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Abrasive wear behavior of SiCp–Sialon composite refractories
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CERAMICS INTERNATIONAL
Ceramics International 41 (2015) 9146–9151 www.elsevier.com/locate/ceramint
Abrasive wear behavior of SiCp–Sialon composite refractories Xiaochao Lia, Shusen Chena, Hao Dinga,n, Zhaohui Huanga,n, Baolin Liub, Minghao Fanga, Yan'gai Liua, Xiaowen Wua, Bin Maa a
School of Materials Science and Technology, Beijing Key Laboratory of Material Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, China University of Geosciences (Beijing), Beijing 100083, China b Key Laboratory on Deep Geodrilling Technology of the Ministry of Land and Resources, China University of Geosciences (Beijing), Beijing 100083, China Received 29 January 2015; received in revised form 23 March 2015; accepted 31 March 2015 Available online 9 April 2015
Abstract The abrasive wear tests were performed on the prepared SiCp–Sialon composite refractories with quartz particles as abrasives. The study aims to explore the effects of load and wear time on wear loss of SiCp–Sialon composite refractories as well as the mechanism of material removal. SiCp–Sialon composite refractories prepared by nitriding reaction sintering consisted of α-SiC, β-Si3N4, and Si4Al2O2N6. The wear loss of SiCp– Sialon composite refractories increased significantly with the increases in test load and test time. The primary wear mechanism of SiCp–Sialon composite refractories is micro-cutting. The mechanism of material removal mainly involves the matrix. The micro-cutting occurred firstly in the matrix and caused the loss of the matrix. Without the protection from the surrounding matrix, the SiC aggregates were eventually stripped. & 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: B. Composite; C. Wear resistance; D. Sialon; E. Refractories; SiCp
1. Introduction Silicon carbide (SiC) and Silicon nitride (Si3N4) composites are the promising engineering materials due to their excellent mechanical properties, particularly the wear resistance performance. The composites can be applied in the fields requiring high wear resistance performance, such as garbage incineration boiler, drill bit, coke dry quenching, circulating fluidized bed boiler, petrochemical industry, and metallurgical industry [1–5]. Sialon possesses the better sinterability and shows more advantages in the development of composites than silicon nitride. Therefore, sialonbased composites have gained increasing attention. The properties and microstructures of the composites can be easily controlled when sialon is chosen as the binder phase of composites [6,7]. It is well known that there is a positive correlation between abrasion resistance and fracture toughness. The wear resistance of composites can be improved by increasing the fracture n
Corresponding authors. Tel./fax: þ 86 10 82322186. E-mail addresses: [email protected] (H. Ding), [email protected] (Z. Huang). http://dx.doi.org/10.1016/j.ceramint.2015.03.325 0272-8842/& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
toughness [8,9]. At present, various methods, such as a reaction-bonded process, [10–12] improving sintering methods, [13,14] introducing the second phase, [15–17] microstructure design, [18,19] adding sintering additives [20–22]. have been proposed to reinforce the fracture toughness of ceramics. The introduction of second phase particulate into composites as binder phase can enhance mechanical properties. SiC is the hardest among known engineering materials. Therefore, SiC particles are promising candidates for further enhancing the wear resistance and increasing the service life of composites. Through the addition of hard SiCp, the hardness of composites is increased and the fracture toughness of the matrix is enhanced at the same time [23,24]. In this paper, in order to improve the wear resistance performance, we employed SiC particles and the second phase Silaon in-situ generated on the matrix to prepare SiCp–Sialon composite refractories, in which SiCp particle were surrounded by Sialon. This preparation process of SiCp–Sialon composite refractories is characterized by the low cost, the simple process, and the high wear resistance of the products. Furthermore, we evaluated the abrasive wear behavior of the prepared SiCp–Sialon
X. Li et al. / Ceramics International 41 (2015) 9146–9151
composite refractories. The study aims to explore the effects of load and wear time on volume wear values of SiCp–Sialon composite refractories. The wear characteristics were characterized with digital camera, optical micrographs, and SEM. Moreover, we discussed the mechanism of abrasive wear and material removal of SiCp–Sialon composite refractories.
