The influence of surface roughness on abrasive wear

Analyses are given of the mechanism of friction and abrasive wear and of the effect of surface roughness on them. Theoretical expressions are derived for ploughing, adhesion and the total friction coefficient of hard conical asperities ploughing a soft metal surface, with the assumption that the asperities of the hard metal are cones with randomly distributed slopes, the mean value of which varies with surface roughness. Simple expressions for the abrasive wear rate and the mean wear particle size are also derived on the basis of a ploughing mechanism of the hard conical asperities on the soft metal surface.A comparison of calculated values based on these theories with experimental data of single-pass wear tests for various soft metals such as copper, cadmium, lead and zinc sliding on low carbon steel plates shows good agreement. The effects of surface roughness on the tangential forces under unlubricated and lubricated conditions as well as the mean wear particle size are theoretically discussed and the theoretical results are compared with experimental data.     

The influence of atmospheric humidity on the abrasive wear of metals

A pin-on-disc apparatus has been used to obtain continuous simultaneous measurements of the wear and friction (sliding force) behaviour of metals on bonded silicon carbide abrasive paper under conditions of controlled humidity. Iron, mild steel and copper exhibit qualitatively similar wear behaviour: the wear rate decreases progressively with the number of passes over the same track. In contrast, the wear rate of titanium remains constant. Variation in atmospheric humidity has little effect on the wear rates of copper or titanium, although a slight effect was found in mild steel and iron. A stronger dependence on humidity was found in the friction behaviour of all four metals, as well as a corresponding relationship between humidity and the specific energy required for metal removal by abrasion. Preliminary results from single-particle scratch tests reveal changes in the contact between a single silicon carbide particle and a polished iron surface at different humidity levels. Although only tentative explanations can be made at this stage for these effects, it is evident that any proposed mechanism must account for the behaviour of both the metal and the abrasive together, rather than of one component of the system alone.     

A physically-based abrasive wear model for composite materials

A simple physically-based model for the abrasive wear of composite materials is presented based on the mechanics and mechanisms associated with sliding wear in soft (ductile)- matrix composites containing hard (brittle) reinforcement particles. The model is based on the assumption that any portion of the reinforcement that is removed as wear debris cannot contribute to the wear resistance of the matrix material. The size of this non-contributing portion (NCP) of reinforcement is estimated by modeling three primary wear mechanisms, specifically, plowing, cracking at the matrix/reinforcement interface or in the reinforcement, and particle removal. Critical variables describing the role of the reinforcement, such as relative size, fracture toughness and the nature of the matrix/reinforcement interface, are characterized by a single contribution coefficient, C. Predictions are compared with the results of experimental two-body (pin-on-drum) abrasive wear tests performed on a model aluminum particulate-reinforced epoxy-matrix composite material.     

Investigation of abrasive wear resistance and wear mechanism of composite alloys

The abrasive wear resistance of composite alloys comprising hard tungsten carbide and soft CuNiMn matrix under different wear conditions has been investigated and compared with CrMo cast iron. It was found that Yz-composite alloy with hard cast angular tungsten carbide has greater wear resistance than CrMo cast iron under two-body wear conditions, but lower resistance than Cr-Mo cast iron under three-body wear conditions. It was found that under three-body wear conditions selective wear of the matrix and digging or fragmentation of tungsten carbide particles dominate in Yz-composite alloy, and microcutting and deformed ploughing is dominant under two-body wear conditions. The abrasive wear resistance of composite alloys under two-body wear condition is independent of bulk hardness, but is closely related to the microhardness of tungsten carbide.     

An equation for the abrasive wear of elastomeric O-ring materials

An empirical equation was obtained via dimensional analysis, which relates the abrasive wear volume to the friction force, specimen load, sliding distance and specimen breaking strength for O-ring materials. Wear experiments on O-rings molded from four nitrile compounds and one polyurethane material were conducted on a special pin-disc-type testing machine. Specimens cut from a size 330 O-ring were held against a roughened rotating steel wear cylinder with a load which varied from 5 to 15 lbf. Both the specimen and the wear cylinder were immersed in an abrasive mud of the type used for oil well drilling. The sliding velocity was held constant at 11 in s^?1. The wear resistance of the polyurethane was two times better than the best nitrile compound.     

Influence of abrasive hardness on the wear resistance of high chromium irons

The resistance to abrasive wear was determined for a series of alloyed white cast irons in a high stress abrasion test which utilizes a specimen in sliding contact with bonded abrasives. These were conducted on silicon carbide, alumina and two sizes of garnet abrasive.The results indicate that the hardness, or type, of abrasive used in the test significantly influenced the wear rate of white irons, i.e. the rate of wear increased with increasing hardness of the abrasive. Also, the results indicate that the type of abrasive used in the test was a significant factor in ranking white irons for resistance to high stress abrasion. When tested on silicon carbide or alumina abrasive, as-cast austenitic irons exhibited lower rates of wear than heat treated martensitic irons; when tested on garnet, an abrasive of lower hardness, those irons with martensitic matrix microstructures exhibited the same or less wear than irons with austenitic matrix microstructures. It was also evident that heat treated irons with martensitic matrix microstructures exhibited varying degrees of resistance to abrasive wear depending on cooling rates and alloy content.     

