Two different grades, WC-20 vol.% Ni and WC-20 vol.% Co cemented carbides, respectively were systematically investigated concerning their microstructure, binder composition, and corrosion behavior. SEM-EBSD analysis verified that both grades have similar WC grain sizes (0.9–1.1 μm). AES analysis confirmed that the binder phase of the respective grade is an alloy of Ni-W and Co-W and that the concentration of W in the Ni- and Co-binder is 21 and 10 at. %, respectively. In synthetic mine water (SMW), the EIS behavior of WC-Ni(W) at the open circuit potential (OCP) conditions was studied for different exposure periods (up to 120 h). The EIS data fitting estimates low capacitance and high charge transfer resistance (Rct) values, which indicate that the passive film formed on WC-Ni(W) is thin and exhibits high corrosion resistance. At the OCP and potentiostatic-passive conditions, SEM investigations confirm the uncorroded microstructure of the WC-Ni(W). The AR-XPS studies confirmed the formation of an extremely thin (0.25 nm) WO3 passive film is responsible for the high corrosion resistance of WC-Ni(W), at OCP conditions. However, above the transpassive potential, the microstructure instability of WC-Ni(W) was observed, i.e., corroded morphology of both WC grains and Ni(W) binder. The electrochemical parameters, Rct, corrosion current density, and charge density values, confirmed that the WC-Ni(W) is a far better alternative than the WC-Co(W) for application in SMW.
In many applications such as metal cutting and metal forming, cemented carbide tools work in sliding friction wear mode resulting in transfer of the metal work material to the tool surface. In these applications, a surface showing good anti-galling properties needs to be balanced with other desired tool material properties. In the present study, the metal transfer and friction characteristics of aluminum in sliding contact with cemented carbide were evaluated by performing tests under dry and lubricated conditions, where an Al tip is put into sliding contact with the polished surface of the cemented carbide under well-defined contact conditions. Cemented carbide grades include a straight WC-Co grade and two grades containing cubic carbides (i.e. TiC, TaC and NbC), to gain fundamental knowledge into the relation between microstructure and composition and anti-galling properties. Post-test characterization using high resolution FEG-SEM and EDS has been used to show the influence of carbide composition (chemical affinity effects) and topography on the tendency to initial material transfer.
In many metal forming processes, certain texturization of the tool is necessary to have some friction that can make the operation possible. One example of that is the use of crosshatching methods on cemented carbide punches to manufacture beverage cans. The deep drawing and ironing process of the aluminum foil during can production involves different wear mechanisms being active on the punch surface, i.e. adhesive and abrasive wear. The present work examines the abrasive wear performance and friction characteristics of two cemented carbide grades by means of scratch and linear reciprocating sliding wear testing with Al2O3 counterparts under dry and lubricated conditions, with smooth polished and textured cemented carbide surfaces respectively. Additionally, well-controlled tests in which an aluminum pin is sliding over the cemented carbide surface were performed to evaluate the initial metal transfer. Post-test characterization shows the influence of carbide microstructure on the friction, material transfer and wear mechanisms. © European Powder Metallurgy Association (EPMA)
Due to increasing demand in manufacturing industries, process optimization has become a major area of focus for researchers. This research optimizes the cryogenic machining of aerospace titanium alloy Ti-6Al-4V for industrial applications by studying the effect of varying the nozzle position using two parameters: the nozzle's separation distance from the tool-chip interface and its inclination angle with respect to the tool rake face. A finite element model (FEM) and computational fluid dynamics (CFD) model are used to simulate the cryogenic impingement of cryogenic carbon dioxide on the tool-workpiece geometry. Experiments are conducted to evaluate cutting forces, tool wear, and surface roughness of the workpiece, and the results are related to the CFD and FEM analyses. The nozzle location is shown to have a significant impact on the cutting temperatures and forces, reducing them by up to 45% and 46%, respectively, while the dominant parameter affecting the results is shown to be the separation distance. Cryogenic machining is shown to decrease adhesion-diffusion wear as well as macroscopic brittle chipping of the cutting insert compared to dry turning, while the workpiece surface roughness is found to decrease by 44% in the case of cryogenic machining.
The surface characteristics of samples of the 2507 super duplex stainless steel with three different surface conditions, i.e. after hot rolling, annealing and blasting plus pickling, respectively, have been investigated. High resolution scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and scratch testing have been used to characterize the oxide scales with respect microstructure, chemical composition, and mechanical properties.