2. Experimental The main starting materials of SiCp–Sialon composite refractories include commercial SiC (α-SiC content Z 98%) with the grain size ranges of about 2–1 mm, 1–0.5 mm, and 0.5–0 mm, respectively, Si powder (silicon contentZ 98%, grain size r 45 mm), Al2O3 powder (Al2O3 contentZ 99%, grain size r 45 mm) and are supplied by Luoyang Refractory Research and Industry Trade Co., Ltd., China. In addition, Al powder (Al contentZ 99%, grain size r 75 mm, Sigma-Aldrich Co.), nitrogen gas (purity Z 99.99%), and calcium lignosulphonate binder were also used. The Sialon phase was designed as Z=2 (Si4Al2O2N6) and its content reached 30 wt%. The compositions of SiCp–Sialon composite refractories are shown in Table 1. The raw materials were fully mixed according to Table 1. Binder (3 wt%) and water (5 wt%) were introduced additionally into the mixture. After being mixed uniformly, the mixture was hydraulically pressed to green bodies of 25 55 8 mm under 40 MPa for 30 s. The green bodies were dried at 110 1C for 24 h in a drying oven. Then these green bodies were further compacted under 200 MPa for 90 s with cold isostatic pressing and dried at 110 1C for 24 h. These green samples were sintered at 1300 1C and 1400 1C for 90 min in a nitrogen atmosphere and then the temperature rose to 1500 1C for 6 h. When the above preparation process was completed, these samples were cooled naturally to room temperature. The abrasive wear test was performed with a MLS-222 rubber wheel abrasive testing machine (Zhangiiakou Taihua Machinery Plant). The schematic diagram can be found in Ref. [25]. The shore A hardness of rubber wheel is 60 HA. The diameter of rubber wheel is 178 mm and its speed is 213 rpm. The test loads were 100 N, 170 N, and 225 N, respectively. The abrasive was obtained according to the following procedure. Firstly, the slurry was prepared by mixing water, Nabentonite, Na2CO3, and sodium carboxymethyl cellulose together according to the proportion of 100:7.5:0.25:0.45. The slurry was allowed to stand for 24 h at room temperature.
Secondly, quartz sand with the diameter of 212–425 mm was added into the slurry. The addition amount of quartz sand was about 1.5 kg per 1000 ml slurry. After being mixed uniformly, 2.5 kg mixed slurry was utilized for each sample in the test and the revolution number of the rubber wheel was 3000. The abrasive wear behavior was characterized by the mass loss of specimens generated during the rotation of the rubber wheel. The specimen surface should be polished, cleaned, and dried before the test. The specimens were washed thoroughly with water and subsequently ultrasonically cleaned for 10 min with pure alcohol after each test. Then the specimens were dried at 110 1C for 24 h in a drying oven. After the specimens were completely dried, the mass of specimens were weighed by electronic analytical balance. Bulk density and apparent porosity were determined by a Archimedes water immersion method. The bending strength was determined according to ASTM C1421-01b (R2007) via a conventional three-point bending method. The crystalline phases of the final materials were determined via X-ray diffraction (XRD, XD-3, Cu Kα1 radiation, λ ¼ 1.5406 Å, Purkinje General Instrument Co., Ltd.) with a scanning rate of 81 min 1. The morphology of abrasion surfaces was observed by optical micrographs and SEM (SEM; JEM6460LV, Japan Electron Optics Laboratory Co., Ltd.).
3. Results and discussion 3.1. Preparation of SiCp–Sialon composite refractories SiCp–Sialon composite refractories were prepared with the raw materials of Si, Al, α-SiC, and Al2O3 by nitriding reaction sintering at 1500 1C for 6 h. SiCp–Sialon composite refractories (Fig. 1) consisted of α-SiC, β-Si3N4 and Si4Al2O2N6. The fundamental properties of SiCp–Sialon composite refractories are listed in Table 2. The Vickers hardness of the matrix and SiC aggregates in SiCp–Sialon composite refractories is respectively 12.4 GPa and 18.2 GPa. It is obvious that the hardness of the SiC aggregates is higher than that of the
Table 1 The compositions of SiCp–Sialon composite refractories. Raw materials
Content (wt%)
SiC particles (2–1 mm) SiC particles (1–0.5 mm) SiC particles (0.5–0 mm) Si powder Al powder Al2O3 powder
40.00 20.00 10.00 16.97 2.73 10.3
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Fig. 1. XRD pattern of SiCp–Sialon composite refractories.
