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Abrasive wear behavior of TiCN cermets under water-based slurries with different abrasives
Tribology International 66 (2013) 35–43
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Abrasive wear behavior of TiCN cermets under water-based slurries with different abrasives Xiaoyong Ren a, Zhijian Peng a,n, Yuanbiao Hu a, Chengbiao Wang a, Zhiqiang Fu a, Wen Yue a, Longhao Qi b, Hezhuo Miao b a Key Laboratory on Deep GeoDrilling Technology of the Ministry of Land and Resources, School of Engineering and Technology, China University of Geosciences, Beijing 100083, P.R. China b State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, P.R. China
art ic l e i nf o
a b s t r a c t
Article history: Received 6 December 2012 Received in revised form 29 March 2013 Accepted 3 April 2013 Available online 17 April 2013
The wear behavior of TiCN cermets was investigated under water-based slurries with coarse angular abrasives of SiC, Al2O3 and SiO2, through a modified ASTM B611 wet-sand rubber-rimmed wheel test system. Under the same conditions, the wear rate increased with increasing abrasive hardness and mass fraction. With increasing sliding distance, under lower abrasive fraction the wear rate increased very slowly, but under higher abrasive fraction it initially increased rapidly, then became steady and even dropped down. Through observing the abraded sample surfaces by 3D white-light interfering surface profiler, the wear mechanism of TiCN cermets was proposed. & 2013 Elsevier Ltd. All rights reserved.
Keywords: TiCN cermets Three-body abrasion Surface analysis Wear modeling
1. Introduction Abrasive wear is a phenomenon in which the hard particles coming from the outside or protruding on the grinding surface skim over and/or plow through the friction surface, resulting in the migration of materials [1,2]. It is one of the primary wear types of materials, contributing almost 63% of the total cost of wear. Abrasive wear is usually classified into two forms: two-body abrasion and three-body abrasion, in which three-body abrasion is the main wear problem arising in agricultural and industrial equipments [3–6]. Much attention has been paid to the abrasive wear behavior of different structural materials and many factors can influence the abrasion of materials [1,7–15]. During abrasive wear, the abrasive particles pass through the surface of materials with a mixed movement patterns, which will possibly lead to different wear mechanisms. For example, the sliding particles would mainly cause micro-cutting and grain fracture when the attack angle of a particle was greater than the critical attack angle, while the rolling particles would mainly result in plastic deformation [7,8]. The test rig can also influence the wear rate and wear mechanisms of structural materials a lot in abrasive wear. For
n
Corresponding author. Tel.: +86 10 82320255; fax: +86 10 82322624. E-mail addresses: [email protected], [email protected]. cn (Z. Peng). 0301-679X/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.triboint.2013.04.002
instance, Gant and Gee [9,10] have investigated the difference of abrasive wear behavior of WC-Co under ASTM G65 and ASTM B611 test systems. In most cases, the test rig was designed and modified to imitate the actual working environment of the materials. Scientists have developed numerous testing systems [11–14] in which ASTM B611 steel wheel abrasion test system [11], specially designed for cemented carbides, has been specifically standardized and described as a suitable one for abrasive wear test. However, in some cases, specific test conditions need to be developed that can simulate the application conditions better than those the standard tests allow [10]. In addition, the influences of various abrasive particles on the wear rate and dominant wear mechanisms of structural materials have also been reported in many studies. According to Refs. [1,6], the hardness ratio (Ha/Hm) between the abrasive (Ha) and tested structural material (Hm) can reflect the influence of the abrasive's hardness on the wear rate and wear mechanism of the materials. Yamamoto et al. [15] have studied the influences of quartz and silicon carbide as abrasive on the wear behaviors of eight kinds of ceramic materials. Olsson et al. [16] have investigated the influence of the type of abrasive particles on the abrasive wear behavior of some structural ceramics. And it was also pointed out in Refs. [1,6] that the size of the abrasive particles could influence the severity of abrasive wear, while all other parameters were constant. Moreover, a strong correlation between the abrasive particle angularity and wear rate was described in Ref. [17] that angular abrasive particles will cause more wear damage than
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rounded or semi-angular particles does, especially for three-body abrasive wear, in which ‘spike parameter-quadratic fit’ (SPQ) is one of the parameters describing the abrasive particle angularity [17]. Titanium carbonitride cermets are important structural ceramics which have been widely applied in the field of metal cutting, geo-engineering and wear components, due to their high hardness, high wear resistance, and superior chemical and thermal stability [18–20]. Moreover, the lighter-weight and lower price of Ti(CN)-based cermets than that of WC-Co hardmetals also made Ti (CN)-based cermets promising materials to replace WC-Co hardmetals for many applications [21]. However, although the abrasive wear behaviors of WC-Co hardmetals were investigated in lots of publications [9,10,22–24], those of TiCN-based cermets have been not very clear so far, especially when they are applied under abrasive wear conditions of different abrasives and abrasive concentrations in slurries, which are universal in geo-engineering applications. In this work, using a modified ASTM B611 wet sand rubber rimmed wheel test system, the abrasive wear behavior of commercially available TiCN cermets (FD22) was investigated in detail under water-based slurries (drilling fluids) with three kinds of coarse angular abrasives, SiC, Al2O3 and SiO2. The wear loss and wear rate of TiCN cermets under different mass fractions of abrasive in water-based slurries were studied. And through the observations of the worn surfaces by three dimensional (3D) white-light interfering surface profiler, the dominate wear mechanisms of TiCN cermets under such working conditions were proposed. The obtained results may be instructive to many similar applications, such as the substrate in slurry pumps, the liner-piston rods of drilling machines, turbine blades, propellers of ships and so on.
2. Experiment details 2.1. Test system The applied test system in this work is a modified ASTM B611 wet sand rubber rimmed wheel test system (model: MLS-225), which has been reported in our previous work about the abrasive wear investigation on WC-Co hardmetals [24]. In this test system, the conventionally applied steel wheel is replaced by a rubber (vulcanized chlorinated butyl rubber) rimmed one. The reason for such modification is that although ASTM B611 steel wheel abrasion test system has been described as a suitable experimental technique in characterizing the abrasion resistance of cermets and even specifically standardized, it has some insufficiencies when specific application conditions have to be simulated [24]. For example, in order to simulate the working conditions of aiguilles in drilling fluid, a series of slurries with different mass fractions of abrasives should be used.
