Mapping of impact-abrasive wear performance of WC–Co cemented carbides

Mapping of impact-abrasive wear performance of WC–Co cemented carbides

Wear 332-333 (2015) 971–978 Contents lists available at ScienceDirect Wear journal homepage: www.elsevier.com/locate/wear Mapping of impact-abrasiv...

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Wear 332-333 (2015) 971–978

Contents lists available at ScienceDirect

Wear journal homepage: www.elsevier.com/locate/wear

Mapping of impact-abrasive wear performance of WC–Co cemented carbides M. Antonov a,n, R. Veinthal a, D-L. Yung a, D. Katušin b, I. Hussainova a a b

Department of Materials Engineering, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia Department of Mechatronics, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia

art ic l e i nf o

a b s t r a c t

Article history: Received 3 February 2015 Accepted 9 February 2015

A reliable evaluation of the wear resistance of materials used in conditions of combined impact and abrasion is of a paramount importance for industrial applications. A new tribo-device for studying impact-abrasive wear performance of materials was worked out. The specimen is pressed against a rotating steel wheel with abrasive being fed by gravity between them. The generator is supplying the tribosystem with impacts of predefined energy in a range of 0–19 J and a frequency up to 55 Hz. Cemented carbides of different binder content (6, 8, and 15 wt%) and carbide grain size (fine, medium, and coarse) were tested for impact-abrasive wear resistance. Maps reflecting the performance of cemented carbides at low and medium stress abrasion as well as medium stress abrasion combined with impact are constructed. The maps assessing the effects of stress intensity, dynamic loading, and combined effect of increase in stress and application of the dynamic load are thoroughly discussed. Microstructural analysis of the wear mechanisms is performed to support the conclusions. & 2015 Elsevier B.V. All rights reserved.

Keywords: Abrasion Impact wear Wear testing Cemented carbides Mapping Cutting tools

1. Introduction The exceptional performance of WC–Co cemented carbide (hardmetal) in many tribological conditions is due to combination of high hardness of the tungsten carbide particles, high fracture toughness of the cobalt binder and strong adhesion between phases [1–4]. There is a huge amount of parameters influencing wear behaviour of cemented carbides; therefore, the mapping of their performance in specific tribo-conditions is still a challenge. For example, properties of the hardmetals are highly dependent on the method and conditions of manufacturing as well as on chemical composition and developed microstructure [1–8]. Increasing the binder content until the optimum value in cemented carbide usually results in increased wear resistance in conditions of dynamic loading [1–13]. It is a well established fact, that the energy dissipated during the wear process can be transferred into the formation of the surface layer with improved wear resistance [14–20]. Hardmetals with medium and high binder content (45 wt%) easily adapt to the wear conditions due to possible shifting or re-embedding of ceramic grains and the availability of a spaces between grains that may be additionally reinforced by products of wear process, which leads to the formation of a mechanically mixed surface layer (MML) [19–23]. Under the

n

Corresponding author. Tel.: þ 372 6203355. E-mail address: [email protected] (M. Antonov).

http://dx.doi.org/10.1016/j.wear.2015.02.031 0043-1648/& 2015 Elsevier B.V. All rights reserved.

dynamic conditions, the binder metal from the subsurface layer is squeezed towards the surface, resulting in a rearrangement of WC grains and the reduction of the mean free path in the subsurface layer [5,24,25]. An excessive (420 wt%) binder content results in high abrasive wear rates due to the facilitated access of the fine abrasive particles [19,20]. Cemented carbides with fine ceramic grains usually have higher hardness, compressive and fatigue strength but lower fracture toughness [9–12] compared to coarse grained composites. Fine size of the carbide grains is favourable prevention of wear by the large abrasive particles; however, if the abrasive particles are subjected to intensive fracturing the fine grained hardmetals lose their advantages and experience quite high wear rates [26–28]. Tungsten monocarbide (WC) grains have a lower hardness than that of fused two-phase (W2CþWC) carbide grains but have higher fracture toughness, and are more resistant to high temperature dissolution and formation of eta phase, although they exhibit a higher cost [29,30]. The content of carbon in the precursor mixture of powders and the parameters of sintering (atmosphere, temperature, duration, heating, cooling rates, pressure, etc.) should be set very precisely to avoid the formation of brittle eta phases or free carbon acting as stress concentrator [31]. The depth of the layer affected by the wear can be as thick as 10 carbide grains depending on the intensity of the wear, but major changes are usually observed within the layer of a thickness equal to the size of 3 carbide grains [19,20]. The increase in local stresses