SEM and EDS-analysis of the oxide scales formed on hot rolled and hot rolled plus annealed samples, show an outer Fe-rich oxide layer and an inner Cr-rich oxide layer close to the interface. While the hot rolled oxide scale displays a relatively porous oxide composed of oxide particles, the hot rolled plus annealed oxide scale displays a more dense, “sintered”, microstructure, i.e. the high temperature during the annealing step promotes a densification of the oxide scale microstructure.
The outer porous Fe-rich layer shows poor cohesive strength and poor adhesion to the underlying Cr-rich layer. In contrast, the inner more dense Cr-rich layer shows strong adhesion towards the 2507 duplex stainless steel. The dense microstructure and strong adhesion of the inner Cr-rich layer is believed to significantly influence the blasting and pickling characteristics.
The evolution of oxide scales on 304 austentic stainless steel during Steckel mill rolling has been investigated by performing pilot trials at Swerim Luleå. The influence of Steckel furnace conditions, i.e. temperature, time and excess oxygen, at reheating between subsequent roll passes have been evaluated and the resulting surface structures have been characterized.
High resolution scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to characterize the oxide scales with respect microstructure and chemical composition. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to analyze the chemical composition at the stainless steel / oxide interface region.
In common for all Steckell rolled samples investigated was a pronounced rough surface morphology and the surface roughness was found to increase with more iterations of rolling. Also, the amount of oxides in the rolled surface tends to increase with longer heating times and more iterations of rolling.
Surface areas, less distorted by the rolling contact, displayed an oxide scale with an outer rather well-defined oxide layer with relatively large grains and an inner, less well defined, oxide layer. EDS-analysis show that the outer oxide mainly consists of Fe2O3, whereas the inner oxide layer corresponds to a chromium rich (Cr,Fe)2O3 oxide combined with areas of partly oxidized stainless steel. ToF-SIMS analysis of the stainless steel / oxide interface region show the presence of B, Ca and Cu in connection to the oxides.
The influence of annealing on the oxide scale characteristics of hot rolled samples of 2507 super duplex stainless steel have been investigated using well controlled lab scale annealing experiments. High resolution scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to characterize the oxide scales with respect microstructure and chemical composition.
SEM and EDS-analysis of the oxide scales after annealing show an outer Fe-rich oxide layer and an inner Cr-rich oxide layer close to the interface. While the hot rolled oxide scale displays a relatively porous oxide composed of oxide particles, the hot rolled plus annealed oxide scale displays a more dense, “sintered”, microstructure.
The annealing peak temperature was found to have a strong impact on the oxide scale microstructure. The higher peak temperature, 1150 °C, resulted in a significantly denser microstructure with more pronounce, larger grains, as compared with the lower peak temperature, 1100 °C, which resulted in a less dense microstructure. In contrast, the influence of annealing atmosphere, was found to be relatively small.
Using Ti6Al4V as a work material, a methodology to systematically investigate the diffusion degradation of cemented carbide during machining is proposed. The methodology includes surface characterization of as-tested worn inserts, wet etched worn inserts, metallographic cross-sectioned worn inserts as well as the back-side of the produced chips. Characterization techniques used include scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Auger electron spectroscopy (AES) and time of flight secondary ion mass spectroscopy (ToF-SIMS).
The results show that the characterization of wet etched worn inserts give quick and useful information regarding the diffusion degradation of cemented carbide, in the present work the formation of a fine crystalline W layer (carbon depleted WC layer) at the tool / work material interface. The present study also illuminates the potential of AES analysis when it comes to analyzing the degradation of cemented carbide in contact with the work material during machining. The high surface sensitivity in combination with high lateral resolution makes it possible to analyze the worn cemented carbide surface on a sub-µm level. Especially AES sputter depth profiling, resulting in detailed information of variations in chemical composition across interfaces, is a powerful tool when it comes to understanding diffusion wear. Finally, the present work illustrates the importance of analyzing not only the worn tool but also the produced chips. An accurate characterization of the back-side of the chips will give important information regarding the wear mechanisms taking place at the tool rake face / chip interface. Surface analysis techniques such as AES and ToF-SIMS are well suited for this type of surface characterization.