In such case, the test results would be seriously affected by or even covered in the influence of the steel wheel when slurries of much low mass fraction of abrasives were used. And this phenomenon could not be ignored even if much harder abrasives were used. Such shortcoming can be overcome by using the rubber rimmed steel wheel. The elasticity of the rubber wheel will make the abrasive grits feed into the very small space between the wheel and the samples easily. Moreover, the size of the abrasive particles would influence the severity of abrasive wear while all other parameters were kept constant [1,6]. The use of rubber rimmed steel wheel could postpone the crushing of the abrasive grits during tests, especially for long sliding distance wear experiments. 2.2. Materials The test samples were made from TiCN cermets (FD22), which were commercially bought from Beijing Unisplendor Founder High-Tech Ceramics Co. Ltd., China. The dimension of the specimens is about 25.5 mm 57 mm 6 mm. Fig. 1 shows the microstructure of a typical TiCN cermet sample through micrographs on its fresh fracture surface by secondary electron scanning electron microscopy (SEM) and on its polished surface by backscattered electron one, revealing that the samples are pyknotic with a quite uniform phase distribution, but the TiCN grain size in the samples is not uniform, varying from 0.5 to 2 μm. The hardness of the applied TiCN cermets (Hm) is about 2200 HV. In order to exclude the influence of residual stress from the mechanical machining of the samples, all the samples were annealed before testing. Three kinds of coarse angular grits, carborundum (SiC, green), corundum (Al2O3, white) and silica (SiO2, white), were used as abrasive in this study. Typical SEM micrographs of the three kinds of abrasives are shown in Fig. 2. From this figure, it can be seen that all the abrasives are coarsely angular and the particles size of carborundum grits is smaller than those of corundum and silica grits. The measured particle size of the abrasives, calculated spike parameter-quadratic (SPQ) value [24], hardness of the abrasives (Ha) and the hardness ratio of the abrasive to TiCN cermets (Ha/Hm) are listed in Table 1. The slurries used in the test consisted of two basic components, drilling fluid (pH¼7) and abrasive grits. The recipes of the slurries used in the test are listed in Table 2. The drilling fluid contained 1 wt% height-viscosity carboxyl methyl cellulose (HV-CMC), 1 wt% xanthan gum (X.G.) and 5 wt% bentonite which were all calculated by weight to water so as to make the drilling fluid possess the same dispersion capability to abrasives. In each batch of slurry, the total amount of the drilling fluid was kept constant, 1070 g, but the mass fractions of the abrasives to water were designed as 5%, 10%, 20%, 30% and 40%, respectively.
Fig. 1. Typical secondary electron SEM micrograph on the fresh fracture surface (a) and backscattered electron SEM micrograph on the polished surface (b) of the applied TiCN cermets (FD22), revealing a wide distribution of TiCN grain size but rather uniform distribution of phases.
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Fig. 2. Typical SEM micrographs of the applied abrasives: (a) SiC, (b) Al2O3, and (c) SiO2.
Table 1 Properties of the abrasives used in the test. Abrasives Particle size distribution (μm)
SiC Al2O3 SiO2
d10
d50
d90
320 383 388
446 600 581
622 953 888
SPQ
Hardness (HV30)
Hardness ratio Ha/Hm
∼0.7140 2900–3000 1.32–1.36 ∼0.8100 2000–2100 0.91–0.95 ∼0.5610 1000–1100 0.45–0.46
Table 2 Compositions of the slurries with different mass fractions of abrasives. Mass fraction of sands/%
5%
10%
20%
30%
40%
Sand/g HV-CMC/g X.G./g Bentonite/g Water/ml
52.6 10.0 10.0 50.0 1000
111.1 10.0 10.0 50.0 1000
250.0 10.0 10.0 50.0 1000
428.6 10.0 10.0 50.0 1000
666.7 10.0 10.0 50.0 1000
2.3. Experimental procedures In order to investigate the wear behaviors of TiCN cermets under drilling conditions, special experimental processes and parameters were designed and adopted in this work. The selected Shore hardness of the rimming rubber on the steel wheel was 70 degree and the circumferential length of the wheel was 0.566 m. During testing, the rotation speed and load were fixed to 498 RPM and 225 N. For each sample, a 1000 r pre-grinding was carried out to avoid the differentials due to the roughness of the machined surface of the cermet samples and to stir the slurry evenly at the same time. After the pre-grinding, the samples were weighed for the basic sample masses. Then the samples were weighed after every 4000 r grinding for calculating the wear loss, and this procedure was carried out for 11 times. After that, the samples
were weighed after every 8000 r grinding, and this procedure was performed for 8 times. It should be emphasized that before and after each wear test, the specimens were cleaned in absolute ethyl alcohol and dried before characterization. And the weighing apparatus was an analytical balance with an accuracy of 0.0001 g. 2.4. Materials characterization The wear loss of the specimens is defined as the volume loss calculated from the measured mass loss using an analytical balance, and the wear rate of the specimens is the wear loss per unit length of sliding distance. The sliding distance is the linear displacement of the wheel rim in this work. In order to reveal the wear mechanisms of the cermets, the abraded surfaces of the cermets were examined by a three dimensional (3D) white-light interfering surface profiler (model: Micro XAM-3D). In addition, the micrographs of typical TiCN cermet sample mentioned above was obtained by secondary electron SEM (model: SSX-550) on its fracture surface and by backscattered electron SEM on its polished surface (model: JSM 7001F). The micrographs of the abrasives presented above were taken by secondary electron SEM (model: SSX-550).
3. Results 3.1. Wear loss vs. sliding distance With the data collected from the samples under conditions with different abrasives, the curves of wear loss of the TiCN cermets vs. sliding distance were plotted, which are shown in Fig. 3. As seen from this figure, with the same abrasive and sliding distance the wear loss of the samples increased with the increase in mass fraction of the abrasives in the slurries; and with the same abrasive and abrasive mass fraction in the slurries, the wear loss increased with the increase in sliding distance. With the same
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3.2. Wear rate vs. sliding distance Fig. 4 illustrates the variation of wear rate on sliding distance on the basis of the collected wear loss data. From this figure it can be seen that with the same sliding distance and abrasive mass fraction in slurries, the samples presented the highest wear rate when SiC was used as abrasive and the lowest when SiO2 was used. With the same abrasive, the wear rate increased with the increase in abrasive mass fraction in the slurries.
Fig. 3. Wear loss vs. sliding distance under the conditions with different abrasives and abrasive mass fractions in the slurries: (a) SiC, (b) Al2O3 and (c) SiO2.
sliding distance and abrasive mass fraction, the samples presented the heaviest wear loss when SiC was used as abrasive, and the lightest when SiO2 was used. Moreover, under the same test conditions, the wear loss of TiCN cermets increased slowly when the abrasive mass fraction in slurries was low, and it increased rapidly when the abrasive mass fraction in slurries was high.
Fig. 4. Wear rate vs. sliding distance under the conditions with different abrasives and abrasive mass fractions in the slurries: (a) SiC, (b) Al2O3 and (c) SiO2.
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However, under the applied test conditions in this work, the variation of wear rate on sliding distance is not a simple increase or decrease when the other conditions were kept constant. When the abrasive mass fraction in the slurry was relatively low (for SiC about below 10 wt%, Al2O3 below 20 wt% and SiO2 below 30 wt%), the wear rate of the cermets increased very slowly with the increase in sliding distance. However, when the abrasive mass fraction in the slurry was high (for SiC about higher than 10 wt%, Al2O3 higher than 20 wt% and SiO2 higher than 30 wt%), the wear rate increased rapidly at the beginning, then became steady and even dropped slightly in the last few kilometers with increasing sliding distance in the given range. 3.3. Micro-morphology of the abraded surfaces In this work, the abraded surface of the cermet samples was examined through section to section so as to describe their
Fig. 5. The schematic diagram of the three areas on the abraded surface of the sample [24].