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(higher energy of impact) usually results in a threshold where the rate of material removal rises significantly, due to a change in the wear mechanism which may be classified as a transition between high and low cycle wear [6]. The high cycle wear mechanism is always preferred since the development of cracks or other damage features takes more time and results in lower wear rates [11,23,32]. In addition to residual mechanical and thermal stresses resulting from the milling and sintering processes experienced during production, stresses induced by the wear influence the performance of the final products. After sintering, WC grains are kept in compression (the thermal expansion coefficient of Co is higher than that of WC) which improves the performance of the WC grains [1–4]. Local heating of contact points (flash temperature) during wear with temperatures reaching 2000 1C may lead to melting of the binder and changed thermal stress states [6,11]. Coarse grained cemented carbides of high binder content have a higher thermal conductivity, which reduces thermal gradients [11,33–35]. The tribolayer composed of original phases (binder and ceramic grains) and products of wear process having usually fine size that are mechanically introduced and mixed has a lower thermal conductivity compared to untreated hardmetals, due to the large number of interfaces [33–36]. The variation of properties within final products made by the powder metallurgy route inevitable due to the variation of stresses experienced by the green body during compaction may be partially solved by hot isostatic pressing [2,12,37]. New binder materials to substitute cobalt are studied to make Co-free corrosion resistant materials suitable for elevated temperatures [8]. Therefore, optimisation of the products for applications requiring sufficient abrasive and impact tolerance is a challenging and complicated task. Depending on the severity of the tribological contact, the materials with the optimum combinations of properties and microstructural features have to be carefully tested and selected [23,38,39]. Laboratory testing provides faster, better controlled, and less expensive testing than field tests [40,41]. There are many applications where materials are working in combined abrasive and impact conditions (drill bits, crushers, picks for road maintenance, car wheel studs, snow plough blades, etc.), while the types of laboratory equipment suitable for this type of testing is very limited. In high-energy milling type of tribo-devices (disintegrator), the resistance of materials against the impact of abrasive particles (up to 10 mm) can mainly be studied [42]. The energy of the impact in an impeller type tester [43,44] depends on the size of the abrasive particles and the impeller velocity. The adjustment of the force between the sample and the abrasive for the device described in [45] (pin against cylinder filled with abrasive) is complicated. Both devices suffer from the deterioration of abradant which results in change of wear conditions during the test. A device (plunger against the plate with abrasive between) described in [46] has a low energy of impact (0.8 J) and a low frequency (2 Hz), and is suitable mostly for short tests at high temperatures due to the deterioration of the plunger. A device presented in [47] has a quite high impact energy (up to 5 J), with a low impact frequency (1.7 Hz). It does not allow abrasive testing without impacts. The fixation of the specimen for this and for the impeller type of devices is hardly suitable for hardmetals (the sample should have a hole) [43,47]. The test with a sample pressed against rock while abrasive is fed in

