A statistical analysis

In this paper, effect of various wear test and material related parameters (applied load, sliding distance, reciprocating velocity, counter surface temperature and weight percentage of silicon) on dry wear behavior of two Al-Si-SiC_p composites under reciprocating conditions was studied using fractional factorial design. Developed mathematical model showed that Al-Si-SiC_p with high silicon content composite is subjected to a lower wear compared to that of low silicon composite. The applied load, sliding distance, reciprocating velocity and percentage silicon weight in composite are the four important and controlling factors; counter surface temperature has a minor effect on the wear of the composite specimens in dry condition.     

Erosive wear on ceramic materials obtained from solid residuals and volcanic ashes

In this study, the performance of ceramic materials that were subjected to solid particle erosion was analyzed. This research was performed to characterize the materials in relation to the wear process. The materials could be used in the construction of devices and machine components that are commonly exposed to environments where volatile, abrasive particles typically cause a high rate of wear. The types of composites used in this study could have useful applications in mechanical components, automotive coatings, etc. These materials are usually obtained from solid residuals and volcanic ashes, in which clay and epoxy resin were used as binders.The erosion testing was performed in accordance with the ASTM G76-95 standard. The samples had a rectangular shape, and their dimensions were 50×25 mm² and 10 mm in thickness. The abrasive particles used were angular silicon carbide (SiC) with a particle size of 420-450 μm. The tests were performed using three different incident angles (30°, 45° and 90°) with a particle velocity of 24±2 m/s. The abrasive flow rate was 70 g/min. The particle velocity and the abrasive flow rate were low in all the tests to reduce the interaction between the incident particles and the rebounding particles in the system. Additionally, the total time of each test was 10 min, and the specimens were removed every 2 min to determine the amount of mass lost. The test specimens were located a distance of 7 mm from the shot blast. The surface of the specimens was examined with a scanning electron microscope (SEM), which characterized the erosive wear damage.The results indicated that all of the ceramic materials reached their maximum erosion rate at an incident angle of 90°. The erosion rate was significantly decreased when the angle of incidence was 30°. Additionally, the ceramics that consisted of volcanic ashes and sand mixed with epoxy resin gave a better erosion resistance compared with the materials that were combined with clay. It was assumed that the combination that was mixed with epoxy resin produced a more compact structure in the specimens, which resulted in a less severe attack of the particles that were acting on the surface of the material. The sand and the volcanic ashes that were mixed with clay, which had the poorest performance in the tests, exhibited similar behavior.It was also observed that the damaged area was extended in all of the cases that used an incident angle of 45°, whereas the depth of the wear scars was higher when an incident angle of 90° (normal incidence) was used. The wear scars were characterized by an elliptical shape at 30° and 45°, which is a characteristic feature when the specimens are impacted at low-impact angles (α≤45°), whereas a circular shape was observed at 90°.     

Surface structure of stainless and Hadfield steel after impact wear

After impact wear, the very surface of stainless austenitic CrMnCN steel and austenitic MnC Hadfield steel revealed a thin fully amorphous layer followed by a layer of nanocrystals embedded in an amorphous surrounding, which was supported by a severely cold worked layer of austenite below. The new high-strength stainless steel contained C + N = 0.82 mass% and exceeded Hadfield steel in respect to proof strength, elongation, work to fracture and wear rate.     

Abrasivity and grindability study of mineral ores

The results of the milling experiments of different mineral ores and laboratory wear testing with different abrasives have shown that the abrasivity of treated materials does not depend only on their hardness, but, to a great extent, on the particle shape of the materials. The grindability of materials milled by collision depends on the properties of materials as well on the treatment parameters (specific treatment energy). The aims of this investigation were (1) to study the abrasivity and the grindability of different minerals (granite, quartzite, etc.) and (2) to predict the relative wear resistance of the materials prospective for the grinding media of milling equipment, using a centrifugal type impact wear tester. Experiments conducted with abrasives of different hardness and with particles of different shape have shown that the wear rate of materials used as wear resistant materials in grinding devices depend more on the angularity of abrasive particles than on their hardness. It was shown that the grindability depends more on the composition and properties (fracture toughness, homogeneity of the structure) than on the hardness of the mineral ores. The main size reduction occurs at first collision, later in the multiple milling of mineral materials particle rounding takes place. The angularity parameter has good correlation with the wear rate in the case of the studied commercial steels as well as with metal matrix composites. Experiments with cermets showed that erosion does not practically depend on abrasive particle shape.     