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difference in morphology of different areas just as done in Ref. [24]. The abraded surface was partitioned into starting area (s-area), middle area (m-area) and ending area (e-area) as shown in Fig. 5. Through the observations of 3D white-light interfering surface profiler, it was found that the micro-morphology of the abraded surface of each sample changed with not only the abrasive sort and mass fraction in the slurry but also the area (section) on the abraded surface. Fig. 6 shows typical surface micro-morphologies of the abraded surfaces from 3D white-light interfering surface profiler while SiC was used as abrasive and different abrasive mass fractions in the slurries were used. Several wear mechanisms, such as plastic deformation, micro-cutting, grooves and grains fracture, were observed on the abraded surface of TiCN cermet samples. But only one or two of them played the dominant role and the dominant mechanisms changed with the abrasive mass fraction in the slurries. When the SiC abrasive mass fraction in the slurry was no more than 5 wt%, micro-cuttings played the dominant role in wear which could be seen in Fig. 6a–c. On the ending area, a few of grain fractures appeared as shown in Fig. 6c. When the SiC abrasive mass fraction was about 20 wt%, the main wear mechanisms were plastic deformation and grooves, which could be seen in Fig. 6d–f. Scratching could be observed on the ending area as shown in Fig. 6f, which might be the result from grain fracture. While the SiC abrasive mass fraction increased up to 40 wt%, plastic deformation and scratching became even more significant as shown in Fig. 6h–i. The material removal was very serious even to form some pits on the abraded surface as shown in Fig. 6i. Fig. 7 presents typical surface micro-morphologies of the abraded surfaces from 3D white-light interfering surface profiler
Fig. 6. Typical surface morphologies of the samples from 3D white-light interfering surface profiler while different mass fractions of SiC abrasive in the slurries were applied: (a–c) 5 wt%, (d–f) 20 wt% and (g–i) 40 wt%, in which (a), (d) and (g) belong to s-area, (b), (e) and (h) to m-area, and (c), (f) and (i) to e-area.
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Fig. 7. Typical surface morphologies of the samples from 3D white-light interfering surface profiler while different mass fractions of Al2O3 abrasive in the slurries were applied: (a–c) 5 wt%, (d–f) 20 wt% and (g–i) 40 wt%, in which (a), (d) and (g) belong to s-area, (b), (e) and (h) to m-area, and (c), (f) and (i) to e-area.
while Al2O3 was used as abrasive and different abrasive mass fractions in the slurries were used. In this case, the material removal of the abraded surface was less serious compared with the situation when SiC was used as abrasive. When the Al2O3 abrasive mass fraction in the slurry was about 5 wt%, the main wear mechanisms were the extrusion of binder phase and slight plastic deformation on the abraded surface, which could be seen in Fig. 7a–c. While the Al2O3 abrasive mass fraction increased to 20 wt%, plastic deformation with shallow grooves became more and more obvious as shown in Fig. 7d–f. When the Al2O3 abrasive mass fraction increased up to 40 wt%, distinct plastic deformation could be observed as shown in Fig. 7h–i. The micro-morphologies of different abraded areas of the samples presented very little difference when the Al2O3 abrasive mass fraction in slurries was identical. Fig. 8 displays typical surface micro-morphologies of the abraded surfaces from 3D white-light interfering surface profiler while SiO2 was used as abrasive and different abrasive mass fractions in the slurries were used. It could be seen that the main wear mechanism was plastic deformation and the material removal of the abraded surface was very slight from this figure. When the SiO2 abrasive mass fraction in the slurry was no more than 5 wt%, plastic deformation was extraordinarily slight with slight binder removal as shown in Fig. 8a–c. As the SiO2 abrasive mass fraction increased, plastic deformation was intensified and the extrusion of binder phase became obvious. When the SiO2 abrasive mass fraction increased up to 40 wt%, a bit of grooves could be seen as shown in Fig. 8h and i.
4. Discussion 4.1. Wear loss of the samples In consideration of the high hardness of the TiCN cermets, in order to obtain a significant information of the wear loss of TiCN cermets, the highest load in this test system (225N), and more than 60 km sliding distance, which is much longer than that of any other previous work, was applied in this work. The Archard's empirical formula as shown in the following equation is usually used to predict the abrasive wear loss of the materials [25] V ¼ k1 PLH −1
ð1Þ
where V is the volume of materials removed by wear, k1 a dimensionless coefficient, P the applied normal load, L the sliding distance and H the Vickers hardness of the applied materials. As seen from Eq. (1), the wear loss of the materials is proportional to the applied normal load and sliding distance. Therefore, it is easily understandable that with the same abrasive and abrasive mass fraction in the slurries, the wear loss increased with the increase in sliding distance, as shown in Fig. 3. According to Refs. [1,6], the hardness ratio (Ha/Hm) between the abrasive and the worn materials impacts the wear loss a lot in abrasive wear. The wear loss increased with the increase in the hardness ratio. The hardness ratio between SiC and TiCN cermets was the highest and the one between SiO2 and TiCN cermets was the lowest among the abrasives used in this work, as shown in Table 1. Therefore, the samples with SiC as abrasive presented the
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Fig. 8. Typical surface morphologies of the samples from 3D white-light interfering surface profiler while different mass fractions of SiO2 abrasive in the slurries were applied: (a–c) 5 wt%, (d–f) 20 wt% and (g–i) 40 wt%, in which (a), (d) and (g) belong to s-area, (b), (e) and (h) to m-area, and (c), (f) and (i) to e-area.
highest wear loss when the other wear test parameters were kept constant, which was almost 5 times the wear loss when Al2O3 was used as abrasive, and 20 times that when SiO2 was used. As the abrasive mass fraction increased in the slurries, the number of abrasive particles sliding across the abraded surface increased, resulting in tighter and more intensive contacts between the abrasive and abraded surface. Therefore, the material removal opportunity increased, and the wear loss of the samples increased with the increase in abrasive mass fraction in the slurries when the abrasive and sliding distance were the same.
