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.     

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.     

A study on the formation of wear debris during abrasion

A set of five material specimens have been tested on five abrasives, some of which are harder, some softer than the materials, using the dynamic abrasive wear tester. Characteristics of selected wear debris have been observed by sem and wear debris of 9Cr2Mo steel analysed by Mossbauer spectroscopy. The test results show three wear mechanisms operating during abrasion: microcutting, plougging deformation and brittle fragmentation. Different abrasives formed different constituents of wear debris due to dissimilar wear conditions. Softer abrasive tended to form more ploughing debris, although some typical microcutting chips were produced. Crushing strength of abrasive may be an important factor in addition to hardness of abrasive. The microstructure of 9Cr2Mo steel wear debris has been changed by abrasion heat; this temperature could be estimated by Mossbauer spectroscopy.     

Correlations between two-body and three-body abrasion and erosion of metals

The effects of various variables on the wear resistance of different pure metals are compared for two-body abrasion, three-body abrasion and erosion. The variables studied are the annealed hardness of the worn metal, the increase in hardness of the worn metal before the wear process due to work hardening and heat treatment, the applied load, the distance travelled, the abrasive particle size and the abrasive hardness. It was found that the effects of most of these variables are similar for the three different wear processes.     

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.     

食物粒度和硬度对人牙釉质三体磨粒磨损特性的影响

在往复滑动摩擦磨损试验台上对比考察了三体磨粒磨损过程中,食物颗粒的粒度和硬度对人牙釉质摩擦学特性的影响。结果表明:当食物颗粒硬度较高时,随着粒度减小,稳态摩擦因数略有降低,牙釉质磨损表面形貌逐渐由剥落为主转变为犁削效应;对于低硬度食物颗粒,随着粒度增加,稳态摩擦因数显著降低,牙釉质磨损表面形貌则由犁削效应转变为轻微擦伤。当食物颗粒粒度相同时,食物硬度对牙釉质的摩擦与磨损行为均有明显影响,食物颗粒硬度越高,稳态摩擦因数越高,磨损越严重。     

Micro/nano-scale differential wear of multiphase materials: pole tip recession in magnetic-tape heads

Wear of multiphase materials at the micro/nano-scale is important in devices such as magnetic tape and disk drives, where the read-write heads are multiphase. Differential wear, which is caused by differences in wear resistance among the heads’ phases, causes the thin-film poles to recede from the bearing surface; this is called pole tip recession (PTR). It is a problem because it increases spacing between the poles and medium, resulting in lower readback amplitude. Here, PTR in tape heads is studied to understand micro/nano-scale differential wear. Test results suggest that three-body abrasion, which leads to primarily plastic wear, is the operative wear mode. Most of the three-body abrasive particles originate from the tape surface; the alumina head-cleaning agents (HCAs) in the tape, which function as load bearing particles at the interface, are believed to be the primary abrasives. Some of the particles originate from the head. These are important if the substrate material is relatively soft. Differential wear can be reduced by choosing a substrate that is harder than the tape’s HCAs, choosing a pole material that is as close as possible to the hardness of the substrate, and lowering the thickness of the head’s thin-film region. Material hardness matching will not reduce differential wear if a substrate is chosen that is less hard than the HCAs. An analytical model that accounts for the observed wear is presented. The model shows that each of the following leads to higher differential wear: increasing the thickness of three-body particles, increasing tension, decreasing thin-film hardness, and increasing the thin-film wear coefficient. An increase in thin-film wear coefficient can be caused by an increase in thin-film thickness or an increase in the number of particles at the interface.     

Ball-cratering abrasion tests with large abrasive particles

The application of a ball-cratering method to test three-body abrasive wear of bulk materials in the presence of large abrasive particles has been investigated. Four types of abrasive particles of different sharpness were used to make slurries: glass beads, silica sand, crushed quartz and alumina. All the particles were sieved to a size of 250–300 μm. Two common industrial materials, mild steel and 27% Cr white cast iron, were used as wear samples. Wear rates of metallic samples were determined and the worn surfaces were examined by optical microscopy, SEM and Talysurf profilometry.It was found that the surface roughness of the ball significantly affects the wear rates and the wear mechanisms of the metallic samples. The surface roughness of the ball steadily increased with testing time and was mainly affected by the angularity of abrasive particles. More angular particles generated higher ball surface roughness. It was found that the gradual increase in the ball surface roughness was responsible for non-linearity of wear rates with sliding time. The increasing depth of the wear craters also contributed to this non-linearity as deeper craters facilitate particle entrainment. Three-body rolling wear dominated when the ball was smooth and the contribution of two-body grooving wear increased with increasing the ball roughness. Softer mild steel samples were more affected by the ball roughness changes than the harder white cast iron samples. Wear surface morphology was also affected by the angularity of particles and by the material properties of wear samples. Particle fracture was found in all four groups of abrasives and the angularity of the particles was slightly altered. Therefore, the ball-cratering test, under the testing conditions used, can be considered as a high-stress abrasion test.     