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matrix. Therefore, the SiC aggregates have the better abrasive wear performance. The surface microstructure of SiCp–Sialon composite refractories is shown in Fig. 2. After polishing (Fig. 2(a)–(c)), the bonding interfaces of the SiC aggregates and the surrounding Sialon matrix were dense. The microstructure of SiCp–Sialon composite refractories was optimized by adding SiC particles and the second phase Silaon in-situ generated on the matrix, which is helpful to enhance the wear properties. However, some pores, which are harmful to the abrasive wear performance, are observed in the matrix of SiCp–Sialon composite refractories. It could lead to the loss of matrix during the abrasive wear tests. A significant transgranular fracture was observed on the fracture surface of SiCp–Sialon composite refractories (Fig. 2(d)).
3.2. Abrasive wear of SiCp–Sialon composite refractories The effects of load and test time on abrasive wear of SiCp– Sialon composite refractories were shown in Fig. 3. The wear loss of SiCp–Sialon composite refractories increases significantly with the increases in test load and test time. Therefore,
the friction force increases with the increase in test load and the material loss increases with the increase in test time. To establish the empirical model and evaluation system for predicting the abrasive wear properties of SiCp–Sialon composite refractories at different test load, we explored the relationship between the wear loss and test time and established the linear fitting according to Fig. 3. Then we obtained the linear relationship between the wear loss and test time and expressed the relationship as follow: Y ¼ At þ B;
ð1Þ
where Y is the wear loss of SiCp–Sialon composite refractories; t is the test time; A and B are the constants determined by the test load. The values of A, B, and fitting degree at different test loads are shown in Table 3. The values of A and B increased with the increase in test load, indicating that the slope of the linear fitting also gradually increased. Therefore, the material loss increased with the increase in test load. 3.3. Mechanism of material removal In the digital photographs of the original and wear surfaces of SiCp–Sialon composite refractories (Fig. 4), the wear surfaces
Table 2 Properties of SiCp–Sialon composite refractories. Property
Apparent porosity (%)
Bulk density (g cm 3)
Bending strength (MPa)
Compression strength Vickers hardness of the binder (MPa) phase (GPa)
Vickers hardness of aggregates (GPa)
SiCp– Sialon
107 0.3
2.737 0.02
5075
Z160
18.271.2
12.47 0.4
Fig. 2. SEM photographs of the bonding between the matrix and aggregate: (a), (b) and (c) the surface of SiCp–Sialon composite refractories after polishing; (b) the fracture face of SiCp–Sialon composite refractories.
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Fig. 3. Effects of load and test time on wear loss of SiCp–Sialon composite refractories.
Table 3 The values of A, B, and fitting degree at different test loads. Test Load (N)
A
B
R2
100 170 225
3.03 10 4 3.35 10 4 4.05 10 4
0.01419 0.02369 0.03176
0.98975 0.97001 0.99292
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of SiC aggregates were very smooth, while the wear on the surrounding matrix of SiC aggregate was very serious (Fig. 4(b)). The wear of SiC aggregate was slight because the aggregate had the high hardness. Because the matrix was the weak part of SiCp– Sialon composite refractories, the wear of the matrix was serious. In the optical micrographs of the wear surface of samples (Fig. 5), the wear surface morphology of SiCp–Sialon composite refractories had many pits and the size of pits was the same as the aggregate size of SiC particles. The phenomenon may be interpreted as follows: the aggregate of SiC particles were pulled out during the abrasive wear experiment. The SEM photographs of the wear surfaces of SiCp–Sialon composite refractories are shown in Fig. 6. The surface of SiC aggregate was very smooth after abrasive wear experiment, while the matrix wear in the surrounding of SiC aggregate was more serious. Therefore, the wear of material was mainly initiated from the matrix, especially the defects of pores within the matrix. Due to the loss of matrix, the combination strength of matrix and SiC aggregate gradually decreases and eventually the SiC aggregates was stripped from the surface of material (shown in Fig. 5). The microstructure study of the wear surface indicates that the primary wear mechanism of SiCp–Sialon composite refractories is micro-cutting. The micro-cutting wear mechanism was generated by quartz abrasive particles. The mechanism of material removal can be interpreted as follows: the micro-cutting occurred firstly in the matrix and then caused the matrix loss, while micro-cutting
Fig. 4. The digital photographs of the original and wear surfaces of SiCp–Sialon composite refractories: (a) original surfaces; (b) the wear surfaces.