4.2. Wear rate of the samples The wear rate is defined as the wear loss per sliding distance in this work. As discussed above, the wear loss of TiCN cermets increased with the increase in the abrasive mass fraction in the slurries and the hardness of the abrasives. Therefore, the wear rate increased with the increase in the abrasive mass fraction on the whole when the same abrasive was applied. With the same abrasive mass fraction, the relationship of wear rate with abrasive was the wear rate with SiC abrasive4 that with Al2O3 4that with SiO2, which is in accordance with the hardness decreasing trend, as shown in Fig. 4. The high hardness of the tested TiCN cermets might be the main cause leading to the very slow increase in wear rate with the increase in sliding distance, when the abrasive mass fraction in the slurries was low. Due to the differences in hardness, particle size and SPQ of the three abrasives, such phenomena happened in this work when the mass fraction of carborundum is lower than
about 10 wt%, that of corundum lower than 20 wt%, and that of silica lower than 30 wt%. When the abrasive mass fraction in the slurry was high, because there was an adaptive process during the wear process, the wear rate of TiCN cermets initially increased very rapidly, then became steady and even dropped down slightly in the last few kilometers with the increase in sliding distance in the given range. At the beginning during the adaptive process, micro-cutting and binder removal were the main wear mechanisms. The microcutting may form the channel to enlarge the contact area between the abrasive grits and the abraded surface [26]. Meanwhile, as more and more binder was removed, more TiCN grain fracture might happen. Therefore, the wear rate increased rapidly during this period. However, as the sliding distance increased, the crushing of the abrasive occurred and some of the angular abrasive might be rounded off during the wear process, which would contribute to the decrease in wear rate, because it is known [1,9] that the severity of wear can be correlated positively with the size of the abrasive while all the other parameters are kept constant. Meanwhile, the re-embedment of the removed fracture fragment of TiCN grains into the binder phase might also happen, which would strengthen the abraded surfaces and reduce the wear rate [9,10,26]. Therefore, the wear rate of the tested TiCN cermets might become steady, and even drop down slightly with the increase in the sliding distance during this period. 4.3. Wear mechanisms of the samples Since the hardness of SiC abrasive (about 2900–3000 HV30) is higher than that of TiCN cermets FD22 (about 2200 HV30) and the
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hardness ratio (Ha/Hm) between the abrasive and the abraded surface is 1.32–1.36 (higher than 1.2), so the abrasive could penetrate into the abraded surface easily [1,6]. When the SiC abrasive mass fraction was 5 wt%, the quantity of SiC abrasive between the rubber wheel and the abraded surface was very little. Under the high load applied in this work, the abrasive grits would slide across the abraded surface rather than roll across it. Therefore, the major wear mechanism was micro-cutting to form channel in this case [7,8,26], as seen in Fig. 6a–c. However, as the SiC abrasive mass fraction increased, more and more SiC grits could feed into the contact surface. Since the abrasive grits crowded in the narrow confine between the rubber wheel and the abraded sample surface, the grits would roll and slide preferentially along the existing grooves at high loads [26]. Thereby, plastic deformation and plowing grooves became the main wear mechanisms as shown in Fig. 6, and the grooves would be deepened and widened during the proceeding wear process. Moreover, it is believed that TiCN grain fracture occurred in association with the plastic deformation, and the repeated wear action might expand the fractures and even form some pits on the abraded surface as shown in Fig. 6i. Hence, the wear loss and wear rate both increased as the SiC abrasive mass fraction in the slurry increased as seen in Figs. 3 and 4. Compared with SiC abrasive, the hardness of the applied Al2O3 abrasive (about 2000–2100 HV30) was very close to the hardness of TiCN cermet samples and even a little lower, and the hardness ratio (Ha/Hm) is 0.91–0.95, indicating that the Al2O3 abrasive grits are difficult to penetrate into TiCN grains and damage the framework of TiCN cermets. However, because the hardness of the abrasive was higher than that of the binder phase in the TiCN cermets, the applied abrasive grits could plastically deform the softer binder phase between the TiCN grains. As the abrasive mass fraction in the slurries increased, the binder removal level was enhanced and the preferential channel of the abrasive grits would cause the plastic deformation of the surface, resulting in the formation of shallow grooves with material pile up at the groove edges as could be seen in Fig. 7. The hardness of the applied SiO2 abrasive (about 1000–1100 HV30) was only about half of the hardness of TiCN cermets used in this work. That means that the SiO2 abrasive grits are even more difficult to penetrate into TiCN grains and damage the framework of TiCN cermets. So, the main wear mechanism in this case was the extrusion and removal of binder phase in the cermets. Compared with the case when Al2O3 abrasive was used, the extent of binder removal was thus very slight as can be seen in Fig. 8. This could also be proved by the slight wear loss and wear rate when SiO2 abrasive was used, as shown in Figs. 3 and 4c As the abrasive mass fraction in the slurries increased, the binder removal level increased and plastic deformation became more obvious as shown in Fig. 8. Moreover, the grooves on the abraded surfaces would be gradually deepened and widened from s-area to e-area as could be seen in Figs. 6–8, demonstrating that the abrasive grits moved preferentially along the existing grooves, thereby deepening them. Such ‘channeling’ effect has been reported elsewhere by Gant et al. in Ref. [26]. In addition, when the abrasive grits feed into the abraded surface, they suffered from a tangential force, which was caused by the revolution of the rubber wheel. From the analysis in our previous work [24], it was known that the abrasive grits suffered from different comprehensive forces at s-area, m-area and e-area. According to the Archard's law [25] and previous works on the abrasive wear of cermets [9,10,24,26], it is reasonable that different areas of the abraded surface displayed different micro-morphologies on the same samples as shown in Figs. 6–8.
5. Conclusions The wear behavior of TiCN cermets was investigated in detail under water-based slurries with three kinds of coarse angular abrasives, SiC, Al2O3 and SiO2, through a modified ASTM B611 wet sand rubber rimmed wheel test system. The conclusions are summarized as following. (1) The wear loss of TiCN cermets increased with the increase in sliding distance, the abrasive mass fraction in slurries and the hardness of the abrasive. (2) The wear rate of TiCN cermets increased with the increase in the abrasive mass fraction in slurries and hardness of the abrasive. With the increase in sliding distance, when the abrasive mass fraction was low (for SiC about lower than 10 wt%, Al2O3 lower than 20 wt% and SiO2 lower than 30 wt%), the wear rate increased very slow; but when it was higher than that, the wear rate increased rapidly at the beginning, then became steady and even dropped down slightly in the last few kilometers in the given sliding distance. (3) The abrasive wear mechanisms of TiCN cermets were mainly depending on the relative hardness between the cermets and abrasives. With SiC abrasive, micro-cutting, grain fracture and plastic deformation with grooves were the dominant wear mechanisms. When Al2O3 was used as abrasive, plastic deformation and plowing grooves were the main wear mechanisms. With SiO2 abrasive, extrusion and removal of binder phase, and slight plastic deformation with grooves were the dominant wear mechanisms. The change of abrasive mass fraction in the slurries had no obvious influence on the sort of wear mechanisms, just affecting the extent of the appeared wear types.
Acknowledgments This work was supported by Grand Survey on Land and Nature Sources of China sponsored by China Geological Survey (Grant no. 1212010916026), Ph.D. Programs Foundation by Ministry of Education of China (Grant no. 20100022110002), Excellent Adviser Foundation in China University of Geosciences from the Fundamental Research Funds for the Central Universities, and Key Laboratory on Deep GeoDrilling Technology of the Ministry of Land and Resources (NLSD201222). References [1] Hutchings IM. Tribology-friction and wear of engineering materials. London: Edward Arnold; 77–240. [2] Avery HS. The measurement of wear resistance. Wear 1961;4:427–49. [3] Burwell JT. Survey of possible wear mechanisms. Wear 1957;1:119–41. [4] Neale MJ, Gee M. Guide to wear problems and testing for industry. New York: William Andrew Publishing; 2001. [5] Harsha AP, Tewari US. Two-body and three-body abrasive wear behaviour of polyaryletherketone composites. Polymer Testing 2003;22:403–18. [6] Pirso J, Viljus M, Juhani K, et al. Three-body abrasive wear of TiC–NiMo cermets. Tribology International 2010;43:340–6. [7] Fang L, Kong XL, Zhou QD. A wear tester capable of monitoring and evaluating the movement pattern of abrasive particles in three-body abrasion. Wear 1992;159:115–20. [8] Fang L, Kong XL, Su JY, Zhou QD. Movement patterns of abrasive particles in three-body abrasion. Wear 1993;162-164:782–9. [9] Gant AJ, Gee MG. Abrasion of tungsten carbide hardmetals using hard counterfaces. International Journal of Refractory Metals and Hard Materials 2006;24:189–98. [10] Gee MG, Gant A, Roebuck B. Wear mechanisms in abrasion and erosion of WC-Co. Wear 2007;263:137–48. [11] ASTM B611-85. Standard test method for the abrasive wear resistance of cemented carbides. Annual Book of ASTM Standards. vol. 02.05; 1995. p. 326–7.
