Micro-scale Abrasive Wear Test Research Articles

Effects of niobium and molybdenum addition on microstructural characteristics and wear properties of 14 wt%Cr white cast irons

White cast iron (WCIs) alloys were developed by adding Nb, Mo, and a combination of both (∼3 wt% Nb, ∼3 wt% Mo, ∼1 wt% Mo-2 wt% Nb) through melting and casting. The objective was to analyze the microstructural characteristics of the alloys, as well as the impact of reinforcing carbides on their mechanical and tribological properties. The alloy containing the highest percentage of niobium exhibited a refined microstructure, tending towards a eutectic structure, unlike the Mo-containing materials with totally hypoeutectic microstructures. The microstructural characteristics of the alloys and morphology of niobium carbides, as well as the percentage of M7C3 eutectic carbides produced were affected by the varying percentages of Nb and the Mo–Nb combination. Moreover, thermodynamic simulations revealed that the NbC carbide precipitated before the M7C3 eutectic carbides, austenite dendrites, and the MC (composed mainly of Nb containing bound Mo) carbide resulting from the Mo–Nb combination. The alloys containing Mo had similar bulk hardness values, while the alloy with the highest percentage of Nb showed a higher bulk hardness value. This was attributed to the effect of Nb on microstructure refinement and on the production of M7C3 eutectic carbides from the alloy. Although there were different reinforcing carbides (NbC, MC and M2C), the differences in microstructural characteristics had no noticeable influence on the Charpy impact energy. Micro-scale abrasive wear test (conducted with SiC abrasive slurry) demonstrated that the reinforcing carbides MC and mainly NbC had a beneficial effect in blocking and preventing the progression of continuous micro-cuttings and formation of grooves. The M7C3 and M2C carbides were less effective at protecting the matrix against the high-hardness SiC abrasive.

Micro-Scale Abrasive Wear Resistance of a Nanoceramic Sealant Applied on Galvanized Low Carbon Steel

The idea for this work came from a market need to obtain coatings or sealants that would extend the useful life of metallic materials in applications that involve exposure to corrosive environments. The main objective of the nanoceramic sealant studied in this work is to extend the life of metallic fasteners. To evaluate the performance of the sealant from other perspectives, microstructural analysis, adhesion test, micro-scale abrasive wear tests and corrosion test were carried out. These tests were performed on samples coated only with white zinc, which is commonly used in the fastener industry, and on samples coated with white zinc followed by application of the nanoceramic sealant. The application of the nanoceramic sealant contributed to the improvement of corrosion resistance and reduction of the corrosion rate. The corrosion rate of the sample coated with the sealant reduced by 62.2% when compared to the sample that only went through the white zinc coating process. The coating showed low adhesion to the substrate with the presence of severe delamination and microcracks. This feature contributed to the low wear resistance presented by the coating under the conditions studied in this work. Less attention, compared to studies involving corrosion resistance, has been given to wear resistance in the fastener industry. The results obtained in this paper show that the study of tribological behavior is an important factor in increasing the efficiency of fasteners applied in harsh environments.

Comparative Micro-Scale Abrasive Wear Testing of Thermally Sprayed and Hard Chromium Coatings

Nowadays, due to the carcinogenic effects of chrome, replacing the hard chromium used for hydraulic components like rods and cylinders is becoming increasingly requested. Thermally sprayed coatings are a solution to the problem; however, proper understanding and characterisation of their tribological behaviour are essential for the successful exploitation of surface engineering. Thus, the main aim of this study is to evaluate the abrasive wear characteristics of two metal sprayed layers, tungsten carbide (WC) deposited through the high-velocity oxygen fuel coating (HVOF) method and Fe alloy coating deposited through thermal spraying with an electric arc with a wire-electrode G3Si1, and compare the results with those of an electrochemically deposited hard chromium layer. Their wear resistance is then related to their hardness. The results highlight the tribological performances of the thermally sprayed coatings. The HVOF WC10Co4Cr coating has a wear coefficient and a material wear volume that are hundreds of times lower than those of the other two coatings.