between, as described in [48] has no dynamic loading. None of these devices have the option to study the effect of inertia of the loading system which may result in significant changes in the wear mechanism and wear rate [49]. Testing of extremely hard materials such as binderless WC ceramics, WC/diamond composites [50] or polycrystalline diamond by simplified scratching or scratching accompanied by impacts [51] is complicated due to the absence of indenters having sufficiently high hardness (higher than that of the materials under investigation), which is required for reliable testing. These materials have extremely high resistance against abrasion; however, they may experience a catastrophic brittle fracture during impact loading. Wear rate graphs of cemented carbides are available and illustrate the general trends [9–12,21,23,41,52,53]. In paper [23] the most often used grades with 5–15 wt% Co content were omitted and the wear data were absent. The maps that simplify the selection and provide a better understanding of cemented carbides behaviour under the studied set of parameters have been quite limited up to now [40,54–60]. Maps showing wear performance of cermets, hardmetals and metal matrix composites in aqueous conditions are presented in [54–56]; wear maps for dry and lubricated sliding of steels and ceramics are given in [40,57,58]; the approach for construction of maps in erosive and abrasive conditions of brittle materials may be found in [59,60]. The aims of the current study are: to build the maps showing the wear rates of the cemented carbides in low stress, medium stress and medium stress with impact conditions; and to map the wear rate variation of materials due to changes in loading conditions.

2. Materials and methods 2.1. Materials The WC–Co cemented carbides with varied WC grain size and cobalt content were produced by a conventional PM routine at Tallinn University of Technology, Laboratory of Powder Metallurgy. All powders were commercially sourced and the description is provided in Table 1. Sintering was performed by hot isostatic pressing (HIP) at different temperatures depending on the cobalt content: 1390 1C (15 wt% Co) and 1450 1C (6 wt% or 8 wt% Co). The properties of the conventional cemented carbides had been intensively studied [1–12,21,23,38,52,53] and are not provided here. The nomenclature of the hardmetal grades follows the designation of WC grain size (fine, medium, and coarse). The carbide grains size of sintered samples determined by linear intercept method (BS EN ISO 643:2012) was within the range of 0.2–1.0, 0.5–2.0 and 2.0–10.0 μm for fine, medium, and coarse hardmetals respectively. Bulk alumina (Al2O3) and wear resistant alloy Hardox 400 [61] were tested along with the cemented carbides for comparison between ceramic, ceramic–metallic, and metallic materials. 2.2. Methods The multifunctional modular tribosystem (MMTS) in configuration C1 was applied for testing of materials in low stress abrasive conditions according to ASTM G65 standard [28] (Table 2).

Table 1 Description of powders used for production of cemented carbides. Designation

Size (mm)

Supplier

Purity (%)

Grade

Fine WC Medium WC Coarse WC Cobalt

0.1 0.9 10.0 0.3

H.C. Starck Wolfram Bergbau und Hütten AG H.C. Starck Pobedit (Russia)

99.0 99.0 99.0 99.3

DN-4.0 CRC 030-40 HC 1000 PK-1Y, GOST 9721-79

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Table 2 Test conditions. Specification

Low stress dry sand rubber wheel test (ASTM G65)

Scheme (configuration) Wheel material Size of wheel

Block-on-ring (C1) Rubber lined steel wheel Diameter 228.6 mm, breadth 12.7 mm Specimen Block, 10  25  50 mm Force against specimen 130 N Abrasive Ottawa sand, 0.2–0.3 mm Feed rate 370 g min  1 Linear abrasion 1436 m, 2.4 m s  1 Average stress at the end of the test due to applied 0.45 MPa force for cemented carbides Energy of impact No impacts Frequency of impact No impacts Inertia of loading system 10 kg Atmosphere Air, relative humidity 50 7 10%, air temperature 25 75 1C