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[12] ASTM G65-94. Standard test for measuring abrasion using the dry sand/rubber wheel apparatus. Annual Book of ASTM Standards, vol. 03.02; 1996. p. 245–56. [13] ASTM G65. Standard test method for measuring abrasion using the dry sand/ rubber wheel apparatus, ASTM International; 2004. [14] ASTM G76-95. Standard test for measuring abrasion using the dry sand/rubber wheel apparatus. Annual Book of ASTM Standards, vol.03.02; 1996. [15] Yamamoto T, Olsson M, Hongmark S. Three-body abrasive wear of ceremic materials. Wear 1994;174:21–31. [16] Olsson M, Kahlman L, Nyberg B. Abrasive wear of structural ceramics. American Ceramic Society Bulletin 1995;74:48–52. [17] Stachowiak GW. Particle angularity and its relationship to abrasive and erosive wear. Wear 2000;241:214–9. [18] Moskowitz D, Humenik M. Cemented titanium carbide cutting tools. Modern Developments in Powder Metallurgy 1966;3:83–94. [19] Zhang S. Titanium carbonitride-based cermets: processes and properties. Materials Science Engineering A 1993;163:141–8.
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[20] Meng JH, Lu JJ. Tribological behavior of TiCN-based cermets at elevated temperatures. Materials Science and Engineering A 2006;418:68–76. [21] Jung J, Kang S. Effect of ultra-fine powders on the microstructure of Ti(CN)– xWC–Ni cermets. Acta Materialia 2004;52:1379–86. [22] Basse JL. Binder extrusion of sliding wear of WC-Co alloys. Wear 1985;105:247–56. [23] Jia K, Fischer TE. Sliding wear of conventional and nanostructured cemented carbides. Wear 1997;203–204:310–8. [24] Rong HY, Peng ZJ, Hu YB, et al. Dependence of wear behaviors of hardmetal YG8B on coarse abrasive types and their slurry concentrations. Wear 2011;271:1156–65. [25] Archard JF. Wear theory and mechanisms, Wear control handbook. New York: American Society of Mechanical Engineers; 35–80. [26] Gant AJ, Gee MG. Wear of tungsten carbide–cobalt hardmetals and hot isostatically pressed high speed steels under dry abrasive conditions. Wear 2001;251:908–15.
Contents lists available at SciVerse ScienceDirect
Tribology International journal homepage: www.elsevier.com/locate/triboint
Abrasive wear behavior of TiCN cermets under water-based slurries with different abrasives Xiaoyong Ren a, Zhijian Peng a,n, Yuanbiao Hu a, Chengbiao Wang a, Zhiqiang Fu a, Wen Yue a, Longhao Qi b, Hezhuo Miao b a Key Laboratory on Deep GeoDrilling Technology of the Ministry of Land and Resources, School of Engineering and Technology, China University of Geosciences, Beijing 100083, P.R. China b State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, P.R. China
art ic l e i nf o
a b s t r a c t
Article history: Received 6 December 2012 Received in revised form 29 March 2013 Accepted 3 April 2013 Available online 17 April 2013
The wear behavior of TiCN cermets was investigated under water-based slurries with coarse angular abrasives of SiC, Al2O3 and SiO2, through a modified ASTM B611 wet-sand rubber-rimmed wheel test system. Under the same conditions, the wear rate increased with increasing abrasive hardness and mass fraction. With increasing sliding distance, under lower abrasive fraction the wear rate increased very slowly, but under higher abrasive fraction it initially increased rapidly, then became steady and even dropped down. Through observing the abraded sample surfaces by 3D white-light interfering surface profiler, the wear mechanism of TiCN cermets was proposed. & 2013 Elsevier Ltd. All rights reserved.
Keywords: TiCN cermets Three-body abrasion Surface analysis Wear modeling
1. Introduction Abrasive wear is a phenomenon in which the hard particles coming from the outside or protruding on the grinding surface skim over and/or plow through the friction surface, resulting in the migration of materials [1,2]. It is one of the primary wear types of materials, contributing almost 63% of the total cost of wear. Abrasive wear is usually classified into two forms: two-body abrasion and three-body abrasion, in which three-body abrasion is the main wear problem arising in agricultural and industrial equipments [3–6]. Much attention has been paid to the abrasive wear behavior of different structural materials and many factors can influence the abrasion of materials [1,7–15]. During abrasive wear, the abrasive particles pass through the surface of materials with a mixed movement patterns, which will possibly lead to different wear mechanisms. For example, the sliding particles would mainly cause micro-cutting and grain fracture when the attack angle of a particle was greater than the critical attack angle, while the rolling particles would mainly result in plastic deformation [7,8]. The test rig can also influence the wear rate and wear mechanisms of structural materials a lot in abrasive wear. For
n
Corresponding author. Tel.: +86 10 82320255; fax: +86 10 82322624. E-mail addresses: [email protected], [email protected]. cn (Z. Peng). 0301-679X/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.triboint.2013.04.002
instance, Gant and Gee [9,10] have investigated the difference of abrasive wear behavior of WC-Co under ASTM G65 and ASTM B611 test systems. In most cases, the test rig was designed and modified to imitate the actual working environment of the materials. Scientists have developed numerous testing systems [11–14] in which ASTM B611 steel wheel abrasion test system [11], specially designed for cemented carbides, has been specifically standardized and described as a suitable one for abrasive wear test. However, in some cases, specific test conditions need to be developed that can simulate the application conditions better than those the standard tests allow [10]. In addition, the influences of various abrasive particles on the wear rate and dominant wear mechanisms of structural materials have also been reported in many studies. According to Refs. [1,6], the hardness ratio (Ha/Hm) between the abrasive (Ha) and tested structural material (Hm) can reflect the influence of the abrasive's hardness on the wear rate and wear mechanism of the materials. Yamamoto et al. [15] have studied the influences of quartz and silicon carbide as abrasive on the wear behaviors of eight kinds of ceramic materials. Olsson et al. [16] have investigated the influence of the type of abrasive particles on the abrasive wear behavior of some structural ceramics. And it was also pointed out in Refs. [1,6] that the size of the abrasive particles could influence the severity of abrasive wear, while all other parameters were constant. Moreover, a strong correlation between the abrasive particle angularity and wear rate was described in Ref. [17] that angular abrasive particles will cause more wear damage than
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rounded or semi-angular particles does, especially for three-body abrasive wear, in which ‘spike parameter-quadratic fit’ (SPQ) is one of the parameters describing the abrasive particle angularity [17]. Titanium carbonitride cermets are important structural ceramics which have been widely applied in the field of metal cutting, geo-engineering and wear components, due to their high hardness, high wear resistance, and superior chemical and thermal stability [18–20]. Moreover, the lighter-weight and lower price of Ti(CN)-based cermets than that of WC-Co hardmetals also made Ti (CN)-based cermets promising materials to replace WC-Co hardmetals for many applications [21]. However, although the abrasive wear behaviors of WC-Co hardmetals were investigated in lots of publications [9,10,22–24], those of TiCN-based cermets have been not very clear so far, especially when they are applied under abrasive wear conditions of different abrasives and abrasive concentrations in slurries, which are universal in geo-engineering applications. In this work, using a modified ASTM B611 wet sand rubber rimmed wheel test system, the abrasive wear behavior of commercially available TiCN cermets (FD22) was investigated in detail under water-based slurries (drilling fluids) with three kinds of coarse angular abrasives, SiC, Al2O3 and SiO2. The wear loss and wear rate of TiCN cermets under different mass fractions of abrasive in water-based slurries were studied. And through the observations of the worn surfaces by three dimensional (3D) white-light interfering surface profiler, the dominate wear mechanisms of TiCN cermets under such working conditions were proposed. The obtained results may be instructive to many similar applications, such as the substrate in slurry pumps, the liner-piston rods of drilling machines, turbine blades, propellers of ships and so on.