The present study focuses on the wear and wear mechanisms of three different cemented carbide grades during orthogonal turning of 316L austenitic stainless steel at different cutting speeds. The influence of WC grain size and cutting speed on the resulting crater and flank wear was evaluated by optical surface profilometry and scanning electron microscopy (SEM). The mechanisms behind the crater and flank wear were characterized on the sub-micrometer scale using high resolution SEM, energy dispersive X-ray spectroscopy (EDS), Auger electron spectroscopy (AES) and time of flight secondary ion mass spectrometry (ToF-SIMS) of the worn cutting inserts and the produced chips.
The results show that the wear rate of cemented carbide drastically increases with increasing cutting speed and that the wear is dependent on the WC grain size; i.e. the crater wear decreases with increasing WC grain size while the flank wear increases with increasing WC grain size. High resolution SEM, AES and ToF-SIMS analysis of the worn cemented carbide within the crater and flank wear regions reveal that the degradation of cemented carbide at higher cutting speeds is mainly controlled by diffusion wear of the WC-phase. This is confirmed by ToF-SIMS analysis of the back-side of stainless steel chips which reveals the presence of a 10 nm thin W-containing oxide film. The results are discussed and interpreted in the light of the conditions prevailing at the tool-chip interface.
Titanium and titanium alloys such as Ti-6Al-4V are generally considered as difficult-to-machine materials. This is mainly due to their high chemical reactivity, poor thermal conductivity and high strength, which is maintained at elevated temperatures. As a result, the cutting tool is exposed to rather extreme contact conditions resulting in plastic deformation and wear. In the present work, the mechanisms behind the crater and flank wear of uncoated cemented carbide inserts in the turning of Ti6Al4V are characterized using high resolution scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and high resolution Auger electron spectroscopy (AES).
The results show that for combinations of low cutting speeds and feeds crater and flank wear were found to be controlled by an attrition wear mechanism while for combinations of medium to high cutting speeds and feeds a diffusion wear mechanism was found to control the wear. For the latter combinations, high resolution SEM and AES analysis reveal the formation of an approximately 100 nm thick carbon depleted WC-layer at the cemented carbide/Ti6Al4V interface due to the diffusion of carbon into the adhered build-up layers of work material on the rake and flank surfaces.
In this work, worn top hammer drill bit buttons after underground drifting in Granodiorite are analysed using scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and electron backscatter diffraction (EBSD) to understand the dominant surface failure and wear mechanisms on the flank wear land region, i.e. the outer side of the gauge row cemented carbide buttons. SEM shows that the worn surface of the flank wear land is partly covered with islands of a thin rock material transfer layer and that the exposed cemented carbide show deformed, cracked and fragmented WC grains. AES gives that the transferred rock material is mainly located on the surface but may penetrate into cemented carbide microstructure to a depth of 1-2 WC grain diameters. Finally, EBSD reveals that the deformation of the cemented carbide in the flank wear land region is located to a thin zone, about ~10 μm in depth.
The initial wear, deformation and degradation of cemented carbide in contact with different rock types are studied using a crossed cylinder sliding test. The sliding distance is limited to centimetres at a time, interrupted by successive SEM analysis. This allows for careful studies of the gradually changing microstructure of the cemented carbide during the test. Five different rock types are included; granite, metal sulphide ore, mica schist, quartzite and marble. All rock types are very different in microstructure, composition and properties. The cemented carbide grade used for the evaluation contains 6 wt% Co and fine (~ 1 µm) WC grains, a grade commonly used in rock drilling. The results show that the cemented carbide microstructure becomes altered already during the very first contact with rock. The initial wear rate and wear character is highly influenced by the rock type. The initial wear of the cemented carbide is highest against quartzite and lowest against marble.
Selective laser melting (SLM) is frequently used additive manufacturing technique capable of producing various complex parts including thin-wall sections. However the surface roughness is a limiting factor in thin sections produced by SLM process when strength is the main criterion. In this study, the influence of build orientation, thickness and roughness on the resulting mechanical properties of as-built test samples was investigated. Various thin sheets of EN 1.2709 maraging steel built in horizontal and vertical orientations produced by SLM were investigated using in-situ micro-tensile testing in a scanning electron microscope. The mechanical strength and deformation mechanisms were analyzed and explained based on thickness and build orientation. Increased ductility was observed in thicker samples as well as in the horizontal build samples. The results illustrate the potential of the in-situ test technique and aspects important to consider in design guidelines for thin AM structures.