The MMTS device was modified (configuration C3, Fig. 1) for testing materials under impact loading and currently undergoes a patenting [62]. The sample (1) is moved by an industrial impact generator (2) using the anti-vibration technology (for reduction of the MMTS frame vibration) from Makita. The rotating steel wheel (3) driven by an electrical motor is fixed to a pendulum-type suspension (4) and the normal load is applied by a deadweight through the loading system (5). The abrasive is loaded to a hopper; the feeding rate is adjusted and the abrasive is introduced into the wear region by a nozzle (6). Fresh abrasive is continuously supplied. The inertia of the loading system can be adjusted by fixing an additional weight (7) to the pendulum suspension. The procedure for measuring the inertia value is described elsewhere [49]. The impact energy can be varied from 0 to 19 J; the maximum frequency is 55 Hz; the inertia value can be as high as 200 kg; the force against a specimen can reach up to 1000 N. Liquid addition during testing is also foreseen, while the aim of the current study was to make a comparison with the results obtained with the conventional low stress dry abrasive test according to the ASTM G65 standard. The impact energy, frequency of impact and velocity are selected to mimic conditions similar to those experienced by drill bits [63]. The timer of the impact generating device allows smart testing. Scheduled impacting during abrasion enables to simulate scenarios existing in the specific applications (drilling of inhomogeneous ground, snow ploughing on uneven roads, etc.). All three test methods employ the same rounded quartz grain sand (A.F.S 50-70 testing sand supplied by U.S. Silica Company, Ottawa) as required by the ASTM G65 standard and also as the most common naturally occurring abradant. Results of the sieving with Fritsch GmbH test sieves are shown in Fig. 2. Some amount of sand (approximately 10–20% and 30–40% for low and medium stress test configurations), which was examined after the test, did not participate in the wear and did not experience any change in size. The abrasive is put to flow shortly before the start and stopped a short time (5–15 s) after the end of the test. Some portion of sand flows around the wear zone. This means that during the low stress test, crushing of the abrasive is close to zero. Approximately 25% of the abrasive is fractured during the test with medium stress, whereas 40% is fractured at medium stress with impacts. The fractured abrasive has a more angular shapes and can cause higher wear, which is why the tests with the steel wheel are considered as medium stress abrasive tests, since a higher portion of abrasive is expected to be fractured during the high stress

Medium stress abrasive test with steel wheel

Medium stress abrasive test with steel wheel and impacts

Block-on-ring (C3) Steel EN 10025 S355, HV10¼ 230 Diameter 85 mm, breadth 6 mm

Block-on-ring (C3) Steel EN 10025 S355, HV10¼ 230 Diameter 85 mm, breadth 6 mm

Block, 5  15  25 mm 49 N (5 kg) Ottawa sand, 0.2–0.3 mm 180 g min  1 200 m, 1.0 m s  1 1.05 MPa

Block, 5  15  25 mm 49 N (5 kg) Ottawa sand, 0.2–0.3 mm 180 g min  1 200 m, 1.0 m s  1 0.95 MPa

No impacts No impacts 33 kg Air, relative humidity 50 7 10%, air temperature 25 75 1C

5.6 J 27.5 Hz 33 kg Air, relative humidity 50 710%, air temperature 257 5 1C

Fig. 1. Schematic diagram of the main moving elements of MMTS/C3 device.

Fig. 2. Abrasive particle size distribution after testing (size in mm).

abrasion [64]. The low and high stress tests using a similar steel wheel size have been performed by applying forces against the specimen of 9.8 N and 196.0 N [28]. The size of wear scars after testing was measured and the average stress level was estimated for cemented carbides (Table 2). A microstructural examination of specimens was conducted using a scanning electron microscope (SEM) Zeiss EVO MA15 supplied with energy dispersive X-ray spectroscopy (EDS) – INCA analyser and HITACHI TM-1000 SEM with EDS module.

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Fig. 3. Wear rate maps of the cemented carbides in dry abrasive conditions: (A) low stress abrasion, (B) medium stress abrasion, and (C) medium stress abrasion with impacts. Results of alumina and wear resistant alloy Hardox 400 testing are given for comparison.