2. Experiment details 2.1. Test system The applied test system in this work is a modified ASTM B611 wet sand rubber rimmed wheel test system (model: MLS-225), which has been reported in our previous work about the abrasive wear investigation on WC-Co hardmetals [24]. In this test system, the conventionally applied steel wheel is replaced by a rubber (vulcanized chlorinated butyl rubber) rimmed one. The reason for such modification is that although ASTM B611 steel wheel abrasion test system has been described as a suitable experimental technique in characterizing the abrasion resistance of cermets and even specifically standardized, it has some insufficiencies when specific application conditions have to be simulated [24]. For example, in order to simulate the working conditions of aiguilles in drilling fluid, a series of slurries with different mass fractions of abrasives should be used.
In such case, the test results would be seriously affected by or even covered in the influence of the steel wheel when slurries of much low mass fraction of abrasives were used. And this phenomenon could not be ignored even if much harder abrasives were used. Such shortcoming can be overcome by using the rubber rimmed steel wheel. The elasticity of the rubber wheel will make the abrasive grits feed into the very small space between the wheel and the samples easily. Moreover, the size of the abrasive particles would influence the severity of abrasive wear while all other parameters were kept constant [1,6]. The use of rubber rimmed steel wheel could postpone the crushing of the abrasive grits during tests, especially for long sliding distance wear experiments. 2.2. Materials The test samples were made from TiCN cermets (FD22), which were commercially bought from Beijing Unisplendor Founder High-Tech Ceramics Co. Ltd., China. The dimension of the specimens is about 25.5 mm 57 mm 6 mm. Fig. 1 shows the microstructure of a typical TiCN cermet sample through micrographs on its fresh fracture surface by secondary electron scanning electron microscopy (SEM) and on its polished surface by backscattered electron one, revealing that the samples are pyknotic with a quite uniform phase distribution, but the TiCN grain size in the samples is not uniform, varying from 0.5 to 2 μm. The hardness of the applied TiCN cermets (Hm) is about 2200 HV. In order to exclude the influence of residual stress from the mechanical machining of the samples, all the samples were annealed before testing. Three kinds of coarse angular grits, carborundum (SiC, green), corundum (Al2O3, white) and silica (SiO2, white), were used as abrasive in this study. Typical SEM micrographs of the three kinds of abrasives are shown in Fig. 2. From this figure, it can be seen that all the abrasives are coarsely angular and the particles size of carborundum grits is smaller than those of corundum and silica grits. The measured particle size of the abrasives, calculated spike parameter-quadratic (SPQ) value [24], hardness of the abrasives (Ha) and the hardness ratio of the abrasive to TiCN cermets (Ha/Hm) are listed in Table 1. The slurries used in the test consisted of two basic components, drilling fluid (pH¼7) and abrasive grits. The recipes of the slurries used in the test are listed in Table 2. The drilling fluid contained 1 wt% height-viscosity carboxyl methyl cellulose (HV-CMC), 1 wt% xanthan gum (X.G.) and 5 wt% bentonite which were all calculated by weight to water so as to make the drilling fluid possess the same dispersion capability to abrasives. In each batch of slurry, the total amount of the drilling fluid was kept constant, 1070 g, but the mass fractions of the abrasives to water were designed as 5%, 10%, 20%, 30% and 40%, respectively.
Fig. 1. Typical secondary electron SEM micrograph on the fresh fracture surface (a) and backscattered electron SEM micrograph on the polished surface (b) of the applied TiCN cermets (FD22), revealing a wide distribution of TiCN grain size but rather uniform distribution of phases.
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Fig. 2. Typical SEM micrographs of the applied abrasives: (a) SiC, (b) Al2O3, and (c) SiO2.
Table 1 Properties of the abrasives used in the test. Abrasives Particle size distribution (μm)
SiC Al2O3 SiO2
d10
d50
d90
320 383 388
446 600 581
622 953 888
SPQ
Hardness (HV30)
Hardness ratio Ha/Hm
∼0.7140 2900–3000 1.32–1.36 ∼0.8100 2000–2100 0.91–0.95 ∼0.5610 1000–1100 0.45–0.46
Table 2 Compositions of the slurries with different mass fractions of abrasives. Mass fraction of sands/%
5%
10%
20%
30%
40%
Sand/g HV-CMC/g X.G./g Bentonite/g Water/ml
52.6 10.0 10.0 50.0 1000
111.1 10.0 10.0 50.0 1000
250.0 10.0 10.0 50.0 1000
428.6 10.0 10.0 50.0 1000
666.7 10.0 10.0 50.0 1000
2.3. Experimental procedures In order to investigate the wear behaviors of TiCN cermets under drilling conditions, special experimental processes and parameters were designed and adopted in this work. The selected Shore hardness of the rimming rubber on the steel wheel was 70 degree and the circumferential length of the wheel was 0.566 m. During testing, the rotation speed and load were fixed to 498 RPM and 225 N. For each sample, a 1000 r pre-grinding was carried out to avoid the differentials due to the roughness of the machined surface of the cermet samples and to stir the slurry evenly at the same time. After the pre-grinding, the samples were weighed for the basic sample masses. Then the samples were weighed after every 4000 r grinding for calculating the wear loss, and this procedure was carried out for 11 times. After that, the samples
were weighed after every 8000 r grinding, and this procedure was performed for 8 times. It should be emphasized that before and after each wear test, the specimens were cleaned in absolute ethyl alcohol and dried before characterization. And the weighing apparatus was an analytical balance with an accuracy of 0.0001 g. 2.4. Materials characterization The wear loss of the specimens is defined as the volume loss calculated from the measured mass loss using an analytical balance, and the wear rate of the specimens is the wear loss per unit length of sliding distance. The sliding distance is the linear displacement of the wheel rim in this work. In order to reveal the wear mechanisms of the cermets, the abraded surfaces of the cermets were examined by a three dimensional (3D) white-light interfering surface profiler (model: Micro XAM-3D). In addition, the micrographs of typical TiCN cermet sample mentioned above was obtained by secondary electron SEM (model: SSX-550) on its fracture surface and by backscattered electron SEM on its polished surface (model: JSM 7001F). The micrographs of the abrasives presented above were taken by secondary electron SEM (model: SSX-550).
3. Results 3.1. Wear loss vs. sliding distance With the data collected from the samples under conditions with different abrasives, the curves of wear loss of the TiCN cermets vs. sliding distance were plotted, which are shown in Fig. 3. As seen from this figure, with the same abrasive and sliding distance the wear loss of the samples increased with the increase in mass fraction of the abrasives in the slurries; and with the same abrasive and abrasive mass fraction in the slurries, the wear loss increased with the increase in sliding distance. With the same
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3.2. Wear rate vs. sliding distance Fig. 4 illustrates the variation of wear rate on sliding distance on the basis of the collected wear loss data. From this figure it can be seen that with the same sliding distance and abrasive mass fraction in slurries, the samples presented the highest wear rate when SiC was used as abrasive and the lowest when SiO2 was used. With the same abrasive, the wear rate increased with the increase in abrasive mass fraction in the slurries.