Cemented carbide is a composite material, most commonly consisting of tungsten carbide grains in a metallic matrix of cobalt. The combination of a hard ceramic phase in a ductile metallic matrix combines high hardness and ability to withstand plastic deformation with toughness to avoid cracking and fracturing. Since these properties are very important in rock drilling, cemented carbides are frequently used in such applications. In earlier work, it was found that granite in sliding contact with considerably harder cemented carbides not only results in plastic deformation of the cemented carbide composite, but also in plastic deformation of some of the individual WC grains. The latter observation is remarkable, since even the two hardest granite constituents (quartz and feldspar) are significantly softer than the WC grains. This tendency to plastic deformation of the WC grains was found to increase with increasing WC grain size. The present investigation aims to increase the understanding of plastic deformation of cemented carbides in general, and the individual WC grains in particular, in a situation representative for the rock drilling application. The emphasis is put on explaining the seemingly paradoxical fact that a nominally softer counter material is able to plastically deform a harder constituent in a composite material. The experimental work is based on a scratch test set-up, where a rock crystal tip slides against a fine polished cemented carbide surface under well-controlled contact conditions. The deformation and wear mechanisms of the cemented carbide are evaluated on the sub-micrometer scale; using high resolution FEG-SEM, EDS, EBSD, BIB and FIB cross-sectioning. The size of the Co-pockets, together with the shape and size of WC grains, turned out to be decisive factors in determining the degree of carbide deformation. The results are discussed with respect to their industrial importance, including rock drilling.
In the present study, the microstructural response of some commercial cemented carbide grades during scratchinghas been analyzed and evaluated by a number of post-test characterization techniques. The influence of Co binder phase content and WC grain size on the deformation and degradation on a WC grain size scale and on a composite scaleare evaluated. The results clearly illustrate the complexity of deformation, degradation and wear of cemented carbide and the dynamics of the diamond stylus / cemented carbide contact during the scratching event. For all cementedcarbide grades the microstructure has a strong impact on the observed degradation mechanisms and the resistance to deformation and degradation was found to increase with decreasing Co content and decreasing WC grain size.
In the present work, the potential of using thin hard CVD and PVD coatings in order to improve the performance of cemented carbide steel wire drawing nibs is evaluated. Coating materials include some state-of-the-art CVD and PVD coatings and pre- and post-coating treatments were used to improve the surface topography of the coated functional surfaces. The tribological performance of the coatings has been evaluated by sliding wear tests and wire drawing experiments under well controlled conditions. Post-test characterization of the coated nibs using 3D optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy illustrates the pros and cons of the two deposition techniques but also that the coatings have a potential to improve the performance of cemented carbide nibs in steel wire drawing applications.
Cemented carbides are the most common cutting tools for machining various grades of steels. In this study, wear behavior of two different cemented carbide grades with roughly the same fraction of binder phase and carbide phase but different grain size, in turning austenitic stainless steel is investigated. Wear tests were carried out against 316L stainless steel at 180 and 250 m/mincutting speeds. The worn surface of cutting tool is characterized using high resolution scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), Auger electron spectroscopy (AES) and 3D optical profiler.The wear of cemented carbide in turning stainless steel is controlled by both chemical and mechanical wear. Plastic deformation, grain fracture and chemical wear is observed on flank and rake face of the cutting insert. In the case of fine-grained, the WC grains has higher surface contact with the adhered material which promotes higher chemical reaction and degradation of WC grains, so chemical wear resistance of the composites is larger when WC grains are larger. The hardness of cemented carbide increase linearly by decreasing grain size, therefore mechanical wear resistance of the composites is larger when WC grains are smaller.
The tribological interaction between a cemented carbide drawing die and a steel wire under lubricated wire drawing conditions has been characterized using 3D optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that wear of the cemented carbides mainly is located to three different wear zones, i) at the entrance of the reduction zone, ii) at the exit of the reduction zone/ entrance of the bearing zone and iii) at the exit of the bearing zone. In the first wear zone, wear of the cemented carbide occurs on a WC grain size level and is controlled by plastic deformation, cracking and fragmentation of individual WC grains. In the second wear zone, wear of the cemented carbide is controlled by chipping of small WC/Co composite fragments resulting in craters, ~ 10μm in diameter.