Combined effect of abrasive particle size distribution and ball material on the wear coefficient in micro-scale abrasive wear tests

Micro-abrasive wear tests were carried out to analyze the combined effect of abrasive particle size distribution and ball material on the wear coefficient. Different particle size distributions were obtained by mixing different fractions of two silicon carbide (SiC) abrasive powders, having average particle sizes of 6.0 μm and 14.4 μm. Tests were conducted using two different normal loads, 0.2 and 0.4 N, AISI 1020 steel samples and balls made of AISI 52100 martensitic steel, AISI 304 austenitic stainless steel, polyurethane rubber and zirconia-alumina. Worn surfaces were analyzed with Scanning Electron Microscopy (SEM) and by optical profilometry. Results have indicated that a change in ball material, with consequential modification in the ratio between the hardness of the body and the counter-body, enabled different behaviors of the wear coefficient with the variation of the granulometric distribution. Such differences are due to the ability of the particles to be embedded and dragged into contact. The wear coefficients were analyzed in each case, resulting in a map to describe the combined influence of granulometric distributions of abrasive particles and ball material on the wear coefficient.

Case study: Abrasive capacity of Limnoperna fortunei (golden mussel) shells on the wear of 3 different steel types

The impact of particles suspended in the water is responsible for the wear of mechanical surfaces in hydraulic systems. The characteristics and concentrations of these particles in the flow directly influence the intensity of the abrasion processes. Within this context, knowledge of the abrasive power of a particle is of great importance. It is known that an invasive species, known as golden mussel shell, has become embedded in several hydroelectric plants of the South and Southeast of Brazil, provoking an increase of the wear caused by shells that pass through the hydraulic system. In this context, the abrasive capacity of ground golden mussel shells on the three metallic materials used in the labyrinth component of the hydraulic turbines was analyzed. To determine the wear pattern and the relationship of the specific wear coefficient of the material (k), due to the increased concentration of golden mussel shell, micro-scale abrasive wear tests were performed on three different steel plates using abrasive suspensions at different concentrations of ground golden mussel shell in distilled water. The abrasivity of the golden mussel shell was also compared with the abrasivity of silicon carbide (SiC), commonly used as standard material in microabrasion tests. The analyses showed that the golden mussel shell is around 16 times less abrasive than the silicon carbide, taking into account the average obtained for the three different materials tested. In addition, the wear mechanisms acting on the SiC tests and those with the golden mussel shell were the same.

Case study: Effects of sediment concentration on the wear of fluvial water pump impellers on Brazil's Acre River

The most important factor causing surface wear in hydraulic systems is the impact produced by abrasive particles suspended in the water flow. The impact conditions, such as mean particle velocity; particle mass; abrasive particle concentration in the liquid flow (number of particles per unit of liquid volume, size distribution of the particles); angle of attack at which the particles collide with the surface; and duration of the effect produced by the particles on the surface contribute to the development of the abrasion process. The wear resistance of the centrifugal pump impellers depends on the characteristics of the materials used in their manufacture and the abrasiveness of the suspended sediments in the pumped water. Despite special care in choosing the material used in its manufacture, abrasive wear is practically impossible to totally avoid. This work analyses the wear of ductile cast iron impeller blades of a centrifugal pump, used at the Fluvial Water Elevation Station (FWES) of the Acre River sedimentary basin in Brazil, due to the sediment concentration variation and the river water level. To determine the wear pattern and the relationship between the material and specific wear coefficient (k) due to increased sediment concentration, a ball-cratering microscale abrasive wear test was performed on samples of ductile cast iron, withdrawn from a used impeller, and abrasive suspensions at concentrations of 1, 2, 3, 5 and 10 g L−1 of river sediment in distilled water. The wear volume to the impeller blades due to the relative velocity of the mixture (water + sediment) and the wear accumulated in an annual hydrological cycle were estimated mathematically. The results showed that: i) the k remains constant regardless of the normal force (FD) applied in the tests in the abrasometer; ii) the wear tests showed the abrasive capacity of the sediments at different concentrations; and iii) the rotational control of the pump speed based on the sediment concentration and the river water level can contribute to a reduction in wear of up to 30% considering the hydrological cycle.