Fig. 3. Wear loss vs. sliding distance under the conditions with different abrasives and abrasive mass fractions in the slurries: (a) SiC, (b) Al2O3 and (c) SiO2.
sliding distance and abrasive mass fraction, the samples presented the heaviest wear loss when SiC was used as abrasive, and the lightest when SiO2 was used. Moreover, under the same test conditions, the wear loss of TiCN cermets increased slowly when the abrasive mass fraction in slurries was low, and it increased rapidly when the abrasive mass fraction in slurries was high.
Fig. 4. Wear rate vs. sliding distance under the conditions with different abrasives and abrasive mass fractions in the slurries: (a) SiC, (b) Al2O3 and (c) SiO2.
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However, under the applied test conditions in this work, the variation of wear rate on sliding distance is not a simple increase or decrease when the other conditions were kept constant. When the abrasive mass fraction in the slurry was relatively low (for SiC about below 10 wt%, Al2O3 below 20 wt% and SiO2 below 30 wt%), the wear rate of the cermets increased very slowly with the increase in sliding distance. However, when the abrasive mass fraction in the slurry was high (for SiC about higher than 10 wt%, Al2O3 higher than 20 wt% and SiO2 higher than 30 wt%), the wear rate increased rapidly at the beginning, then became steady and even dropped slightly in the last few kilometers with increasing sliding distance in the given range. 3.3. Micro-morphology of the abraded surfaces In this work, the abraded surface of the cermet samples was examined through section to section so as to describe their
Fig. 5. The schematic diagram of the three areas on the abraded surface of the sample [24].
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difference in morphology of different areas just as done in Ref. [24]. The abraded surface was partitioned into starting area (s-area), middle area (m-area) and ending area (e-area) as shown in Fig. 5. Through the observations of 3D white-light interfering surface profiler, it was found that the micro-morphology of the abraded surface of each sample changed with not only the abrasive sort and mass fraction in the slurry but also the area (section) on the abraded surface. Fig. 6 shows typical surface micro-morphologies of the abraded surfaces from 3D white-light interfering surface profiler while SiC was used as abrasive and different abrasive mass fractions in the slurries were used. Several wear mechanisms, such as plastic deformation, micro-cutting, grooves and grains fracture, were observed on the abraded surface of TiCN cermet samples. But only one or two of them played the dominant role and the dominant mechanisms changed with the abrasive mass fraction in the slurries. When the SiC abrasive mass fraction in the slurry was no more than 5 wt%, micro-cuttings played the dominant role in wear which could be seen in Fig. 6a–c. On the ending area, a few of grain fractures appeared as shown in Fig. 6c. When the SiC abrasive mass fraction was about 20 wt%, the main wear mechanisms were plastic deformation and grooves, which could be seen in Fig. 6d–f. Scratching could be observed on the ending area as shown in Fig. 6f, which might be the result from grain fracture. While the SiC abrasive mass fraction increased up to 40 wt%, plastic deformation and scratching became even more significant as shown in Fig. 6h–i. The material removal was very serious even to form some pits on the abraded surface as shown in Fig. 6i. Fig. 7 presents typical surface micro-morphologies of the abraded surfaces from 3D white-light interfering surface profiler
Fig. 6. Typical surface morphologies of the samples from 3D white-light interfering surface profiler while different mass fractions of SiC abrasive in the slurries were applied: (a–c) 5 wt%, (d–f) 20 wt% and (g–i) 40 wt%, in which (a), (d) and (g) belong to s-area, (b), (e) and (h) to m-area, and (c), (f) and (i) to e-area.
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Fig. 7. Typical surface morphologies of the samples from 3D white-light interfering surface profiler while different mass fractions of Al2O3 abrasive in the slurries were applied: (a–c) 5 wt%, (d–f) 20 wt% and (g–i) 40 wt%, in which (a), (d) and (g) belong to s-area, (b), (e) and (h) to m-area, and (c), (f) and (i) to e-area.
while Al2O3 was used as abrasive and different abrasive mass fractions in the slurries were used. In this case, the material removal of the abraded surface was less serious compared with the situation when SiC was used as abrasive. When the Al2O3 abrasive mass fraction in the slurry was about 5 wt%, the main wear mechanisms were the extrusion of binder phase and slight plastic deformation on the abraded surface, which could be seen in Fig. 7a–c. While the Al2O3 abrasive mass fraction increased to 20 wt%, plastic deformation with shallow grooves became more and more obvious as shown in Fig. 7d–f. When the Al2O3 abrasive mass fraction increased up to 40 wt%, distinct plastic deformation could be observed as shown in Fig. 7h–i. The micro-morphologies of different abraded areas of the samples presented very little difference when the Al2O3 abrasive mass fraction in slurries was identical. Fig. 8 displays typical surface micro-morphologies of the abraded surfaces from 3D white-light interfering surface profiler while SiO2 was used as abrasive and different abrasive mass fractions in the slurries were used. It could be seen that the main wear mechanism was plastic deformation and the material removal of the abraded surface was very slight from this figure. When the SiO2 abrasive mass fraction in the slurry was no more than 5 wt%, plastic deformation was extraordinarily slight with slight binder removal as shown in Fig. 8a–c. As the SiO2 abrasive mass fraction increased, plastic deformation was intensified and the extrusion of binder phase became obvious. When the SiO2 abrasive mass fraction increased up to 40 wt%, a bit of grooves could be seen as shown in Fig. 8h and i.
4. Discussion 4.1. Wear loss of the samples In consideration of the high hardness of the TiCN cermets, in order to obtain a significant information of the wear loss of TiCN cermets, the highest load in this test system (225N), and more than 60 km sliding distance, which is much longer than that of any other previous work, was applied in this work. The Archard's empirical formula as shown in the following equation is usually used to predict the abrasive wear loss of the materials [25] V ¼ k1 PLH −1
ð1Þ
where V is the volume of materials removed by wear, k1 a dimensionless coefficient, P the applied normal load, L the sliding distance and H the Vickers hardness of the applied materials. As seen from Eq. (1), the wear loss of the materials is proportional to the applied normal load and sliding distance. Therefore, it is easily understandable that with the same abrasive and abrasive mass fraction in the slurries, the wear loss increased with the increase in sliding distance, as shown in Fig. 3. According to Refs. [1,6], the hardness ratio (Ha/Hm) between the abrasive and the worn materials impacts the wear loss a lot in abrasive wear. The wear loss increased with the increase in the hardness ratio. The hardness ratio between SiC and TiCN cermets was the highest and the one between SiO2 and TiCN cermets was the lowest among the abrasives used in this work, as shown in Table 1. Therefore, the samples with SiC as abrasive presented the
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Fig. 8. Typical surface morphologies of the samples from 3D white-light interfering surface profiler while different mass fractions of SiO2 abrasive in the slurries were applied: (a–c) 5 wt%, (d–f) 20 wt% and (g–i) 40 wt%, in which (a), (d) and (g) belong to s-area, (b), (e) and (h) to m-area, and (c), (f) and (i) to e-area.
highest wear loss when the other wear test parameters were kept constant, which was almost 5 times the wear loss when Al2O3 was used as abrasive, and 20 times that when SiO2 was used. As the abrasive mass fraction increased in the slurries, the number of abrasive particles sliding across the abraded surface increased, resulting in tighter and more intensive contacts between the abrasive and abraded surface. Therefore, the material removal opportunity increased, and the wear loss of the samples increased with the increase in abrasive mass fraction in the slurries when the abrasive and sliding distance were the same.