Austenitic stainless steels generally display poor tribological properties in sliding contacts partly due to their strong adhesion and transfer tendency to the counter surface. As a result machining of austenitic stainless steels is frequently associated with significant problems such as high stresses and high temperatures resulting in rapid tool wear. In the present study, the influence of coating micro topography on the initial material transfer of 316L stainless steel in sliding contacts has been evaluated using a scratch testing equipment. Coating materials include modern CVD Ti(C,N)-Al2O3-TiN and PVD (Ti,Al)N-(Al,Cr2)O3 coatings deposited on cemented carbide and pre- and post-coating grinding and polishing treatments were used to obtain different micro topographies of the coating surface. Pre- and post-test characterization of the surfaces was performed using high resolution scanning electron microscopy, energy dispersive X-ray spectroscopy and optical surface profilometry.
The results show that the intrinsic topography of the as-deposited CVD and PVD coatings promotes material transfer. For the as-deposited CVD coating the nanoscale topography of the crystals controls the transfer while for the PVD coating the µm-scale droplets and craters control the transfer. Post-polishing of the coating, especially in combination with pre-polishing of the substrate, significantly improves the tribological performance of the surface reducing the friction coefficient and the material transfer tendency. However, the presence of µm sized droplets and craters in the PVD coating limit the possibility to obtain a smooth post-polished surface and its resistance to material pick-up. In contrast, post-polishing of the CVD coating does not suffer from intrinsic coating defects which results in low friction and a very high resistance to material pick-up.
Due to a combination of high hardness and toughness, resulting in excellent wear resistance, cemented carbides are commonly used as the rock crushing component in rock drilling. The present paper presents a unique study where the very initial stages of deformation and wear of cemented carbide in sliding contact with rock are followed in small incremental steps. After each step, a pre-determined area within the wear mark is characterized using high resolution SEM and EDS. This facilitates analysis of the gradual deformation, material transfer, degradation and wear. The deterioration mechanisms found in this sliding test are similar to those observed in actual rock drilling. Cemented carbide grades with different microstructures show significant differences, where a higher amount of Co and a larger WC grain size both are associated to more wear.
Automating the detection of processing conditions that may lead to defects in the wire during the wire drawing process is of high interest to the industry. Current practise is based primarily on operator experience. Increasing demands on product quality and process robustness emphasises the need for development of robust in-process detection methods. This work is focusing on investigating the potential of using vibration monitoring to detect process deficiencies or variations that may lead to defects in the product. Wire drawing of a carbon steel in different lubricating situations was used to investigate vibration signal response together with force measurements and surface investigation of the wire product. The results show that vibration measurement is capable of detecting loss of lubrication that leads to poor surface quality of the wire.
The wear behavior of cemented carbide rock drill buttons is influenced by many factors, which include the composition and microstructure of the cemented carbide material, the nature of the rock material, and the conditions of the rock drilling operation. Depending on the type of rock and on the drilling procedure used, the cemented carbide is exposed to substantially differing mechanical and thermal conditions. In the present study, the surface degradation and wear mechanisms of cemented carbide drill buttons exposed to iron ore rock drilling have been characterized based on a combination of high resolution scanning electron microscopy (SEM), focused ion beam cross-sectioning (FIB), energy-dispersive X-ray spectroscopy (EDS) and electron back scatter diffraction (EBSD).The results show a significant difference in surface degradation and wear between the front and peripheral buttons of the drill bits. While the front buttons display a relatively smooth worn surface with shallow surface craters the peripheral buttons display a reptile skin pattern, i.e. plateaus, 200-300. μm in diameter, separated by valleys, typically 40-50. μm wide and 15-30. μm deep, The reptile skin pattern is obtained in regions where the peripheral buttons are in sliding contact against the drill hole walls and exposed to high surface temperatures caused by the frictional heating. The results indicate that the reptile skin pattern is related to friction induced thermal stresses rather than mechanical contact stresses, i.e. the reptile skin pattern is formed due to thermal fatigue, rather than mechanical fatigue, caused by the cyclic frictional heating generated at the cemented carbide button/iron ore interface.