Fig. 5. Optical micrographs of the wear surface of SiCp–Sialon composite refractories.
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Fig. 6. SEM photographs of the wear surface of SiCp–Sialon composite refractories.
led to only slight wear on the SiC aggregate. Therefore, the SiC aggregate added into the composites can improve the wear resistance properties to a certain degree. However, without the protection from the surrounding matrix, the SiC aggregates are stripped and eventually lead to the material removal. As can be summarized from the above study about the abrasive wear that there are many factors which may have an influence on the abrasive wear properties of SiCp–Sialon composite refractories, such as SiC particle size and distribution, particle and matrix interface and matrix density, etc. Therefore, the abrasive wear properties of SiCp–Sialon composites can be further enhanced by optimizing the microstructure. 4. Conclusion SiCp–Sialon composite refractories prepared by nitriding reaction sintering consisted of α-SiC, β-Si3N4, and Si4Al2O2N6. The wear loss of SiCp–Sialon composite refractories increased significantly with the increases in test load and test time. The aggregate added into the composites can improve the wear resistance properties to a certain degree. The primary wear mechanism of SiCp–Sialon composite refractories is microcutting. The mechanism of material removal is mainly ascribed to the matrix. The micro-cutting occurred firstly in the matrix and then caused the matrix loss, without the protection from the surrounding matrix, the SiC aggregates were eventually stripped. Acknowledgments This work was financially supported by National Natural Science Foundation of China (Grant No. 51272241) and Research
Fund for the Doctoral Program of Higher Education of China (Grant no. 20130022110006). We also thank Key Projects in the National Science & Technology Pillar Program under grant number 2013BAE03B01-13. References [1] W. Zhang, H. Wang, Z.-H. Jin, Gel casting and properties of porous silicon carbide/silicon nitride composite ceramics, Mater. Lett. 59 (2005) 250–256. [2] A.K. Gain, J.-K. Han, H.-D. Jang, B.-T. Lee, Fabrication of continuously porous SiC–Si3N4 composite using SiC powder by extrusion process, J. Eur. Ceram. Soc. 26 (2006) 2467–2473. [3] G. Pezzotti, M. Sakai, Effect of silicon carbide nano dispersion on the mechanical properties of silicon nitride, J. Am. Ceram. Soc. 77 (1994) 3039–4041. [4] M. Hnatko, D. Galusek, P. Sajgalik, Low-cost preparation of Si3N4–SiC micro/nano composites by in situ carbothermal reduction of silica in silicon nitride matrix, J. Eur. Ceram. Soc. 24 (2004) 189–195. [5] J.-Z. Yang, M.-H. Fang, Z.-H. Huang, X.-Z. Hu, Y.-G. Liu, H.-R. Sun, J.-T. Huang, X.-C. Li, Solid particle impact erosion of alumina-based refractories at elevated temperatures, J. Eur. Ceram. Soc. 32 (2012) 283–289. [6] A.K. Mallik, K.M. Reddy, N.C. Acikbas, F. Kara, H. Mandal, D. Basu, B. Basu, Influence of SiC addition on tribological properties of SiAlON, Ceram. Int. 37 (2011) 2495–2504. [7] B. Bitterlich, S. Bitsch, K. Friederich, SiAlON based ceramic cutting tools, J. Eur. Ceram. Soc. 28 (2008) 989–994. [8] Z.B. Yu, D.P. Thompson, A.R. Bhatti, Fabrication and characterization of SiC fiber reinforced lithium-α-sialon matrix composities, Compos. Part A-Appl. Sci. Manuf. 33 (2002) 621–629. [9] C.M. Huang, D. Zhu, Y.R. Xu, W.M. Kriven, C.Y. Yuh, SiCf/O'SiA1ON composite: properties and oxidation retained properties, Mater. Sci. Eng. A 220 (1996) 176–184. [10] E.Q. He, J.S. Yue, L. Fan, C. Wang, H.J. Wang, Synthesis of single phase β-SiAlON ceramics by reaction-bonded sintering using Si and Al2O3 as raw materials, Scr. Mater. 65 (2011) 155–158.