4.2. Wear rate of the samples The wear rate is defined as the wear loss per sliding distance in this work. As discussed above, the wear loss of TiCN cermets increased with the increase in the abrasive mass fraction in the slurries and the hardness of the abrasives. Therefore, the wear rate increased with the increase in the abrasive mass fraction on the whole when the same abrasive was applied. With the same abrasive mass fraction, the relationship of wear rate with abrasive was the wear rate with SiC abrasive4 that with Al2O3 4that with SiO2, which is in accordance with the hardness decreasing trend, as shown in Fig. 4. The high hardness of the tested TiCN cermets might be the main cause leading to the very slow increase in wear rate with the increase in sliding distance, when the abrasive mass fraction in the slurries was low. Due to the differences in hardness, particle size and SPQ of the three abrasives, such phenomena happened in this work when the mass fraction of carborundum is lower than
about 10 wt%, that of corundum lower than 20 wt%, and that of silica lower than 30 wt%. When the abrasive mass fraction in the slurry was high, because there was an adaptive process during the wear process, the wear rate of TiCN cermets initially increased very rapidly, then became steady and even dropped down slightly in the last few kilometers with the increase in sliding distance in the given range. At the beginning during the adaptive process, micro-cutting and binder removal were the main wear mechanisms. The microcutting may form the channel to enlarge the contact area between the abrasive grits and the abraded surface [26]. Meanwhile, as more and more binder was removed, more TiCN grain fracture might happen. Therefore, the wear rate increased rapidly during this period. However, as the sliding distance increased, the crushing of the abrasive occurred and some of the angular abrasive might be rounded off during the wear process, which would contribute to the decrease in wear rate, because it is known [1,9] that the severity of wear can be correlated positively with the size of the abrasive while all the other parameters are kept constant. Meanwhile, the re-embedment of the removed fracture fragment of TiCN grains into the binder phase might also happen, which would strengthen the abraded surfaces and reduce the wear rate [9,10,26]. Therefore, the wear rate of the tested TiCN cermets might become steady, and even drop down slightly with the increase in the sliding distance during this period. 4.3. Wear mechanisms of the samples Since the hardness of SiC abrasive (about 2900–3000 HV30) is higher than that of TiCN cermets FD22 (about 2200 HV30) and the
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hardness ratio (Ha/Hm) between the abrasive and the abraded surface is 1.32–1.36 (higher than 1.2), so the abrasive could penetrate into the abraded surface easily [1,6]. When the SiC abrasive mass fraction was 5 wt%, the quantity of SiC abrasive between the rubber wheel and the abraded surface was very little. Under the high load applied in this work, the abrasive grits would slide across the abraded surface rather than roll across it. Therefore, the major wear mechanism was micro-cutting to form channel in this case [7,8,26], as seen in Fig. 6a–c. However, as the SiC abrasive mass fraction increased, more and more SiC grits could feed into the contact surface. Since the abrasive grits crowded in the narrow confine between the rubber wheel and the abraded sample surface, the grits would roll and slide preferentially along the existing grooves at high loads [26]. Thereby, plastic deformation and plowing grooves became the main wear mechanisms as shown in Fig. 6, and the grooves would be deepened and widened during the proceeding wear process. Moreover, it is believed that TiCN grain fracture occurred in association with the plastic deformation, and the repeated wear action might expand the fractures and even form some pits on the abraded surface as shown in Fig. 6i. Hence, the wear loss and wear rate both increased as the SiC abrasive mass fraction in the slurry increased as seen in Figs. 3 and 4. Compared with SiC abrasive, the hardness of the applied Al2O3 abrasive (about 2000–2100 HV30) was very close to the hardness of TiCN cermet samples and even a little lower, and the hardness ratio (Ha/Hm) is 0.91–0.95, indicating that the Al2O3 abrasive grits are difficult to penetrate into TiCN grains and damage the framework of TiCN cermets. However, because the hardness of the abrasive was higher than that of the binder phase in the TiCN cermets, the applied abrasive grits could plastically deform the softer binder phase between the TiCN grains. As the abrasive mass fraction in the slurries increased, the binder removal level was enhanced and the preferential channel of the abrasive grits would cause the plastic deformation of the surface, resulting in the formation of shallow grooves with material pile up at the groove edges as could be seen in Fig. 7. The hardness of the applied SiO2 abrasive (about 1000–1100 HV30) was only about half of the hardness of TiCN cermets used in this work. That means that the SiO2 abrasive grits are even more difficult to penetrate into TiCN grains and damage the framework of TiCN cermets. So, the main wear mechanism in this case was the extrusion and removal of binder phase in the cermets. Compared with the case when Al2O3 abrasive was used, the extent of binder removal was thus very slight as can be seen in Fig. 8. This could also be proved by the slight wear loss and wear rate when SiO2 abrasive was used, as shown in Figs. 3 and 4c As the abrasive mass fraction in the slurries increased, the binder removal level increased and plastic deformation became more obvious as shown in Fig. 8. Moreover, the grooves on the abraded surfaces would be gradually deepened and widened from s-area to e-area as could be seen in Figs. 6–8, demonstrating that the abrasive grits moved preferentially along the existing grooves, thereby deepening them. Such ‘channeling’ effect has been reported elsewhere by Gant et al. in Ref. [26]. In addition, when the abrasive grits feed into the abraded surface, they suffered from a tangential force, which was caused by the revolution of the rubber wheel. From the analysis in our previous work [24], it was known that the abrasive grits suffered from different comprehensive forces at s-area, m-area and e-area. According to the Archard's law [25] and previous works on the abrasive wear of cermets [9,10,24,26], it is reasonable that different areas of the abraded surface displayed different micro-morphologies on the same samples as shown in Figs. 6–8.
5. Conclusions The wear behavior of TiCN cermets was investigated in detail under water-based slurries with three kinds of coarse angular abrasives, SiC, Al2O3 and SiO2, through a modified ASTM B611 wet sand rubber rimmed wheel test system. The conclusions are summarized as following. (1) The wear loss of TiCN cermets increased with the increase in sliding distance, the abrasive mass fraction in slurries and the hardness of the abrasive. (2) The wear rate of TiCN cermets increased with the increase in the abrasive mass fraction in slurries and hardness of the abrasive. With the increase in sliding distance, when the abrasive mass fraction was low (for SiC about lower than 10 wt%, Al2O3 lower than 20 wt% and SiO2 lower than 30 wt%), the wear rate increased very slow; but when it was higher than that, the wear rate increased rapidly at the beginning, then became steady and even dropped down slightly in the last few kilometers in the given sliding distance. (3) The abrasive wear mechanisms of TiCN cermets were mainly depending on the relative hardness between the cermets and abrasives. With SiC abrasive, micro-cutting, grain fracture and plastic deformation with grooves were the dominant wear mechanisms. When Al2O3 was used as abrasive, plastic deformation and plowing grooves were the main wear mechanisms. With SiO2 abrasive, extrusion and removal of binder phase, and slight plastic deformation with grooves were the dominant wear mechanisms. The change of abrasive mass fraction in the slurries had no obvious influence on the sort of wear mechanisms, just affecting the extent of the appeared wear types.
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