Comparison of wear properties of tool steels AISI D2 and O1 with the same hardness

Two commercial cold work tool steels, AISI D2 and O1, were heat treated in order to obtain the same hardness 700 HV (60 HRc) and were subsequently tested in three different modes of wear, namely in adhesion, three-body and two-body abrasion, by using pin-on-disk, dry sand/rubber wheel apparatus and pin abrasion on SiC, respectively. Even though AISI O1 and D2 steel are heat treated to the same hardness, they perform differently under the three modes of wear examined. The results show that the steel microstructures play the most important role in determining the wear properties. For relatively low sliding speeds AISI O1 steel performs up to 12 times better than AISI D2 steel in adhesive wear. For higher sliding speeds, however, this order is reversed due to oxidation taking place on the surface of the AISI D2 steel. The wear rate of both tool steels in three-body and two-body abrasion wear is proportional to the applied load. In three-body abrasive wear, AISI D2 exhibits a normalised wear rate about two times lower than the AISI O1 tool steel, and this is due to the presence of the plate-like hard carbides in its microstructure. Both tool steels perform 3–8 times better in three-body abrasive wear conditions than in two-body abrasive wear.     

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.     

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.     

On the wear of reinforced thermoplastics by different abrasive papers

Single-pass two-body abrasion tests were run on unfilled and glass-fibre-and glass-sphere-filled polyethylene terephthalate sliding dry against different abrasive papers. The abrasive grains varied in hardness and size. Wear mechanisms were studied by using scanning electron microscopy. A functional relationship was developed between the single-pass wear rate under severe abrasive conditions (dominated by microcracking events) and a term considering the hardness and macrofracture energy of the composites as well as a probability factor for microcracking. The probability factor includes parameters of the abrasive counterbody and some geometrical and frictional details of the composite investigated.     

Ball-cratering abrasion tests of high-Cr white cast irons

The application of a ball-cratering method to test three-body abrasive wear of bulk materials in the presence of large abrasive particles has been investigated. Three high-Cr white cast irons (WCIs) with different material properties were used as wear samples. Abrasive slurries contained two types of abrasive particles, silica sand and crushed quartz. Silica sand and crushed quartz particles have similar chemical composition and hardness but differ in sharpness. Wear rates of WCI samples were determined and the worn surfaces were examined by optical microscopy, SEM and Talysurf profilometry.It was found that the ball-cratering test can differentiate between the wear resistances of materials with similar properties. The wear resistance of WCIs in the presence of silica sand increased with increasing the hardness of the wear sample and decreasing the size of carbides in the microstructure. Smaller silica sand particles caused less wear damage than larger silica sand particles, even though the smaller particles were slightly sharper than the larger ones. When silica sand and quartz particles of the same size were used, the angular quartz particles caused much higher wear than the rounded silica sand particles. Surface morphologies of the wear craters on the WCI samples were examined in an SEM and then compared with the morphologies of the worn surfaces from slurry pumps. It was found that the silica sand particles generated surface morphologies similar to those found in the worn slurry pumps. In these surfaces the matrix was preferentially worn out and hard carbides were protruding. Wear surface morphologies produced by the angular quartz particles were different. They consisted of numerous superimposed indents and the microstructure phases were not distinguishable. This indicates that the type of abrasive particles used in ball-cratering testing significantly affects the test outcomes in terms of wear rates and wear surface morphology.     

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.     

Low load multiple scratch tests of ceramics and hard metals

Abrasion is caused by the repeated scratching of materials by individual particles in an abrasive, often under fairly light loads. This process has been simulated by carrying out scratch tests on a range of ceramics and hard metals. An array of different scratches was carried out on each sample with a different number of repeats along the same track for each scratch. The magnitude of the damage was measured by the width of the scratches. The frictional force between the indenter and test sample was also measured.

Although the width of single pass scratches in some of the harder materials was smaller than in softer materials, in multiple pass scratches, the final widths of scratches in some of the harder materials were greater than in the softer materials. This was due to differences in the contribution of fracture in the development of damage in multiple pass scratches.