Micro-Scale Abrasive Wear Testing of CrN Duplex PVD Coating on Pre-Nitrided Tool Steel

Specific wear rates were calculated from a series of micro-scale abrasive tests by means of the calotte-grinding method. The tested material was a CrN coating deposited by arc evaporation on ion-nitrided AISI H13 steel. Characterizations included: phase analysis, chemical composition, metallography, microhardness, micro-scratch resistance and nano-indentation hardness. On wear testing, the counter body was a 30 mm diameter steel ball rotating at a tangential speed of 9.42 m/min and normal load of 0.54 N. The abrasive was a mono-crystalline diamond micro abrasive paste, 1 micrometer grit. Wear volumes were calculated by measuring the wear scars at various test intervals. In non-perforating tests, Archard's wear equation was directly employed for calculating coating wear rate as the slope of the linear least square data fit. In perforating tests, Allsopp's method was employed for the simultaneous determination of coating and substrate wear rates, from the slope and intercept values of the linear least square data fit. Coating specific wear rate values obtained from both non-perforating and perforating tests were very consistent, with a relative difference within 6%. Relative errors in specific wear rate values were estimated to be of the order of 0.05 for the coating and 0.2 for the substrate.

Wear study of Innovative Ti-Ta alloys

In this paper a wear study of innovative Ti-Ta alloys is present. Samples of Ti-30%Ta, Ti-52%Ta, were produced by laser cladding. This technology uses a high power density generated by a laser beam to melt the base material and the filler material. The interaction between the laser and the substrate is a function of the radiation absorption properties of the material and that conditions the heat flow. Laser technology allows working with high temperatures and melting powders of titanium and the alloying elements as tantalum. As this is a continuous process enables rapid cooling of the molten material and the consequent solidification. The principal importance of these innovative alloys is the low Young’s Modulus, the closest to Young´s Modulus of the bone, the biocompatibility of titanium and tantalum and consequently its applicability to biomedical industry. The wear behavior is an important factor that influences the structural integrity of materials and must be studied for innovative alloys. So in this work the micro-scale abrasive wear tests were used to characterize the wear behavior of Ti-30%Ta, Ti-52%Ta alloys. The results shows that the wear volume increases linearly as the rotation of the ball test and with the sliding distance and the analysis of the ball cratering shows that for this test there just grooving abrasion and the volume wear abrasion is higher for the highest hardness alloy.

Effect of abrasive particle size distribution on the wear rate and wear mode in micro-scale abrasive wear tests

In this work, the particle size distribution of two powders was initially analyzed, indicating an approximately normal (Gaussian) distribution with average particle size on the order of 2μm in one case and 6μm in the other. Both powders were composed of silicon carbide (SiC) particles. The two original powders were then mixed with different mass fractions, providing a series of SiC powders that were used in micro-scale abrasive tests with fixed-ball configuration. The wear tests were conducted on ASTM 1020 carbon steel and results were analyzed in terms of wear rate as well as wear mode (“rolling abrasion” or “grooving abrasion”). Results have indicated that the mass fraction of the original powders has a significant effect on the wear modes observed at the micro-scale level and that the wear rate does not follow a direct relationship with the mass fraction of the powder with larger average particle size.

Wear resistance performance of thermally sprayed Al3Ti alloy measured by three body micro-scale abrasive wear test

Thermally sprayed aluminium alloys are often used as coatings to protect steel structures from corrosion. However, in many applications the alloys also need to be sufficiently wear resistant to prevent premature removal of the coatings. The addition of titanium to sprayed aluminium coatings is one approach to enhance the wear resistance. In this study the wear performance of a newly developed and commercially available aluminium coating with 3wt% Ti was studied in terms of its microstructure, hardness and wear resistance. Micro-scale abrasive wear tests were conducted on the pre-sprayed alloys, and the arc sprayed coatings produced from these alloys in order to determine the influence the spraying process has on the structure and wear properties of the coatings. The wear performance of the coatings with Ti was compared with a 99.5wt% Al coating, a thermally sprayed 13% Cr steel coating and with the mild steel substrate.Significant changes were observed in the microstructure of the sprayed coatings when compared with pre-sprayed alloys. The aluminium with 3wt% Ti coating exhibited a large increase in its hardness value compared with the pre-sprayed alloy and it was significantly harder than the 99.5wt% Al coating. It was observed that under micro-scale abrasive wear test conditions, the coefficient of wear of the coating with 3wt% Ti was 33% lower than that of the 99.5wt% Al coating and it was approximately the same as that of the 13wt% Cr steel coatings.