3. Results Quantitative results of the dry abrasive tests in the form of maps are presented in Fig. 3. The limits between various rates of wear (low, medium and high) are different for the low and medium stress maps and are given below the map to facilitate the tracking of the effects of

the binder content and hard particle size. The cemented carbide with medium grain size (0.5–2.0 mm after sintering) and 6 wt% of cobalt binder exhibited the lowest wear rate under all applied conditions. The performance of the fine-grained cemented carbide was worse, while coarse-grained hardmetals had the lowest resistance against wear. Increased stress state always resulted in a higher wear rate, for

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Fig. 4. Maps showing the effect of change in dry abrasive test conditions on wear rate of cemented carbides: (A) effect of rise in contact stress, (B) effect of additional impacts, and (C) effect of rise in contact stress and additional impacts. Results of alumina and wear resistant alloy Hardox 400 testing are given for comparison.

all the investigated materials. Under low stress abrasive conditions, the performance of alumina was comparable to cemented carbide, and the wear rate of Hardox 400 under low stress conditions was the highest. Maps presenting the effects of the stress, additional impacts and combined effect of increase in stress and application of the dynamic load were built (Fig. 4). The limits between regimes differ from map to

map and are shown below the maps to facilitate the tracking of the effects of the binder content and hard particle size. Hardox 400 suffered less from the increased stress level than hardmetals. Alumina was extremely sensitive to the stress level, and suffered quite severely from impacts. Additional impacts led to reduced wear rates for the cemented carbide with the lowest binder content. The coarse-grained

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cemented carbides suffered less from impacts than the fine-grained or the medium-grained ones. The intensity of carbide grains fracturing increased from low stress abrasive to medium stress abrasive, and also in medium stress abrasive testing with impacts (Fig. 5). The grains which experienced low stress abrasion maintained their integrity with only single transgranular cracks, characterised as a high-cycle wear mechanism (Fig. 5B). The addition of impacts intensifies cracking; all grains fractured into fine fragments (Figs. 5C and F). The depth of the affected zone (mechanically mixed layer and compacted layer) was close to 10 mm for the coarse-grained cemented carbides (size of one carbide grain, Fig. 5F). The formation of the cracks parallel to the surface (subsurface cracking) indicated that the energy of the wear process was sufficient to cause removal of much of the surface material, due to the low-cycle wear mechanism (Fig. 5F). Significantly lower damage was observed for the medium load abrasion without impact (Fig. 5E). The

cemented carbide with medium size WC grains experienced mostly shifting, gradual wear, and removal of single carbides without developing macro cracks under the surface layer (Fig. 5D).

4. Discussion In order to achieve the maximum abrasion resistance it recommended to use cemented carbides with 3–13 wt% of cobalt; for mining, the binder content should be from 6–12 wt% [65]. The medium-grained (2–6 mm) cemented carbides with 6–15 wt% cobalt binder content are suitable for percussive mining tools, mining and civil engineering tools, for masonry and stone cutting tools [9]. The medium and coarse cemented carbides (2–20 mm) with 6–15 wt% binder content are introduced as suitable for oil and gas drilling, mineral and ground engineering tools [10]. Grades with high binder

Fig. 5. SEM images of cemented carbides. Backscattered electron (BE) and secondary electron (SE) images.

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content (10–25 wt% Co; 0.5–3.0 mm grain size) were expected to perform well as metal cutting and cold-forming tools [9]. The maximum resistance in impact conditions is provided by hardmetals with Co binder content from 15–25 wt% [65]. According to Figs. 3 and 4, the cemented carbides with the medium grain size tungsten carbide (0.5–2.0 mm after sintering) and 6–8 wt% of the cobalt binder have the best wear resistance in combined impact-abrasive conditions. This is in a good agreement with the data available in the literature [9,10,65], indicating that the laboratory test conditions were capable of mimicking the real conditions and provide similar wear mechanisms. The hardmetals intended for the combined impact and abrasive wear should have lower binder content than those designed for impact only (to resist embedding the products of wear process), and higher binder content than those intended for pure abrasive processes (to provide sufficient fracture toughness). In reference [23] it is also noticed optimum level for fracture toughness (binder content) that enables the maximum wear resistance against abrasion. In case of hardmetals with excessively high Co content a mechanical mixture developed between the grains and penetrating sufficiently deep is not capable of supporting these grains that leads to their breakage (Figs. 5 and 6). In addition, ceramic grains may experience overheating and thermal cracking due to low heat dissipation caused by the surrounding mechanically mixed phases. The cyclic formation of protective mechanically mixed layer (MML) at the top of carbides enables improved wear resistance of hardmetals. Fracturing the carbides below this layer (due to impacts) weakens the bonding, which leads to the removal of the protective layer. After that, the MML starts to grow again. Hardmetals with medium carbide size provide the better ability for attachment and sufficient resistance of MML against the shear stresses (introduced by the abrasive process) by mechanical interlocking (Fig. 5F and Fig. 6). The thickness of the MML and the compacted layer underneath the MML does not exceed a size of one and two WC carbide grains, respectively. The thickness of the affected zone (mechanically mixed and compacted layers) is higher for the combined abrasion