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[19] V.X. Lima Filho, J.P. Davim, C.A. Cairo, J.M. Ferreira, Preparation and characterization of SiAlON matrix composites reinforced with combustion synthesis rod-like SiAlON particles, Int. J. Refract. Met. Hard Mater. 27 (2009) 647–652. [20] M.I. Jones, H. Hyuga, K. Hirao, Y. Yamauchi, Wear behaviour of single phase and composite sialon ceramics stabilized with Y2O3 and Lu2O3, J. Eur. Ceram. Soc. 24 (2004) 3271–3277. [21] S. Kurama, M. Herrmann, H. Mandal, The effect of processing conditions, amount of additives and composition on the microstructure and mechanical properties of α-SiAlON ceramics, J. Eur. Ceram. Soc. 22 (2002) 109–119. [22] C. Santos, J.V.C. de Souza, K. Strecker, S. Ribeiro, O.M.M. Silva, C.R. M. Silva, α-SiAlON ceramics with elongated grain morphology using an alternative sintering additive, Mater. Lett. 58 (2004) 1792–1796. [23] Z.H. Huang, J.T. Huang, M.H. Fang, S.F. Huang, Y.G. Liu, X.X. Wu, J.Z. Yang, The effects of SiCp addition on the z-value and mechanical properties of β-Sialon-SiCp refractories, J. Ceram. Soc. Jpn. 20 (2012) 387–392. [24] M. Belmonte, M.I. Nieto, M.I. Osendi, P. Miranzo, Influence of the SiC grain size on the wear behaviour of Al2O3/SiC composites, J. Eur. Ceram. Soc. 26 (2006) 1273–1279. [25] J.A. Hawk, D.E. Alman, J.J. Petrovic, Abrasive wear of Si3N4–MoSi2 composites, Wear 203–204 (1997) 247–256.
CERAMICS INTERNATIONAL
Ceramics International 41 (2015) 9146–9151 www.elsevier.com/locate/ceramint
Abrasive wear behavior of SiCp–Sialon composite refractories Xiaochao Lia, Shusen Chena, Hao Dinga,n, Zhaohui Huanga,n, Baolin Liub, Minghao Fanga, Yan'gai Liua, Xiaowen Wua, Bin Maa a
School of Materials Science and Technology, Beijing Key Laboratory of Material Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, China University of Geosciences (Beijing), Beijing 100083, China b Key Laboratory on Deep Geodrilling Technology of the Ministry of Land and Resources, China University of Geosciences (Beijing), Beijing 100083, China Received 29 January 2015; received in revised form 23 March 2015; accepted 31 March 2015 Available online 9 April 2015
Abstract The abrasive wear tests were performed on the prepared SiCp–Sialon composite refractories with quartz particles as abrasives. The study aims to explore the effects of load and wear time on wear loss of SiCp–Sialon composite refractories as well as the mechanism of material removal. SiCp–Sialon composite refractories prepared by nitriding reaction sintering consisted of α-SiC, β-Si3N4, and Si4Al2O2N6. The wear loss of SiCp– Sialon composite refractories increased significantly with the increases in test load and test time. The primary wear mechanism of SiCp–Sialon composite refractories is micro-cutting. The mechanism of material removal mainly involves the matrix. The micro-cutting occurred firstly in the matrix and caused the loss of the matrix. Without the protection from the surrounding matrix, the SiC aggregates were eventually stripped. & 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: B. Composite; C. Wear resistance; D. Sialon; E. Refractories; SiCp
1. Introduction Silicon carbide (SiC) and Silicon nitride (Si3N4) composites are the promising engineering materials due to their excellent mechanical properties, particularly the wear resistance performance. The composites can be applied in the fields requiring high wear resistance performance, such as garbage incineration boiler, drill bit, coke dry quenching, circulating fluidized bed boiler, petrochemical industry, and metallurgical industry [1–5]. Sialon possesses the better sinterability and shows more advantages in the development of composites than silicon nitride. Therefore, sialonbased composites have gained increasing attention. The properties and microstructures of the composites can be easily controlled when sialon is chosen as the binder phase of composites [6,7]. It is well known that there is a positive correlation between abrasion resistance and fracture toughness. The wear resistance of composites can be improved by increasing the fracture n