Abstract The influence of tool surface topography on the initiation and build-up of transfer layers in the orthogonal turning of 316L austenitic stainless steel have been studied under well controlled conditions. Tool materials include CVD Ti(C,N)-Al2O3-TiN and PVD (Ti, Al)N-(Al,Cr)2O3 coated cemented carbide inserts prepared using different grinding and polishing treatments. Post-test characterization of the inserts was performed using high resolution scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the transfer tendency of work material is strongly affected by the surface topography of the rake face. For both types of inserts, the initial transfer and the build-up of transfer layers are localised to microscopic surface irregularities on the rake face. Consequently, an appropriate surface treatment of the cemented carbide substrate before coating deposition and the as-deposited CVD and PVD coating can be used in order to reduce the transfer tendency and the mechanical interaction between the mating surfaces. Also, an improved surface finish was found to reduce coating wear and consequently the crater wear rate of the inserts investigated. This can most likely be explained by the reduced tendency to discrete chipping of coating fragments in the contact zone and the formation of a thin transfer layer composed of Al, Si, Ca, O with beneficial friction properties which are promoted by a smooth coating surface.
In this work, the friction and wear behavior of bare copper was investigated for the first time under lubricated sliding conditions in diluted ethanol solutions of butylhosphonic (C4P), octylphosphonic (C8P), dodecylphosphonic (C12P), and hexadecylphosphonic (C16P) acids. The technique aims towards a more environmentally friendly lubrication to be used in shaping of copper sheets. Bare copper samples were subjected to unidirectional sliding using a tribometer with ball-on-disk contact geometry. Copper substrates (20 mm2×1 mm) were run against 100Cr6 ∅10 mm ball bearing counterbodies. All tests were conducted using the same sliding conditions with a normal load of 10 N, tangential velocity of 0.01 m/s, at room temperature of 20 °C. Worn surfaces were analyzed by Scanning Electron Microscopy, Optical Microscopy and White Light Interference Profilometry. When comparing to sliding tests in the pure ethanol solvent, significant decreases in terms of wear track dimensions, transferred material on the ball and friction coefficients are observed when active molecules are present in the solution. These form protective tribofilms exhibiting lubricating and anti-wear properties. Deeper studies on the tribological behavior of copper in C4P solution show that both low friction and low transfer of work material to the ball prevail in a specific range of low molecule concentration (5×10-4 M; 25×10-4 M). Even if the molecules are introduced during the test, after a few cycles, the tribological behavior improves, regardless of both friction level and copper surface degradation. Finally, specific friction tests were performed to further investigate the mechanisms. It was found that two mechanisms are involved; firstly molecules grafting onto the surface directly reduces friction, and secondly transformation of these grafted molecules into a tribofilm during the first mechanical contact cycles reduces it even further.
To differentiate between the roles of surface topography and chemical composition on influencing friction and transfer in sliding contact, a series of tests were performed in situ in an SEM. The initial sliding during metal forming was investigated, using an aluminum tip representing the work material, put into sliding contact with a polished flat tool material. Both DLC-coated and uncoated tool steel was used. By varying the final polishing step of the tool material, different surface topographies were obtained. The study demonstrates the strong influence from nano topography of an unpolished DLC coated surface on both coefficient of friction and material transfer. The influence of tool surface chemistry is also discussed.
The wear behavior of cemented carbide rock drill buttons is influenced by many factors, which include the composition and microstructure of the cemented carbide material, plus the conditions of the rock drilling operation, such as drilling parameters, drill button geometry and the nature of the rock material. Depending on the type of rock and on the drilling procedure used, the cemented carbide is exposed to substantially differing mechanical and thermal conditions. Under conditions of high mechanical stress and high temperatures, typical for drilling in highly abrasive rocks such as granite, the worn cemented carbide buttons are usually very smooth, with the roughness limited to within the size of individual WC grains. When drilling under conditions of moderate mechanical stress and high temperatures, typical for drilling in low-abrasive rock, such as ores with e.g. magnetite, the surface damage of the buttons usually includes a macroscopic surface wear pattern, commonly referred to as “reptile skin”, in an otherwise smooth surface. The crack growth associated to the valleys of the reptile skin pattern eventually leads to catastrophic fracture of the button, unless the cracked surface layer is repeatedly ground off before the cracks grow too deep. So despite the low general wear rate, the wear life of drill buttons becomes severely restricted by the surface cracks. The present study focuses on revealing the degradation mechanisms behind the formation of the reptile skin. This is done by analyzing drill buttons exposed to different stages of degradation and wear from drilling in iron ore. The work is based on a combination of high resolution scanning electron microscopy (SEM), focused ion beam microscopy (FIB), energy-dispersive X-ray spectroscopy (EDS) and electron back scatter diffraction (EBSD).