Wear behaviour of some low alloyed steels under combined impact/abrasion contact conditions

The wear behaviour of some low alloyed steels has been investigated using a laboratory impeller–tumbler wear test equipment in which the steel samples are worn by angular granite particles under combined impact/abrasion wear contact conditions. The wear of the steels was evaluated by weight loss of the steel samples while the wear mechanisms of the steels were investigated by post-test light optical microscopy (LOM), scanning electron microscopy and energy dispersive X-ray analysis. The worn steel surfaces display a very rough surface topography with pronounced craters and distinct grooves caused by high and low angle impacts, i.e. abrasive wear, respectively. Besides, fragments of embedded granite particles are frequently observed in the worn surface of the steels. The wear of the steels tends to decrease with increasing steel hardness. However, instead of using the bulk hardness value the hardness of the worn/plastically deformed surface layer should be used when modelling the wear resistance. Further, the wear resistance of the steels was found to be dependent on the microstructure and chemical composition. Steels with similar type of microstructure show a linear decrease in weight loss with decreasing grain size and increasing carbon content.     

Friction and wear behaviour of WC-Co-Cr3C2-VC cemented carbides obtained from nanocrystalline mixtures

The effect of adding Cr₃C_2, VC or a mixture of both as a grain growth inhibitors to cemented carbides obtained from WC-12 wt.%Co nanocrystalline mixtures on the behaviour of friction and dry sliding wear have been studied. All the wear tests were performed on a tribometer with ball on disc configuration, using a WC-6 wt.%Co ball as a counterpart with normal contact loads of 40 and 60 N, sliding distance of 2000 m and a sliding speed of 0.1 m/s. A significant reduction in the wear rates was observed by the effect of the aforementioned additives, in particular for the VC, which showed an increase in the wear resistance of the order of 90%. The analysis of wear and surface damage were correlated to the observed behaviour.     

Accelerated wear testing as an aid to failure diagnosis and materials selection

The needs and advantages of accelerated wear testing are discussed, with particular reference to aerospace applications. Examples are given from recent work on plastics-based dry-bearing liners to illustrate how accelerated wear tests can provide information relevant to materials selection, identification of the main parameters influencing wear and definition of the relationships between wear, material composition and structure. Prediction of the service life of dry-bearing liners, however, presents problems and full-scale component tests are usually required     

Friction and wear properties of cu and fe-based P/M bearing materials

The performances of porous bearings under different operating conditions were experimentally investigated in this study. Material groups studied are 90%Cu+10%Sn bronze and 1%C + % balance Fe iron-based self-lubricating P/M bearings at constant (85%) density. In the experiments, the variation of the coefficient of friction and wear ratio of those two different group materials for different sliding speeds, loads, and temperatures were investigated. As a result, the variation of the friction coefficient - temperature for both constant load, and constant sliding speed, friction coefficient - average bearing pressure, PV - wear loss and temperature-wear loss curves were plotted and compared with each other for two materials, separately. The test results showed that Cu-based bearings have better friction and wear properties than Fe-based bearings.     

新型车轮材料的磨损特性试验研究

采用JD-1型轮轨试验机对四种新型车轮材料做材料摩擦磨损特性试验研究,采用JA4103型电子称重仪对磨损后的试件进行磨损量测量,利用JB-6C轮廓仪对磨损后的轮廓进行分析。试验结果表明,在相同实验条件下,材料的磨损量随着含碳量的增加而减少,含碳量越高,耐磨性越强。磨损后磨痕粗糙度明显增加,磨痕的粗糙度与材料的含碳量、硬度等都没有明显的关系,并且本试验得到的磨痕粗糙度Ra为0.4μm左右。材料的耐锈蚀性与材料中的含铬量有着直接的关系,铬元素的抗锈蚀能力明显。     

On evaluation of wear resistance of tooth enamel and dental materials

A survey of the literature shows that in many studies on the wear resistance of tooth enamel or dental materials a large scatter of experimental data has been obtained when wear tests were performed at a fixed load. Despite the steady loading, wear conditions vary during sliding, since tooth enamel as well as dental materials have inhomogeneous structure. This leads to changes in contact interactions between sliding surfaces, and as a result, we get changes in the friction and wear behaviour of tested materials. This is why at the same loading the wear can be different. In this study, more reliable approach to evaluation of the wear resistance of human enamel and dental materials is proposed. The procedure is based on the correlation between the volumetric wear and the friction energy dissipated during sliding. The model can be useful to compare the wear resistance of different dental materials tested in different ambient conditions.     

