Two body dry abrasive wear of TiC–NiMo cermets

Abstract

The present paper covers the two body dry abrasive wear of a series of titanium carbide base cermets with different amounts of NiMo binder phases (20–60 wt-%) using a 'block on abrasive grinding wheel' test machine. The wear coefficient of the cermets decreases with increasing TiC and Mo contents in the composite, which corresponds to an increase in bulk hardness. The volume loss increases with the increases in the sliding distance and the applied normal load, as predicted by the Rabinowitcz equation. The post-run wear tracks of the worn blocks were analysed by SEM to determine the wear mechanisms. The material is actually removed by several processes which scale the process of groove formation, including the formation of subsurface cracks by a fatigue process under repeated abrasion.     

Three-body abrasive wear of TiC–NiMo cermets

The mechanism of three-body abrasive wear of TiC-base cermets was studied. The wear rate of a series of cermets with different percentage of NiMo binder phase (20–60 wt%) was studied. Silica sand was used as an abrasive. The wear rate of the cermets decreases with the increase of TiC and Mo content, which corresponds to the increase in the bulk hardness. The post-run wear tracks of the worn blocks were analyzed with SEM. The material is removed by several processes such as extrusion and removal of the binder and also fractures of the carbide grains and the carbide network.     

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.     

Friction and dry sliding wear behaviour of cermets

The friction and wear behaviour of cermets/steel rubbing pairs were investigated. Friction and wear tests were carried out using three different crèmets on the base of tungsten, titanium and chromium carbides under dry sliding conditions against steel disk (0.45% C). Sliding wear tests were carried out using modified block-on-ring equipment at a sliding speed of 2.2 m/s and normal load 40 N.It is shown that wear resistance and coefficient of friction depend on the type and chemical composition of the cermets. The WC–Co cermets have the highest wear resistance. The wear rate of WC–Co and TiC–NiMo cermets increased with increasing binder content in the cermets. The wear of Cr₃C₂–Ni cermets is more complicated and depends on the composition of cermets. The wear of WC–Co cermets is caused mainly by preferential removal of the cobalt binder, followed by fracture of the intergranular boundaries and fragmentation of the carbide grains. The main wear mechanism in the TiC–NiMo cermets is polishing (micro-abrasion) and adhesion, resulting in a low wear rate. The main wear mechanism of Cr₃C₂–Ni cermets involves thermal cracking and fatigue-related crushing of large carbide grains and carbide framework and also adhesion.     

Abrasive erosive wear of powder steels and cermets

Composite materials produced by powder metallurgy provide solutions to many engineering applications that require materials with high abrasive wear resistance. The actual wear behaviour of a material is associated with many external factors (abrasive particle size, velocity and angularity) and intrinsic material properties of wear (hardness, toughness, Young modulus, etc.). Hardness and toughness properties of wear resistant materials are highly dependent on the content of the reinforcing phase, its size and on the mechanical properties of the constituent phase. This study is focused on the analysis of the (AEW) abrasive erosive wear (solid particle erosion) using different wear devices and abrasives. Powder materials (steels, cermets and hardmetals) were studied. Wear resistance of materials and wear mechanisms were studied and compared with those of commercial steels. Based on the results of wear studies, surface degradation mechanisms are proposed. The following parameters characterizing the materials were found necessary in materials creation and selection: hardness (preferably in scale comparable with impact), type of structure (preferably hardmetal type) and wear parameters characterizing material removal at plastic deformation.     