Characterization and prediction of abrasive wear of powder composite materials

Composite materials produced by powder metallurgy provide a solution in many engineering applications where materials with high abrasion and erosion resistance are required. The actual wear behaviour of the material is associated with many external factors (particle size, velocity, angularity, etc.) and intrinsic material properties (hardness, toughness, Young modulus, etc.). Hardness and toughness properties of such tribomaterials are highly dependent from the content of reinforcing phase, its size and from the mechanical properties of the constituent phases. In this study an attempt is made to model the erosion wear behaviour of composite materials, to calculate the wear rate and to correlate erosion rates with experimental results and material parameters. Powder composites cermets and metal-matrix composite materials reinforced with different content of hard phase were used as examples in this research. Wear mechanisms of materials were investigated. Following from the main mechanisms of erosion wear the models of plastic deformation and brittle fracture are developed for prediction of erosion of powder composite materials. It was demonstrated, that the erosion rate of hardmetal-type materials can be predicted using the results obtained by microindentation methods. The use of hardness distribution parameters is justified with materials with low binder content.     

Effect of temperature fields on wear of nonmetallic materials at abrasive machining

Wear characteristics of silicate glass and sapphire at abrasive machining have been studied. The data obtained and the analysis of images of worn surfaces have allowed the authors to conclude that two modes of material damage run simultaneously; these are the local melting of the glass followed by its squeezing towards the contact exit and periodical fatigue fracture (growth of microcracks). Under a short-term effect of high thermal stresses the glass was found to undergo thermal cracking even outside the contact site. The crystalline material (sapphire) demonstrated anisotropy of fatigue strength under abrasive wear, when its wear rate in two perpendicular directions differed almost by an order of magnitude. The possibility of sapphire damage outside the contact site is explained by the position of the maximal surface temperature region being some distance ahead of the zone of the abrasive tool-blank contact.     

Effect of high hydrostatic pressure on the external friction coefficient

Experiments are carried out to determine the molecular and mechanical components of the specific friction force under the effect of hydrostatic pressure of up to 140 MPa. The molecular component of the friction coefficient declines by up to two times under the effect of the hydrostatic pressure in various fluids. It is found that the combined influence of the temperature and hydrostatic pressure on the mechanical properties and the contact pressure leads to considerable variations in the deformation component of the static friction coefficient in plastic contact at temperatures of up to 200°C and under pressures of up to 140 MPa. The dependence of the hardness of structural materials on the hydrostatic pressure is analyzed to predict the effect of the latter on the deformation component of friction. It is shown that with increasing pressure within the above range the hardness grows in proportion to the square of the pressure and is inversely proportional to the initial hardness. The formula for calculating the dependence of the indentation depth of a spherical indenter in elastic contact on the hydrostatic pressure is derived.     

The influence of primary carbides and test parameters on abrasive and erosive wear of selected PM high speed steels

The aim of this investigation has been to further the understanding of the contribution given by the primary carbides to the abrasive and erosive wear resistance of six HSS's, and to evaluate different test methods. With abrasives significantly harder than the primary carbides of the HSS's, two- and three-body abrasion rates showed only small variations with primary carbide volume fraction, size and type. However, using abrasives/erodants softer than the carbides the qualitative results were similar for the two- and three-body abrasion tests and for the erosion test, with the wear resistance increasing with the volume fraction primary carbides.     

Principles of abrasive wear

The mechanisms of abrasive wear are reviewed and laboratory test methods assessed. The results of abrasive wear tests on technically pure metals, heat treated steels, cold work hardened materials, hard wear resistant materials and minerals against fixed abrasive grains are discussed. The correlation between abrasive wear resistance and the physical properties of materials is established; the effect of the relative hardness of the abrasive and impact loading is considered. The basic principles of abrasive wear derived are outlined.     

A technique to study abrasive wear in contacts with particulate materials

A rig has been developed to study the abrasive wear of materials in sliding contact with solid particles. The equipment has a wide pressure and velocity range and can be used to simulate the tribological conditions inside pulverizers. Using the rig, a number of different materials have been tested and classified according to their resistance to abrasive wear in rubbing contact with particulate coal. The investigation was divided into two parts, in each part a different shape of grinding blade (test material) was used in order to focus attention on the different wear phenomena. Tests with triangular blades can provide useful information about the wear properties of various materials. Apart from the maximum wear resistance, the initial drop in wear resistance IDWR can be determined. The value of IDWR gives information about the contribution of the brittle fracture of the sharp edges and asperities to the total wear of the blade.     