Tribological enhancement of AISI 420 martensitic stainless steel through friction-stir processing

Friction Stir Processing (FSP) has been used to modify the microstructure and properties of AISI 420 stainless steel. The effects of FSP on the steel's microstructure, hardness and wear resistance have been measured and compared with the properties of a conventionally hardened AISI 420 and with D2 tool steel. Optical microscopy, X-ray diffraction and micro-hardness have been used to characterise the steel, and two types of wear tests; dry reciprocating ball-on-flat and micro-scale abrasive wear testing, have been used to determine the processed steel's wear performance under two quite different wear mechanisms. The results show that FSP of AISI 420 can produce higher hardness (maximum HV0.3=722) and better wear performance than conventional heat treatments and in some regions better hardness and tribological performance than D2 tool steel. FSP appears to induce the austenite to martensite transformation within the AISI 420, but the resulting microstructures appear to be significantly different from the conventionally heat treated material.

Friction coefficient and abrasive wear modes in ball-cratering tests conducted at constant normal force and constant pressure—Preliminary results

The micro-scale abrasive wear test by rotative ball has gained large acceptance in universities and research centers, being widely used in studies on the abrasive wear of materials. Two wear modes are usually observed in this type of test: “rolling abrasion” results when the abrasive particles roll on the surface of the tested specimen, while “grooving abrasion” is observed when the abrasive particles slide; the type of wear mode has a significant effect on the overall behaviour of a tribological system. Several works on the friction coefficient during abrasive wear tests are available in the literature, but only a few were dedicated to the friction coefficient in micro-abrasive wear tests conducted with rotating ball. Additionally, recent works have identified that results may also be affected by the change in contact pressure that occurs when tests are conducted with constant applied force. Thus, the purpose of this work is to study the relationship between friction coefficient and abrasive wear modes in ball-cratering wear tests conducted at “constant normal force” and “constant pressure”. Micro-scale abrasive wear tests were conducted with a ball of AISI 52100 steel and a specimen of AISI H10 tool steel. The abrasive slurry was prepared with black silicon carbide (SiC) particles (average particle size of 3 μm) and distilled water. Two constant normal force values and two constant pressure values were selected for the tests. The tangential and normal loads were monitored throughout the tests and their ratio was calculated to provide an indication of the friction coefficient. In all cases, optical microscopy analysis of the worn craters revelated only the presence of grooving abrasion. However, a more detailed analysis conducted by SEM has indicated that different degrees of rolling abrasion have also occurred along the grooves. The results have also shown that: (i) for the selected values of constant normal force and constant pressure, the friction coefficient presents, approximately, the same range of values and (ii) loading conditions play an important role on the occurrence of rolling abrasion or grooving abrasion and, consequently, on the average value and scatter of the friction coefficient in micro-abrasive wear tests.

Laser engineered surfaces from glass forming alloy powder precursors: Microstructure and wear

Fe-based metallic glass forming powders have been deposited on mild steel substrates using high power laser cladding. Coatings microstructures have been analysed by scanning- and transmission-electron microscopy and at varying substrate dilutions, have been found to comprise a 100 to 500 nm interdendritic austenitic phase and a dendritic dual-phase of ferrite/martensite. The application of double layer coatings has shown microstructural refinement. This leads to a needle-like microstructure resulting in a nanoindentation tested hardness increase from ~ 11 GPa up to almost 15 GPa. The layers have been subjected to both dry sliding wear and 3-body microscale abrasive wear testing. The dry sliding results show the layers to exhibit excellent wear resistance – particularly at high speed (50 cm s − 1 ) with wear rate values of ~ 1 × 10 − 8 mm 3/Nm being recorded for the double layer coatings. The single layer coatings reveal a micro-wear mechanism connected with the slip between the ferrite and martensite in the dendritic dual-phase. Microscale abrasive wear testing also reveals that the layers have a good wear resistance, with wear scars exhibiting characteristic material removal by micro-chipping. There is no preferential abrasion of any one phase, nor are track over-lap areas, cracks or pores found to result in varying wear scar dimensions.