Hardness and fracture toughness are often used as the prime material parameters to characterise cemented carbides used in rock drilling. However, the deformation and wear of cemented carbide are too complicated to be described by these parameters alone. The cemented carbide and the wearing rock mineral are both composite materials, containing phases with widely varying hardness. Moreover, the deformation behaviour of the individual phases may be strongly anisotropic, as for the WC grains in the cemented carbide. The wear of the cemented carbide typically occurs on the scale of individual grains or smaller. Contrastingly, the hardness stated for both is typically a macroscopic value, averaged over numerous grains, orientations, etc. The present investigation aims to contribute to the understanding of the relations between microstructure, properties and wear mechanisms of cemented carbide buttons in rock drilling. It is focused on the role of scale of deformation in relation to size of the different phases of the cemented carbide. This is achieved by simplifying the contact situation of the rock drill button to a single stylus sliding contact between a granite stylus and a polished cemented carbide surface. The deformation and wear of this well controlled contact is then evaluated on the sub-micrometer scale; using high resolution FEG-SEM with EBSD, FIB cross-sectioning and AFM. The results show that even an extremely local deformation, such as slip within individual WC grains, affects the tribological contact, and that the nominally much softer granite may cause deformation both within individual WC grains, and on the composite scale. The results are discussed with respect to their significance for wear of cemented carbides in rock drilling. (C) 2015 Elsevier Ltd. All rights reserved.
Cemented carbides are composite materials comprising metal carbide grains in a more ductile metallic binder. This microstructure results in a combination of high hardness and toughness, making them commonly used as rock crushing parts in rock drilling, where they usually show wear on a very fine scale. The hardness and toughness can ultimately be tuned for the application by adjusting the carbide grain size, binder fraction and composition.In the present investigation, the initial micro-scale deformation and wear of polished cemented carbide surfaces is studied by micro scratching with diamond and granite styli, and also by instrumented micro and nanoindentation. The deformation and wear is evaluated on the sub-micrometer scale using high resolution FEG-SEM and FIB cross sectioning. The selected microstructures include besides four cemented carbide grades that are commonly used in rock drilling also binderless and Ni containing grades. This wider range of cemented carbides is used to gain fundamental insights into the relations between microstructure and micro-scale deformation and wear. The results are discussed with respect to their significance for wear of cemented carbides in rock drilling operations.
The wear characteristics of a high cBN content PCBN cutting tool during hard milling of two different hardened cold work tool steels have been evaluated. Post-cutting examination of the worn cutting inserts was performed using high resolution field emission gun scanning electron microscopy, energy dispersive X-ray spectroscopy, Auger electron spectroscopy and optical surface profilometry. Also, the machined work material surfaces and collected chips were characterized in order to evaluate the prevailing wear mechanisms. The results show that both flank and crater wear are controlled by continuous wear due to tribochemical reactions, adhesive wear and mild abrasive wear. Besides, the cutting inserts show a tendency to micro-chipping along the cutting edge especially at higher cutting speed. The latter mechanism was also found to be dependent on type of work material. High lateral resolution Auger electron spectroscopy of the crater region shows that the worn surface is covered by a thin SixOy rich tribofilm with a thickness of 50-500 nm, the tribofilm being thicker on the binder phase regions. Also, the Co-rich regions of the binder phase seem to be more tribochemically affected by the prevailing contact conditions as compared with the W-rich regions of the binder phase and the cBN phase.
Increasing focus on environmental issues in industrial production has urged sheet metal stamping companies to look for new tribo-systems in order to substitute hazardous lubricants such as chlorinated paraffin oils. The efficiency of chlorinated paraffin is due to the fact that the lubricant reacts chemically with the tool and workpiece material forming thin films, which adhere strongly to the surfaces and reduce the tendency to metal-metal contact and material pick-up. Production tests of new, environmentally benign tribo-systems are, however, costly and laboratory tests are preferred as a preliminary simulative method to investigate alternative tribo-systems. The present paper presents a case study where an industrial process, consisting of deep drawing with two subsequent re-drawings, was selected and four potential new tribo-systems were tested including different workpiece materials, i.e. AHSSs and stainless steels. The performance of the tribo-systems was analyzed in the laboratory by means of a newly developed simulative test as well as in an industrial production process. The results obtained show a good agreement between the laboratory test and the industrial production process regarding the tribological performance, i.e. tendency to material pick-up and galling, of the evaluated tribo-systems. Moreover the SEM analysis shows that different workpiece materials result in different types of material pick-up.