Corresponding authors. Tel./fax: þ 86 10 82322186. E-mail addresses: [email protected] (H. Ding), [email protected] (Z. Huang). http://dx.doi.org/10.1016/j.ceramint.2015.03.325 0272-8842/& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
toughness [8,9]. At present, various methods, such as a reaction-bonded process, [10–12] improving sintering methods, [13,14] introducing the second phase, [15–17] microstructure design, [18,19] adding sintering additives [20–22]. have been proposed to reinforce the fracture toughness of ceramics. The introduction of second phase particulate into composites as binder phase can enhance mechanical properties. SiC is the hardest among known engineering materials. Therefore, SiC particles are promising candidates for further enhancing the wear resistance and increasing the service life of composites. Through the addition of hard SiCp, the hardness of composites is increased and the fracture toughness of the matrix is enhanced at the same time [23,24]. In this paper, in order to improve the wear resistance performance, we employed SiC particles and the second phase Silaon in-situ generated on the matrix to prepare SiCp–Sialon composite refractories, in which SiCp particle were surrounded by Sialon. This preparation process of SiCp–Sialon composite refractories is characterized by the low cost, the simple process, and the high wear resistance of the products. Furthermore, we evaluated the abrasive wear behavior of the prepared SiCp–Sialon
X. Li et al. / Ceramics International 41 (2015) 9146–9151
composite refractories. The study aims to explore the effects of load and wear time on volume wear values of SiCp–Sialon composite refractories. The wear characteristics were characterized with digital camera, optical micrographs, and SEM. Moreover, we discussed the mechanism of abrasive wear and material removal of SiCp–Sialon composite refractories.
2. Experimental The main starting materials of SiCp–Sialon composite refractories include commercial SiC (α-SiC content Z 98%) with the grain size ranges of about 2–1 mm, 1–0.5 mm, and 0.5–0 mm, respectively, Si powder (silicon contentZ 98%, grain size r 45 mm), Al2O3 powder (Al2O3 contentZ 99%, grain size r 45 mm) and are supplied by Luoyang Refractory Research and Industry Trade Co., Ltd., China. In addition, Al powder (Al contentZ 99%, grain size r 75 mm, Sigma-Aldrich Co.), nitrogen gas (purity Z 99.99%), and calcium lignosulphonate binder were also used. The Sialon phase was designed as Z=2 (Si4Al2O2N6) and its content reached 30 wt%. The compositions of SiCp–Sialon composite refractories are shown in Table 1. The raw materials were fully mixed according to Table 1. Binder (3 wt%) and water (5 wt%) were introduced additionally into the mixture. After being mixed uniformly, the mixture was hydraulically pressed to green bodies of 25 55 8 mm under 40 MPa for 30 s. The green bodies were dried at 110 1C for 24 h in a drying oven. Then these green bodies were further compacted under 200 MPa for 90 s with cold isostatic pressing and dried at 110 1C for 24 h. These green samples were sintered at 1300 1C and 1400 1C for 90 min in a nitrogen atmosphere and then the temperature rose to 1500 1C for 6 h. When the above preparation process was completed, these samples were cooled naturally to room temperature. The abrasive wear test was performed with a MLS-222 rubber wheel abrasive testing machine (Zhangiiakou Taihua Machinery Plant). The schematic diagram can be found in Ref. [25]. The shore A hardness of rubber wheel is 60 HA. The diameter of rubber wheel is 178 mm and its speed is 213 rpm. The test loads were 100 N, 170 N, and 225 N, respectively. The abrasive was obtained according to the following procedure. Firstly, the slurry was prepared by mixing water, Nabentonite, Na2CO3, and sodium carboxymethyl cellulose together according to the proportion of 100:7.5:0.25:0.45. The slurry was allowed to stand for 24 h at room temperature.