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and impacts conditions (Fig. 5E and F) due to intensive squeezing (extrusion) of the binder metal and development of a sub-surface zone with the formation of rigid contacts, which later lead to the cracking of the WC grains. If the energy of the impact is increased, then it is possible to assume that coarse-grained hardmetals with higher toughness, high binder content (8 wt% of Co) will have the highest wear resistance (Fig. 4B), since they suffer less from impacts.

5. Conclusions 1. A method and device for the combined abrasive-impact wear testing of the cemented carbides and other materials was developed. 2. Maps showing the performance of the cemented carbides in a low stress abrasive, a medium stress abrasive and a combined medium stress abrasive with impact conditions were built. Maps assessing the effects of the stress state, the addition of dynamic loading (impacts), and the combined effect of increased stress and addition of dynamic loading were also provided. 3. Cemented carbides with 0.5–2.0 mm WC and 6–8 wt% cobalt binder content had the highest resistance against combined abrasion and impacts. Presumably, cemented carbides with larger grain sizes and higher binder contents will provide the lowest wear rate, if the impact energies are higher. 4. The performance of cemented carbides in the combined abrasive and impacts conditions is to a great extent governed by the binder content and the particle size. The cemented carbide with sufficient binder content to provide ductility, while hindering the embedment of abradant fragments between the WC grains is favourable. Medium size grains are required to provide attachment of the protective mechanically mixed layer (MML) through mechanical locking. 5. The thickness of the mechanically mixed layer (MML) and the compacted layer underneath the MML does not exceed a size of one and two WC carbide grains, respectively.

Fig. 6. Features of cemented carbide surface and subsurface layer transformation under combined abrasion and impacts.

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6. The timer of the impact generating device allows smart testing. Scheduled impacting during abrasion enables to simulate scenarios existing in the specific applications.