High-temperature abrasive wear testing of potential tool materials for thixoforming of steels

High temperature abrasive wear performance of Inconel 617, Stellite 6 alloys and X32CrMoV33 hot work tool steel was investigated. The wear resistance of the latter is degraded at 750 °C due to its inferior oxidation resistance. Extensive oxidation co-occuring with abrasive wear at 750 °C leads to substantial material loss due to the lack of a protective oxide scale, sufficiently ductile to sustain the abrasion without extensive spalling. The wear resistance of the Inconel 617 and Stellite 6 alloys, on the other hand, improves at 750 °C owing to protective oxides that sustain the abrasion without spalling.     

Features of wear of brittle inorganic materials during friction and abrasive machining

Laser confocal microscopy reveals fatigue cracking under the surface of silicate glass upon friction and abrasive machining. Surface cracking is also registered and its maximum depth is determined, indicating that its longitudinal cross section has an irregular profile. The stage of fatigue wear of the glass corresponding to debris nucleation shouldbe visualized. It is established that the mass wear rate and the maximum surface cracking depth are correlated: once a definite sliding velocity is reached, the cracking becomes deeper and the wear rate intensifies in both types of tests. The obtained results prove that several wear mechanism can occur simultaneously during abrasive machining of brittle inorganic materials, namely, brittle chipping, low-cycle fatigue, thermomechanical fracture, and local melting (under critical loading conditions).     

Abrasive wear of high speed steels: Influence of abrasive particles and primary carbides on wear resistance

A ball cratering test has been used to investigate the abrasive wear of high speed steels with different volume fraction and size of primary carbides. Three different abrasives, SiC, Al₂O₃ and ZrO₂ were used. Wear mechanisms were investigated by scanning electron microscopy (SEM). A good correlation between the hardness of the abrasives and the abrasive wear coefficient was found. Higher abrasive wear resistance was determined for steels containing coarser primary carbides compared to those without or with smaller carbides. The most pronounced difference in abrasive wear resistance was found for Al₂O₃ abrasives. This indicates that in ball cratering the abrasive medium has to be chosen properly, i.e. with a hardness adjusted to those of both primary carbides and martensitic matrix, to obtain results suitable to rank high speed steels with respect to abrasion resistance.     

Diamond particle shape: Its measurement and influence in abrasive wear

The classification of diamond particles in terms of their abrasive characteristics is addressed in this work. Specifically, diamond particles of different grades have been studied in terms of their shape to identify useful trends and correlations with experimental wear rate. Ten diamond types, typically used by the abrasives industry and exhibiting varied shape, were selected. They included highly geometric single crystals, crushed single crystals, and polycrystalline diamond particles, with nominal diameters of between 65 and 197 μm. Electronic boundary projections were obtained using a digital-camera-equipped optical microscope, which were then processed using proprietary software. The parameters calculated include: diameter (minimum, minor and maximum), aspect ratio, convexity and sharpness. Interesting correlations were found between convexity and sharpness that engendered both these parameters to be considered as useful measures of wear rate. This was reinforced by experimental wear tests, using grinding wheels manufactured from six of the 10 diamond types, which demonstrated excellent correlations of sharpness (0.991 correlation coefficient), and convexity (0.987 correlation coefficient), with the wear rate of a polyurethane workpiece.     

Some observations on two-body abrasive wear

Pin-on-disc-type two-body abrasion tests were carried out on five metals with seven particle sizes over a range of loads, lengths of travel and sliding speeds. The familiar results that two-body abrasive wear is proportional to load and to distance travelled were confirmed. The “size effect”, in which particles below about 100 μm produce progressively less wear, was shown to be independent of load, sliding speed and prior cold working. Increasing the sliding speed from 1 to about 100 mm s^?1 produced an increase in wear resistance of about 50% for AISI 1020 steel. An increase in velocity above 100 mm s^?1 had little effect on the wear resistance. Plots of the wear resistance against the hardness of the annealed metal showed significant deviations from the linear relationship reported in the literature. The result is influenced by both sliding velocity and particle size.     

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.     

The influence of speed on the wear of sintered iron-based materials

A pin-on-disc-type wear test rig was used to study the influence of speed on the wear of sintered iron, sintered Fe-5Cu and sintered Fe-5Cu-5C materials over a range of speeds of 0.5 –16 m s^?1 at a constant load of 40 N. With increasing speed the wear rate decreases to a minimum and then increases. Over the entire range of speeds two types of wear are observed: these are mild wear below a speed of 8 m s^?1 and severe wear above a speed of 8 m s^?1. The results are discussed in terms of friction records, wear particle size and composition, wear track study and topographic and metallographic studies of worn specimens.     

The relationship between the abrasive wear resistance,hardness and microstructure of ferritic materials

The relationship between the abrasive wear resistance and bulk hardness of ferritic materials in the pearlitic and martensitic conditions has been investigated. For pearlitic materials the abrasive wear resistance and bulk hardness are dependent on the pearlite content and for martensitic materials the abrasive wear resistance and bulk hardness are dependent on the square root of the carbon content. Thus for each structure there is a linear relationship between abrasive wear resistance and bulk hardness, but it is suggested that the material microstructure has a greater influence on wear resistance than the bulk hardness.