Secondly, quartz sand with the diameter of 212–425 mm was added into the slurry. The addition amount of quartz sand was about 1.5 kg per 1000 ml slurry. After being mixed uniformly, 2.5 kg mixed slurry was utilized for each sample in the test and the revolution number of the rubber wheel was 3000. The abrasive wear behavior was characterized by the mass loss of specimens generated during the rotation of the rubber wheel. The specimen surface should be polished, cleaned, and dried before the test. The specimens were washed thoroughly with water and subsequently ultrasonically cleaned for 10 min with pure alcohol after each test. Then the specimens were dried at 110 1C for 24 h in a drying oven. After the specimens were completely dried, the mass of specimens were weighed by electronic analytical balance. Bulk density and apparent porosity were determined by a Archimedes water immersion method. The bending strength was determined according to ASTM C1421-01b (R2007) via a conventional three-point bending method. The crystalline phases of the final materials were determined via X-ray diffraction (XRD, XD-3, Cu Kα1 radiation, λ ¼ 1.5406 Å, Purkinje General Instrument Co., Ltd.) with a scanning rate of 81 min 1. The morphology of abrasion surfaces was observed by optical micrographs and SEM (SEM; JEM6460LV, Japan Electron Optics Laboratory Co., Ltd.).
3. Results and discussion 3.1. Preparation of SiCp–Sialon composite refractories SiCp–Sialon composite refractories were prepared with the raw materials of Si, Al, α-SiC, and Al2O3 by nitriding reaction sintering at 1500 1C for 6 h. SiCp–Sialon composite refractories (Fig. 1) consisted of α-SiC, β-Si3N4 and Si4Al2O2N6. The fundamental properties of SiCp–Sialon composite refractories are listed in Table 2. The Vickers hardness of the matrix and SiC aggregates in SiCp–Sialon composite refractories is respectively 12.4 GPa and 18.2 GPa. It is obvious that the hardness of the SiC aggregates is higher than that of the
Table 1 The compositions of SiCp–Sialon composite refractories. Raw materials
Content (wt%)
SiC particles (2–1 mm) SiC particles (1–0.5 mm) SiC particles (0.5–0 mm) Si powder Al powder Al2O3 powder
40.00 20.00 10.00 16.97 2.73 10.3
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Fig. 1. XRD pattern of SiCp–Sialon composite refractories.
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matrix. Therefore, the SiC aggregates have the better abrasive wear performance. The surface microstructure of SiCp–Sialon composite refractories is shown in Fig. 2. After polishing (Fig. 2(a)–(c)), the bonding interfaces of the SiC aggregates and the surrounding Sialon matrix were dense. The microstructure of SiCp–Sialon composite refractories was optimized by adding SiC particles and the second phase Silaon in-situ generated on the matrix, which is helpful to enhance the wear properties. However, some pores, which are harmful to the abrasive wear performance, are observed in the matrix of SiCp–Sialon composite refractories. It could lead to the loss of matrix during the abrasive wear tests. A significant transgranular fracture was observed on the fracture surface of SiCp–Sialon composite refractories (Fig. 2(d)).
3.2. Abrasive wear of SiCp–Sialon composite refractories The effects of load and test time on abrasive wear of SiCp– Sialon composite refractories were shown in Fig. 3. The wear loss of SiCp–Sialon composite refractories increases significantly with the increases in test load and test time. Therefore,
the friction force increases with the increase in test load and the material loss increases with the increase in test time. To establish the empirical model and evaluation system for predicting the abrasive wear properties of SiCp–Sialon composite refractories at different test load, we explored the relationship between the wear loss and test time and established the linear fitting according to Fig. 3. Then we obtained the linear relationship between the wear loss and test time and expressed the relationship as follow: Y ¼ At þ B;
ð1Þ
where Y is the wear loss of SiCp–Sialon composite refractories; t is the test time; A and B are the constants determined by the test load. The values of A, B, and fitting degree at different test loads are shown in Table 3. The values of A and B increased with the increase in test load, indicating that the slope of the linear fitting also gradually increased. Therefore, the material loss increased with the increase in test load. 3.3. Mechanism of material removal In the digital photographs of the original and wear surfaces of SiCp–Sialon composite refractories (Fig. 4), the wear surfaces
Table 2 Properties of SiCp–Sialon composite refractories. Property
Apparent porosity (%)
Bulk density (g cm 3)
Bending strength (MPa)
Compression strength Vickers hardness of the binder (MPa) phase (GPa)
Vickers hardness of aggregates (GPa)
SiCp– Sialon
107 0.3
2.737 0.02
5075
Z160
18.271.2
12.47 0.4
Fig. 2. SEM photographs of the bonding between the matrix and aggregate: (a), (b) and (c) the surface of SiCp–Sialon composite refractories after polishing; (b) the fracture face of SiCp–Sialon composite refractories.