A pin-on-disc investigation of novel nanoporous composite-based and conventional brake pad materials focussing on airborne wear particles

Wear particles originating from disc brakes contribute to particulate concentration in the urban atmosphere. In this work novel nanoporous composite-based and conventional brake materials were tested against cast-iron discs in a modified pin-on-disc machine. During testing airborne wear particles were measured online and collected on filters, which were analysed using SEM and EDX. The morphology of airborne wear particles containing elements such as iron, oxygen, and copper is presented. These results show that two of the nanoporous materials generated 3-7 times less airborne wear particles than the conventional materials. Both the conventional and nanoporous materials displayed a bimodal number distribution.     

Investigations on the influence of graphite filler on dry sliding wear and abrasive wear behaviour of carbon fabric reinforced epoxy composites

In this experimental study, the dry sliding wear and two-body abrasive wear behaviour of graphite filled carbon fabric reinforced epoxy composites were investigated. Carbon fabric reinforced epoxy composite was used as a reference material. Sliding wear experiments were conducted using a pin-on-disc wear tester under dry contact condition. Mass loss was determined as a function of sliding velocity for loads of 25, 50, 75, and 100 N at a constant sliding distance of 6000 m. Two-body abrasive wear experiments were performed under multi-pass condition using silicon carbide (SiC) of 150 and 320 grit abrasive papers. The effects of abrading distance and different loads have been studied. Abrasive wear volume and specific wear rate as a function of applied normal load and abrading distance were also determined.The results show that in dry sliding wear situations, for increased load and sliding velocity, higher wear loss was recorded. The excellent wear characteristics were obtained with carbon-epoxy containing graphite as filler. Especially, 10 wt.% of graphite in carbon-epoxy gave a low wear rate. A graphite surface film formed on the counterface was confirmed to be effective in improving the wear characteristics of graphite filled carbon-epoxy composites. In case of two-body abrasive wear, the wear volume increases with increasing load/abrading distance. Experimental results showed the type of counterface (hardened steel disc and SiC paper) material greatly influences the wear behaviour of the composites. Wear mechanisms of the composites were investigated using scanning electron microscopy. Wear of carbon-epoxy composite was found to be mainly due to a microcracking and fiber fracture mechanisms. It was found that the microcracking mechanism had been caused by progressive surface damage. Further, it was also noticed that carbon-epoxy composite wear is reduced to a greater extent by addition of the graphite filler, in which wear was dominated by microplowing/microcutting mechanisms instead of microcracking.     

Contact temperatures and their influence on wear during pin-on-disk tribotesting

It is important to take contact temperatures into account when developing friction and wear tests for potential tribomaterials and when analyzing the results of those tests. This paper presents some of the most useful analytical and numerical methods that can be used to predict surface temperature rises in dry or boundary lubricated pin-on-disk tribotests. The objective is the development of relatively simple, accurate, and easy-to-use expressions that can be used to predict contact temperatures in pin-on-disk sliding contacts. Results of the methods are compared for several different cases, and experimental verification of the predictions are also presented. The resulting expressions are applied to investigate wear of a ceramic (zirconia), metal (stainless steel) and polymer (polyethylene) in pin-on-disk tests.     

Comments on “Micro-scale abrasive wear testing of PVD coatings on curved substrates” [by K.L. Rutherford and I.M. Hutchings]

Previously published expressions for the wear volume in the micro-scale abrasion test for curved specimen surfaces (K.L. Rutherford and I.M. Hutchings, Tribology Letters 2 (1996) 1–11) were based upon erroneous assumptions about the wear-scar geometry. Accurate volumes have now been computed, and the errors in the use of the original analytical equations are shown to be negligibly small (<0.5% error) for all practical cases. This revised version was published online in August 2006 with corrections to the Cover Date.     

A study on wear coefficients and mechanisms of steam generator tube materials

Reciprocating sliding wear tests were performed to evaluate wear properties of Inconel 600MA and 690TT steam generator (SG) tube materials against 405 and 409 ferritic stainless steels. With increasing normal loads and sliding amplitudes, the wear rate of tube materials increased but a wear transition occurred only in Inconel 690TT. Subsurface deformation strengthening seemed to be an important factor that determines the wear resistance of tube materials. After the wear test, the worn surfaces were observed to investigate the wear mechanism of tube materials using SEM. The results indicated that there are different mechanisms of wear particle removal between the tube materials. The differences are related to the degree of work hardening due to the differences in chromium content in the tube materials. Based on the present results, wear coefficient values for the life estimation of SG tubes were calculated according to the work-rate model at each test condition. The wear rate is lower for Inconel 690TT compared to that for Inconel 600MA. Finally, parameters that should be considered for evaluation of wear coefficients were discussed.     