Relationship between test severity and wear mode transition in micro-abrasive wear tests

Recently, the micro-scale abrasive wear test has gained large acceptance in universities and research centers, being widely used in studies on the abrasive wear of materials. The purpose of this work is to relate a quantity called test severity ( S test) with the abrasive wear mode transition. The analysis took into consideration the hardness of the materials; the contact pressure ( P) between the specimen and the ball and the equipment configuration (fixed-ball or free-ball). Tests were conducted with balls of AISI 52100 steel and specimens of ISO P20 cemented carbide (WC-Co) and AISI M2 tool steel. The abrasive slurry was prepared with black silicon carbide (SiC) particles (average particle size of 5 μm) and distilled water. The results were analyzed in plots of S test and A g/ A p as a function of test time ( t) and V as a function of P, where A g is the projected area fraction with grooving abrasion; A p the total projected area and V is the volume of the worn crater. The results allowed observing that the value of S test decreased from the beginning to the end of all tests. When the results obtained with fixed-ball and free-ball equipment were compared, this decrease in S test was similar in the case of the WC-Co specimen, for which the hardness of the specimen ( H s) was larger than the hardness of the ball ( H b). The decrease in S test was different in the case of the AISI M2 specimen, for which H s < H b. Tests were also associated with a decrease in the ratio A g/ A p as a function of test time. A transition from mixed mode into pure rolling abrasion occurred at similar test times in the cases with similar severity evolution and, for the AISI M2 specimen, occurred earlier for the condition with lower test severity.

Micro-scale abrasive wear of coated surfaces-prediction models

Micro-scale abrasive wear testing is widely used to characterise thinly coated surfaces. Beyond the several advantages of this technique, the possibility of finding the specific wear rates both for the substrate and for the coating with only one set of tests on coated specimens is certainly an important reason for the rapid spread of the micro-scale abrasive technique. It has not yet been established if the coating and the uncoated substrate can be characterized separately, with the results subsequently being used to calculate the wear characteristics of thin-coated surfaces. This paper concerns the development of a model to predict the behaviour of coated surfaces, based on previous characterisation of the coating and of the substrate in non-perforating tests. By comparison with experimental results, the method developed is used to forecast the abrasion resistance of TiN and of thinly coated copper specimens.

Dependence of microscale abrasion mechanisms of WC-Co hardmetals on abrasive type

Sintered WC-Co hardmetals are employed as wear resistant materials in a wide variety of applications, some of which require resistance to abrasive wear. Such materials usually contain WC particles of less than 10 μm in size. Assessment of wear resistance is often made with tests such as those described in the ASTM standards G65 and B611 both of which employ abrasive particles significantly larger than the size of the carbides in the hardmetals. However, when the abrasive particle size is of the same order of magnitude as the carbide size (or less), then the mechanism of wear changes as the abrasive particles are able to interact with the carbides and matrix phase separately. In certain conditions of use, abrasion of WC-Co materials may primarily be due to small abrasive particles and thus, conventional abrasion tests may not be appropriate. In this work, microscale abrasive wear testing of a range of WC-Co sintered hardmetals was examined with three types of abrasive particle slurries (diamond, silicon carbide and alumina suspended in water) all with a similar size distribution in the range 1–10 μm. The hardmetals varied in carbide size and binder volume fraction resulting in a range of hardnesses between 9.4 and 16.4 GPa. The silicon carbide and alumina abrasives primarily caused wear by preferential removal of the binder phase followed by pullout of the WC particles. As expected, with a given WC grain size in the hardmetal, the wear rate increased as the binder volume fraction increased. However, with a fixed binder phase volume fraction, the wear rate increased as the WC grain size in the hardmetal decreased (i.e. as hardness increased). Behaviour with the diamond abrasive was very different, and apparently not dominated by binder phase removal and carbide pullout. Here, the wear rates of all the cermets examined were similar and may be explained following the model of Engqvist and Axén (Tribology Int., 32 (1999) 527–534).