Microstructure and abrasive wear resistance of cast Ni-Cr-C alloys

The abrasive wear behaviour of directionally solidified Ni-Cr-C alloys was investigated using a pin-type test. M₇C₃ carbide volume fractions (CVF) were varied from 0 to 40%. Two sets of alloys with different carbide and dendrite spacings were abraded with bonded SiC and corundum particles, varying the grit size and applied load. M₇C₃ carbides greatly improved the abrasive wear resistance against fine-grained SiC particles within the whole range of compositions. By refining the primary carbide structure in hypereutectic alloys, the wear resistance against coarse-grained SiC particles was also improved with increasing CVF although SiC is known to be much harder than M₇C₃. Coarse SiC abrasive particles had a detrimental effect on the wear resistance of all hypoeutectic alloys and, even more, of hypereutectic alloys if the primary carbides were coarse. In testing with corundum, the wear resistance always improved with increasing carbide volume fraction.Wear damage was arranged in three classes. First, SiC and corundum abrasives were partially broken from the substrate at the entrance edge of the specimen. The edges of SiC grains stayed sharp during the wear process whereas the edges of corundum particles were rounded or the corundum was crushed by M₇C₃ carbides. Secondly, damage in the wear surface occurred by fracturing of the edges of carbides facing the wear surface. In addition, SiC abrasives were able to groove carbides. Thirdly, coarse SiC grains transmitted shear stresses causing severe subsurface damage leading to microstructure disintegration and spalling of primary carbides. SiC transmitted larger shear stresses than corundum because the latter was separated by a thin layer of wear debris from the unworn material.The microstructural parameters influencing wear were CVF, size, morphology and distribution of carbides. Optimum wear resistance depended on the abrasive mineral. Alloys with high CVF and coarse primary carbides were best suited for wear with corundum whereas fine primary carbides were required to resist wear by SiC.     

Dry three-body abrasive wear behavior of WC reinforced iron matrix surface composites produced by V-EPC infiltration casting process

This paper fabricated tungsten carbide (WC) particles reinforced iron matrix surface composites on gray cast iron substrate using vacuum evaporative pattern casting (V-EPC) infiltration process, investigated dry three-body abrasive wear resistance of the composites containing different volume fractions of WC particles, comparing with a high chromium cast iron. The fabricated composites contained WC particles of 5, 10, 19, 27, 36, and 52 vol.%, respectively. The results in abrasive wear tests showed that, with the increase in the volume fraction of WC particles, the wear resistance of the composites first increased until reached the maximum when the volume fraction of WC was 27%, then decreased, and was 1.5–5.2 times higher than that of the high chromium cast iron. The changes of the wear resistance of the composites with the volume fraction of WC particles and the mode of material removal in dry three-body abrasive wear condition were analyzed.     

Microabrasion of WC–Co hardmetals in corrosive media

In microabrasion, the influences of corrosive carrier media on the mechanisms and severity of material removal are still poorly understood. This means that with a few notable exceptions, good models for the prediction of materials behaviour are still not readily available. Ball cratering is still a technique which is in its infancy, but is yet sufficiently developed for a test programme to be undertaken using corrosive media.In this preliminary study, the technique has been applied to the microabrasion wear of a selection WC-based hardmetals. For the alkaline and neutral carrier media it was found that volume loss was inversely proportional to hardness. This was not in the case for the acidic media. Scanning electron microscopy of the wear surfaces indicated that the breakdown of the hardness–volume loss relationship in the acidic media was due to the coarser carbide grains (i.e. in the hardmetals of lower bulk hardness) remaining in situ rather than being removed by abrasive processes. Longer-term tests indicated that there were transients in the material removal process, giving a higher wear rate at the start of a test.     

Abrasive wear behaviour of B4C particle reinforced Al2024 MMCs

In this study, the effects of volume fraction and particle size of boron carbide on the abrasive wear properties of B₄C particle reinforced aluminium alloy composites have been studied. For this purpose, a block-on-disc abrasion test apparatus was utilized where the samples slid against the abrasive suspension mixture at room conditions. The volume loss, specific wear rate and roughness of the samples have been evaluated. The effects of sliding time, particle content and particle size of B₄C particles on the abrasive wear properties of the composites have been investigated. The dominant wear mechanisms were identified using scanning electron microscopy. The results showed that the specific wear rate of composites decreased with increasing particle volume fraction. Furthermore, the specific wear rate decreased with increasing the size of particle for the composites containing the same amount of B₄C. Hence, it is deduced that aluminium alloy composites reinforced with larger B₄C particles are more effective against the abrasive suspension mixture than those reinforced with smaller B₄C particles.     

Mechanical properties and features of erosion of cermets

The erosive wear resistance of cermets with different composition, structure and properties has been investigated. It has been shown that cermets erosive wear resistance cannot be estimated only by hardness, characterised by resistance to penetration. The differences in wear resistance between cermet materials with equal hardness level can be attributed to differences in their resistance to fracture. The present paper discusses some features of the material removal process during the particle–wall collision. Solid particle erosion tests on eight materials have been performed using silicon carbide and silica abrasive particles within a range of erodent size of 0.1–0.3 mm, impact angles from 30 to 90° and particle velocity from 30 to 80 m s⁻¹. In order to clarify the details of the impact, the process of interaction of solid particles with cermet targets was studied using a laser Doppler anemometer (LDA) measuring technique. Systematic studies of the influence of the impact variables on the collision process have been carried out.     