Acknowledgements This work was supported by Estonian Ministry of Education and Research (IUT 19-29) and by Estonian Science Foundation (grant 8850). The authors would like to acknowledge the financial support of European Commission for the project NeTTUN, from the Seventh Framework Programme for Research, Technological Development and Demonstration (FP7 2007-2013) under Grant agreement 280712. The authors wish to thank M. Viljus from the Centre for Materials Research of Tallinn University of Technology for help with sample analysis. References [1] K.J.A. Brookes, World Directory and Handbook of Hardmetals and Hard Materials, International Carbide Data, UK, 1996. [2] C.G. Goetzel, Cermets, ninth ed., ASM Metals Handbook, Vol. 7, ASM, Metal Park, Ohio (1984) 798–815. [3] G.S. Upadhyaya, Cemented Tungsten Carbides, Production, Properties and Testing, Noyes Publications, USA, 1998. [4] V.I. Tret’yakov, The basics of Q5 metal science and production technology of sintered hard metals, Metallurgiya, Moscow, 1976 [in Russian]. [5] I. Hussainova, M. Antonov, A Zikin, Erosive wear of advanced composites based on WC, Tribol. Int. 46 (2012) 254–260. [6] I. Hussainova, M. Antonov, Assessment of cermets performance in erosive media, Int. J. Mater. Prod. Technol. 28 (2007) 361–376. [7] I. Hussainova, I. Jasiuk, M. Sardela, M. Antonov, Micromechanical properties and erosive wear performance of chromium carbide based cermets, Wear 267 (2009) 152–159. [8] I. Hussainova, M. Antonov, N. Voltsihhin, J. Kübarsepp, Wear behavior of Cofree hardmetals doped by zirconia and produced by conventional PM and SPS routines, Wear 312 (2014) 83–90. [9] Understanding cemented carbide, Sandvik, H-9100a-ENG, 〈www.hardmater ials.sandvik.com〉. [10] Cemented carbide, Sandvik new developments and applications, Sandvik, H-9116 ENG, 2005, 〈www.hardmaterials.sandvik.com〉. [11] M. Heiniö (Ed.), Rock Excavation Handbook, Sandvik Tamrock Corp., Finland, 1999. [12] Kennametal specialty carbide products, A93-350(10)A5, 〈www.kennametal.com〉. [13] I. Hussainova, Microstructural design of ceramic-metal composites for tribological applications, Key Eng. Mater. 334-335 (2007) 125–128. [14] G. Nicolis, I. Prigogine, Self-Organization in Nonequilibrium Systems: From Dissipative Structures to Order Through Fluctuations, Wiley, USA, 1977. [15] B.I. Kostetskii, Structure and surface strength of materials in friction, Strength Mater. 13 (1981) 359–368. [16] A.A. Voevodin, J.S. Zabinski, Supertough wear-resistant coatings with ‘chameleon’ surface adaptation, Thin Solid Films 370 (2000) 223–231. [17] G.S. Fox-Rabinovich, I.S. Gershman, K. Yamamoto, A. Biksa, S.C. Veldhuis, B.D. Beake, A.I. Kovalev, Self-organization during friction in complex surface engineered tribosystems, Entropy 12 (2010) 275–288. [18] U. Beste, On the Nature of Cemented Carbide Wear in Rock Drilling Comprehensive Summaries of Uppsala Dissertations, Faculty of Science and Technology, Sweden, 2004. [19] M. Antonov, I. Hussainova, Cermets surface transformation under erosive and abrasive wear, Tribol. Int. 43 (2010) 1566–1575. [20] M. Antonov, I. Hussainova, J. Pirso, O. Volobueva, Assessment of mechanically mixed layer developed during high temperature erosion of cermets, Wear 263 (2007) 878–886. [21] M.G. Gee, A. Gant, B. Roebuck, Wear mechanisms in abrasion and erosion of WC/Co and related hardmetals, Wear 263 (2007) 137–147. [22] K.H. Zum Gahr, Sliding wear of ceramic–ceramic, ceramic–steel and steel– steel pairs in lubricated and unlubricated contact, Wear 133 (1989) 1–22. [23] K.H. Zum Gahr, Wear by hard particles, Tribol. Int. 31 (1998) 587–596. [24] J. Larsen-Basse, Binder extrusion in sliding wear of WC–Co alloys, Wear 105 (1985) 247–256. [25] M. Antonov, P. Kulu, F. Sergejev, I. Hussainova, R. Veinthal, New high frequency surface fatigue wear tester: design and first results, in: J. Kleemola, A. Lehtovaara (Eds.), Proceedings of the 13th Nordic Symposium in Tribology, Tampere University of Technology, 2008. [26] I. Konyashin, B. Ries, Wear damage of cemented carbides with different combinations of WC mean grain size and Co content. Part I: ASTM wear tests, Int. J. Refract. Met. Hard Mater. 46 (2014) 12–19. [27] I. Konyashin, B. Ries, D. Hlawatschek, Y. Zhuk, A. Mazilkin, B. Straumal, F. Dorn, D. Park, Wear-resistance and hardness: are they directly related for nanostructured hard materials? Int. J. Refract. Met. Hard Mater. (2014), http://dx.doi.org/10.1016/j. ijrmhm.2014.06.017.

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