D. Wei et al. /Ceramics international 32(2006)549-554 results in the formation of microcracks. Eventually, the [61 R.S. Bhattacharya, A.K. Rai, High energy (Me v)ion beam modifica- accumulation and propagation of microcracks result in th Mos2 coatings on ceramics, ASME/STLE Tribology formation of coarse cracks on the worn surface of sn1o ference Preprints 1992 Preprint No. 92-TC-6A [7 F. Brenscheidt, S Oswald, A Muchlich, Wear mechanisms in titanium Consequently, the propagation of coarse cracks leads to anted silicon nitride ceramics, Nucl. Instrum. Methods Phys. Res. the formation of large flakes on the worn surface of SN10. In B129(1997483-486 addition, as can be seen from Fig. &d, the surface of each 8] PJ. Blau, B. Dumont, D N. Braski, Reciprocating friction and wear coarse flake is smooth which is due to the lubrication action behavior of a ceramic-matrix graphite composite for possible use in and low hardness of h-BN diesel engine valve guides, Wear 225-229(1999)1338-1349 [91 A Gangopadhyay, S. Jahanmir, Friction and wear characteristics of In order to understand thoroughly the effect of h-BN silicon nitride-graphite and alumina-graphite composites, TriboL. e tribological properties of h-BN/Si3 N4 ceramic co Trans.34(2)(1991)257-265 sites, further works need to be conducted [10 S. Jahanmir, Firction and Wear of Ceramics, Marcel Dekker Inc, New York,1994,pp.163-198. [11] A.G. Evans, P B. Marshall, Wear mechanism in ceramics, in: Proceed- gs of the International Conference on fundamentals of friction and 4. Conclusions Wear of Materials, ASME, Pittsburgh, 1980, pp. 439-452. [12]L K. Rueh, T.T. Ying, Kinetics of B-Si3N4 grain growth in Si3N4 Hot-pressed h-BN/Si3N4 ceramic composites with a ramics sintered under high nitrogen pressure, J. Am. Ceram Soc. 76 small quantity of h-BN can maintain high relative density The growth of B-Si3N4 grains is hindered by h-bN [13] PJ. Becher, Silicon nitride ceramics scientific and technology particles and the diameter and aspect ratio of B-Si3N4 grains [14) L. Chien-Wei, L. Siu-Ching, Jeffrey Goldacker, Relation between mposites decrease with increasing h-BN content. strength, microstructure, and grain-bridging characteristics in in-situ The aim of decreasing the hardness and elastic modulus inforced silicon nitride J Am Ceram Soc. 78(2)(1995)449-459 of Si3 N4 ceramic appropriately and maintaining its high 15 flexural strength and fracture toughness by introducing a pressure sintering of a-silicon nitride, J. Am. Ceram. Soc. 75(1) (1992)103-108 mall quantity of h-BN into Si3N4 ceramic was achieved [16] F.C. Peillon, F. Thevenot, Microstrucral designing of silicon nitride The friction coefficient of h-BN/Si3N4 ceramic compo- related to toughness, J. Eur. Ceram Soc. 22(2002)271-278. sites decreases with increasing h-bn content due to the [171 F.P. Becher, Y.E. Sun, P K Plucknett, Microstructural design of silicon lubrication action of h-BN and the reduced B-Si3N4 grains tride with improved fracture toughness I, effect of grain shape and size,J.Am. Ceram.Soc.81(11)(1998)2821-2830 size. A spalling mode of failure has been observed on the [18] N. Hirosaki, Y. Akimune, Effect of grain growth of B-Si3N4 on surface of sno and SN10 ength, weibull modulus, and fracture toughness, J. Am. Ceram. c.76(7)(1993)1892-1894 [19] P.J. Becher, Silicon nitride ceramics scientific and technology References dvances, Mater. Res. Soc. 8(1993)147-158. 201 A.J. Pyzik, A.R. Prunier, B. Pyzik, Microstructural engineering of [1] G. Shuqi, H. Naoto, Y. Yashinobu, Hot-pressed silicon ceramics with silicon nitride ceramics. in: Int. Conf. Silicon nitride 93. Stuttgart lerman. 1993 Lu,O3 additives: elastic moduli and fracture toughness, J. Eur. Ceram. Soc.23(2003)537-545 [21]R V. Weeren, C D. Stephen, The effect of grain boundary phase [2] Y. Sang-Young, A. Takashi, Y. Eiichi, The microstructure and creep characteristics on the crack deflection behavior in a silicon nitride deformation of hot-pressed Si N4 with different amounts of sintering aterial, Scripta Mater. 