Dimensional analysis for abrasive wear behaviour of various polyamides

Abrasive wear behaviour of a series of polyamides (PAs) with different methylene to amide ratio (CH₂/CONH) was analysed using Buckinghams dimensional analysis method and efforts for quantifying the contribution of the material properties towards the abrasive wear performance were also made. In order to calculate the wear coefficient (K), the data based on the experimental wear volume, operating parameters and the material properties were fitted into the non-linear wear equation. The non-linear wear equation was derived based on pi theorem using the dimensional analysis technique. The wear coefficient K decreased as load and abrasive grit size were increased. The theoretical and experimental wear volume correlated well in most of the cases. Among the selected material properties, the fracture stress (_*) and the critical crack length (C_*) were found to be the most important parameters, which controlled the abrasive wear behaviour of PAs.     

Experimental study of lapping and electropolishing of tungsten carbides

Lapping and electropolishing (EP) experiments for tungsten carbide blocks were executed. The effectiveness of the lapping experiment is evaluated in terms of the material removal rate, the surface roughness, and wear of the workpiece. The material removal rate describes the thickness removal of the workpiece under a fixed surface area. Wear describes a microscopic study of the wear track. The results show that the material removal and surface roughness increase as the grain size of the abrasive increases. Four main wear mechanisms -- abrasive wear, fracture, adhesive wear and scratch -- are observed during the lapping of tungsten carbide using silicon carbide abrasive. In the electropolishing experiment, four different machining characteristics -- sub-electropolishing, crack, electropolishing, and pitting -- can be analyzed as the applied current is increased. Although material removal is close to Faraday’s law during electropolishing, it disagrees with Faraday’s law after 400 s of sub-electropolishing.     

Oxidation-abrasion of TiC-based cermets in SiC medium

The aim of the current study was to investigate the effect of oxidation on abrasive wear behaviour of TiC based cermets at temperatures ranging from 20 to 900 °C. Three types of material performance maps were constructed: oxidation rate maps, wear rate maps and maps showing the effect of oxidation on abrasion. Discussion on the performance of different cermet grades is supported by the SEM images combined with EDS and XRD analysis. The results should facilitate the selection of TiC-based cermets providing optimum composition of cermets for high temperature applications.     

Ductility and the abrasive wear of an ultrahigh strength steel

Ploughing of material to either side of the grooves made by abrasive particles and single indenters was observed for both abrasive wear and single point cutting. The degree of ploughing decreases as the hardness of the material being tested increases. It is possible to incorporate ploughing into the usual equation for the volume abrasive wear rate by introducing a term 1 ? f, where f is the fraction of a wear groove ploughed to either side of the abrasive particle but not removed from the surface. The equation becomes volume wear rate $\text{≈}\text{L(1?f}\text{H}{}_{\mathrm{s}}$ where L is the applied load and H_s is the surface hardness. Although it is possible to relate 1 ? f to hardness through single point scratching experiments, there is evidence that 1 ? f could depend primarily on ductility and not on hardness. As an initial step in exploring the dependence of this ploughing term on the mechanical properties of the abraded material, a simple model of the abrasive wear process is proposed. This model is evaluated in terms of the abrasive wear and tensile properties of a low alloy steel heat treated to hardnesses ranging from 496 to 680 HV.     

Influence of abrading particle size on the wear performance of various polyamides

Various polyamides (PAs) containing different CONH₂/CH₂ ratios were selected for abrasive wear studies. Eleven types of silicon carbide (SiC) papers varying in particle size (10–175 μm) were selected as abrading counterfaces. The wear performance under single‐pass conditions indicated that the selected PAs did not show a size effect, in contrast to the case of metals and some other polymers. Wear rates were of the order of 2–17 × 10⁻¹¹ m³/Nm. Scanning electron micrographs of some of the worn papers indicated correlations between wear and the size and number of wear debris particles and the amount of material transferred to the papers.     

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.     