Tribological Properties of Laser Processed Fe-Cr-C Alloys

A laser rapid-alloy-prototyping technique, was used to produce a number of alloys with compositions lying in the Fe-rich corner of the Fe-Cr-C system. These alloys were prepared in the form of thick coats deposited on a carbon steel by variable powder feed rate laser cladding. The microstructure of the alloys was analyzed by SEM and their mechanical properties were evaluated by microhardness tests, ball-cratering micro-scale abrasive wear tests and scratch tests. Although a poor correlation between the hardness of the alloys and their wear behavior was observed, the correlation between their wear resistance and the fab factor, measured from the scratch tests, is acceptably good. These results are discussed and analyzed on the basis of the microstructural characteristics of the alloys.

Micro-scale abrasive wear of silicon nitride, sialon–TiB 2 composites and D2 tool steel using a multiple load method

The addition of TiB 2 to sialon has previously been shown to lead to improvements in tribological performance when using pin-on-disc testing. In this study the specific wear rates of Si 3N 4, sialon–TiB 2 composites and D2 tool steel have been measured using micro-scale abrasive testing. Two variations of the micro-scale abrasive wear test have been used, free ball and fixed ball, and the results are compared. A method has been developed for the accurate measurement of the specific wear rate using multiple loads on the fixed ball apparatus. The multiple load method eliminates the dependence of the result on the accuracy of the balancing of the load arm. Scanning electron microscopy has been used to study the active wear mechanisms and the effect of increasing the applied load. The “severity of contact” model has been evaluated as a method for predicting the transition from three body rolling wear to two body grooving wear with varying load. Increasing the applied load led to slurry starvation and ridge formation before the predicted two body grooving wear could occur.

On the influence of retained austenite in the abrasive wear behaviour of a laser surface melted tool steel

In this work, the influence of the proportion of retained austenite in the abrasive wear resistance of a laser surface melted martensitic stainless tool steel is analysed. Samples of a 0.5 wt.% C, 13 wt.% Cr + Fe martensitic stainless tool steel were surface melted using a CW CO 2 laser. By changing the processing parameters, samples with proportions of retained austenite varying from 15 to 100% were produced. Microscale abrasive wear tests were performed in the samples. The wear behaviour of the laser melted samples was compared with that of a sample of the same steel in the conventional quenched and tempered condition. It was observed that the wear behaviour of the material depends on the proportion of retained austenite but also of the test conditions, namely of the applied load. For the lower test loads, it was observed that the material submitted to conventional heat treatment presents higher wear resistance; on the contrary, for the higher test loads, it was observed that some of the laser melted samples present a wear resistance higher than that of the conventionally treated material. The analysis of the worn surfaces shows that, in the laser surface melted samples, the stress-induced transformation of austenite into martensite plays an important role in the increase of the wear resistance of the material with increasing applied load.

Microscale abrasion–corrosion behaviour of WC–Co hardmetals and HVOF sprayed coatings

WC–Co hardmetals are employed as wear resistant materials in a wide variety of applications, some of which require resistance to abrasive wear. In some instances, sintered materials are employed, whilst in other situations, WC–Co coatings are deposited onto a component by thermal spraying. WC–Co materials, be they sintered materials or coatings, usually contain WC particles of less than 10 μm in size. When assessing the abrasive wear performance of such materials, tests such as those described in the ASTM standards G65 and B611 are commonly used which employ abrasive particles significantly larger than the size of the carbides in the hardmetals. However, when the abrasive particle size is of the same order of magnitude as the carbide size (or less), then the mechanism of wear changes as the abrasive particles are able to interact with the carbides and matrix phase separately. In certain conditions of use, abrasion of WC–Co materials may primarily be due to small abrasive particles and thus conventional abrasion tests may not be appropriate. In this work, microscale abrasive wear testing of WC–Co sintered hardmetals and coatings was examined. Coatings were thermally sprayed by both liquid-fuelled and gas-fuelled high velocity oxy-fuel (HVOF) systems. The microscale abrasion testing employed abrasive particles in a size range 2–10 μm in both acid and neutral slurries. Generally, it has been observed that microscale abrasion of both the sintered and coating materials occurs predominantly by preferential removal of the binder phase followed by pullout of the carbide. Binder phase removal is accelerated by corrosion in acid media. The wear behaviour of the various materials examined was related to the microstructure and the conditions of the abrasive wear test.