X. Li et al. / Ceramics International 41 (2015) 9146–9151
Fig. 3. Effects of load and test time on wear loss of SiCp–Sialon composite refractories.
Table 3 The values of A, B, and fitting degree at different test loads. Test Load (N)
A
B
R2
100 170 225
3.03 10 4 3.35 10 4 4.05 10 4
0.01419 0.02369 0.03176
0.98975 0.97001 0.99292
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of SiC aggregates were very smooth, while the wear on the surrounding matrix of SiC aggregate was very serious (Fig. 4(b)). The wear of SiC aggregate was slight because the aggregate had the high hardness. Because the matrix was the weak part of SiCp– Sialon composite refractories, the wear of the matrix was serious. In the optical micrographs of the wear surface of samples (Fig. 5), the wear surface morphology of SiCp–Sialon composite refractories had many pits and the size of pits was the same as the aggregate size of SiC particles. The phenomenon may be interpreted as follows: the aggregate of SiC particles were pulled out during the abrasive wear experiment. The SEM photographs of the wear surfaces of SiCp–Sialon composite refractories are shown in Fig. 6. The surface of SiC aggregate was very smooth after abrasive wear experiment, while the matrix wear in the surrounding of SiC aggregate was more serious. Therefore, the wear of material was mainly initiated from the matrix, especially the defects of pores within the matrix. Due to the loss of matrix, the combination strength of matrix and SiC aggregate gradually decreases and eventually the SiC aggregates was stripped from the surface of material (shown in Fig. 5). The microstructure study of the wear surface indicates that the primary wear mechanism of SiCp–Sialon composite refractories is micro-cutting. The micro-cutting wear mechanism was generated by quartz abrasive particles. The mechanism of material removal can be interpreted as follows: the micro-cutting occurred firstly in the matrix and then caused the matrix loss, while micro-cutting
Fig. 4. The digital photographs of the original and wear surfaces of SiCp–Sialon composite refractories: (a) original surfaces; (b) the wear surfaces.
Fig. 5. Optical micrographs of the wear surface of SiCp–Sialon composite refractories.
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Fig. 6. SEM photographs of the wear surface of SiCp–Sialon composite refractories.
led to only slight wear on the SiC aggregate. Therefore, the SiC aggregate added into the composites can improve the wear resistance properties to a certain degree. However, without the protection from the surrounding matrix, the SiC aggregates are stripped and eventually lead to the material removal. As can be summarized from the above study about the abrasive wear that there are many factors which may have an influence on the abrasive wear properties of SiCp–Sialon composite refractories, such as SiC particle size and distribution, particle and matrix interface and matrix density, etc. Therefore, the abrasive wear properties of SiCp–Sialon composites can be further enhanced by optimizing the microstructure. 4. Conclusion SiCp–Sialon composite refractories prepared by nitriding reaction sintering consisted of α-SiC, β-Si3N4, and Si4Al2O2N6. The wear loss of SiCp–Sialon composite refractories increased significantly with the increases in test load and test time. The aggregate added into the composites can improve the wear resistance properties to a certain degree. The primary wear mechanism of SiCp–Sialon composite refractories is microcutting. The mechanism of material removal is mainly ascribed to the matrix. The micro-cutting occurred firstly in the matrix and then caused the matrix loss, without the protection from the surrounding matrix, the SiC aggregates were eventually stripped. Acknowledgments This work was financially supported by National Natural Science Foundation of China (Grant No. 51272241) and Research
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