Wear Transition as a Means of Fracture Toughness Evaluation of Hardmetals

The main objective of this investigation was to define operating parameters for a novel method for the simultaneous evaluation of abrasion wear resistance and fracture toughness of hardmetals. The optimal design of a tribotester and a testing procedure from the operational cost and time criteria point of view was another target of the investigation. The method of testing is based on the finding that the wear transition stage, typical for the early and unsteady stage of the wearing process, is controlled by brittle fracture of hardmetal specimens while the following steady-state is controlled by abrasion processes. The brittle fracture of edges will control the wearing-in process only if the edges are initially sharp, the material is fairly brittle (e.g., hardmetal, cermetal), and material is tested on the edge as in the presented tribotester. Precise identification of the tribological transition for every hardmetal grade was possible thanks to the particular specimen shape (with three distinct edges) and to periodic monitoring of specimen mass loss. The fracture-mechanics-based model developed during the course of this investigation was used in the calculation of fracture-toughness values for the hardmetal grades tested. The rating of hardmetals according to their fracture toughness as well as their resistance to abrasive wear in rubbing contact with particulate alumina are presented. The effect of additional hot isostatic pressing (HIPing) on mechanical properties of the hardmetals tested is also illustrated.     

Comparison on abrasive wear of SiCrFe, CrFeC and Al2O3 reinforced Al2024 MMCs

The effects of volume fraction and size of SiCrFe, CrFeC, and Al₂O₃ particulates on the abrasive wear rate of compo-casted Al2024 metal matrix composites (MMCs) were studied. The process variables like the stirring speed, position and the diameter of the stirrer have affected the diffusion between particulates and matrix.The abrasive wear rate was decreased by the increase in particulate volume fraction of SiCrFe and CrFeC intermetallic reinforced composites over 80 grade SiC abrasive paper. The wear rates of the all composites decreased with aging treatment, and the best result was seen for the composite having a hybrite structure as SiCrFe and CrFeC particulates together. Nevertheless, the fabrication of composites containing soft particles as copper favors a reduction in the friction coefficient.     

Amorphous diamond coating of tungsten carbide and titanium carbonitride for erosive slurry pump component service

Tungsten carbide spray coatings have become well established for resisting abrasion and erosion in pumps used in conventional oil production and in oil sands operations. To achieve additional benefits from the extreme wear resistance of tungsten carbide its use is being extended to solid forms for some critical components. Slightly harder titanium carbonitride-based cermets have much lower density and coefficient of thermal expansion and for these reasons are being considered as an alternative to tungsten carbide. PVD amorphous diamond coating also has potential to further increase the service life of selected pump parts fabricated from solid cermets. Micro-abrasion testing and single scratch and nano-indentation evaluation have been carried out on non-coated and PVD amorphous diamond coated WC-4.8% TaC–4.5% TiC/6% Co–1% Cr and TiCN-17% WC/8% Mo materials. Data obtained illustrate that the tungsten–carbide based product has superior wear properties to the titanium carbonitride material and that PVD amorphous diamond coating of both cermets enhanced wear resistance significantly and displayed potential for successful service application.     

Micro-abrasion mechanisms of cast CoCrMo in simulated body fluids

The abrasion seen on some of the retrieved CoCrMo hip joints has been reported to be caused by entrained hard particles in vivo. However, little work has been reported on the abrasion mechanisms of CoCrMo alloy in simulated body environments. Therefore, this study covers the mapping of micro-abrasion wear mechanisms of cast CoCrMo induced by third body hard particles under a wide range of abrasive test conditions. This study has a specific focus on covering the possible in vivo wear modes seen on metal-on-metal (MoM) surfaces. Nano-indentation and nano-scratch tests were also employed to further investigate the secondary wear mechanisms—nano-scale material deformation that involved in micro-abrasion processes. This work addresses the potential detrimental effects of third body hard particles in vivo such as increased wear rates (debris generation) and corrosion (metal-ion release). The abrasive wear mechanisms of cast CoCrMo have been investigated under various wear-corrosion conditions employing two abrasives, SiC (4 μm) and Al₂O₃ (1 μm), in two test solutions, 0.9% NaCl and 25% bovine serum. The specific wear rates, wear mechanisms and transitions between mechanisms are discussed in terms of the abrasive size, volume fraction and the test solutions deployed. The work shows that at high abrasive volume fractions, the presence of protein enhanced the wear loss due to the enhanced particle entrainment, whereas at much lower abrasive volume fractions, protein reduced the wear loss by acting as a boundary lubricant or rolling elements which reduced the abrasivity (load per particle) of the abrasive particles. The abrasive wear rate and wear mechanisms of the CoCrMo are dependent on the nature of the third body abrasives, their entrainment into the contact and the presence of the proteins.