34(1996)1567-1573 dditives, J Mater Res. 11(1)(1996)120-126. [22] D.R. Petrak, J D. Lee, Silicon nitride/boron nitride composite with [3 H L Ekkehard, V.S. Michael. Fracture toughness and thermal shock enhanced fracture toughness. US Patent 5,324, 694(28 June 1994) [23] K.H. Zum Gahr, w Bundschuh, B Zimmerlin, Effect of grain size on behavior of silicon nitride-boron nitride ceramics.J. Am. Ceram. Soc friction and sliding wear of oxide ceramics, Wear 162-164(1993) 75(192)67-70 [4] J. Yiping, Current study on hybrid bearing and ceramic ball, Wear 2 [24A.K Mukhopadhyay. Y.M. Mai, Grain size effect on abrasive wear (2002)33-35 (in Chinese) [5] Y Shimura, Y. Mizutani, Wear of ceramics at high temperatures and its mechanisms in alumina ceramics, Wear 162-164(1993)314-321 [25] B. Wallis, Influence of the microstructure of ceramic materials on their ment by metallic coating. in: Wear of Materials, ASME (1991)405-410. wear behavior in mechanical seals, Lub. Eng. 50(1994)789-799results in the formation of microcracks. Eventually, the accumulation and propagation of microcracks result in the formation of coarse cracks on the worn surface of SN10. Consequently, the propagation of coarse cracks leads to the formation of large flakes on the worn surface of SN10. In addition, as can be seen from Fig. 8d, the surface of each coarse flake is smooth, which is due to the lubrication action and low hardness of h-BN. In order to understand thoroughly the effect of h-BN on the tribological properties of h-BN/Si3N4 ceramic compo￾sites, further works need to be conducted. 4. Conclusions Hot-pressed h-BN/Si3N4 ceramic composites with a small quantity of h-BN can maintain high relative density. The growth of b-Si3N4 grains is hindered by h-BN particles and the diameter and aspect ratio of b-Si3N4 grains in composites decrease with increasing h-BN content. The aim of decreasing the hardness and elastic modulus of Si3N4 ceramic appropriately and maintaining its high flexural strength and fracture toughness by introducing a small quantity of h-BN into Si3N4 ceramic was achieved. The friction coefficient of h-BN/Si3N4 ceramic compo￾sites decreases with increasing h-BN content due to the lubrication action of h-BN and the reduced b-Si3N4 grains size. A spalling mode of failure has been observed on the surface of SN0 and SN10. References [1] G. Shuqi, H. Naoto, Y. Yashinobu, Hot-pressed silicon ceramics with Lu2O3 additives: elastic moduli and fracture toughness, J. Eur. Ceram. Soc. 23 (2003) 537–545. [2] Y. Sang-Young, A. Takashi, Y. Eiichi, The microstructure and creep deformation of hot-pressed Si3N4 with different amounts of sintering additives, J. Mater. Res. 11 (1) (1996) 120–126. [3] H.L. Ekkehard, V.S. Michael, Fracture toughness and thermal shock behavior of silicon nitride-boron nitride ceramics, J. Am. Ceram. Soc. 75 (1992) 67–70. [4] J. Yiping, Current study on hybrid bearing and ceramic ball, Wear 2 (2002) 33–35 (in Chinese). [5] Y. Shimura, Y. Mizutani, Wear of ceramics at high temperatures and its improvement by metallic coating, in: Wear of Materials, ASME (1991) 405–410. [6] R.S. Bhattacharya, A.K. Rai, High energy (MeV) ion beam modifica￾tion of sputtered MoS2 coatings on ceramics, ASME/STLE Tribology Conference Preprints 1992 Preprint No. 92-TC-6A-1. [7] F. Brenscheidt, S. Oswald, A. Muchlich, Wear mechanisms in titanium implanted silicon nitride ceramics, Nucl. Instrum. Methods Phys. Res. B 129 (1997) 483–486. [8] P.J. Blau, B. Dumont, D.N. Braski, Reciprocating friction and wear behavior of a ceramic-matrix graphite composite for possible use in diesel engine valve guides, Wear 225–229 (1999) 1338–1349. [9] A. Gangopadhyay, S. Jahanmir, Friction and wear characteristics of silicon nitride-graphite and alumina-graphite composites, Tribol. Trans. 34 (2) (1991) 257–265. [10] S. Jahanmir, Firction and Wear of Ceramics, Marcel Dekker Inc, New York, 1994, pp. 163–198. [11] A.G. Evans, P.B. Marshall, Wear mechanism in ceramics, in: Proceed￾ings of the International Conference on Fundamentals of Friction and Wear of Materials, ASME, Pittsburgh, 1980, pp. 439–452. [12] L.K. 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Mai, Grain size effect on abrasive wear mechanisms in alumina ceramics, Wear 162–164 (1993) 314–321. [25] B. Wallis, Influence of the microstructure of ceramic materials on their wear behavior in mechanical seals, Lub. Eng. 50 (1994) 789–799. 554 D. Wei et al. / Ceramics International 32 (2006) 549–554