A study on wear resistance of the white layer

The white layer has received some consideration, but there are two different opinions on its wear characteristics. It is considered to be of tribological advantage in some instances. However, the microcracks and voids formed by adiabatic shearing are precursors to fracture and should decrease the wear resistance. As to the white layer previously generated by impact wear, the wear characteristic of the white layer is studied by a pin on disc machine in the present paper. It is found that the white layer causes delamination of material, which increases the wear loss significantly. The delamination of the white layer, being prior to the cutting wear, is the primary wear mechanism for materials with the white layer.     

Effect of counterparts on the friction and wear behavior of polyelectrolyte multilayers

Polyelectrolyte multilayers (PEMs) were prepared on Si substrates by alternative deposition of poly(sodium 4-styrenesulfonate) (PSS) as polyanion and poly (diallyldimethylammonium chloride) (PDDA) as polycation. The PEM film was characterized by means of ultraviolet-visible light absorption spectrometry and atomic force microscopy. The friction and wear behavior of the polymer film sliding against brass, 440C stainless steel, Si₃N₄ and WC balls was evaluated on a microtribometer. It was found that the multilayer film was uniform and compact, and it registered a lowered friction coefficient and extended antiwear life while sliding against soft counterparts, in particular, a brass ball. This could be because the polymeric transfer film had an enhanced adhesion on the soft metallic counterpart in the presence of inter-transferred metallic debris. Contrary to the above, the PEM film had a higher friction coefficient and shorter antiwear life while sliding against Si₃N₄ and WC balls, possibly owing to a higher shearing stress in the presence of stiff and hardly deformable hard counterparts. In other words, the polymeric transfer film on the hard couterparts, if any, would be easily scaled off, leading to decreased antiwear life. Moreover, the differences in the friction and wear behavior of the PEM film sliding against different counterparts were closely related to the differences in the chemical and crystallographic structure of the counterparts (ceramics Si₃N₄ and WC, and metals brass and stainless steel).     

Fretting wear behaviour of hypereutectic P/M Al–Si in oil environment

The fretting wear behaviour of forged hypereutectic P/M Al–Si in contact with hardened steel and Cu–Sn–Pb bearing material is investigated. Fretting tests are performed with a view to the movement in the contact between the small end of the connecting rod and the piston pin in a car engine. Therefore, the tests are carried out under engine oil lubrication at temperatures up to 150°C. The behaviour of the Al alloy is compared to that of steel, the current connecting rod material. Some tests under non-lubricated conditions are also performed. The correlation between the friction coefficient, the wear volume and the microscopic wear mechanisms is discussed. After the running-in wear, a stable wear condition is reached for the Al–Si/steel contact.     

Effects of hip-loading input on simulated wear of Al2O3–PTFE materials

The objective of this study was to compare the effects of static, sinusoidal and physiological load-profiles on wear of Al₂O₃–PTFE materials. This was an accelerated wear model of clinical relevance. In nine experiments, the peak load-levels were varied from 1 to 4 kN in a hip simulator with multi-directional kinematics and with bovine serum used as the lubricant. Systematic wear differences were checked using three sizes of femoral heads in each experiment. The Paul load-profile used was found to be more aggressive than sinusoidal, raising the polytetrafluoroethylene (PTFE) wear-rates by 28%. The PTFE cups showed a very mild response to increased load magnitudes, only 11–20% increase evident in volumetric wear per 1 kN increase in load. One recommendation was that simulator wear-studies adopt a 0.25–2.5 kN Paul load-profile as their standard. An experiment with 0.84 kN constant-load also performed satisfactorily, with PTFE wear-rates actually higher than with the 1 kN sine and Paul load-profiles. Some wear anomalies were encountered due to the use of serum lubrication. Combinations of large head size, high load-magnitudes, the Paul load-profile and the high serum protein concentrations used in this study were at times contributing factors. Use of low-protein serum solution may be advisable for wear studies, not only to properly simulate the polymeric wear characteristics but also to minimize the degradation artifacts more prevalent in higher protein-concentrations.