It was found that fracture was a predominant form of damage to both hard metals and ceramics. In the case of the hard metals the fracture was on a fine scale, but with the ceramics fracture occurred on a larger scale, often removing large fragments of material.

These results, and the results of the friction measurements are correlated with the results of a microstructural examination of the mechanisms that occurred. They are also compared with a microstructural assessment of the early stages of wear in the abrasion of these materials.     

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.     

Influence of atmospheric humidity on abrasive wear — II. 2-body abrasion

Specimens of glass, steel, copper and an aluminium alloy were abraded on silicon carbide abrasive papers under controlled levels of atmospheric humidity. Under the testing conditions used, all materials show an increase in wear rate between 0 and 65% r.h. At higher humidity levels the softer materials show a decreasing wear rate, while the harder materials show a continuing increase. Atmospheric moisture decreases the fracture strength of the SiC abrasives. This results in improved cutting efficiency at low humidity and in grit deterioration at high humidity. The magnitude of the effect on wear rates is strongly dependent on experimental conditions, in particular load per abrasive, distance of contact with the specimen surface and supply of fresh abrasives.     

Abrasion resistance of nanostructured and conventional cemented carbides

The abrasion resistance of nanostructured WC-Co composites, synthesized by a novel spray conversion method, is determined and compared with that of conventional materials. Scratching by diamond indenter and abrasion by hard (diamond), soft (zirconia) and intermediate (SiC) abrasives was investigated. The size of the scratch formed by the diamond is simply related to the hardness of the composite. Plastic deformation, fracture and fragmentation of the WC grains increase with their size. Nanoscale composites show purely ductile scratch formation. Nanocomposites possess an abrasion resistance approximately double that of the most resistant conventional material: this is a higher gain than the increase in hardness which is at most 23%. This large gain is due to a specific grain size effect on abrasion resistance in the case of diamond and SiC abrasive and to a very rapid increase of abrasion resistance with hardness in the case of the softer (SiC and ZrO₂) abrasives. The observation of the abraded surfaces of conventional composites reproduced the known mechanisms: plastic deformation and fracture of WC grains by hard abrasives; removal of binder phase and fall-out of WC by soft abrasives. Magnetic fields from the ferromagnetic Co prevent the observation of abrasion mechanisms in the very fine-structured nanocomposites.     

Effect of carbide size on the abrasion of cobalt-base powder metallurgy alloys

A study of the effect of carbide size on the abrasion resistance of two cobalt-base powder metallurgy alloys, alloys 6 and 19, was conducted using low stress abrasion with a relatively hard abrasive, A1₂O₃. Specimens of each alloy were produced with different carbide sizes but with a constant carbide volume fraction. The wear test results show a monotonie decrease in wear rate with increasing carbide size.Scanning electron microscopy of the worn surfaces and of wear debris particles shows that the primary material removal mechanism is micromachining. Small carbides provide little resistance to micromachining because of the fact that many of them are contained entirely in the volume of micromachining chips. The large carbides must be directly cut by the abrasive particles. Other less frequently observed material removal mechanisms included direct carbide pull-out and the formation of large pits in fine carbide specimens. These processes are considered secondary in the present work, but they may have greater importance in wear by relatively soft abrasives which do not cut chips from the carbide phase of these alloys. Some indication of this is provided by limited studies using a relatively soft abrasive, rounded quartz.     

The wear of ultrafine WC–Co hard metals

The wear performance of ultrafine-grained tungsten carbide–cobalt (WC–Co) hard metals during three-body abrasion and particle erosion has been evaluated and compared to that of similar conventional coarser grained hard metals. The tungsten carbide grain size varied between 0.5 and 3 μm with cobalt contents ranging from 6 to 15%. Silica particles were used in both forms of testing. Erosion was carried out at 60 ms⁻¹ at an impact angle of 75° and abrasion at a velocity of 0.5 ms⁻¹ and a load of 50 N.

The wear resistance of the ultrafine grades was found to be at least double that of the closest conventional fine grained hard metals. These increases in wear performance are considerably higher than any corresponding increase in hardness which is, at most, 25% and is not achieved at the expense of fracture toughness which is maintained at a similar level to that of conventional fine grained hard metals. The increase in wear resistance coincides with a change in the mechanism of material removal. Sub-micron materials experience ductile deformation and bulk removal of material whilst coarser grades display more localised response with extensive fragmentation of the WC grains.